AWR Intelligent Drive System Pt.11: More metalwork.

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New stainless steel screws, 35mm long, to ensure a more secure grip in the Dec saddle, Tollok bush. Adding the second channel on top of the first had increased the overall thickness to 10mm. Care must be exercised with choice of screw length to avoid the screws butting against the material enclosing the Tollok bush. This would prevent the bush tightening properly. I turned a brass cylinder with counter-bored 'step' to house the Dec/saddle Tollok bush.

The ss washers were turned to the perfect size in the lathe to just clear each other without overlapping or gaps. Some small flats had to be ground to clear the alloy channel to left and right.

The wide spread of load distribution when the ten screws are all torqued to spec should provide a very "stiff" joint between the Dec. shaft and saddle. The view hole is to ensure the saddle is pressed against the end of the Dec. shaft.

Oversized, stainless steel, coachwork washers bored out in the lathe to suit the 16mm studs in the bearing housings.

Quite a number can be stacked in the 3-jaw chuck and all bored simultaneously.

The slight 'doming' of the washers is not an illusion. The small degree of spring will act as a rather mild lock washer. Not one to be trusted with vibration but fine for this application.

Extra grub screw holes drilled and tapped 120° apart around the bosses of the toothed belt, drive pulleys. The extra grip provided will be useful in retaining the pulleys securely on their shafts. The grub screws are M4 and ridiculously long. Though they easily miss the large holes I made in the motor support plate. The invisible 'third' screw in each pulley is the original length.

I could shorten the grub screws for cosmetic reasons but can't really see the point. I'd also lose the crater tips unless I re-drilled the ground off tip. Or, I could simply order some more screws of the correct length. I suppose they do a look a bit silly on the smaller pulleys. If I drill dimples in the worm shafts for extra grip that would help to solve the larger pulley, screw length problem.

To obtain the 120° radial spacing I used a spacer under each jaw of the 3-jaw lathe chuck in turn. Then marked the boss with a sharp lathe tool in the tool holder. The pulleys were held gently in the machine vice on the pillar drill's  table. Alignment for the radial drilling on the new pillar drill was started by eye ensuring the drill would pass straight through the bore diametrically. I started with a tiny 1mm drill [1/25th"] in the pin chuck in the big drill's main chuck to make the pilot holes. Followed by large drills to get the M4 matching screw size bore. 3.2mm seemed to work well enough with the 1st taper tap.

I am very pleased with the smoothness and perfect concentricity of the big, new, pillar drill. It makes using even the tiniest drills effortless at the highest speed. [2740rpm] My 30 year old pillar drill chuck always wobbled eccentrically. Making it a lottery where the drill would start unless I center punched first. I promise to clean off the swarf before putting the pulleys to use.

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7" f/12 R35 iStar Folded Refractor: New rotating focuser ring and baffle tube.

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 I decided to replace the cardboard focuser baffle tube with the aluminium. The plywood ring required replacement. So I cut out two squares of 10mm aluminium with the miter, circular saw. Then bored and turned them into matching, round rings in the lathe. 

The slight extra weight will aid the folded OTA's balance point. Which is presently very nose heavy, like many refractors.

Ring cut from 10mm sheet aluminium, faced and turned to size inside and out.

Counter-boring  the second side in my old S&B 'Sabel' lathe for the Vixen 2" focuser. I removed 5mm.

I had to use the 4 jaw chuck to have enough clearance for the depth of boring.

The rather tatty, old plywood ring with its aluminium copy alongside.The fixing holes have yet to be countersunk to remove the burrs.

The new ring clamped in place. I also cut two rings of PTFE/Teflon using sharpened workshop dividers. This saves wastage instead of sawing. One ring for each side of the backplate reduces friction between the all aluminium rubbing surfaces.

The focuser now rotates much more smoothly than it ever did with the plywood ring in place.

It is important that there is no flop or the baffle will fall off-center.

 The new focuser baffle tube fitted to the new ring. I laid a 60cm rule across the tops of the two folding mirrors to ensure safe clearance of the baffle tube from the optical path.

The inside of the 80mm alu. tubing is remarkably rough. Ideal for killing glancing reflections once it is coated in matt black paint. A thin, metal baffle will be cut to fit into/onto the end of the tube and all components painted matt black.

The larger of the two folding optical flat mirrors sits below. With its transparent food tub cover pressed over the collimation cell for protection. I left the label on to remind me to remove the cover.

With the temperature in the workshop hovering at +1C, 33F I had to bring the matt black painted baffle tube indoors to dry. The water-based, blackboard paint is supposed to take 48 hours to dry even at normal temperatures. The paint is very easy to use, goes on thickly and cleans off my hands very easily. Though I have now taken to routinely wearing surgical gloves for such tasks to avoid using harsh hand cleansers.

I spent a coupled of hours, wrapped up well, playing with collimation and finding the balance point of the folded refractor. First I removed the two solid stainless steel handles from the objective bayonet plate. This moved the balance more towards the focuser but not by as much as I had imagined.

Flashing a torch onto the various surfaces made it easier to identify which aperture I was trying to center during collimation. I am tempted to fit small hinges instead of securing bolts and rubber washers on the top, third point of the large, triangular, mirror collimation cells. At present the cells rise and fall slightly depending on the pressure on the springs on the other two points of the large triangles. Mirror height is important to collimation and I have slotted the mirror support bars to allow for this anyway. The folded refractor should eventually become a permanent feature on the big mounting. Repeated collimation should then not be necessary.

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AWR Intelligent Drive System Pt.10: More [useful] scrap metal!

Yesterday's visit to the scrap merchant produced some nice 80mm round alloy tubing and some shorter lengths of 70mm square. Plus a large sheet of thinner, flat aluminium for baffles. I had been forced to buy expensive roof flashing for refractor baffles before now. I want to add another full baffle to the folded refractor. Probably using the focused sun to guide the hole marking. A folded refractor needs some very odd baffle cut-outs. Almost figure of 8 holes are sometimes required as the light bounces back and forth between the optical flats. 

The 80mm round tube is lighter at 2mm wall than the square stuff. It should be ideal for extending the refractor focuser to a small first [or rather last] baffle. This will help exclude stray light on the folded 7" refractor. Apart from a single, thin, flat baffle I did not spend much effort in baffling. I did manage to find a cardboard poster tube and cap to act as a focuser baffle but wanted something more permanent for the longer term.

If I ever find an affordable Herschel prism, for solar viewing, the plastic and cardboard baffle would have been at the intense end of the focused heat. I found no difficulty setting fire to plywood with the bare 7" objective. Even at f/12 there is plenty of heat in the focused sun. Fortunately a full aperture, Baader foil filter rejects all of this heat before it reaches the 'innards' of the telescope. So there is no real risk of a fire. Now I have to discover a way to fit the 80mm tube to the inner face of the Vixen 2" R&P focuser. The cardboard tube was just a perfect push fit. Though I worried about it dropping out and landing on the first, folding, optical flat when the OTA was vertical. The alloy tube will have to be more securely fixed!

