High torque low RPM motor?

[Rhythm House Drums]

I'm looking for a high torque motor with low RPM (or adjustable). I'm not really too knowledgeable on motors, but I have an idea in mind and if I can find one for what I need, it just might work. Anyone know of a place to get these? I dont want to spend too much on it.. it's really just to help me out cause I'm lazy... it'll turn a hand crank instead of me.

 

[ehpoole]

You have a few possible choices... er... alternatives... to resolve your "laziness"

1) If it absolutely has to be done in a "direct drive" configuration and variable speed control is needed at extremely low speeds you can use a powerful DC motor and a PWM (Pulse Width Modulated) speed controller. However, at extremely low RPMs the output of the motor will be a bit "jerky" because it will be powered on/off in brief pulses ... not a problem at higher speeds but it can become noticeable at very low RPMs. It also helps if there is a flywheel of some mass that can help absorb and smooth out the jerkiness at lower RPMs. You often see setups similar to this in some variable speed lathes and many exercise treadmills.

2) Your next option is a motor with a geared step-down gearbox which will allow a much faster (and lower torque) motor to turn the output shaft at much lower speed (and much greater torque). Every halving of the motor's input RPM will also double the output torque -- run it 8 times slower and you'll have 8 times as much torque.

3) More typical of larger woodworking tools is the traditional belt drive and pulley system. By using differential pulley sizes you can increase or decrease output RPMs and inversely decrease or increase the output torque (just like with the gearbox in #2). However, about the slowest induction motor you are likely to find is around 900RPM, though if you look hard enough you may find some 450RPM motors... with 1800RPM and 3600RPM far more common -- so you may need a very large differential in pulley sizes to get your speeds low enough if you require extremely low speeds.

4) You can use a 3-phase inverter-rated induction motor and a VFD that can output very low frequencies to drive the 3-phase motor at variable speed. You'll have to review the specs for both the VFD and the inverter-rated induction motor to determine what the final torque output will be at whatever the lowest target RPM/frequency will be.

5) You can use a combination of #2 and #3 as well by opting for a drive motor with built-in (or bolt-on) reduction gearing (the gearbox) and differential pulley sizes to further reduce the RPMs.

6) You can also choose to use a reduction gearbox on the DC motor in #1 to allow you to run the DC motor at higher RPMs to help avoid the "jerkiness" of the PWM speed controller at extremely low speeds since the gearbox will allow you to run the motor at a higher RPM than the output shaft.

7) By some obese hamsters and mount a squirrel cage for them to run on -- they'll get exercise and you'll get some rotary motion (albeit at low torque, so you may need to raid a pet shop to multiply your torque).

8) Windmills have a nice "retro" tech feel to them that could be perfect for your application.

 

[Mike Davis]

I set up a grain grinder to run 160 rpm with a 1750 rpm motor. I used two sets of pulleys and a secondary shaft (jackshaft). I can't remember the pulley sizes offhand but a very small one on the motor to a large on the shaft which has a small on the other end then going to a large one on the grinder.

http://www.engineeringtoolbox.com/pulley-diameters-speeds-d_1620.html

http://www.daviddecristoforo.com/Misc/monster_drive_config.pdf

 

[scsmith42]

www.surpluscenter.com is where I source things like this. They have a variety of motors, gear drives, etc.

 

[SeanStuart]

You might consider getting a used treadmill from CL and salvaging. That will give you the motor and speed control.

 

[Rick M]

If you decide to use pulleys to reduce the rpm there are some convenient web based gear or pulley calculators but some of them give you wrong numbers, might want to use your own math or at least double check.

 

[Willemjm]

You have a few possible choices... er... alternatives... to resolve your "laziness"

1) If it absolutely has to be done in a "direct drive" configuration and variable speed control is needed at extremely low speeds you can use a powerful DC motor and a PWM (Pulse Width Modulated) speed controller. However, at extremely low RPMs the output of the motor will be a bit "jerky" because it will be powered on/off in brief pulses ... not a problem at higher speeds but it can become noticeable at very low RPMs. It also helps if there is a flywheel of some mass that can help absorb and smooth out the jerkiness at lower RPMs. You often see setups similar to this in some variable speed lathes and many exercise treadmills.

2) Your next option is a motor with a geared step-down gearbox which will allow a much faster (and lower torque) motor to turn the output shaft at much lower speed (and much greater torque). Every halving of the motor's input RPM will also double the output torque -- run it 8 times slower and you'll have 8 times as much torque.

