My new project: Pig Roaster, Rotisserie Motor suggestions please
 

Hey guys,

Well as the title states my latest project is to build a pig roaster :party:. Not exactly an R/C project, although it certainly has the potential for that in the future.
I am trying to find a bugdet minded motor setup to use for my rotisserie and when it came to motors you guys were the first ones I thought of.

So what I need is a motor that turns at about 2 rpm thru a gear reduction or what ever. 120v is probably the best option but 12v might be doable using a car battery and maybe a battery charger on to keep the power up. I have found a motor that is sold for this purpose, but the price is crazy, I'd like to keep it under $100 for a motor if possible. Anyway here is the link to the motor to help out with motor specs.
E-Z Que Commercial Heavy Duty 110 UL approved, 2 RPM 1/4 horse power, TEFC shaded pole gear motor

http://www.ezqueinc.com/motors.htm

There has to be some sort or motor or gear reduction system that will work for my app 1-4rpm or so and not cost an arm and a leg.

For the speed final required, pretty much any motor should work since it will be geared quite low. I am assuming here that you don't need to roast a WHOLE pig. A whole pig is HEAVY and could be difficult to turn without making sure it is balanced and there are bearings on the end.

How about an old washing machine motor, refrigerator compressor motor, fan motor (dekstop size) or something similar? Whatever you get, make sure it is rated for continuous duty, not intermittent duty.

And even if you don't get the exact speed you want, get it as close as possible with gearing and then use a dimmer control to tweak it. You'll need a dimmer capable of driving an inductive load though, and one with a decent rating, but it should be easy to find at Menards, Home Depot, Lowe's, etc.

Brian thanks for the quick reply. Actually yes it will be the entire pig, we usually roast about a 100 lb pig. We will have bearings for the rotissrie shaft to run on, basically 2 large sheilded bearings per side spaced just far enough apart so the shaft sits between them. Balance isnt a huge issue as the turning speed is so low it doesnt really create a big problem.

I had though of using an old furnace motor or washer motor to run this, but arent most of those motors in the 1750 rpm range or so? To get down to 2 rpm that would be approx. 1000:1 gear reduction and I am not sure how to accomplish that efficiently. How much can I reduce the rated motor rpm with a dimmer switch?

The best way I can think of to get the max reduction in rpms would be to use a worm drive unit. You may be able to find a few surplus planetary gear drives and use a few in series (if each provides 10:1 ratio, only three are needed to get 1000:1 total), but I'm not sure those will handle the torque/wear. An R/C robot store should have all kinds of gear setups.

You generally gear for the max speed you would possibly want, and use a dimmer to give you ranges from 0 to that max value. In your case, you could also use it to get a little closer to your desired speed if gearing is not possible/feasible. Since you want 2rpm, I would get no higher than 8-10rpm with gearing and use the dimmer for the rest. Some expirementing will be required of course.

That is pretty much the problem I'm having is to find something rugged enough yet cost efficient to get me the right rpms. I figured the dimmer would only buy me a few rpms and as you said would only be able to fine tune. I would be happy if I could get anything under 8 rpm with gear reduction.

Here is a place that has a variety of gears, but no worm drives: http://www.robotmarketplace.com/prod...ical_main.html

Good link, thanks Brian.

Wellll, you could use ten 28T/14T sprockets/chains to get your 1000:1 ratio. Would probably weigh more than the pig, not to mention frictional losses. But it would look impressive. :smile:

Or, use four 84T/14T gear clusters to get ~1200:1.

What about a garage door opener?

I was thinking the same thing. Those are pretty cheap, and the chain drive output spins pretty slow. You could use another sprocket off the chain drive to get even more reduction. And BrianG's dimmer idea would work as well, just have to wire the motor directly to the feed, and bypass the internals. Or you could modify the controls and have cordless control, but that is probably not worth it.

ESC MMM

Motor: http://www.hobbycity.com/hobbycity/s...idProduct=5141

And a bunch of reduction

Hopefully a garage door opener would last a long time being spun for hours on end. They're designed for <20 sec bursts a few times a day. I would think it would hold up though..

I thought about that too, but I figure that the rotational load of a pig would be much less than lift a garage door. Maybe a small fan blowing over the motor would help with motor temps.

Yes, True. I think a heat shield to protect the electronics from the fire shouldn't be overlooked either. One of those aluminum for sale signs would make good, cheap material if a heat shield was needed.

I'm thinking that pretty much ANY motor would work given the amount of torque increase provided by gear reduction. Even a weak motor capable of 10 oz-in of torque would have over 52 ft-lbs of torque when geared 1000:1.

Other options: vacuum cleaner motor (either the main motor or the spinning brushes motor), overhead bathroom fan (can get these for ~$15 at a home improvement center), drill motor (would have some gear reduction built in), etc. Out of these, a cheap drill might be the best bet for cost and the gearing built-in. Might be able to get away with "only" 500:1 gearing. :smile:

EDIT: Just checked Harbor Freight and a simple 3/8" corded drill is $20.