Motor to drive dome?

[bloodhound31]

Just got a quote from a roller-door company today in Canberra... $12,500!!!!!

All I want is an electric motor with low speed, high torque and a forward and back switch. Something I can put a pneumatic tyre on to push against the inside of the dome ring. How hard could that be? :mad2:

$12 and a half K!!?!??? The whole building thus far has only cost me around 8K!!! What the???


Anyway, I need to drive the dome around. It only weighs half a ton, but I can push it around manually with some effort, but it's easy enough. I'm certainly not exerting half a ton of force on it....

Anyone got any pointers? More importantly, my electrician needs to know how much draw it would put on the electricity.

Baz.

[bojan]

I would be looking into something like sliding door opener..
200W is more than enough, provided gearbox (with worm gear) is adequate (heavy duty).
http://www.ebay.com.au/itm/Nice-Robuskit-Slide-Gate-Operator-Motor-Kit-110V-24V-/120701548700?pt=LH_DefaultDomain_0&hash=item1c1a5f789c (http://www.ebay.com.au/sch/i.html?_sacat=0&_from=R40&LH_PrefLoc=2&rt=nc&_nkw=nice+slide+motor)

We have rep here in Oz (for Nice door opener)

EDIT: here it is: http://www.niceforyou.com/en/2-sliding-gates.html


Or, second-hand windshield wiper motor from big truck.. for example something like this: http://www.ebay.com.au/itm/12-volt-motor-gearbox-/181073800037?pt=AU_B_I_Electrical_T est_Equipment&hash=item2a28d6eb65

Not much more than $50 ~ $100, me thinks.

[bloodhound31]

Thanks matey!

Are you sure a windscreen wiper motor from a truck would do it!!?? I wouldn't think something designed to move a couple of light swing-arms would come even close to moving a steel dome with a 5 metre diameter weighing half a ton.....

[bloodhound31]

What about a 12V 4WD winch? Could I rig that up to a pneumatic wheel to do the job? Would it be strong enough? If it will pull a car out of a bog, surely this is ideal. It would be slow and strong I would think.

Am I barking up the wrong tree here?


Baz.

[wasyoungonce]

Yeah I agree.

I've played with car windscreen motors and had them as garage door openers....they work a treat. Nowdays garage door OEMs use cheaper dedicated motor but the older windscreen wiper motors were excellent, plenty of torque and easy to service.

I've also seen them run on 24V...hooking qty 2 downlight transformers together.

If you try to drill thru the motor output shaft to put on your own cog gear. Use a hand drill at very very low speed. Like 1~2rpm or something like that. They are hardened steel...very difficult to drill unless low speed.

edit:
yep a winch would work...but cost more!

[bojan]

All depends on gearbox.. slower output speed, higher torque.
If build-in gearbox is not slow enough, you can add one more stage (from something else.. power tools?)

[bloodhound31]

Oh OK, no worries. Thanks mate.

Baz.

[ChrisM]

Baz,

I'm pretty sure that turning your (or almost any) dome would be much easier if two motors - installed on opposite sides of the dome - are used. The simple reason for this is that a balanced torque would be provided to the dome, whereas using just a single drive results in a lateral (sideways) force on the dome, pushing it over against one side.

To test this, just get a second person and try it by hand first.

A car winch would probably be absolute overkill.

Chris

[Tandum]

Baz, it might be worth your while to try and PM Bert. He is definitely an automation nut and got my dome spinning like a top. He supplied everything I needed.

[OzEclipse]

Hi Baz,

You can go the overkill route or else you need to work out how much starting force is required to get the dome moving, allow some more for any tightening from corrosion or distortion of the building as it ages and then convert it to torque to work out what sort of motor. How are you going to drive the dome ie transfer the motor force to the dome?

Also decide how quickly you want to spin the dome? Then do you want be able to add a synchronized dome slot control? A 4wd winch motor would be big overkill. They can pull 10 tonnes. Though it might be convenient because they are already geared, they are also very very noisy usually with a high pitched whine. Neighbours might not appreciate it at 3am.

I suggest you go and speak to the guys at Delta Electric down at Philip. they mostly repair motors but I think they also sell reconditioned stuff. You'll need a reversible motor - either DC or a double start AC


Joe

[bloodhound31]

Thanks guys. I will look at each of your suggestions in turn over the next week and ring a couple of the places suggested to see if they can help me with a simple solution.

I intend to place a pneumatic tyre up against the dome ring on the inside to drive it. I may even put a bearing'd roller on the outside, in the narrow gap between the building wall and the dome skirt, just to give it something to push against.

Not sure about overkill being, "huge" with a car winch. I found plenty online that are rated to only one or two tonne. Nothing wrong with a bit of over-engineering, especially when it's only a couple of hundred bucks.

Loving the suggestions though! Thanks to you guys, I now have a few decent avenues to check out.

Bless ya's!

Baz.

[blue19]

Hi Guys.

Saw this thread and thought I would show you my solution, its need tidy and cheap if you can find the right mobility scooter (Must be a twin motor) so you can can have a motor on opposite sides of the dome, all the eclectics are from the scooter itself, dome even beeps when reversing. Drive are direct using rubber boat rollers pressed on the motor gearbox shafts and then they intern site on rollers so the weight of the dome its self provides the drive weight/ friction so nothing slips work as we say down here "Sweet as Bro" check out the link below for all the pictures.

Cheers

Steve

http://blue19.com/gallery5/v/scope_stuff/new-site/?g2_page=6

[TimberLand]

For what it is worth I'm going to be moving my dome with heavy duty stepper motors and 25:1 worm drives one on each side, they are 5 volt 5 amp and I picked them up at a scrap metal yard, these two will pull with about 100kg of force which should be enough for me. Given though the electronics to drive them will be bit custom but that is part of my day job.

