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Automating a 2.1 metre Pulsar Dome. Phase Two- Motorised Shutter

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After automating the dome on my Pulsar Obsy which has been a revelation, I have spent a considerable time researching how I could automate on what is a very basic manual shutter. The existing shutter slides on the aperture side of the dome and supported by two curved aluminium rods at the rear. What I will require is to create a runner system to allow the shutter to open & close smoothly, be aligned & contained to enable attaching a motor and drive system, thus allowing software automation.

The rollers are 30 mm dia nylon roller bearings, four per side of the shutter opening. This will allow the shutter to slide smoothly over the open aperture.



The rear side of the dome needed to be built up so I could affix tracks to enable the shutter to slide smoothly to the rear of the dome. This was relatively tricky as I had to build rear track support blocks to line up with the existing shutter. I plumped for wooden supports as I had to mount the on a sloping curved dome and as they had  to be mounted vertically, creating some rather complex compound angles and curves. These were bonded in place and further secured with stainless screws from within the dome. Then having formed the arc in which the shutter will run I attached UPVC strips to complete the assembly. The sides will be cladded with UPVC.


The calculations had to be quite precise as I didn't have much breathing space :shocked:


To be continued...........




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Side supports have now been fitted to the rear roll off section of the Dome and does it need a clean :shocked:


Next is to build the Shutter Motor Assembly:-


Unfortunately, installing the motor requires a cut-out in the roof of the Dome. A barrier will need to be built to stop any water ingress.




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Motor assembly has been built & installed in position with the Observatory Dome:-


Next.....To bond the drive belt to the base strip & initial test.


Edited by sloz1664
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  • 1 month later...

Hi @sloz1664 Steve,

That looks absolutely fantastic!

As you know, I've been following your work and implementing your design in my 2.7m Pulsar. I've got the timing belts fitted, and am about to test the rotation. However, I've already tested the shutter drive and found that my 12V wiper motor isn't up to that task. I can open and close the shutter, but it's a heavy shutter and the load on the motor changes significantly across the range of travel from fully open to fully closed. The torque available is not enough to keep the movement under control.

I see from your images that you're using what looks like a planetary gear motor. I've been looking at these ones: https://gimsonrobotics.co.uk/categories/dc-electric-motors/products/gr-ep-52-high-torque-planetary-gearmotor-12v-and-24v-versions and they have much higher torque and lower output speed than the wiper motor - plus the smaller body diameter means I can use a smaller timing pulley without the motor body catching on the shutter, which will also help. So this seems like a better choice - and as far as I know is similar to the ones used in the off-the-shelf Pulsar solution. 

Does this look sensible to you - and could you tell me which motor you've used?

And one other question - can you explain how, in your bracket, you've managed to support the motor at the end opposite the pulley? There's obviously enough play in that to allow the spring to keep the other end in contact with the belt. Very nice.




Edited by NigeB
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Hi Nigel, 

Nice to hear from you. Going back, my original shutter was certainly not designed for automation and I had to modify it so much to make it run nice and smooth & also to ensure it keeps aligned to contact the limit switches. The motor is a Chinese clone, purchased on Ebay and unfortunately I have no details to hand. I will investigate and report back.  I didn't want to buy an expensive motor as, to be frank, I didn't think I could modify the shutter to be able to motorise it. The motor has enough guts to driver the shutter, but kept slipping on the drive belt, due to flex in the shutter and I've had to add some modifications to enable it to run smoothly. 


The two rollers stop the shutter from lifting due to the pressure between the drive gear and the drive belt.

Automating the shutter is still an on-going project. I have built Hugh Gillespie's Magic Wire project and I have installed it in the Pulsar. I have it opening and closing the shutter, but, I'm having issues with the limit switches not working as they should.

I have attached the Magic Wire manual for your perusal. If you need any addition information please do not hesitate to ask.


Magic Wire Manual.pdf

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Hi Steve,

Many thanks! Interesting, slippage is what I'm also seeing (but only the first few cm, which I understand in terms of the force exerted by the shutter at that part of the travel, and I think I may be able to fix it with some better spring tensioning design for the motor mount). I can see how the wheels you've implemented would help this.

