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The new aluminium angle has arrived safely from Germany. The first 'new metal' I have ever ordered online. Now I can try various arrangements of metalwork to resist worm or motor flexure or twisting under power.
The new aluminium angle has arrived safely from Germany. The first 'new metal' I have ever ordered online. Now I can try various arrangements of metalwork to resist worm or motor flexure or twisting under power.Open side view of the angle wrapped over the motor and simultaneously supporting the worm in its housing.
The 6mm thickness of the aluminium is ideal for putting some tension on the belt. Though exactly how much tension is required in normal use is still an unknown.
The white socket for the motor's removable plug is seen against the black body on the right of the stepper motor. The choice of motor orientation requires that the socket and plug must face either backwards or forwards. It would be difficult to fit the plug if that side was wrapped by an angle profile.
View from the others side with the RA stepper motor 'wrapped' with one angle profile. Another piece of angle leans against the upright leg of the motor angle and rests on the base plate. Both angles would be bolted together and the lower angle bolted down to the base plate.
The polar axis angle of 55° means that the RA stepper motor could be well protected from above by the angle profiles. This would leave the motor cable well out of sight [and danger] under the wormwheel. Since there is no relative movement between the motor and the mounting its cable can be safely fixed to the mounting.
The Declination motor does move relative to the mounting so will need careful attention given to its cable dressing and retention. It should never be assumed that the cable is safe at all telescope orientations. Monitoring the cable cannot be easily carried out in the pitch dark nor from a 'warm' room or remote computer. So every possible orientation must be thoroughly tested against cable stretching or even being cut by moving parts of the instrument.
End
view, without pulleys, showing the arrangement of one angle profile
covering the motor and another resting up against it. Here I have
attached the motor cable to ensure I haven't overlooked any motor fitting
problems.
At 70mm wide [outside] the angle profile dimensions are about 4mm too wide to rest on the base plate when covering the motor. This is easily removed to allow the motor to rest on the base plate.
The shorter inside widths of the legs [or webs] of the 'L' do not allow them to be
'nested' inside each other while still being fully wrapped around the motor.
The difference in stiffness between nested and butted up against each other is probably too little to worry about. The upright legs will be bolted together anyway over a large area of 6mm metal. Probably using countersunk head screws where the angle profiles rest against the motor body to avoid a gap.
The difference in stiffness between nested and butted up against each other is probably too little to worry about. The upright legs will be bolted together anyway over a large area of 6mm metal. Probably using countersunk head screws where the angle profiles rest against the motor body to avoid a gap.
A much simpler motor fixing arrangement would involve a vertical length
of the angle profile acting as the motor and worm fixing plate. The spare
leg of the upright angle would be bolted to a second piece of aluminium angle
resting flat on the 10mm base plate. At 6mm thickness [1/4"] the angle profile would be much stiffer than the present 5mm flat plate. This idea is tempting for its simplicity and visual 'simplicity.'
I think I [slightly] prefer the 'belt and braces' arrangement of both motor-worm end plate and [double angle] base plate support. The only obvious remaining weakness with the more complex system is that the motor itself is held directly only by its end plate fixing. Enclosure by the angle profile provides only something to rest against. Since the motor is obviously designed for one end fixing only I doubt this aspect needs further improvement.
This image shows the motor covering angle profile cut to the full length of the worm housing. I can't see much point in making it any shorter. This will provide maximum support to the worm housing. Vertical [csk head] screws will clamp the worm housing to this angle on the horizontal surface on top of the motor.
AWR says the stepper motors will get very warm in use. This is because power is applied constantly to maintain stator position between poles. Which begs the question whether the motor should [or may] be fully enclosed in bare metal. Or left exposed for natural cooling by convection and radiation to its surroundings.
Does the motor actually benefit from the application of lots of solid metal in close contact? This would certainly increase its thermal surface area and offer a heat sink.
The 70mm square x 4mm wall thickness tube I found last week offers an interesting, full enclosure, solution. Motor end plates held with long studs could easily hide the motors completely from view. Though access would still be required for the plug and socket, the aperture need not be very large. A chamfer at the cable outlet would avoid a sharp edge to chafe against in the longer term.