I downloaded the AWR ASCOM driver, last night, which was recommended by AWR. I had quite a tussle at first to get the download  past the W10 watchdog. It seemed I needed to download the latest ASCOM platform, before the AWR driver would install properly. Things went better after that and I played a little with the "virtual" telescope simulation. Then I watched some YT videos of the ASCOM and Stellarium telescope control. No videos on AWR have been uploaded yet. I may be the first to do so once I have something to show. Not just a boring old computer screen but a moving mounting.

As I have said before, I am hoping to use Stellarium for direct Gotos with mouse clicks on the "live" computer screen. Which should then dutifully follow the field of view of the telescope to the target. I shall have to wait for a fully functioning mounting first. One which has been properly polar aligned. Before I can make the most of this software and AWR's Intelligent Goto drive system. The ASCOM driver is supposed to be more user friendly for PC control and offers a much greater range of possibilities. Auto tracking and powered focuser options exist. Plus the ability to follow different object which change in RA and Dec. Asteroids, comets and satellites have such traits. Presuming, of course, that the drive system can move the telescope quickly enough. 

Still no mention of dispatch of the 6mm aluminium angle so I can't mount the stepper motors yet. The 70mm square tube could have been adapted to the job but is slightly too thin wall [at 4mm] for this purpose. I have no desire to risk flexure at this late stage of drive and driver expense and effort. Had I found the newly arrived, square alloy tubes earlier I might have been sorely tempted to use them instead.

I keep looking at the possibility of covering the worms and wormwheels with the base sections of large, round, baking pans. This would help to exclude the grime which is attracted when such objects are exposed. Particularly if they are lubricated. The pans offer a neat solution for these covers if I can cut off the bases neatly and without any distortion. The material thickness is not substantial and immediately loses its remarkable rigidity when the vital rolled rim is removed. When the rim is left in place, even with the base mostly cut away, the pan still retains most of its strength. I used this method to mount the 1/20th wave, Zerodur optical flats in the folded refractor.

Unfortunately these covers would be far too large to spin in my 9" lathe. You can't just take a hacksaw to such a job either. It needs something much finer toothed or even a powered tool. A jeweller's saw cannot cut at right angles and coping saws do not have fine enough blades. Perhaps a slitting saw in a drill in a fixed jig would do it? Rotate the pan slowly against the tool. Rather than moving the tool around the pan.

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AWR Intelligent Drive System Pt.9. Worm support metalwork 3.

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30 years after I bought the cheapest Chinese pillar drill available at the time, I have replaced it with a bigger and better one. The smaller pillar drill had clapped out head bearings from new which needed replacing. It worked after a fashion, after that, but was always noisy, grossly under-powered and ran far too fast even at the lowest of its 5 speeds. Now I have 12 speeds down to 180rpm and a much more useful throat depth. 

The major cost was in having to handle a huge lump of machinery weighing nearly 70kg. Then find a space for it in my cluttered workshop. I had to adapt and beef up the original shelving with 3/4" plywood and support it with independent 'legs'  to avoid overloading the [heavy duty but still amateur] shelving units. The workshop required a once in a lifetime tidy which it is unlikely to forget.

The next job was to photograph the ridiculously tiny pulley selection chart inside the drill's hinged lid. Then blow it up to a useful size to just fit on A4 paper. I then printed a clear black and white image, with pulley numbers added, and pinned it to the wall behind the drill.

I still have to attend to the table locking lever which is a grossly undersized, hinged, waste of space. The present device does not offer remotely enough leverage without lots of unnecessary hand strength at full arm's reach. Easily fixed without altering the drill.

The new drill proved easily able to drill steel in 16mm diameter from a suitably large pilot hole. The old drill couldn't manage 10mm safely.

The next problem was finding some 6mm [1/4"] aluminium angle for the motor fixing brackets. I had various sizes up to 50 x 50 x 5mm but nothing at all in 6mm. A 20 mile cycle ride produced nothing from my engineering sources. So I resorted to the Internet and placed an order with a German company willing to deal with private customers.

With a little help from Google translate I ordered a couple of 30cm lengths of 70 x 70 x 6mm angle. These will be cut to shorter lengths and one angle "wrapped around" each stepper motor. Vertical, countersunk screws will fix down the worm housings to lie right on top of the motors. An 'inverted' angle will then be "nested," one inside the other, to bolt down the worms to the 10mm base plates. The front motor plates will continue to join the motors to the worm housings.

Serious Danish metal stockists are strictly wholesale. They might as well be situated on the Moon as far as I am concerned. Neither Amazon nor eBay[UK] had anything to offer and the prices and postage were higher on eBay for the same profiles.

Once the worm/wheel mesh is perfectly adjusted I shall probably add narrower sections of 6mm angle, or solid metal strip, at the fronts of the motors, to further reinforce them against twisting away from the wormwheels under load. Slots with through bolts will allow the vital but small degree of movement.

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AWR Intelligent Drive System Pt.8. Worm support metalwork 2. RA.

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The worm housing, supporting material will be made entirely of metal and of adequate cross section to avoid all flexure. The problem is that there is quite a space to make up between the top surface of the 10mm support plates and the bases of the worm housings. As can be seen by the height of the oak blocks in the images in previous posts.

More on this later as my ideas coalesce into solid metal. Not rushing in produces dozens of different thought experiments before the precious [sic] metal stock is even touched. My present, favourite idea is a bar with a sturdy, vertical pivot at one end. Screw adjustment at the far tip will provide maximum leverage and sensitivity of fit between worm and wheel.

The Stepsyn stepper motors are 60mm square in cross section x about 80mm long. Plus the raised plug and socket on one side only. The black body is flush with the alloy end flanges on all four sides.

Interestingly, the RA worm housing needs to be lifted by about 66mm above the support plate for the worm to mesh correctly with its wheel.

I wonder whether the motor could not become a solid part of the support structure? The image shows the belt not quite tight enough with 5mm of packing between the motor and worm housing. 5mm channel, or angle, would fit between them nicely.

First I need a vertical face to screw the motor onto something. There are cutaway corners to the black body to allow long tools to reach the fixing bolts/screws/nuts. Though rods with threads could be mounted in the cutouts to support the motor from the opposite end. Motor support is usually from one end flange only just behind the pulley. Though this has some complications.

I have assorted plate including 10mm and 5mm, and some angle and channel. Though 5mm thick material between motor and worm housing doesn't leave any room for any other material under the motor. If I use angle profile under the motor that leaves no room for some means of support between the motor and worm housing. I shall have to think about this carefully. It seems a shame not to use the motor for solid support of the worm.

I still need worm depth of engagement adjustment even if the two become one solid unit. It would be better to have the motor protected by the worm and wheel if possible.  A single plate could act as a bulkhead for the motor fixing screws and one end of the worm housing. Sadly, Beacon hill have been very mean with the worm shaft free length beyond the housing. If I push the pulley out any further [5mm] there is little or no shaft left to hold the pulley safely in place. As can be seen in the image inside the large pulley bore even though the pulley is pressed tight against the worm housing.

