RPM reduction options?

Who can tell me what I need to know about reduction gears and other options for reducing electric motor RPMs. I want to built a motorized mixer/paddle for my mash tun (why not) , I have the motors but need to reduce the RPMs significantly, so I figure I need a reducer of some sort. A gear reducer seems to be one option, the other would be some electronic controller, but I don't want to burn out my engine. Who has the answer I need. Board don't fail me now! I figure if Dude can get a cardboard box smoker, maybe I can get lucky myself.

Depending on your setup, bicycle gears work well. You can get a 4:1 reduction with two gears, 16:1 with four.

I have a small speed reducer that I use with my hand drills, but don't remember where I got it. It gives a 7:1 reduction.

Controllers are only good for 50-100% of normal speed, you start having heating problems after that.

What RPM is the motor and about how fast do you want the stirrer to turn?

david_42 said:

Depending on your setup, bicycle gears work well. You can get a 4:1 reduction with two gears, 16:1 with four.

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That'll reduce the torque being applied to the motor at the same time, won't it? I've got to imagine the good BP is trying to stir a LOT of grain.

You could solder a rheostat into the circuit before the motor or plug the motor into a rheostat which plugs into the wall. However, it would be tough to figure out exactly what RPMs you’re running at and it might reduce the lifespan of the motor.

When people motorize grain mills they usually use 2 sheaves and a belt to go from about 1700 to around 300 RPM. Youd have to use a guard or something so some ******* don't loose any fingers.

I could try to help but I'd need to know more about the motor and more about what capabilities you'd need from it. Any more info available?

A rheostat will only work for a DC motor which you probably aren't using... reducing the voltage to an AC synchronous motor can damage it. Using some type of reduction gear would work and it would increase the torque, not decrease it. You can also purchase an AC controller to control your AC speed. Personally, I'd just scrounge a reduction gear assembly somewhere... I like the bicycle gear idea.

This may be a crazy idea but could you salvage gears from an old gear reduction automobile starter and flywheel........I mean hunting around junkyards can be fun. Well, on second thought that would be one large gear just waiting to cause pain and destruction but it would certainly slow the rpms down but designing a method of mounting might be a chore.

the_bird said:

That'll reduce the torque being applied to the motor at the same time, won't it? I've got to imagine the good BP is trying to stir a LOT of grain.

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That's exactly what he wants to do - the more gear reduction, the less torque at the motor end (small gear), and the more torque can be applied at the work end (large gear). A proper reduction should actually increase the life of the motor.

There are some reasonably priced gear motors available online at Grainger and McMaster Carr, but their gear reduction boxes tend to be expensive. A gear/sprocket setup like david_42 suggests is probably your cheapest option. Another option is a pulley/belt setup. Avoid the speed controller/rheostat option - that'll kill your power and burn your motor out quickly.

You'll want a BIG reduction to stir mash - lots of torque, low speed. For example, a standard 1750 RPM AC motor would need about a 30:1 gear reduction to give you 60 RPMs (one revolution per second).

Would an electric winch work, very slow rpms with the low end capacity in the thousands. This route would provide a handy bracket for easy mounting. Just a thought.

I don't know what your speed and torque needs are, but I'd check ebay for some cheap gearhead motors. A good gearhead can get you a huge reduction. I was doing a project about a year ago where I needed a decent bit of torque at low speeds, found a little 18VDC gearhead motor that weighed about 6 oz. The motor itself was about 17000 RPM and like 1 oz-in torque, but the gearhead was 187:1. I added a 2.5:1 external gearset to it and used a simple, cheap, homemade pulse width modulator for speed and directional control. Ran it at 24V, it didn't even get warm. Total probably cost me 20 bucks, controller included. I know that's too small for your needs, but you could probably find something scaled up from that on ebay pretty easily.

Use an old fashioned "ice cream maker." Motor is perfect, modify the stirrer as needed. Garage sale, ten bucks, problem solved.

Here at home we have a farming/mechanical supply store called http://princessauto.com i bought a gearbox there to make a homemade spit to roast pigs and lambs . It works great it can spin a 150lb pig with no problem at a nice slow rpm.

DublOh7 said:

Use an old fashioned "ice cream maker." Motor is perfect, modify the stirrer as needed. Garage sale, ten bucks, problem solved.

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Same thought I had. The gearing in those things is built to slowly crank thick stuff for long periods of time. Sounds like the perfect solution.

The unit for medium to large ice cream makers is just about the same diameter as a sanke keg, too...

How about this motor, it has a lot of torque and the speed can be reduced with a rheostat..

http://www.sciplus.com/singleItem.cfm?terms=6101&cartLogFrom=Search

'Cept for it's 12 volt and DC. Be kind of a pain to rig up to run on line voltage from the house.

Considering the size of your tun, I retract my comments about the ice cream maker. I was just looking through eBay and the biggest ones I could find for a reasonable price were up to six quarts. One of your "average" sized brews would fry that sucker.

You're the industrious type, BP. Build something we'll drool over.

I use a paint stirrer ($7) in a variable speed electric drill that has worn out bearings. I fix it to my boil pot using combination of 1/2" copper tubing, wood and miscellaneous hardware. Total cost of the setup, except the 20 year old drill, was about $15. To control the speed, I have a wood strip behind the handle and one touching the trigger. The strips are joined by 1/4" bolts fastened with wing nuts. To increas the speed, I tighten the wing nuts. Noisy, but I can brew on my electric stove and not burn anything. Agitation while using my immersion chiller greatly speeds cooling.