I get a fairly useful range using the circuit I provided the link for.
My next step will be to rig up some voltage control as well, maybe with
vactrols or maybe just with CV or PWM to a transistor. But yes, the
motor stalls at a certain point, and I would say that the response is
much more "linear" than "exponential" ;-) For extremely detailed control
over motors, you should look into stepper/servo motors, but in that case
you'd be better controlling it with some kind of microcontroller like an
Arduino.

What I use the motors for, BTW:

http://www.umatic.nl/tonewheels.html

best!
Derek

yahoo@... wrote:

>> Hi Dieter,
>>
>> thanks for the advice. The PWM-based circuit that Derek mentioned
>> should help overcome that "offset" voltage in the motor, right (as in
>> such a pulse-based circuit, you always apply the full 12V
>> voltage.....just not all the time).
>>
>> Basically the idea is to use a CV to modulate the PW of a VCO (the
>> a-111 goes from 0% PW to 100% PW IIRC), then use this VCO to drive a
>> power amp as shown here http://solorb.com/elect/pwm/
>> pwm1/ .....which basically is similar to controlling RPM with the CV.
>>
>> (omitting the comparator circuit, and plugging the 111 into R9).
>>
>> This is gonna be fun :-)
>>
>>
>> Cheers,
>> denis
>
> I'm not sure if the PWM will solve the offset problem. After all the motor
> works as a "low pass" filter for the PWM. Consequently e.g. a 25% PWM
> voltage with 12V level should cause the same result as 3V DC. As far as I
> know the main reason for PWM was the power dissipation of the control
> electronics as switching causes much less unneeded heat than linear DC
> control. It's the same for switching power supplies vs. linear power
> supplies (e.g. smaller heat sinks for switching supplies). But I'm not the
> motor specialist and maybe I'm wrong.
>
> Dieter
>
> btw. we did some VC motor applications for Kraftwerk but in this
> appliactions servo motors were used and the CV controls the position of the
> robot elements (via Midi-CV) rather than the RPM.
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
>

--
derek holzer ::: http://www.umatic.nl ::: http://blog.myspace.com/macumbista
---Oblique Strategy # 105:
"Listen to the quiet voice"