Perhaps I could counter-bore a much thicker joining end plate. Say 10mm tick with recesses for both pulley bosses? Thicker material would have enough room and strength for an upward facing pivot screw through the base support plate for worm mesh adjustment. The motor would be very firmly held down to the base plate once the pivot screw was tightened. The screwed mesh adjustment would take place at the far end of the worm and motor. This will keep it safely out of reach of the belt and pulleys.

So far the worm housing is still only supported by one end. Now I need two overlapping angles in a squared 'Z' form to fix the worm housing down just inboard of the motor. The motor itself would rest directly on the 10mm main supporting base plate.

One angle profile would fit between motor and worm housing with the other leg turned downwards. Countersunk screws would join the worm housing to this top piece of angle. Both vertical legs of the angle profiles will be bolted firmly to each other. The lower piece of angle will rest on the base plate and will only be bolted firmly down once the worm mesh is set precisely. The angle section resting on the base plate will needs slots to allow some linear screw movement for worm meshing.

Some adjustment of the motor relative to the worm housing might be beneficial for belt tightness adjustment. Ideally the motor has to move away from the worm and wheel because the worm must mesh with the wheel. Not easy to achieve if the two are fixed to a face plate with recesses for the pulley bosses. Reaching the pinch bolts for the pulleys would need attention. Holes for a hex key? A slightly shorter belt would tension better with both worm and motor coincident. I have some 5mm channel which might tie the motor and worm more tightly together. 

Adding an idler wheel [or bearing?] for belt tension adjustment to the front plate would be very easy. That would leave the position of the worm housing relative to the motor a much freer choice. See rough drawing above for the general layout.

Posed shot of the unfinished motor plate.
Note the 6mm space between worm housing and motor ready for the support angle profiles.

I made the motor plate oversize [80mm x 120mm] out of a scrap of 5mm aluminium. This required a 36mm hole for the protrusion on the front of the stepper motor and a 32mm hole for the 34t pulley boss on the worm. I didn't have any drills or hole saws of the correct size so I bored the large holes in the 4-jaw chuck in the lathe. Hole saws would have been the best and quickest way to do these, preferably slightly oversized for clearance. I also drilled the four small, fixing holes for the RA stepper motor and clamped it temporarily.

Now I need to narrow the plate near the top to make room for the wormwheel and then drill some small holes to fix the end of the worm housing to the motor plate with screws. Then make the two nested angles in 5mm aluminium. I shall use Nyloc nuts and stainless steel screws to ensure these don't work loose. Though the motors are supposed to get quite hot in use. Which might suggest an alternative locking method. The close proximity of so much bare metal should help to act as a heat sink.    

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AWR Intelligent Drive System Pt.7. Worm support metalwork 1.

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I originally made 5mm [1/5"] x 150mm aluminium, worm support plates but these could still flex. A later find of a long length of scrap, 10mm aluminium [also 6" wide] offered a much stiffer alternative. The miter saw will be used to cut the strip squarely to length. With a light application of lamp oil as a cutting fluid.

The original 5mm worm support plates. Holes provide clearance for the axis shafts and longitudinal 16mm studs.

That said, the 10mm thick aluminium is not a trivial material to saw, cut and drill. I had to use the lathe for the larger drills and hole saw fitted in the 3-jaw chuck. This required the very lowest back gear speed and the lathe bed as a safety stop against rotation of the plate. I then carefully feed the tailstock barrel in to slowly push the material onto the drills and hole saw. The barrel pushes squarely and the drill can safely enter the hollow MT2 barrel when it breaks through.

My dirt cheap, old pillar drill doesn't have remotely enough torque or stiffness to drill large holes. The lowest of five speeds is still far too high for larger drills. The holes can even come out hexagonal if I push my luck! Though usually the drill stalls first. Once a pilot hole has been opened out to the safe capacity of the drill I move over to the lathe for much greater safety and smooth, round holes.

The availability of scrap aluminium is not an ideal design parameter for telescope making. The builder quite literally becomes a slave to the materials available. This forces the designer to comply with what they have to hand and owning/buying the necessary tools to make it happen. Wishful thinking will not help here. I seem to have spent a lifetime wandering around scrap yards. Though not continuously, I hasten to add. I have developed a feeling for what is useful and what is beyond my capacity however hard I try. Gone are the days when I'd bring back solid 4" shafts and huge, matching, plumber block bearings. Or 24" cast iron, lathe face plates to build polar axes, for fork mountings. With each component almost too heavy to lift.

If you can afford to pay for castings and/or a skilled machinist then count yourself very fortunate. Though you probably won't save much money over a Chinese, mass-produced commercial design by the time it is finished. You will only have yourself to blame if it does not function optimally. The latest, mass produced design probably emerged after a whole series of iterations. The designers will be using CAD and enjoying feedback from the design and production team for start to finish. Many mountings improve almost annually as users complain or make positive suggestions for improvements. Though it often seems the Chinese designers do not read the forums.

One should always be incredibly grateful for whatever [scrap] materials turn up to your advantage. I don't think one should try to haggle too much. Or the scrap dealer will quickly lose interest in helping the oddball. You are the strange one who actually wants to take something away and may even pay well for it! Rather than forming an orderly queue to sell more scrap material to him for cash in hand. A degree in diplomacy helps to avoid being sent hurriedly on your way. Climbing over heaps of sharp metal to rescue one useful piece is just foolhardy and downright dangerous. Any accidents will become his responsibility. So take great care, act sensibly, be polite and put nobody at risk.

I have been extraordinarily lucky in finding enough flat strips of 10mm and even 20mm plate in [mostly] good surface condition. Alas, finding suitably heavy alloy angle has resisted all further visits. Metals can be bought on eBay UK and DE  but the Danish metal stockholders will not deal with private customers. Trying to buy a few small pieces of 4mm plate from a local engineering firm proved rather costly. Though they did have to guillotine a couple of quite modest pieces to size. With digital readouts on the machine it was only a matter of moments to set and cut. A return visit provided no suitably heavy angle for worm support in their entire stock of aluminium alloy.

The new 10mm support plates will still be trapped between the bearings housings and the axes heavy flange bearings. The four equally heavy 16mm, [~3/4"] corner studs [all threads] will prevent all movement. I shall probably have to use solid blocks of metal rather than angle profile to support the worm housings.

It will be up to me to provide finely adjustable, but immovable support for the worm housings. An earlier plan to use solid oak support blocks was ditched when the blocks changed their dimensions with moisture content. They could also be compressed by their fixing bolts. After carefully setting up I would come back later to find the friction or backlash had changed. Not a good start and it wasn't due to variations in the wormwheel. I would do full rotations of the wormwheel to ensure all was well at random diameters. A rechargeable drill on the worm shaft helps to speed things up.

