skybadger

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 Mike.

I also wanted to thank you for the invaluable information on your sky badger website - I've ben browsing it for the past few weeks and have picked up lots of valuable information from it. I didn't realise you were active on SGL.

I'm also going to implement your suggestion of timing belt (as described on your website).

So if I may, can I briefly outline my plan to you for dome rotation, and if you are able to suggest any improvements that would be great:

Two suitable [will use a spring scale to measure] motors, each fitted with a timing pulley, 180 deg separation. Timing belt laid face inwards along inner circumference of base ring. Will fabricate steel motor brackets that hold the timing pulleys against the belt under spring compression - effectively a suspension system.

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 ?

I'm astonished if the inclinometer gives you that accuracy, and the magnetometer wobbles all over the place due to the changing metal distribution of the mount and you moving nearby presence.

I would expect the gyro to be able to point you at 30' accuracy though.

Mike

There have been thoughts on tracking the end of the telescope via a 3-axis gyro or magnetometer to tel the dome where to rotate to base don the position of the scope.

Creating your own hand controller using the arduino should be a good project, the power drivers are cheaply available on ebay, so it comes down to getting the code doing what you want.

There's also a kit IR hand remote on ebay for a couple of pounds - just include the interface on your shield.

I'm not sure what you intend the gyro unit to do though.

Good luck

Mike

Next task is shutter control. Anyone used a light winch?

I have now also bought a second hand Polaris. I believe it is the older older model since there are wall flanges that prevent use of a driving wheel on the internal rim. To address this I am just replacing two of the support wheels with pulley wheels driven by a motor attached to the frame. It needs at least two pulleys wheels since not all support wheels are in contact. I may yet drive directly this way if I can't get even enough conta t and have to go sprung.

Positional control is via the magnetometer over rf to the dome, which requires a solar panel, a battery and a charge controller. No great shakes there. Motor control from robotelectronics.co.UK and pointing via POTH from ASCOM to address rates and flip. The primary issues I have found using this is that the battery must get enough charge during the day. Not always easy.

Mike

If you are taking pictures of objects like planets, you will need to magnify the image to a decent size .

Most people do this two ways - eyepiece project or barlow projection . Afocal projection introduces too many surfaces that aren't required unless you are using a camera you can't take the lens off.

Eyepiece projection and barlow projection use either the barlow or an eyepiece in the way. I use both frequently.

I find that if I focus the eyepiece in the eyepiece projection mount its only a small difference in focus to have the camera focused when you swap them over. The biggest issue is making sure that the image in the eyepiece is in the centre so when you put the camera in, you can see it at all. My normal way of getting around this with a bright object is to defocus a large way and then you are bound to get a portion of the image in the field. Focus and re-point and you are done.

The barlow is similar but the range of magnification you get is smaller maybe x2-x5,  where you can pick and choose from your eyepieces and the back focus distance used  more easily to get a projected  image size you are comfortable with.

I don't think I understand your reticence about additional focus distance - the barlow and eyepiece projection methods add lots of distance to the end of the telescope.

Coming back to DSOs and extended objects - for those you won't normally use any projection at all and considering the size of saensor you have,  the 1.25" nosepiece will do fine.

Mike

Err,no. You cannot run ascom over the network unless you have fancy serial over ip or manage to get dcomm remoting working.there is indi however .

Here's mine - its a Boots beauty case and contains almost everything. The foam I get from a local materials shop and carve with a very sharp scalpel to any shape needed. I did try wetting and freezing but its a lot of grief for not a lot of benefit.