Powering a Rotating Dome

[OzDave]

I've been thinking about how to get power to the upper (rotating) part of a dome observatory. Obviously powering the fixed lower portion is easy, but getting power to things sited in the rotating portion is non-trivial unless you fit a battery in the rotating part. That is one possibility, but I wanted to see if anyone had ideas for other ways to get power to the rotating part.

Ideas I have seen:

1. Dome part is only powered when in home position and relies on this position to make contacts for the power to flow. When not at home, the dome does not have power in the rotating portion.

2. Slip-ring system, where there are power rails going around the fixed lower portion and some kind of brush transfer mechanism attached to the rotating part to transfer power.

3. Some kind of contactless slip-ring system, which I've not been able to find out much about yet. I guess that would have to be based on induction or something.

Has anyone got experience of powering rotating things?

David

[FraserClarke]

2. Slip-ring system, where there are power rails going around the fixed lower portion and some kind of brush transfer mechanism attached to the rotating part to transfer power.

This is how big domes are powered. We have this system in our dome, but I'm afraid I don't have any information about the manufacturers.

You can get also get signal slip rings which will carry relatively fast network connections through a rotating joint, but I imagine most people just worry about carrying mains power and then use wifi/radio for signal communications.

[OzDave]

I think slip rings are probably overkill / too complicated / expensive for a small backyard dome. I am currently thinking of a battery in the rotating part to provide power for shutter and perhaps some lights. When the fome is parked the battery can either be manually hooked up to charge or could mate with charging contacts only available in the home position.

Sent from my iPhone using Tapatalk - now Free

[FraserClarke]

Sounds like a very sensible approach for a small dome, especially if you're going to be going into it regularly.

[Chris Rowland]

My only experience is powering a compass sensor that transmits the dome position to the controller. That runs off 2 AAs and I'm going to accept that they will need changing every year or two.

For more power I'd be tempted to look at having a battery that's kept topped up with a solar cell. A 12V 7Ah battery should be enough to drive a shutter and a small solar cell that's enough to keep it charged costs about £10 when it's on offer at Maplin's.

Do you really need lights on the dome?

Chris

[OzDave]

Primarily I would want power for the shutter, but I thought some LED strip lighting in the top section might be useful from time to time. Not very often obviously if I'm not in the dome and it is set for an imaging session. But during maintenance, it might come in handy to have some lights. They are a secondary concern really though.

I agree that a 12V 7Ah battery should be able to do the job and I think that this is the route I will take. The solar power idea is good also as we do get a lot of sun being in Greece. I think when the dome is parked, I could make it so that the top part switches to mains power rather than battery, and the battery goes into charge mode. I'll have to figure out how that would work electrically as I'd like it to be automatic when the dome is in the home position.

[dmahon]

What compass sensor do you use?

[OzDave]

What compass sensor do you use?

I was going to build a 2-bit rotary encoder wheel that will follow the dome rotation. I got that idea from the pages on lesvedome automation. I plan to build the mechanics either from suitable lego pieces with the optical detectors mentioned on the lesvedome page, or buy a rotary encoder potentiometer thing and sttach a wheel to that and some sort of sprung bracket arrangement to make it follow the dome.

I would hook up the encoder to an arduino board with some custom software.

This is all hypothetical at this stage as I'm yet to build the obsy. Just planning things....

Sent from my iPhone using Tapatalk - now Free

[skybadger]

Did the battery and charger thing for my dome. Works fine during summer, needs a larger solar panel than 4W for winter..