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Leeds, England, (dis)UK
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I don't really know which section to put this in... Motors, Programming or other!

I have one of the very small, cheap dc electric motors which I have fitted into a model vehicle. Presently it is driven through a 2N2222. So far so good.

In order to control the motor's speed I use PWM. However, when starting from zero, once the pulse width gets to a certain value the vehicle shoots off like the proverbial scalded cat. So I am thinking along the lines of reducing the frequency of the PWM in order to hopefully give the motor a 'kick' at the lower pulse widths in order to start it rotating.

Has anyone else had experience of this sort of thing?

Merry Christmas

David.
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Are you 100% sure that the drive transistor isn't saturating fully on at some stage, rather than pulsing in sync with the PWM signal.
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No I'm not, and I'll check that out later.
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I don't really know which section to put this in... Motors, Programming or other!

I have one of the very small, cheap dc electric motors which I have fitted into a model vehicle. Presently it is driven through a 2N2222. So far so good.

In order to control the motor's speed I use PWM. However, when starting from zero, once the pulse width gets to a certain value the vehicle shoots off like the proverbial scalded cat. So I am thinking along the lines of reducing the frequency of the PWM in order to hopefully give the motor a 'kick' at the lower pulse widths in order to start it rotating.

Has anyone else had experience of this sort of thing?

Merry Christmas

David.

The PWM frequency is a fixed value and would not have an effect on what you are seeing. The PWM outputs a variable 'duty cycle' value of from 0 to 255 to represent 0% to 100% of power applied to the motor. However each motor will have a different starting value where it will just start to turn and because of motor friction and mechanical load placed on it will never be pwm value of 1 just starts to turn. So by experimentation you are going the have to find the 'magic' pwm minimum value X that just starts the motor to turn and then you will know that the usable pwm range for your motor/load condition will be from pwm X to pwm 255. Once you find the proper usable range of pwm values you can use then just restrict your sketch to using just those values.

That makes sense?

Lefty
 
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Leeds, England, (dis)UK
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Oh yes, that all makes sense. It's just that I'm likening it to a similar situation I experienced as a youngster with a model railway / railroad. With the simple variable resistance controller you could get better control by using the half wave rectification feature. I'm assuming that this gave the motor half as many 'jolts' a second as full wave thus giving finer control? Hence my thoughts about reducing the PWM frequency?

Of course this could all be the product of a fertile imagination!
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