DIY - Dome Automation

[pmlogg]

Thanks for that.

I searched on the Levedome group and found someone in Ireland who was trying to motorise a Pulsar dome in March 2009. I couldn't find any details of the final result so I've emailed him to find out how he got on.

It is the first step, achieving drive to the Pulsar dome, that poses the greatest problem as the design does not leave much clear space for mounting of drive chains etc.

[ribuck]

What is the main concern you have ? attaching some kind of chain etc to the inside of the dome due to it being fiberglass ?

you could possibly try something like strips of pvc like this and see if it would stick with hot glue, then you dont have worry of screw holes in fiberglass. Just not sure if would work in winter as glue becomes very brittle when the temprature drops below zero.

[pmlogg]

Sorry for not previously replying to your post - I was away on holiday and it was long off the bottom of the list when I got back.

The system in your image is what the Pulsar owner in Ireland is planning to try. He has the kit but when I last emailed him he hadn't yet tried to fiti it to his dome.

It is the way to fix the driving surface to the dome that is the problem. The Pulsar is constructed in 4 quadrants with flanges projecting inwards around 40mm. Sealant is applied between the matching flanges and bolts pass through to hold the structure together. As a result there is no smooth surface to mount a trackway or chain. Cutting a section out of the flanges would be one option but I would be worried that the quadrant sections might not stay rigidly together.

Another option would be to build out from the dome wall itself but 40mm is a lot of building out to be supported by the dome walls. Perhaps a combination of the 2 methods might work, cutting part of the flange away but not all the way back to the inner surface of the dome and then building out to the thickness of the remaining flange depth. Using 4 sections of perforated track it would seem possible to space the holes so that they wouldn't line up with the residual flanges.

Having had my dome for some months now I have not yet found hand rotating to be a problem. The shutter is wide enough, with the telescope I'm using, to mean that I can leave the dome for up to 30 minutes without having to adjust its position. I don't know how much longer I would want to leave the system on its own anyway without checking for cloud cover or simply that all was still going OK.

Motorisation remains a goal but one that I have decided to put onto the back burner until I have the time and money to devote to the project.

Thanks however for your advice which I will refer to when the time comes.

[GeoC]

Some progress made. My device uses a car wiper motor to rotate the dome. A rubber wheel presses against the smooth outside surface of the fibreglass 'ring'. To increase friction a strip of non-slip tape seems to work well.

See video here

I am now building version 2 and hope to incorporate a quick release mechanism so that the dome can also be rotated by hand.

George

[pmlogg]

George

Thanks for the YouTube link. I enjoyed the video clip.

I could see that the mechanism was not fitted permanently so movement was necessarily gentle. Do you envisage being able to rapidly slew with the mount or just use the proposed quick release for simple push alignment?

With the motor moving with the dome, how to you see the electricity supply to it - a battery like Pulsar's own system? And for maintaining alignment of the OTA and shutter during tracking is your plan to the motor system sense the rotation of the mount or do you have another control system in mind for that?

Finally, how is the build of Version 2 going?

Thanks

Peter

[GeoC]

Hi Peter,

Sorry not to have replied sooner - I only just saw your post.

Version 2 has come and gone. The mechanism was attached firmly to the dome but I found that the rubber friction wheel tended to slip in some places around the dome. This may be due to the variable thickness of the fibreglass - 4-6.5mm.

I have now tried the method I suggested in earlier posts, namely a timing belt and pulley wheel. I used car body repair stuff to make the inside of the fibreglass smooth, and also used it at the four joins on the outside. This is shown on my website page - Pulsar 2.7m Dome Automation

which will answer some of your other questions.

The battery goes around with the dome. I will try to use infra-red or radio links to avoid trailing cables, but that may be a few months away still.

The mark III version has passed the initial tests as shown in this video

I still have a quick release system in action, but I think I will be able to do fast slews with this method.

George

[skybadger]

I haven't checked the entire thread to see if I have already put this up there - I have an instance of a car wiper motor using a sprocket on timing belt glued to the inside of the dome. The motors on on sprung brackets. The drive for the motors is powered by dc power from teh central battery. The power for the position sensor is a magnetomer (magnetic compass) accessed through wireless I2C over an easyradio link.

The details are www.skybadger.net

regs

Mike

[pmlogg]

George, I've had a look at the video clips and your web pages. I see that your system follows the same principal as the factory version for dome rotation but with a more positive connection via the timing belt. Have you tried the system yet in conjunction with your position sensor attached to the mount?

Mike, I see that you are able to have the motor conventionally mounted on the non-rotating wall. This is ideal but hard to achieve with the Pulsar domes - I'm still waiting to see an example of someone who has achieved it. With the motor moving with the dome a wireless control system would be the preferred long-term solution.

Thanks

Peter

[GeoC]

Peter,

I am awaiting delivery of two tension springs that will keep the pulley wheel in firm contact with the belt. I can then start refining the electronics. I am not using a position sensor as such, more a dome obstruction detector. The infra-red sensor will sit on the end of the telescope and will sense when the edge of the aperture is coming close and then rotate the dome out of the way.

[Gina]

Peter,

I am not using a position sensor as such, more a dome obstruction detector. The infra-red sensor will sit on the end of the telescope and will sense when the edge of the aperture is coming close and then rotate the dome out of the way.

That's a good idea

[GeoC]

The tension springs do a good job of holding the wheel firmly against the timing belt, and also allow an easy quick release for manual slewing.

The mechanical part of the construction is now complete.

The next step is to put the electronics into a project box and refine the software for the microcontroller.

George

[GeoC]

The mechanical parts are now working well. The first attempt at wireless control had problems because the range of the transmitter- receiver was feeble. I will move to 433MHz.

Till then I am using a simple timer that moves the dome a small amount every ten minutes. The rate can be varied for when a slower speed is required.

This web page chronicles the project

Pulsar 2.7m Dome Automation

George

[GeoC]

The new 433MHz wireless control is a big improvement. The project is now at a useable stage. See the video demonstration: