Arduino Forum

Using Arduino => Motors, Mechanics, and Power => Topic started by: apples on Sep 25, 2013, 02:08 pm

Title: How slow can you run a DC motor?
Post by: apples on Sep 25, 2013, 02:08 pm
How slow can I run a DC Gear motor at?

If my motor shaft rpm is say 6000rpm, and it has a gearbox that brings is output shaft down to 60rpm.

How slow can I turn that motor and still get full power?  Does the motor need max rpm to make max power?  I would nee the output shaft
to spin as low as 1rpm to 10rpms.
Title: Re: How slow can you run a DC motor?
Post by: drewdavis on Sep 25, 2013, 02:51 pm
Quote
it has a gearbox that brings is output shaft down to 60rpm. How slow can I turn that motor and still get full power?



Why not use some more gears? You would get the slow speed you need and have even more torque!


Any chance you could give us the link to what you have.
Title: Re: How slow can you run a DC motor?
Post by: MarkT on Sep 25, 2013, 05:07 pm
When in a servo control loop, any speed.
Title: Re: How slow can you run a DC motor?
Post by: apples on Sep 25, 2013, 09:16 pm
I have not got a motor yet, just trying to research and get info first.

But looking at something like these:
http://www.servocity.com/html/10_rpm_precision_gear_motor.html
http://www.servocity.com/html/robotzone_gear_motors.html

I wonder how noisy these are?
If I could make up a belt gear reduction that would be really quiet, but I think
That would involve a lot of pulleys to get the rpm down that low.


Title: Re: How slow can you run a DC motor?
Post by: jack wp on Sep 25, 2013, 09:33 pm
A stepping motor is a bit more complicated to control, but it can be run ultra slow (1 revolution per month, eg.).
If you want to stick with a standard motor, geared down, you can use PWM to make it pretty slow. You should be able to get the 1rpm pretty easy.
Title: Re: How slow can you run a DC motor?
Post by: apples on Sep 26, 2013, 02:00 pm
Well I had thought of using a stepper motor.  This project will use battery power and I was told that a stepper will use max power all the time, even when it is sitting still.  Where as a normal DC motor only used power when it is off and running.

Title: Re: How slow can you run a DC motor?
Post by: jack wp on Sep 26, 2013, 05:57 pm
I am not a stepping motor expert, but I believe it is your choice. If you want to lock the motors position, you can apply current to hold it in place. If you want to turn off the current, and some other force tries to move the motor it can. Do you have some force on the motor that would make it move if not powered?
Title: Re: How slow can you run a DC motor?
Post by: apples on Sep 27, 2013, 03:05 am
No force there.  It will just run along a horizontal surface.  But I guess I could later on add in a solenoid device that when the power is cut it flick outwards and lock a mechanical device to stop movement.

I like the stepper idea because, yes it might use more power, but I will only need to use it for a short amount of time.  I do not think that the battery will go flat in that time.  So maybe a stepper it a good choice.

I actually have a stepper here too.
Title: Re: How slow can you run a DC motor?
Post by: Stingray on Sep 30, 2013, 02:24 pm
Ordinary electric motors produce their maximum torque at 0 rpm. Torque decreases roughly linearly with increasing speed. Power (which is not the same as torque) is maximized at an intermediate shaft speed that depends on the particular motor.

If you want very slow output speeds and large output torque, it can be useful to use worm gears. These also have the advantage that they tend to be "self-locking." Nothing is going to move on its own if you turn off the motor.