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Date:	Thu, 05 Jun 2014 21:26:36 -0400
From:	"Stephen R. Besch" <sbesch AT buffalo DOT edu>
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To:	geda-user AT delorie DOT com
Subject:	Re: [geda-user] Seized gear motor ~ steering questions and advice
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Rob,

By siezed I assume you mean that applying 12V directly no longer 
operates the motor. Two things come to mind and one depends upon whether 
the motor is brushless or not. If the motor is brushless then it must 
have an internal switching circuit for commutation. Such an electronic 
commutator is possibly incompatible with a PWM style driver and may have 
been destroyed - appearing to sieze the motor. Especially if it failed 
shorted - remember shorting a DC motor will cause it to act as a Brake. 
On the other hand, a brush commutated motor should have no problem with 
a PWM driver.  The second possibility has to do with the motor itself - 
this would be a strictly mechanical problem. Once or twice I have had 
the stator magnets come loose on a DC motor - obviously causing siezure. 
Nevertheless, I can't connect the dots between the PWM and the magnets 
coming loose. Obviously, a gear could be broken as well, but I would bet 
against that. In the end, you may have to open the motor case to 
discover the problem. If it's a brushless motor my bet goes with smoked 
electronics in the motor.


Stephen R. Besch

On 06/05/2014 06:39 PM, Rob Butts wrote:
> I got a cheap 12V gear motor from ebay and was using it to turn the shaft
> of a trolling motor.  The control circuit for it is a pwm controlled 3amp 8
> pin motor driver.  With the trolling motor on a stand I simply applied 12V
> from a battery to the gear motor to ensure that it would in fact turn the
> trolling motor shaft.  This worked fine in either direction.  I have a
> photointerrupter mounted adjacent to the shaft to keep track of turning and
> direction.
>
> I then tried powering the gear motor via the motor driver circuit.  I set
> the pwm to about 30% duty cycle and set it to power the gear motor for 100
> ms.  I could hear a brief sound.  I then changed the pwm to 80% duty cycle
> and changed it to 500 ms.  There wasn't really a sound and now the gear
> motor is seized.
>
> Any thoughts to why it seized?  To be honest I have no idea if the gear
> motor is brushless or brushed.
>
> After reading a tech note from Allegro I think I should be using a stepper
> motor.  I have no experience with stepper motors.  Is this a better way?
> It seems like I would have more control of direction (steps the motor
> turns).
>
> Thanks!!!
>


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