The other problem in my case is the lack of torque from the wiper motor, and that's more fundamental. Those planetary gear motors are much better from that perspective, but tricker to mount - however, I may need to embrace that challenge. In parallel I'm also weighing up the chain approach which @hughgilhespie has implemented. Your system seems to work beautifully. But the 2.7m shutter is pretty heavy, and I'm slightly concerned that for this reason, the timing belt might be "on the edge" for shutter operation in my setup. At least the same motor can be used for both approaches, so it's not a big financial hit to try one then the other - but I want to avoid cutting the dome and then finding I have to adopt the alternative approach. Some temporary fixings may be in order.

I've also got MagicWire as part of the system (I had some exchanges with you via the SGL messages channel a while back) - the boards are made up and seem to be functioning. It's just those awkward little mechanical gremlins that I need to combat!

I put a telescope in the dome for the first time last night. Even though the automation is not ready yet, I can't stand seeing the clear evenings we've had lately and not be able to at least take a look at Mars and the moon...

Thanks for your ongoing postings - they are really the primary guide I've been using to implement the automation of my system.





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Hi Nigel, 

In retrospect I would have implemented the "full loop" drive chain approach, but I was worried about what happens at the fully open & fully closed positions and the amount of play this system has. However, the limit switches take care of this as they switch off the power and any play is taken up by gravity. The drive system I implemented, requires accurate placement of the limit switches and no allowance for error, which is a daunting, as if I had a limit switch failure it would keep trying to drive the shutter past it's stop. To overcome this I have checked the ampage under full load and fused 1 amp above this load.

Have a look at a more powerful truck windscreen motor, although I would have though a standard windscreen motor would have sufficed. What sort of sliding mechanism is your shutter using at the moment?

Just an update. After a few discussions with Hugh Gillespie regarding the electrical gremlins I had, I now have a fully functioning shutter system and are now implementing the safety systems ready for a fully automatic system. 

BTW the Magic Wire system works a treat :)


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Hi Steve,

That's interesting. I'm toying with the chain approach and have had a very helpful exchange with @hughgilhespie regarding the design of his system, in parallel with the discussion with you here. 

I'm reluctant to give up on the belt yet - you've clearly managed to make it work, and actually seeing some of Hugh's solutions to the chain guide, has given me an idea for improving my implementation of the belt drive. I got the dome rotation working at the weekend (relief!), but in doing so I realised that the pressure needed between the pulley and belt  to get skip-free performance was somewhat more than I'd expected. I can't possibly get that on the shutter in the current version. But I can now see how to mount a metal support frame inside the top of the dome to achieve that. Combined with a higher torque motor, I think this might work - and if not, the motor will be useful for the chain.

Re: sliding mechanism. It's quite a nice design - the shutter has a set of plastic (maybe PTFE) cylindrical blocks bolted to the inner surface of the sides. These engage in a wide groove which is moulded into the outside of the raised lip which runs on either side of the slit from front to back. The groove is closed at each end so once you bolt everything together, the shutter slides smoothly back and forwards but can't drop out.

For now I'm going to focus on getting the rotation finished and stick to manual shutter, but as soon as that's done, I'll upgrade the shutter motor/mount and see what happens.

Thanks again !




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Well, last night I set up SGPro to run 5.5 hours of images to start at astro darkness, a test for the newly implemented shutter and the dome in general. At 9:24 pm SGPro kicked in, connected PHD2, opened the shutter, slewed the mount to the required target and synced the dome. So far, so good. After plate solving and focussing the imaging commenced as normal. So off to bed and see what tomorrow brings. Awoke to the Dome sitting in it's parked position and the shutter firmly closed. On entering the Obsy I found the mount parked and 5.5 hours of images stored on the hard drive. The one failure is a vbs script I had written to power off the electrics had not been implemented. Not a big deal as I know this works perfectly in Voyager.

One happy chappie


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3 hours ago, sloz1664 said:

Well, last night I set up SGPro to run 5.5 hours of images to start at astro darkness, a test for the newly implemented shutter and the dome in general. At 9:24 pm SGPro kicked in, connected PHD2, opened the shutter, slewed the mount to the required target and synced the dome. So far, so good. After plate solving and focussing the imaging commenced as normal. So off to bed and see what tomorrow brings. Awoke to the Dome sitting in it's parked position and the shutter firmly closed. On entering the Obsy I found the mount parked and 5.5 hours of images stored on the hard drive. The one failure is a vbs script I had written to power off the electrics had not been implemented. Not a big deal as I know this works perfectly in Voyager.

One happy chappie


Brilliant result Steve - congratulations!

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