Usual apology for not posting things in a frequent or timely fashion. This post will probably be quite boring to anyone thinking “OK, where are the pictures of galaxies?”
One of the hardest things we have been trying to achieve is getting the dome to rotate electrically. I read online that you could do it with windscreen wiper motors, so I went to the scrapyard in Tottenham on White Hart Lane.
The gentlemen there can get you loads of stuff and seem completely unphased by my not caring what car it comes from. I’ve been back to visit a second time now as we destroyed the first couple of motors.
They come with part of the old mechanism attached but Edo got that off and cleaned them up for us. The idea is to attach a cog on the end and then use it to drive timing belt which we put up all around the interior of the dome. Timing belt is the belt with teeth on inside a car engine which coordinates the opening and shutting of the valves with the rotation of engine. They couldn’t sell us this so we had to buy it from a specialist who was able to get us a single 10 metre length which was good as we need more than 9 metres for our 3 metre diameter dome. We also bought a cog from them.
The rest of what we did is better explained in video form. So if you are interested, feel free to click but beware, this has been a lot of fiddly frustrating work by Edo, Sunayana and myself over the summer and the length of the video reflects this.
So you see it only goes one way, but we hope to fix that soon. Please note there are TWO switches. One is to make it go left and right, it will only go left for now but we will fix that. The other is currently top secret. All will be revealed if we ever get phase 2 to work. Sorry, WHEN we get phase 2 to work…
Dark London Skies 
Hi, Malcolm,
Please contact me – I’d like to talk to you about your experience in motorising your dome using a timing belt system (and computer control). I’m hoping to do something similar with my own dome. Regards, Peter.
Well we aren’t using computer control, never got round to it.
But the timing belt and cog and windscreen wiper motors work well
What works less well is our crappy mounts for the motors. I wouldn’t offer advice on this as ours are unreliable. But definitely make them out of metal…
Thanks, Malcolm. You say ‘motors’. Does that mean you have more than one? Are they mounted diametrically opposite to even the load on the dome? Or did you need two to provide enough power? Do you nudge them occasionally to keep pace with the sky? Using an Arduino perhaps. In which case do you use PWM to slow the motors down or just tweak a relay momentarily? Sorry for all the questions – perhaps you could email me direct and then I could telephone you? I’d definitely use metal – I have some large aluminium angle from a project years ago 😉 There is an Observatory page on my web site, and you can see there is a solid timber rim right round the dome at a suitable position to accept a toothed belt. Oh, just a another question, what glue did you use?.
Hi Peter, exactly, they are mounted opposite to even the load on the dome and I reckon we would need the power of two anyway for our old dome. You might have a very super smooth and sturdy and light action in which case you might get away with one. We trivially got the arduino to move the dome but we couldn’t work out a reliable feedback mechanism to log the position of the dome. What do people do generally? Truthfully this was a project which I never had time to complete. Currently my undergrads are desiging parts to get the rotation working again more reliably.
We found a company in the UK who made the large cogs and the very long timing belt for custom jobs like ours. We used Evostik to stick the belt on :- http://www.screwfix.com/p/evo-stik-impact-adhesive-off-white-to-amber-250ml/38770. I’ll check out your website as soon as I get a minute.
Thanks again, Malcolm.
If I go the toothed belt route, I plan on using HTD pattern, 8 mm pitch – is that near yours? If you browse this thread (it’s quite a long one and you’ll need to enrol to see the photos) you’ll see what another guy has done, including Arduino code for computer control, and get some idea of what I’m thinking of doing.
http://ukastroimaging.co.uk/forums/index.php?topic=65588.0
Peter