Skara

I'm in the process of starting a sculpture project that I plan to have move around a bit by having parts of it slowly rotate.

So far, I've taken apart a $15 drill and tested it out. It works, but it's... really really fast. I think I need to buy some kind of speed controller?? Is this right?
I need a way to make it go really slow, and I think it'll be more likely to move bigger objects this way without burning up, no? What do I need to buy and how might I hook this up?
Also, I'll have multiple motors all going at varying speeds (but all slow). Maybe 2-20 RPM, if that makes a difference. Some motors will probably be those little dinky motors the size of a thumbnail for very small parts.

As for weight, it will be made out of varying types of wood. I would preferably have the entire thing rotate slowly, but if that won't work that'd be ok. Each piece might be anywhere from 1/2oz to 2lb. Probably nothing bigger than that.

Also, how can I attach multiple motors of varying sizes together and run them off a single wall outlet. What do I need to make this happen?

Thanks for any help!

audioguru

If you slow down an electric motor electrically without a tachometer driving a speed controller then it won't have any torque. It needs torque to start and if the load increases.

You need gears or pulleys to slow it down.

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Skara

Ah.. Thanks. Alright, gears and pulleys. How, exactly, does this work? Is there some beginners reference with diagrams somewhere I can read??

Also still wondering about the power source question.

dknguyen

I assume you now how a lever works? More force over a small distance can be turned into less force over a longer distance? Same thing with gears and pulleys. THey are just round levers- if you spin a smaller gear (or wheel) once, it will have moved around it's circumferance less than a larger wheel. But if you grab something like a huge steering wheel, it's takes less force to turn than a smaller steering wheel because the lever arm (radius from center to edge) is longer. But to move the same angle, you must move farther along the circumferance when you turn it (travel more distance).

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Skara

Ahem. Ah. Well, that's basic. Thanks.
I guess I'll toy around with that for a while.

Dean Huster

From the "surplus electronics" catalogs, you can buy motors attached to gear boxes that will have the torque and low speed you need for most project.

Dean

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jpanhalt

Search e-bay for gear motor. There are 461 of them on the US site. Here is one example:http://cgi.ebay.com/One-DC-12V-12-V-...QQcmdZViewItem

At the speed you are talking about, there really is no substitute for a gear motor -- even a clock drive is a gear motor. John

Hank Fletcher

Something like a powerful window or windshield wiper motor would work well, but even with their own gearing, you're still looking at about 50 to 100 RPM. To get closer to your goal of 2 to 20rpm, you could use one of those types of motors with a further mechanical advantage through a couple pulleys, maybe a 5:1 ratio or greater. You could make the pulleys yourself if you've got a lathe, or you could buy heavy duty ones they actually use in lathes from a hardware store (and a belt, too!). This would be a good way to get the speed you want, and would be quite a robust solution - this could easily rotate a 200lb sculpture from 12V (with enough current), presuming the rotation is around the centre of mass and z-axis.

For smaller parts, use the same gearmotors with less power. For even smaller parts, use even smaller gearmotors, such as those available from hobby robotics sites:
http://www.robotshop.ca/home/product...ors/index.html

Hank Fletcher

Sorry, I hadn't noticed that the largest part you have to move is only 2ibs. For that weight, and presuming rotation in any axis and at most 20rpm, hobby robotics motors will be good enough (and generally on par or cheaper than the $15 you've spent on your drill). The only caution I can recommend is that if you're rotating a large, oddly shape piece, and not from its centre of mass, that this could put a lot of strain on the gearmotor output shaft. In that case, you'll want to beef-up the connection with a bearing that will take most of the load that would otherwise be perpendicular to the shaft.

gerty

A friend just finished a project ussing a motor from from a barbeque grill. It turned at the proper speed (gear reduction) and was rated continous duty.

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Skara

Hm. yeah, I've got a little hobby motor, but it turns so fast I don't see how I could ever get it slow enough.

I do have a lathe; what materials are appropriate for a pulley? Could I use scrap wood or should I go with a heavy plastic?
Also, do you have any tips for making a belt?

things

Just grab a worm gear and mount it on a motor, they are very slow, but at a fair bit of torque

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jpanhalt

Worm gears work great for slow speed and they effectively are auto-braking. That is, it is extremely hard (if at all possible) to turn the motor by turning the output shaft. On the downside, layout is more critical than with spur gears and they impart a 90° shift.

A pre-made gear motor, such as the BBQ grill would still be my first choice for slow speed and quiet operation. The planetary gear ones are probably the most quiet and slowest. Cheap, import winches (like at Harbor Freight) are another source of planetary drives and have very slow outputs. Old clockworks (many suppliers on the Internet) will give you three choices of speed (1 rpm, 1 rph, and 1 or 2 rpd.

If you want to go with pulleys/sheaves to get a second stage of speed reduction, these sources may be helpful:

http://www.mcmaster.com/
http://sdp-si.com/catalogs.htm

Check under the term "sheaves" as well as pulley. Some places are particular about that term, others are not.

John

Edit: Forgot the question about materials. Delrin (acetal) is a great plastic for such purposes. Round belts are easy to work with and quiet. The sheaves/pulleys are a little harder to machine for them though.

grim

for something fairly light duty like this, have you considered Lego?

not the toy stuff, but the grown up engineering experimentation and development system (ok, it's still a toy really)

motors, gears, everything you need, and it all fits together with no tools.

linky

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Hank Fletcher

Cheap, surplus gearmotors are the way for you to go, but they still might be slightly too fast for what you want. Oooo... you have a lathe?! Scrap wood can make for some nice pulleys. If you ever want to pay to class it up, aluminum can make some really nice pulleys (but expensive!).

Elastic bands (thick, wide ones) make good belts. Larger belts can be made from surgical tubing. Shoelaces and even just good old cord works, too. Whatever you use, you want to make it stretch just a bit to get it over the groove in your pulleys. Make sure it doesn't have to stretch so much that there's undue stress put on the motors' shafts, though (for instance, when using surgical tubing).