3) More typical of larger woodworking tools is the traditional belt drive and pulley system. By using differential pulley sizes you can increase or decrease output RPMs and inversely decrease or increase the output torque (just like with the gearbox in #2). However, about the slowest induction motor you are likely to find is around 900RPM, though if you look hard enough you may find some 450RPM motors... with 1800RPM and 3600RPM far more common -- so you may need a very large differential in pulley sizes to get your speeds low enough if you require extremely low speeds.

4) You can use a 3-phase inverter-rated induction motor and a VFD that can output very low frequencies to drive the 3-phase motor at variable speed. You'll have to review the specs for both the VFD and the inverter-rated induction motor to determine what the final torque output will be at whatever the lowest target RPM/frequency will be.

5) You can use a combination of #2 and #3 as well by opting for a drive motor with built-in (or bolt-on) reduction gearing (the gearbox) and differential pulley sizes to further reduce the RPMs.

6) You can also choose to use a reduction gearbox on the DC motor in #1 to allow you to run the DC motor at higher RPMs to help avoid the "jerkiness" of the PWM speed controller at extremely low speeds since the gearbox will allow you to run the motor at a higher RPM than the output shaft.

7) By some obese hamsters and mount a squirrel cage for them to run on -- they'll get exercise and you'll get some rotary motion (albeit at low torque, so you may need to raid a pet shop to multiply your torque).

8) Windmills have a nice "retro" tech feel to them that could be perfect for your application.

That is a very good reply, complements. (Including item 7). I have window shopped a few times converting the reeves drive on my lathe with either a VFD, or a DC drive, the latter being a bit more costly, but giving more torque at the 100rpm range. Problem is if really done well, it costs more than a new lathe.

 

[NCTurner]

Look into an industrial sewing machine motor.

 

[Rhythm House Drums]

Thanks for all the ideas! Would it be a bad idea to tap into my lathe? Maybe a flywheel with a small grooved pulley wheel. Run a belt from that to a larger wheel on my roller. My lathe is 2hp and runs down to 50rpm. Maybe I could even open up the belt door and just run a belt in there, right off the motor? Any reason this would be a bad idea?

 

[Touchwood]

Thanks for all the ideas! Would it be a bad idea to tap into my lathe? Maybe a flywheel with a small grooved pulley wheel. Run a belt from that to a larger wheel on my roller. My lathe is 2hp and runs down to 50rpm. Maybe I could even open up the belt door and just run a belt in there, right off the motor? Any reason this would be a bad idea?

+1 for Surplus Center

I have one of these, if that's sort of speed, torque you're looking for

http://www.surpluscenter.com/item.asp?item=5-1770&catname=electric

Don

 

[Rick M]

Thanks for all the ideas! Would it be a bad idea to tap into my lathe? Maybe a flywheel with a small grooved pulley wheel. Run a belt from that to a larger wheel on my roller. My lathe is 2hp and runs down to 50rpm. Maybe I could even open up the belt door and just run a belt in there, right off the motor? Any reason this would be a bad idea?

I don't see why not.

 

[Mike Davis]

Running a roller mill for making your metal rims?

I think the lathe would be a great way to go. Might need a jack shaft to let the lathe run a little faster to get more torque.

 

[ehpoole]

Thanks for all the ideas! Would it be a bad idea to tap into my lathe? Maybe a flywheel with a small grooved pulley wheel. Run a belt from that to a larger wheel on my roller. My lathe is 2hp and runs down to 50rpm. Maybe I could even open up the belt door and just run a belt in there, right off the motor? Any reason this would be a bad idea?

I only really have one concern with regards to your suggestion, and it is really up to you how you weigh in on this. Otherwise there is no reason you can not do so.

My concern would be the open belt (as in, no safety cover) which can be a very real risk; the longer the belt the greater the relative risk. If a tool gets away from you and falls into the open space of the belt, that tool can get launched in a very dangerous manner. More importantly,though, if you have small children or pets then the risks of an open belt are multiplied considerably as they do not have an understanding of the extraordinary danger posed by such. However, if you can guarantee that you are the only person (or creature) present during the operation then it really falls to you to decide.

Anyone who has ever had to rush their cat to the animal clinic after an unfortunate encounter with an engine (belt) is all too familiar with the danger! (BTDT - poor "bobtailed" Shadow!)