New 10mm worm support plate beside the old 5mm. It took ages to cut the large hole to clear the axis shaft. After failing to make any depth from either side I had to drill dozens of tiny holes in the circular track to help the hole saw on its way. I made the plate slightly longer in case I need the space.

Don't waste money on cheaper hole saws. The Millarco 65mm hole saw was worn out by taking only two 5mm cuts in aluminium despite using only 45 rpm and lamp oil as a cutting fluid. With the DIY outlets closed by Saturday lunch time I shall have to wait until Monday now to buy a real hole saw. Not some cheap crap which can only manage one hole in cardboard packaging.

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AWR Intelligent Drive System Pt.6: Worms and wormwheels Pt.2.

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AWR places great emphasis on the need for very stiff worm supports to avoid all flexure. If the bracketry should flex [at all] then it will also unwind again when the drive load is removed. Leading to lost motion during acceleration or overshoot during Goto maneuvers. A perfect recipe for frustration in pointing precisely to the desired [often all but invisible] object.

Once the perfect fit has been achieved the worm brackets must also be firmly fixed with suitably large bolts. Or the drive power available will literally dislodge the worm housings. Meanwhile the worm housings need fine, radial screw adjustment towards and away from the circumference of the wormwheels. There is really only one perfect position for a worm nestled against its matching wormwheel. It must be square to the wheel or the threads and teeth will not allow the necessarily fine adjustment needed.

The pulley to worm, shaft fixing screws must lodge onto small flats or dimples on the worm shaft to avoid them loosening over time. The tiny grub screws provided might be better replaced with stainless steel, hex socket head screws. This would allow more torque to be applied to the screws.

The worm housing bearings must also be prevented from linear movement. The tiny grub screw on top of the bearing housing is hardly adequate except to restrain the bearing from falling out. Over-tightening of this screw can easily lock the bearing solid against rotation! An outboard plate at each end of the housing will prevent bearing shift. The pulley boss will prevent lateral movement towards the worm but may benefit from a thin, low friction thrust disk. PTFE/Teflon might be a good choice but can creep under heavy loads.

Wormwheel and worm mock-up on oak blocks.The arrows show the positions of the radial nylon plugs which provide a [barely] slipping clutch against the axis shaft. Grub screws provide the adjustment of pressure/friction/slippage. 

AWR suggested these clutch grub screws be tightened enough to prevent slippage until it just matches the motor stall point. Which sounds to me as if no slippage is desired but the worm/wheel is protected from a total obstruction or hard blow to the OTA.

Which means that hand pushed slews of the OTA would lose the ability to manage further Gotos. The telescope's "aim" would be lost if it was moved independently of the drive system's position sensing. To maintain accuracy after a a hand slew would require shaft rotation sensing and feedback. Rather than  reading the stepper motor position relative to the worms/wormwheels. The AWR drive system seems to be treating the wormwheels as if they were solidly connected to the axes for all intents and purposes. The clutch is simply a final safety measure against physical destruction of the wormwheel teeth.

All movement and pointing of the telescope must be done with stepper motor power alone. Which is very different from the usual [and grossly under-powered] synchronous motor drives following a hand slew. The AWR system is much more like how large, modern telescopes would be pointed. The desired position of the field of view is fed into the drive computer. The telescope then sets off by the shortest route to home in [i.e. Goto] that point in the sky. With enough accuracy to place the desired object safely in the field of view. Fine tuning of the object's position is then carried out with the Intelligent Handset's buttons harnessing the stepper motors at very low speed. It is all a matter of scale. A very large telescope, weighing many hundreds of tons, would not even notice a puny human being giving it a firm shove.

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AWR Intelligent Goto Drive System Pt.5. Worms and wormwheels Pt.1.

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Both Beacon Hill worms in their profiled 'housings' are shown alongside with the 34t timing pulleys fitted. Note how the worm size and pitch have to match their own particular wormwheel. The 11" wheel worm is in the foreground with the 8" wheel worm behind.

The number of teeth [287] remains constant. While the circumference of the wormwheel sets the tooth [or screw] pitch. Or rather vice versa. The desired number of teeth x the pitch sets the circumference and thence the diameter of the wormwheel. Only specific wheel diameters/circumferences will produce teeth of a useful pitch which can be actually be cut as a "screw thread" for the matching worm. So it is better to start with the pitch of the worm and design the wheel to match the required number of teeth. 360 teeth is a popular number but makes for very fine teeth in smaller wheel diameters.

Beacon Hill uses 287 teeth. Why? Because 1436/287 = 5.  1436 = the number of minutes in 23 hours and 56 minutes [and 4 seconds.] Which is the sidereal [star] day which is slightly shorter than the average solar day.

A normal [single start] worm and wheel reduce the rotational speed of the worm by the number of teeth on the wormwheel. 287:1 allows a 5 rpm synchronous motor to accurately follow the stars. The 287 teeth are also much more robustly sized, than 360, in any likely amateur instrument sizes.  [6-12" diameters are popular]

A poorly constructed or badly adjusted mounting will allow a finely pitched worm to drag sideways over the relatively tiny, wormwheel teeth. You may well imagine the damage that might cause! Big teeth need a very much sloppier fit before they will allow the worm to escape from the wheel teeth. They are also far more forgiving of fit between the worm and the wheel teeth. There is no loss of accuracy nor grave disadvantage in having a "higher gear ratio" than 360:1. So 287 teeth is actually a good choice from a number of standpoints.  

A worm is rather like a section of screw thread whose diameter must also match its wormwheel. A completely random choice of [odd] pitch would make the worm all but impossible to produce in a normal screw-cutting lathe. A worm is not a normal [i.e. nuts and bolts] screw thread. Because the tops and bottoms are flattened in the form of an ACME thread. These threads are commonly used for vices, G-cramps [C-clamps] and other very heavily loaded screwed devices. Lathes, mills and other machines use them for driving the slides, tables or tools along very accurately with very little wear.

Only the flanks [sides] of the teeth do the driving and the worm must not bottom in the wheel teeth. If they bottom then that would set the clearance between the flanks of the worm "thread" and the wheel teeth. The space between two components must be adjusted have just enough clearance to avoid any backlash. i.e. Without any free rotary movement of the wormwheel. An absence of backlash can only be achieved with accurately cut wormwheels and worms. The radius of the teeth cut on the circumference of the wheel must not change. On a telescope wormwheel the teeth are in fact short slots with a radius to match the diameter of the worm. Spur gears have "straight cut" teeth which make rather poor wormwheels. There would be very little contact area over very few teeth leading to backlash and rapid wear. The correctly formed wormwheel teeth provide a very snug, intimate fit on the worm over a much greater number of teeth. 

