skybadger

Hi Gina. Fair enough but I assumed most of that, which is where the question is coming from. 13M ticks is a small fraction of an arc second per tick, so maybe it's a case of precision not resolution. Hi Hugh. I was looking at the www.harmonicdrive.net product selector pages and also some motors on the bay from FHA. Assuming you behave as if the harmonic gear head is an exceedingly stiff planetary gear, typical ratios are still only 100:1, which means yet more gearing is required. So still looking for that understanding. Mike

Hi all has anyone got any experience of fitting direct drive motors to a telescope mount, possibly replacing the worm wheel with a different drive train ? I'm looking at the catalogues and trying to work out what the likely cost and engineering effort mighth be and talking to someone who has already pursued this would be helpful. I am looking into converting my AE type B mount into a gearless mount driven from a direct drive motor on the botto of the RA shaft or belt driven at the top. The payload of the mount is typically around 30Kg and so I reckon a output of about 15Nm will do the trick, although higher for direct drive. I also read that direct drive with inbuilt encoder can do 13M ticks per rotation but the spec says the positioning precision is 90" - what does this mean ? Any thoughts ? Mike

I recommend the wireless esp too. the ode is easy to setup. the programming process is also trivial as long as you have a good power supply. I have one on the bench being a web server to drive some motors. there's an encoder module, a pid module , the web server, and a json module. what could go wrong ? Mike

Thanks Chris I forget whether its b or C. I suspect its actually a B. The C's were the biggest and had the worm inboard on the cutout polar axis. Only seen that on the 16" fork mount.. The worm gear is under the black strip of home made cover. Balancing is interesting since I haven't got any clutches. Mike

Here's mine. VC200l carrying a short focus 80mm finder on an Altair dual bar. At the other end, a Vixen NA140SF with FLO adjustment carrier, itself carrying a Skywatcher ST70 with Quark, all mounted on an up-rated AE of Luton class B with Skysensor control. Mike

Thanks for that Hugh - one ordered. Was getting frustrated trying to work out what filed was tripping the credit card purchase failure. Mike

Thanks for this. I have been trying withe Webcam and 12mm lens I bought for the purpose. The lens wouldn't come to infinity focus though. So I removed the lens and got a very good image without any lens at all.I need to make it smaller though which means getting closer to the focal plane. To achieve this I pulled the casing apart and now have just the boss camera which I'll glue to a tripod mount on a piece of angle. Cheers Mike

Hi all I am trying to get good clear images of the Foucault test images of my mirrors. The image of the source at the image plane is about 3 to 4mm across. I purchased a 12mm lens for my pc900 webcam to operate at infinity focus but it can't reach it - the lens unscrews. So I tried to get an image without a lens and it was really clear - but also really large . This is taken about 3mm outside of focus using a ronchi grating on my 12" F/2.7 cassegrain paraboloid primary, hence the hole in the middle. What do others do ?. I don't have enough space for access with a DSLR lens. regards Mike

Here it is - took longer cos I forgot. Wheels in interior - on bottom sliding section which slides under the large section. View of overlap between large and small sliding sections. Hope this does what you want. Mike

Not yet - youll have to give me a coupe of days..

Hi choo choo - the wheels just press against the inside lip. So the door slides o the outer rim and two arms come through the slot and hold wheels against the inner rim to stop the door blowing off. The ones I have are the rubber tyred steel wheels from RS or Wixroyd, bought in a bag of 10. Mike

My first dome had a lift off lower piece with a moulded overlap on the top segment. The top just rested on Teflon strip at the edges and was retained using internal wheels running along the inside edge. The current one has a lower piece that slides under the top when pulled up using a cable..Again the top rides on a Teflon strip. I did design a shutter running on allloy edging but it gets complicated and frictional if not used sparingly. Mike

Thanks for the reference. Glad its useful.. Hugh has got one of those new fangled domes - my replacement dome is a polaris with large internal edges preventing a wheel from simply driving the inside edge while pinching against the outer one for tension. My previous dome could also only drive the inside edge for a number of other reasons. So recently I have been doing the same as you and trialling driving the dome with some new drive bogies turning sticky banebot wheels against the edge. My bogies have to fit the narrow gap (80mm) between external wall and internal dome dropped edge. Testing is about to start and some tinkering will be necessary I think. In the end instead of a sprung lever to hold the motor I used a pair of steel rods, some linear shaft bearings and springs to hold the drive drive the wheel in parallel against the outer lip of the inside edge (not complicated at all really...). I'll continue to use the magnetometer to read the bearing until I rig up an encoder. Either way I''ll still need a wireless comms link to the dome to run the dome door opener when I rig that up. Robin from SGL came up with the linear bogies pattern so creds to him. Mike

You'd have to work that out from the weight of your dome and the rolling friction. Or get a spring scale and measure the starting force required and rolling force required to make it move. The torque can then be measured from that. One motor has to be able to exert that force at the radius of the drive wheel you are using. Two motors means you can reduce the required torque by say sqrt(2). You have to remember that the windscreen motors use a worm wheel as the final drive so they get a big torque through a large gear reduction. I am using some other motors with a reduction gear box to the same effect, having used windscreen motors successfully before. The bigger issue s making sure you can get all that torque to the dome without slippage. Hence two or even three motors may be required depending on how circular the dome is and whether you can get pressure on both sides of the dome. regs Mike

Ah, I think that is probably the bit I am missing. Ruler and tape measure did mine. Then a bit of fine tuning. Regs Mike

Yes but those offsets are a one-time entry only based on the location of the mount with respect to the centre of the dome and the height of the mount with respect to the aperture base height. M

I don't understand why you need those offsets. Poth and maxim will both handle them internally. Mike

Don;t you need a space between 'program' and 'files' ?

Did the idea of posting a catalogue of pictures not materialise ?