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Idea's to connect motor to dome to drive it


ribuck
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Hi all,

I had been working on my automated dome project but i've hit a snag. I've tried using rubber wheels to turn my dome, but they just aren't getting enough traction to turn it properly.

Can anyone sugguest any ideas on how to physically attach my motor to my dome to get enough traction to turn it.

I'm starting to think of some chain and cog method just dont know where to start to find such chains or how to attach them to the dome.

Rich.

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I'm sure one of the domes in the Dalby Forest Observatories is chain driven. I believe the chain is fixed to the underside of the dome base, and a motor bolted to the obs wall, has a chain driven sprocket which mates up to the chain. It is all well covered to prevent visitors getting grease all over their clothing.

The chain seemed to be fitted inside a metal channel, to facilitate the proper curvature. It is a very positive drive, and necessary, as a friction method would be a bit unreliable.

I would imagine this to be an expensive way to do it though.

Ron.

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Just a thought about the above from Barkis. If you mounted a motor on the wall (ie fixed) with its drive pointing up into the dome, then a sprocket wheel would mesh with a chain that was secured around the dome (the chain being flexible in one direction only - assuming bicycle chain type). If you have the motor well geared down then you would not need a particularly powerful motor. I wonder if a car window motor or windscreen wiper motor would be OK - for a 12v power supply, of course.

Hope this helps.

Edited by Bizibilder
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You could make up some clips from thin steel that the chain would "clip" into? You may even get away with "U" staples round the chain pins - if there is also enough room for the sprocket - maybe use a wide motorbike chain on a thin push bike sprocket to give yourself enough room?

A thought - Do you need to be able to rotate the dome a full 360? maybe just a segment - enough for a couple of hours rotation - would be enough. You could then just have several bits of chain (or one moveable chain segment) and move your motor to suit?

One thing about slow systems - like the one to drive a dome - is that they can be very crude and still be entirely successful, its only when things start moving "quickly" (whatever that means!) that the system has to be set up to run precisely.

PS I've just read your other threads - looks like an interesting project!

Edited by Bizibilder
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Thinking crudely!! If you were to use a short chain, all you would have to do is secure the ends! (With a couple of nails!!) The bit between would still work as the sprocket wheel pushed against it - after all - bike wheels all work slack!!

Hope this helps. (With added sophistication, of course)

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Hi John,

Thanks for the links, Yes it needs to be flexible as it's for a circular dome so unfortunately the first link is no good and the second link wont work as they are only 70mm long so i would need lots and lots of them.

The sprocket is also tiny as they are designed for moving very lightweight small robots and unfortunately i'm trying to move a 6.5ft wide dome weighing about 30kg.

Rich.

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How much force do you need to rotate the dome?

We use 6RPM motor/gearboxes to drive the scope tracking, they may well be too slow for you use.

A wiper motor/gearbox is a useful source of power and because of the gearing has a lot of torque for few amps; it is also reversible.

I would suggest the dome be supported on say 2" dia bearings and they that rotate with the dome. Using rubber will give you a lot of extra drag.

You could always use a cord drive, much like the old radios used to use to move the pointer on the straight dial.

PS Here are a few pictures of the main dome and it's construction. http://www.astronomycentre.org.uk/modules.php?name=coppermine&cat=5

Edited by keithatrochdale
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Hi Keith,

The motor isn't the problem, I have a very high torque Parvalux motor which is capable of shifting over 120kg+ easily. It's geared to 6PRM as well.

I just need a way to physically connect to the motor to the dome, i.e. some sort of chain or belt drive system.

Keith can you elaborate on the bearings you mentioned ? Are the bearings themself part of the ring mounting structure ?

Rich.

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If its only 30kg why does the tyre method not work? Does the dome sit on roller skate wheels or alike to make sure it spins freely?

The bike chain and sprocket would work pretty easily if the motor was fixed and you wrapped the chain round the OD of the dome.

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John,

My dome has 3 large industrial grooved castors which sit on a home made plastic ring. I think a lot of the problem is that it doesn't run 100% smoothly, so i'm looking at the problem from 2 different sides.

I'm first looking into getting a better running system, just waiting to hear back from some people, if i get it running more smoothly the rubber wheel may work, but to be 100% sure i'm looking at other methods.

I just found a great pic a few moments ago, which may solve the problem of how to attach a chain.

It looks like some people have been using a double chain configuration, using one of the chains to attach it to the dome and the upper chain to drive the dome.

looks like a simple way to attach it.

double_chain.jpg

Edited by ribuck
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