Help with DC motor low RPM control!

Hello everybody! I'm doing a project using a DC motor, and I'm controlling it's speed with a PWM.

My DC Motor runs up to 12V, and is also a geared motor.

If I apply 12V to the engine it runs very well, but when I decrease the voltage to less than 7,5V the engine just don't move!

Would it be because of the rotor's inercia? Could it be because of the friction generated by the gearbox (maybe bad lubrication)? Is there a way to make the motor run in a low speed (something like in 1V or 2V)?

Unfortunatelly I don't have any other information about the motor since it's not mine, and the owner doesn't even know the brand of it... =/

Thanks everyone! =)

What is providing the switching for the PWM?
Your voltage drop across your device may be reducing the voltage at the motor too much.

I'm using a L298 IC

If it may be a voltage drop, would it be valid to check the voltage that goes to the motor wiring using a multimeter?

Thanks and regards!

Only if you set the PWM drive to 100%

I must drive the PWM in 100% to check to voltage on the motor with a multimeter?

Yes, because otherwise your non-DC PWM waveform will confuse your multimeter. 100% (" analogWrite (motorPin, 255) ; ") will just turn the motor solid on.

AWOL:
Yes, because otherwise your non-DC PWM waveform will confuse your multimeter.
100% (" analogWrite (motorPin, 255) ; ") will just turn the motor solid on.

Hmmm very well stated! Thanks for the tip!!

But just to check! Couldn’t the rotor’s inercia or maybe a bad gearbox lubrication impose too much resistance to make the motor run?

Thanks again =)

Yes, they could. But only you can see the motor.

Thanks a lot! =)

If you have an old style multimeter with a needle and a dial, it will give you the correct average voltage reading when using PWM; but a digital multimeter will give you erratic readings except when the PWM is set to 0% or 100%.

I think those chips can have up to a 2v drop across them (check the data sheet).