In fact one can use a screw cutting tap to 'hob' the teeth on the circumference of the wheel. In the case of the Beacon Hill wheels the large diameter of the matching worm would require a very large diameter tap. Getting enough thread cutting length on the tap to be able to support it properly at both ends adds to the problems with large diameter wormwheels. The cost of such a large tap might run into the hundreds of pounds or dollars. Now add in the cost of a large thick blank of machining quality aluminium. You might as well cut out the "middle man" [yourself] and buy a commercial worm and wormwheel set form one of the respected suppliers.

Though a scrap length of [unworn] acme threaded rod could be slotted lengthwise to form the vital cutting faces as seen in the screw cutting tap. Normally the circumference of the wormwheel would be gashed with a small circular saw or fly cutter to form a guide for the tap's thread to form. The wheel blanks has to be firmly mounted and turned one tooth a time as the cutter or saw is wound into the wormwheel to make each tooth. The easiest way for an amateur to divide a wheel is using commercial perforated strip wrapped tightly around a plywood disk. A sturdy plunger is then inserted into each hole in turn to lock the large disk a fixed number of times around the circumference. Roofing reinforcement strip is an example of a perforated strip available in long lengths.. There may be others with smaller spacing of the holes to keep the master dividing plate within reasonable bounds. 287cm / Pi = 91.3xcm diameter. About 3' diameter is not impossible to mount on the same axle as the intended wormwheel.

Trying to plunge a large tap [as shown] straight into the edge of the wheel could become a disaster. With no guarantee that the teeth would even have the correct pitch and the vibration might be awful. Commercially made wormwheels are usually power driven at exactly the correct speed to match the rotation of the special cutter to ensure the pitch is very accurate. The enormous cost of the machine and its range of specialist cutters ensures a very high price unless a huge number of wormwheels are made. 

The spacing of the teeth [pitch] known as wheel dividing, must be identical the whole way around the wormwheel. If the pitch of the teeth change [at all] then the worm cannot bed closely against the wheel. Lapping, that is running the worm against its wheel with an abrasive medium, can help. Though it is a slow process and can ruinously damage both wormwheel and worm.

Only the very finest abrasives should be used. [Metal polish?] Beacon Hill advise against such measures except when using plain oil to polish the rubbing surfaces. The danger is that abrasives can lodge in the metal surfaces and continue to cause wear over a very long period. If the wear is considerable then the pitch could change. Or the width of the 'screw' threads on the worm could become thinner. While the gaps in the wheel teeth might broaden. Producing such a sloppy fit [and tooth bottoming] that backlash would rear its ugly head.

However, if lapping is done to perfection the worm eventually becomes a 'diablo' and has contact over a much greater number of teeth in the wormwheel. The huge worms and wormwheels on the great professional telescopes were usually lapped with optical rouge. This ensured uniformity of pitch, low friction and a perfect fit. Though these people were experts at what they were doing.

Chris Lord has an interesting discussion on his lapping technique of the stainless steel worms on the bronze wormwheels. He was trying to improve them when he fitted an AWR system to his truly massive, Calver, antique telescope. Just don't blame me or your wormwheels if you ruin them through ignorance. Having abrasive liquids running about will easily trash any bearings if it gets near them.

 Chris Lord's calver stepper piece:

Scroll down to Implementation for his description of lapping his worms to the wormwheels.

But note the very tough materials he was working with, the relatively small worm diameters and very fine teeth! Do not assume that a relatively coarse pitch worm and wheel, like Beacon Hill's brass on aluminium, will respond in a remotely similar fashion! Better limit yourself to "Solvol Autosol" polishing paste if you are sorely tempted to "have a go." But don't say I told you so. I am warning you against even trying unless you have a modicum of mechanical or engineering common sense. You'd have to be absolutely certain the worm was perfectly meshed and absolutely square. Or you might as well throw them away.  Get any abrasive in the worm bearings and you can throw those away too. Don't say you haven't been warned if you are daft enough to try this on any other mounting! If you think chucking half a tin of "Brasso" in "the works" of your own mounting will improve it then you aren't remotely qualified enough to try!

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AWR Intelligent Goto Drive System Pt.4 Intelligent Handset V speed.

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AWR Technology (Astronomy - Electronics, Motors, GOTO drives, Sidereal Clocks, Display Units)

A 5m long yellow cable is a Cat6 network cable is provided for connection of the IH to the Microstep drive box. Allowing plenty of freedom to move around the telescope. Or even reach the workshop/warm room. If only I had one! It reached 25F or -4C inside the workshop a couple of days ago and the entire mounting is still sparkling with hoar frost!

The cables to the stepper motors are also very generous in length and all have latched plugs and sockets. Though I do feel a cable anchor at each end of the IH cable might be useful. There is a guard on each end of the cable to stop accidental contact with the little latching/release tabs. However, the vulnerability of this cable in the dark places rather a lot of trust in the relatively fragile little plugs.

A second socket on the base of the IH provides a connection to a PC for point and click control using Stellarium or similar 'planetarium' software. Which is a very useful provision because it saves a further length of cable to reach the PC from the drive box. BTW. Stellarium may need a special download from their website for telescope click and Goto control. Later editions have a small telescope image on the bottom line to show the telescope control is lying dormant and ready to be resuscitated.  

The Intelligent Handset screen on first power-up. BUT: See note in BOLD above. The AWR initial copyright screen is available by pressing F4 from the normal [default] screen shown. The text appears truly black to my naked eye. The camera lies again! Note how the bottom row of drive instructions in the display changes to lower case when active. [After F1, 2, 3 & 4 button selections just below the screen.]

King refers to standard [stellar] drive rate.
--- Shows a code letter W, P or C depending on what is happening.

LST is Local Sidereal Time.

SITE A is one of four possible locations. Lat & Long are easily stored [to the nearest second of arc] to avoid repeatedly entering locations by hand if regular but different observing sites are used. Many amateurs must escape from light pollution at their own home. So they drive out into the countryside to a familiar spot free of extraneous light. AWR can still work even in the Outback with a properly fused 12V battery. Most car and motorcycle batteries can easily fry an egg if short circuited! Both leads to the AWR Microstep box terminals should be fused. AWR recommends inline car fuses of suitable ratings.

I like the way the text almost fills the small screen rather than demanding a microscope to read undersized text. Old age and reading glasses often come hand in hand. Needing glasses at the telescope, just to read the screen, would probably wear thin after a while. I think I shall be able manage without. Though a square [plastic?] magnifying glass could be taped over the screen for easier legibility if it proves necessary in practice. Luckily I only have one dioptre of reading error so I am hoping the lit screen is easily legible when lit.

I captured a couple of short videos to show the huge differences in drive speed [i.e. stepper motor rotation] but they [the videos] were much too amateurish [i.e. shaky] to share online. First I need to arrange both motors and the full IH in simultaneous view with the camera on a steady tripod. Capturing the screen readout will need some care to be useful to curious YT viewers. Mental rehearsal will help to avoid wasting the valuable time of the viewer. Far too many YT video makers waste huge chunks of viewer's time where nothing useful or interesting is happening on screen.