The other thought I have is a company in Sydney called Motion Dynamics sells all sorts of planetary and worm drives that are 12-48 volt, DC and brushless and the prices are quite reasonable. I have purchased a number of their combinations and they work as specified.

High power motor controllers that I use are from RobotEq in the states and they are almost bullet proof and drive real heavy duty loads up to 120 amps at 60 volts, they are proportional and reversible and again the prices are not silly.

Just my two cents worth

Justin.

[AdrianF]

I remember a while ago Supercheap had some smallish 12v winches for sale. If I remember rightly they were 2500 lb jobs. Fairly cheap at $99. Should be strong enough to rotate a dome.

Adrian

[bloodhound31]

What's the dimension between the bottom ring and the one above it with all the rollers and wheel sandwiched in between?

[rcheshire]

Barry. I have a 6v 10 lead heavy duty stepper and a 5v 5 lead heavy duty stepper. Welcome to both if they are suitable. Bought them for about 5 dollars years ago. Both big motors.

[blue19]

Sorry I replied higher up the page here it is again.

Hi Guys.

Saw this thread and thought I would show you my solution, its need tidy and cheap if you can find the right mobility scooter (Must be a twin motor) so you can can have a motor on opposite sides of the dome, all the eclectics are from the scooter itself, dome even beeps when reversing. Drive are direct using rubber boat rollers pressed on the motor gearbox shafts and then they intern site on rollers so the weight of the dome its self provides the drive weight/ friction so nothing slips work as we say down here "Sweet as Bro" check out the link below for all the pictures.

Cheers

Steve

http://blue19.com/gallery5/v/scope_s...ite/?g2_page=6 (http://blue19.com/gallery5/v/scope_stuff/new-site/?g2_page=6)

[blue19]

Ill Measure it tomorrow but around 60mm, it all just worked out fine as far as dimensions go ......

Steve

[el_draco]

I scored two motors out of ex-gov electric lift work-stations. They come with a bunch of gearing and associated circuitry. You might also try this source.

[Paul Haese]

Barry, if you have not bought anything yet, you should consider looking at Scope Dome for their drive system. Its heavy duty and affordable. I paid $2500 + GST for the USB2 wifi card with motor, system and rack. Beefy stuff and will drive your system easily. You would need to sort out how to avoid have an umbilical cord but I think it might work for you.

[bloodhound31]

Thanks for the kind offer mate. Without seeing some pics I'm not sure how I can use them though.



Thanks Steve. I only have 20mm between rings and to lift the lot means I have to modify the dome seal and skirt. I still think I'll be approaching the rolling from the side.



Thanks mate.



Thanks Paul, I get $50 a fortnight play-money if I'm lucky so $2500+GST is far from affordable.

For now I'm still going to go with the car-winch idea. I'm still pretty time-poor at the moment and the dome is pushing around manually just fine so there's no rush yet.

Once I come up with a solution and fit it, I'll let you all know how it went and if it might need other approaches.

Bless ya's!

Baz.

[Kunama]

For a cheap rack Baz, you need several motorcycle chains, ( you get them free from Joe's Motorcycles ) then just patiently weld the chain to the dome's base ring. Next you need 2 motorcycle sprockets from the transmission not the rear wheel and a couple of motors of a small electric winch to drive with.

Very cheap system but hours of spot welding involved !!!

Cheers, Matt

[bloodhound31]

Thanks Matt. I did that with the last observatory and had nothing but problems with it. It worked for a while, but in the end it was one of the main reasons I tore it all down and started again.

Baz.

[Tandum]

If the dome is on a metal track and that track is supported on wheels with bearings then you should be able to turn it by hand. So a car wiper motor will also turn it. If you are not using a metal track then what the **** are you doing?

[bloodhound31]

WHOA! :eyepop: Settle down there petal. What's with the strong language? You might want to throw in an emoticon or two to tone down the attitude of the sentence... that or toss it out and re-write it.... :shrug:

[rcheshire]

Steppers 5v 200 steps. 6.9v 10 lead 400 steps. With a microprocessor, can be positioned accurately.

[ChrisM]

Baz,

When I previously said that a winch would be overkill, I should have added that such a high torque drive could put your construction at risk unless there is some sort of protection in the system to limit how much torque can be applied. The weight of your dome compared with the winch rating is almost irrelevant; they certainly do not need to be one and the same or even close. (The Parkes radio telescope superstructure is turned in azimuth by quite small motors and gearboxes.)

If you use a pneumatic tyre as the drive, then the tyre would need to slip if the dome became jammed for some reason. If you used a positive drive to the dome (such as a sprocket & chain), you would need to limit the winch's output torque somehow; maybe a smaller than usual fuse, or an electronic shear pin (if they're available for DC drives).

Chris

[bloodhound31]

Thanks Chris. I'll keep it in mind.

Baz.

[rcheshire]

Out of interest, do you need something the size of a washing machine motor? I take it stepper motors are not ideal?

[bloodhound31]

Thanks mate, the steppers are probably not ideal but I thank you very much for your very kind offer.

I've mentioned it a few times in this thread now, that I'm going with the car-winch. There are a number of cheap ones that are rated at a couple of ton which is more than enough, plus they are 12V, already geared for slow and smooth motion, and the wiring of the electrics is about as simple as it gets. - No electronics, no programs, just a simple toggle switch with a forward, neutral and reverse position on it. Done.

I am going with a pneumatic tyre up against the dome ring which will be all built into a steel frame with a tensioning rack on it, much like an alternator is tensioned against the fan-belts in a car motor.

Thanks everyone for your suggestions. Even if I haven't gone with your ideas, you have all given me the information I wanted to make an informed decision.

Cheers!

Baz.