The workshop was at a miserable 35F, +2C again. Which was very rather unpleasant to work in. I was quite comfortable in my down jacket but my nose kept dripping and my feet were too cold. So I went back indoors to ponder my motor support options overnight.
The double angle arrangement felt rather clumsy and needed a lot of base plate acreage. I would need to greatly extend the base plates if the full angle profiles were arranged on the 'outside' of the motors. A slightly lesser problem if the angles went inside under the wormwheel. Or the legs resting on the base plates were much reduced in width?
But, then, what to do with the cable plug and socket? Exposed to view or hidden with a modest aperture for the plug? Though there is no absolutely no need for the plug to be removable provided the cable has easy egress. Unplugging [if necessary] can easily be done at the end of the short motor cable. Or even back at the Drive Box. The white motor plug need only be pulled when the motor/worm support arrangements are fully dismantled. So no big deal.
I think I [slightly] prefer the 'belt and braces' arrangement of both motor-worm end plate and [double angle] base plate support. The only obvious remaining weakness with the more complex system is that the motor itself is held directly only by its end plate fixing. Enclosure by the angle profile provides only something to rest against. Since the motor is obviously designed for one end fixing only I doubt this aspect needs further improvement.
This image shows the motor covering angle profile cut to the full length of the worm housing. I can't see much point in making it any shorter. This will provide maximum support to the worm housing. Vertical [csk head] screws will clamp the worm housing to this angle on the horizontal surface on top of the motor.AWR says the stepper motors will get very warm in use. This is because power is applied constantly to maintain stator position between poles. Which begs the question whether the motor should [or may] be fully enclosed in bare metal. Or left exposed for natural cooling by convection and radiation to its surroundings.
Does the motor actually benefit from the application of lots of solid metal in close contact? This would certainly increase its thermal surface area and offer a heat sink.
The 70mm square x 4mm wall thickness tube I found last week offers an interesting, full enclosure, solution. Motor end plates held with long studs could easily hide the motors completely from view. Though access would still be required for the plug and socket, the aperture need not be very large. A chamfer at the cable outlet would avoid a sharp edge to chafe against in the longer term.
The workshop was at a miserable 35F, +2C again. Which was very rather unpleasant to work in. I was quite comfortable in my down jacket but my nose kept dripping and my feet were too cold. So I went back indoors to ponder my motor support options overnight.
The double angle arrangement felt rather clumsy and needed a lot of base plate acreage. I would need to greatly extend the base plates if the full angle profiles were arranged on the 'outside' of the motors. A slightly lesser problem if the angles went inside under the wormwheel. Or the legs resting on the base plates were much reduced in width?
But, then, what to do with the cable plug and socket? Exposed to view or hidden with a modest aperture for the plug? Though there is no absolutely no need for the plug to be removable provided the cable has easy egress. Unplugging [if necessary] can easily be done at the end of the short motor cable. Or even back at the Drive Box. The white motor plug need only be pulled when the motor/worm support arrangements are fully dismantled. So no big deal.
I have just ordered some shorter s.s. grub screws for both pulley sizes. [5 & 10mm] This will allow me to make much stiffer 10mm motor-worm fixing plates instead of the present 5mm. The present, overlong grub screws would require very large holes to clear them in the new motor-worm plate. Access for tightening of the grub screws will also be much improved if they are near to flush with the pulley bosses. The unused thread lengths of the ridiculously longer grub screws offers no increased retention at all.
Apologies to those surprised [or even bored] by my endless textual [externalized] discussion. After half a century of making rough drawings I now do all my designing in my head. With my descriptive detail intended to prod my few remaining [sheep like] grey cells into a 'final solution.' This saves on wasting my very limited materials when I am usually at the mercy of scrap yard finds. I like to visualize all my options before committing myself to sawing, turning or drilling. Things must look right as well as perform to the best of my ability to actually construct my visual-textual pipe dreams.
Click on any image for an enlargement.
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