I would guess [very roughly] that the fastest [Slew] motor shaft speed is about 90rpm. It is slightly too fast  to count full rotations by the usual "one thousand, two thousand," verbal system without hurrying unduly.

The 14/34 pulleys and belt provide a reduction of 2.4:1. So say ~ 38rpm is applied to the worm shaft. 38/287 = ~0.13rpm on the mounting's axes.  0.13/60x360 = 0.8 degrees per second. AWR claims their system should slew at about half a degree per second. To move the telescope from fully East to West, over a full 180 degrees, would take between two and three minutes. Though remember that this figure is is based on a very rudimentary rpm count. Only an active system with a real telescope would indicate the correct speed of a slew. Those who want faster slews can obtain them from AWR, at a price, for a 24Volt 'turbo' system.

I watched the Dec screen reading change on the handset as the Dec motor was slewed and would judge the movement was just under one degree per second. The motor shafts, despite crawling around almost invisibly on the slowest settings, were impossible to stop by hand. I gripped the small pulley as tightly as I was able during normal RA [stellar or King rate] drive and the motor never missed a beat. There was absolutely no change in sound or anything to suggest it was struggling to rotate normally. Multiply that power by 2.4 for the pulley gearing and the torque more than doubles. Multiply by 287 and it should be able to lift the mounting right off the ground! Albeit rather slowly. So some care must be exercised to ensure nothing ever blocks the movement of the wormwheels or the OTA.  

Lest ye consider the suggested slew speeds pedestrian: It should always be remembered that an accurate Goto will save an enormous amount of the observer's time in not having to search for an object. Particularly a dim one. In fact Goto may be the only way for some observers to find many objects in light polluted conditions. Including full moon. Though it is not usually chosen as a Goto target. Unless, of course, you live in Beijing! Moon? What moon? 😵

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AWR Intelligent Goto Drive System Pt.3: First Test!

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AWR Technology (Astronomy - Electronics, Motors, GOTO drives, Sidereal Clocks, Display Units)

Since all the sockets are clearly marked and all the cable plugs 'handed' I assembled the entire system "instructions unaided" before switching on. Though first I had to find a  continental mains plug. Since only a 13A UK square pin mains plug cable was provided. No big deal. The AWR power supply uses the common figure-of-8 plug on the mains input.

Using low  voltages for the drive system and motors avoids having mains out at the damp-exposed telescope which is often sited out on wet grass. The PS [Power Supply] can and should be housed safely under cover or [better] indoors, or the shelter of a shed or "warm room." Though this will require an ample, low voltage female/male banana extension cable. Preferably with shielded banana plugs and sockets. As supplied, the power supply will be out beside the telescope with the AWR drive system itself. Probably on the end of a mains extension cable unless you stop and think!

An imaging/Goto PC and monitor are likely to be under shelter unless a laptop is used. It seems logical to keep the only mains voltage item well protected too. The PS is clearly marked for "Indoor Use." Running an extra few yards of several amps at 12V DC will require something slightly better than the absolute, skinniest speaker cable available. If only to avoid voltage drop or heating from internal resistance. 

Loudspeaker cables often use banana plugs but the live pins must never be touched together. AWR has overcome this shorting problem locally with the telescopically shielded [male] plugs. The other end of the low voltage cable is anchored in the sealed power supply box. I wouldn't recommend running the PS off a mains extension cable without the protection an RCCD in the UK. Follow best electrical safety practice elsewhere.

Banana plugs are low voltage, single polarity so adding a speaker extension cable of adequate cross section is straightforward enough. This option should be very seriously considered if you want to avoid having mains out at the telescope. The speaker extension cable will run from the shielded male plugs on the AWR's PS captive cable out to the AWR Drive Box sockets.

A red diode shows the Microstep Drive Box has power. While a green diode is provided on the power supply. 

Whoops! I should have read the instructions on the AWR website. I was supposed to plug the IH [Intelligent Handset] in after power up to get the initial copyright screen. I later discovered that pressing F4 produced the copyright screen on demand. The system is supposed to start tracking normally once the Copyright screen has changed to default. This may not be what you want if your telescope is parked in a confined space. 

To avoid further confusion The Handbook, referred to on the AWR website, is also the IDS Manual. A downloadable, 59 page guide to using the AWR drive system. 

For normal use the IDS Manual acts as a useful reference but the Intelligent Handset is remarkably logical in its menus. Provided the telescope mounting is properly set up first a reasonably savvy user should be underway in using Goto control in no time.  

All seemed to be well on first power up except for the remarkably slow rotation and quietness of the stepper motors to directional button presses.  For some reason I had imagined they would literally whizz [scream?] round. Well, all telescope drive motors scream in the YT videos! 😊

 The small fans on the Resistance dropper box are rather noisy when close-to. These are to dump unwanted heat. Suggesting they will require some thought in siting the electronic equipment to avoid thermal effects on the telescope image. I am now imagining a flexible hose to warm the poor [old] observer at the telescope. Though I am probably exaggerating the free heat available. Probably a northerly airflow will suffice to avoid heat plumes. 😎

Both motors will happily run simultaneously and in opposite directions.  It may be that when following Goto instructions the motors will spin faster? Remember that the motor speed is further reduced by 2.4:1 the pulleys and then by a further 287 times by the worm and wheel. From memory, slew speeds up to half a degree a second are claimed for the system. With controlled acceleration and braking no less. Probably a good idea when swinging a long and heavy telescope across the heavens. Touching any one of the direction control buttons will stop a slew before any unwary visitor is beheaded or the priceless APO refractor dewshield crashes into the dome! Common sense suggests that a new user sets the limits and horizon parameters before loosing his telescope on a Goto tour in a confined space!

IMPORTANT SUN NOTE: A daylight Goto may easily sweep across the sun! [What sun?] Since the actual path of a Goto slew cannot be predicted the OTA should be capped during daylight slews. Or, have a full aperture solar filter fixed safely in place in daylight. For the same reason: Never leave a telescope unattended in daylight if children could ever get near enough to blind themselves at the eyepiece! Do not assume they can not get in! We returned home one day to find several of the neighbour's children enjoying a guided tour of our closed rural garden by a 7 year old. Including toddlers excited by the fish in the goldfish pond! We put a padlock on the gate after that.

Following a [forced] lunch break a second drive test followed. Proving that Slew is the fastest mode and the others are very much slower. Literally crawling round [at different speeds] to allow Guiding, Centering and Moving without the danger of overshoot at high magnifications. All perfectly logical if you think about it for a moment. It would require quite some patience to count the number of motor rpm of the other drive rates: [Guide, Center and Move.] It is quite amazing and certainly impressive to see a motor shaft rotating so incredibly slowly for the first time! No intermediate gearboxes either.

Regarding the connection of the AWR system to your PC you must ensure you have a 9-pin [female] serial port on your computer. Not an everyday occurrence these days. At first I failed to realise that the 9-pin ports on both my computers were female VGA outlets for monitor connection. I scratched my head and thought it would be a simple matter of getting a 9-pin male/male adapter. Sadly, life isn't that simple.

