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Lowest RPM


#1

Hello there,

I’m just curious to know if you have a small to medium dc 12v motor and connected it to a speed controller what would be the minimum output RPM?
I’m trying to step down to about 1rpm through using a set of v-pulleys and belts, I dont want to use a gear-head because they make a terrible noise, unless you have the money to pay for a good one. Anyway silence is the key with this project.
I’m hoping if I can get reduce a motors rpm down to say 50-100rpm with the speed controller, then with a few v-pullys and belts I should be able to drop it down to what I need.
What do you think?


#2

I’ve tried this and the results are very disappointing. Some small motors just won’t turn at a few rpm because of internal friction, unless they have precision shafts and ball bearings.

Most small to medium DC motors run several thousand rpm at their rated voltage, and rpms are proportional to average motor voltage (no load). This means that you have to reduce the average voltage by over a factor of roughly a thousand to get to a few rpms. You won’t have any usable torque left at that low rotational velocity.

On the other hand, stepper motors are nearly silent and can rotate as slowly as you like.


#3

I see, there’s alot more to this then I first thought. Hows the torque on a stepper motor running at low rpm’s?
I’m just checking them out now, very cool!
How would the torque be on something like this? pololu.com/product/1200
Thats the kind of size I’m after i may be able to go one size up?
Can you explain what “holding torque of 3.2 kg-cm” means?


#4

The torque is proportional to the motor current, so it depends on the motor winding resistance, the power supply voltage and the motor driver PWM percentage.

Holding torque is the maximum torque that you can apply to the motor shaft when it is holding position, fully powered, before the shaft starts to rotate.

There are lots of good tutorials about stepping motors on the web. More than you ever wanted to know can be found here: cs.uiowa.edu/~jones/step/