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I have had the friction wheel, drive assembly clamped to the octagon since I built it. There was every chance it would fail to perform or become unreliable. So I left it clamped despite it looking ugly and unfinished.
Today, I decided to screw the parts to the octagon top ring. I chose to use 100mm [4"] galvanized, roofing sheet screws. These have an 11mm hex head which means I could use a hex socket ratchet for speed and torque.
The bicycle crank, fitted with a cut down plastic pedal spindle, is fixed to a sealed, bicycle, bottom bracket bearing and axle. The hole for the BB is skewed in the 2x4 lever arm to bring the 4" industrial urethane wheel tangential to the dome's base ring.
I had to find the longest, one piece, sealed BB axle available. This was to ensure clearance for the crank as it turned in one inner "corner" of the octagon. It just clears the hold down disk on the nearest dome support wheel bracket. Provided the handle [plastic pedal spindle sleeve] on the crank is used normally there is no danger of trapped fingers.
I had to find the longest, one piece, sealed BB axle available. This was to ensure clearance for the crank as it turned in one inner "corner" of the octagon. It just clears the hold down disk on the nearest dome support wheel bracket. Provided the handle [plastic pedal spindle sleeve] on the crank is used normally there is no danger of trapped fingers.
The far end of the 2x4 lever supports a 5kg [10b] weight. Due to the leverage, this provides a much greater upward force on the 4" friction, drive wheel under the dome's base ring. The upward force is enough to produce clearance from the nearest dome support roller. If the roller were to take up any of the downward load then the friction drive roller would probably slip. I left the support wheel in place as insurance to avoid changes in dome level as the drive roller rose and fell.
In practice there is never any slippage and the effort required to turn the drive crank is absolutely trivial. The push or pull on the crank is so light I can turn the dome with my pinky. [Little finger.] Yet it has provided a 100% reliable drive since the moment I installed it.
The lever's pivot axle [fulcrum] is mounted in the pressed steel frame from which I borrowed the 4" urethane roller. The BB bearing is clamped to an aluminium plate via its own clamping ring. The plate is then bolted to the lever arm.
I had to remove the bearings from the friction roller to make it solid with the crank axle. Otherwise the crank would just turn and the roller [and dome] stay still. A square axle, cut down crank boss was pressed into the roller bore. I needed my lathe to make the crank boss nicely square to the BB axle and cylindrical to the exact size [Ø] to fit the roller bore. I still have plenty of old bike spares bought as complete bikes for donor materials. It was cheaper to buy a whole mountain or racing bike, back then, for less than £5, just for a nicer brake. Than to buy a single brake fixing bolt from a bike shop. All the bike frames went to the recycling yard eventually but I kept any spares which might come in useful.
I had to remove the bearings from the friction roller to make it solid with the crank axle. Otherwise the crank would just turn and the roller [and dome] stay still. A square axle, cut down crank boss was pressed into the roller bore. I needed my lathe to make the crank boss nicely square to the BB axle and cylindrical to the exact size [Ø] to fit the roller bore. I still have plenty of old bike spares bought as complete bikes for donor materials. It was cheaper to buy a whole mountain or racing bike, back then, for less than £5, just for a nicer brake. Than to buy a single brake fixing bolt from a bike shop. All the bike frames went to the recycling yard eventually but I kept any spares which might come in useful.
Most observatory owners go to enormous lengths to avoid manual drives. They use computers and software and racks and gears and endless complexity to use a drive motor with all that entails. When I am observing or imaging I rise from my seat for only a moment. Give the crank a gentle turn and the dome rotates effortlessly to its new position. Though it can get noisy when I really rev it up for a few practice turns.
The drive is also instantly reversible and faster accelerating and spinning than most amateur's [or professional's domes.] The length of the crank and the ratio between the 4" wheel and the 10' dome base ring has proved to be absolutely perfect. Though a real perfectionist would add a chain drive to bring the hand crank down to a more comfortable level. I have never felt the need so far. Besides, I'd probably walk into the pedal spindle in the dark!
I'm afraid I have absolutely no idea who that old bloke is in the video below. He seems to hang around here most of the time. He keeps muttering; "All me own work, Guv!" As if it was supposed to mean something. Though, admittedly, he does make quite a handy "extra" for when I need the dome cranking and that sort of thing. Simple jobs like that. I don't let him near anything sharp in case he hurts himself and sues me.
The drive is also instantly reversible and faster accelerating and spinning than most amateur's [or professional's domes.] The length of the crank and the ratio between the 4" wheel and the 10' dome base ring has proved to be absolutely perfect. Though a real perfectionist would add a chain drive to bring the hand crank down to a more comfortable level. I have never felt the need so far. Besides, I'd probably walk into the pedal spindle in the dark!
I'm afraid I have absolutely no idea who that old bloke is in the video below. He seems to hang around here most of the time. He keeps muttering; "All me own work, Guv!" As if it was supposed to mean something. Though, admittedly, he does make quite a handy "extra" for when I need the dome cranking and that sort of thing. Simple jobs like that. I don't let him near anything sharp in case he hurts himself and sues me.
Because YouTube no longer allows embedded videos, without automatically showing new suggestions, I have had to set the video to loop. Hopefully this will save any of Google's porn from showing up on my blog which might be viewed by a younger person. It used to be possible to simply tick a box on YT to stop video auto suggestion after an embedded video ends. Power corrupts. Google power corrupts absolutely.
Click on any image for an enlargement.
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