Update: 3.2.17:  AWR Recommends the FTDI USB:Serial adapter and fortunately had them in stock. The image shows the USB to serial adapter. The driver loaded automatically into W10 as soon as I inserted a USB port on my computer. I haven't had a chance to try connecting it to the AWR system yet as it has just arrived in the post. Excellent service from AWR and the postal services! The translucent, blue "shoulders" of the serial plug light up with diodes to indicate when data is transmitted or received.

These USB:Serial adapters are also available from RS but remember that VAT must be added as well as the postage. Cheaper USB:Serial adapters and cables are available but may not work. Some users may want to fit a serial port 'card' into their computer cabinet instead. 

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AWR Intelligent Goto Drive systen: Pt.2: What's in the box?

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I have split the original post to avoid long download times.

One end of the Microstep Drive Box with sockets for the stepper motor cables, Resistance Box [unmarked 12 pins lower socket] and for the 12V 7A power supply.

And, the other end, with AWR logo and sockets for the Intelligent handset [IH], Simple handset [center] and automatic guider connection. [CCD1.] 

The 7A 12V DC power supply with insulated, telescopic banana[?] plugs.

All the necessary cables are provided for connecting the entire system.














Sanyo Denki stepper motor with latched cable attached. These motors are so heavy there can't be much room left for any "fresh air" inside. 'Solid' is probably the best term.

Loose P-clips are provided for cable strain relief once the motors are safely mounted to sturdy brackets


The shaft end where the small, toothed, drive pulley will be fitted.

The loose green cable is presumably for earthing.

5mm pitch x 10mm wide timing belts and the 14:34 pulleys provide a 2.4:1 reduction in worm rotation speed from the stepper motors to the worm shafts. While simultaneously increasing torque by a similar amount. This means slower slews but more power for moving and controlling heavier OTAs or overcoming mounting/wormwheel friction/OTA imbalances.  All of these should, of course, be minimized to provide maximum slew performance during Goto instructions from these sophisticated drive systems.

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AWR Intelligent Goto Drive System. Pt.1 What's in the box?

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AWR Technology (Astronomy - Electronics, Motors, GOTO drives, Sidereal Clocks, Display Units)

For those considering an AWR Goto Drive system I offer the following user experience:
Note that I am just another private customer with no other commercial connection to AWR. So WYSIWYG, warts and all. There is so little written about AWR drive systems online that I thought I'd share my own thoughts. I shall add some YT videos when I have something to show.

Normally I add images to my blogs in any size I consider 'cosmetically' attractive. However, in the interests of those still connected to the 'Interweb' by a very long piece of damp string I have kept the many images smaller than usual. This makes the text layout unusually untidy. You'll just have to blame the cheapskates in power who won't give their citizens a 'proper' Internet service but can still afford "defense" spending. I have enjoyed a reliable, 57/57Mbps, optical fiber connection for some years. So tend to forget that in some backward countries, like the US, UK and Australia, there are still those much less fortunate. My sincere commiserations.  

Meanwhile, back in darkest, rural Denmark: The substantial 36 x 28 x 18cm, 8kg cardboard box contained the following items: [All well packed.]

Fit and finish is all very tidy. With security zip ties on many of the plug:cable terminations. The plugs and sockets are all easy to fit. Plug removal is as simple as pressing the locking side 'bars' inwards. There is bound to be a technical term for these: Latches? The only likely confusion is reversing the cables between the RA and Dec motors. Easily fixed simply by swapping the cables over at one end. The stepper motors themselves are identical.

Note: In the image I have added a 30cm [12"] transparent rule on top of the main components for scale.

List:
IH2. Intelligent [Goto] handset.
Microstep drive box.
Resistance dropper box with twin, serial fans for cooling.
12V DC 7A Edac power supply.
Two [remarkably heavy] stepper motors 210.
Umpteen cables.
Two sets of reduction pulleys and AT5 toothed belts in 5mm pitch x 10mm width.
Pulley ratios of 14:34t were supplied. 14:32 is optional for lighter loads.
Lower gears provide more power [torque] but slower slews. I shan't complain and swapping pulley sizes is easy enough if I discover ample power for faster slews with my ~35-40lb OTAs.

4 sheets of A4 paper: Invoice, Payment details, factory construction sheet with specs. Drawing of standard pulley set-up. No instructions, at all, were provided. [The AWR website simply says to assemble and test.] Anybody who can connect up a smart TV and Hifi System should have no problem.

A downloadable 'Handbook' is listed on the AWR website but the link failed to respond with a download in W10. So look for the IDS Manual link instead. Which is exactly the same thing as the 59 page Handbook but as a downloadable PDF file.

The 'Goto' Intelligent handset [IH2] provides direct GOTO telescope drive control with various drive rates and is re-programmable by the user.

The IH2 can also contain various sky catalogues [as downloads] and menu filters for direct input Goto instructions in RA and Dec. Expanded object catalogues are also  available for download. These all cost extra.

The central four [Slew] buttons provide the familiar direction controls. E, W, N & S for an equatorial mounting. The Mode/Menu buttons F1, F2, F3 &F4 decide the speed of motor rotation and therefore telescope movement via the slow motion, 287:1 worm and belt drives.

The IH handset is larger than I had imagined but this is arguably more 'handy' when wearing gloves at the telescope. Nor is it so easy to lose in the dark! An adjustable brightness [15 steps] illuminated screen provides position, RA & Dec and/or other information depending on the selected Mode/Menu. AWR prefers the term Menu but I like Mode better for changed sets of actions or instructions. Suit yourselves. You will anyway. 

A printable IH instruction 'tree' [Menu] is available on the AWR website for all the normal button presses. The IH can even be fixed to a surface near the telescope or hooked into a bracket with 'ears'  if it is not to be handheld. A docking station + power supply is available at extra cost to keep the timekeeping crystal cosy [and more accurate.] A button cell provides internal power to the crystal but not its oven.

Point and click Goto, via a PC or laptop [or tablet?] is available via popular Planetarium software. The [independent] ASCOM:AWR driver [£50] provides extra drive facilities and is recommended by AWR.

You should note that if you want to control the AWR drive system with a PC then you need a 9-pin serial port on your computer. If you don't have a serial port then ask AWR to supply their recommended [FTDI] USB:Serial adapter with your AWR Intelligent drive package. The supplied serial cable plugs into the second socket  at the base of the IH2 handset. The adapter goes between the PC's USB socket and the female serial plug.

And, no, you cannot fit the supplied PC [female] serial connection cable to a 9-pin VGA [female] display port. Don't ask me how I know this! <blush> I've only been playing with computers since the first ZX81 came out in the middle of the last century. Let's just call it a [another] senior moment. 😳

Click Newer Posts for the next episode[s] of my lengthy user review.

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AWR Intelligent Drives on the way. Or not?

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AWR[Tech] UK have confirmed that the 8kg parcel, containing my Intelligent Goto Drive system, is finally on its way. I was promised mid December delivery, well in time for Christmas, but it is now January 13th.

Hopefully, I shall be able to share some images and perhaps a YT video when I have something to show. But no, it seems we shall all have to be even considerably infinitely more patient. A flight delay means UPS is rescheduling delivery. It was sitting in Köln in Germany early on Friday 13th at 4am. It is now 8.00, 8.15, 8.30, 8.45am, 9.00, 10.30, 11.00, 11.30am  without any update on the tracking. Will I get the "Express" service my £100 for P&P is paying for and "Guaranteed?" Check back later...

Nope! According to Danish UPS customer services the flight delay means that I shan't see my package until Monday. UPS do no Saturday deliveries in Denmark. Not even Guaranteed Express delivery.

Thank you UPS for completely failing to provide the service for which I paid so lavishly. I checked the Cologne airport webcams. Completely clear and even the grass is green. What snow? Did they mean a delay for the plane leaving the UK?

Saturday 14th: A tracking update: At 4am today, my UPS parcel moved for the first time in 24 hours after not having moved at all. Guaranteed delivery was by end of day YESTERDAY.

Now, 6 10  12 14 28 hours after its departure scan from Cologne it has still not landed. Abduction by a UFO? Traveling by Pony Express? Is that what the 'P' in UPS stands for? Urgent Pony Sh..? Hmm. The Cologne airport is still completely clear of snow on all their webcams.

Sunday 15th and the package still hasn't arrived anywhere.

UPS doesn't seem to know how to spell Köln in German or Cologne in English. Settling for Koeln. Which hardly seems professional, nor shows any respect for their dimmer customers who are following parcel tracking on the UPS website in some unknown language. Koeln? Try searching for that! Dugh?

I'll keep you informed if there is any progress on the parcel. I see UPS.uk has an appalling score on Trust-Pilot.  0.5 out of 10! Not much sign of sponsored bias there!  😉

Monday 16th and it seems that the parcel was scanned into Vejle in Denmark on the Saturday 14th but not shared with the online tracking service until this morning [Monday]! It is now shown as out for delivery "by end of the day" A four day 12th-16th "Overnight Guaranteed"  Express delivery service. 

Finally arrived 12.00 by private courier.

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2" shaft mouting Pt.64 RA wormwheel position.

I am still struggling with the final choice of a high or low RA wormwheel position. In the lower position, on the bottom tip of the Polar Axis shaft, the 11" diameter wheel overlaps the base plate. It also requires a clamping bush to stop it literally falling off the end of the shaft. It would be difficult to apply any extra clamping pressure to achieve a supplementary clutch.

Placing the RA wormwheel at the top of the Polar Axis, directly under the 7" diameter cylinder, provides much more room. However, in this position it increases the cantilever of the declination bearing housing by an extra 40mm. Or an increased height of about 1.5" above the top PA flange bearing. 

Given the ample, 50mm shaft diameter I doubt this increased overhang has any real meaning except cosmetic. Particularly as the shaft is only leaning at 35° from the vertical at my 55° northerly latitude. A fork mounted on the PA would cause a huge overhang in comparison with the modest overhang of my German Equatorial design. Moreover, the disk on wheel arrangement is commonly used in telescope mountings as the very stable, pin and plate bearing. What I lose on the cantilever swings I gain on the plate roundabouts. Top it is.

By inserting a PTFE [US:Teflon] disk between the wormwheel and 7" junction cylinder I gain a very large, slipping clutch. [see image] This would provide more driving force without risking damage to the wormwheel during manual or driven slews. The entire weight of the OTA and Declination Axis would load this clutch disk. The Beacon Hill wormwheels use three, radial nylon plugs in their hubs which rub on the axis for their slipping clutches. Stainless steel grub screws provide adjustment of friction levels. How these small pads would cope with a powerful stepper motor during a Goto slew is anybody's guess.Chris Lord seemed to suggest it wouldn't work with a heavy mounting and OTA.

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2" shaft mounting Pt.63 It's all weighing me down.

Here is the original component weight list from an earlier post.
All weights are approximate.

                                    Lbs   

Dec Hse + PA shaft.....62.0   
Bare dec shaft.............28.0
PA hse.........................28.0
Saddle...........................3.5

RA wormwheel..............8.5
2 Worms + bush............6.0
Dec wormwheel............5.0

2 x worm plates............5.0
                                   ___      
Total........................~146.0

Fork............................25.0
Counterweights..........45.0
OTA...........................40.0

New Total................~256 lbs !!

Plus front plate and turnbuckle. Then there is still the weight of the two, 10mm plates for worm support to be added. Plus the stepper motors, pulleys and drive belts.

I also weighed my now-resurrected folded refractor at ~35lbs without finder or the full length, slip-over dewshield. I removed one solid, stainless steel handle from the objective's bayonet plate to improve the rather nose-heavy balance. A finder somewhere near the focuser will also help improve the balance point. A shorter tail on any refractor reduces the arc of movement at the eyepiece when swinging from vertical to horizontal.

I shall fit the folded refractor as the first test of the new mounting. Hopefully usable from a seated position when  pointing overhead and using a star diagonal. So high was the folded refractor on the MkIV on its tall pier that I needed a stepladder to mount the OTA and to observe!

By sitting on a suitable object and using a tape measure I have discovered that I need a minimum eyepiece height of 120cm at the eyepiece. This is with the 2" star diagonal fitted and the OTA pointing overhead.

The bare mounting's declination axis is 55cm above the ground when horizontal and the saddle to the east or west of the polar axis. The folded refractor is 85cm from the eyepiece to its center of gravity. Which would place the eyepiece 30cm below the ground on the bare mounting. 55-85 = -30cm. By adding 30 cm to 120cm the pier needs to be 150cm high to bring the eyepiece to 120cm. To double check: 150 + 55 = 205.  205 - 85 = 120. ✔ Which is the required eyepiece height. [i.e. When the OTA is vertical, the star diagonal is fitted and the telescope is focused at infinity.]

This pier height seems rather high considering the MkIV's pier is 160cm high and the MkIV mounting much more squat than the big new mounting. I was hoping to avoid climbing ladders to mount the OTA. Albeit in the [hopefully] short term until I have built the observing platform. The answer is to put the folded refractor back on the MkIV to check my calculations match reality.

I thought I'd make a slotted steel angle, pyramidal pier to use as a test stand. The broad base can be covered in thick plywood and loaded with paving slabs to ensure total stability. I don't want the heavy mounting toppling! One "drop test" is more than enough!

The distance of the counterweights from the Polar Axis are not very different from the distance to the axis of both refractors. So any similar OTA would require quite similar counterweights to their own weight to balance. 
 
I have been using a digital luggage scale to weigh the individual parts and it seems close enough.

After an overnight frost the temperature has risen to 42F. With my being in the workshop and breathing out moisture, every metal, glass and plastic surface is covered in visible dew! The rain and high humidity don't help.  

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