for a linear actuator,
will be pretty hard to have the last position hold,
with the decoder resolution. I'm thinking to combine the actuator with a
stepper. Usual the stepper is left as mechanical ballast. When the pedal
is released and no forward or reverse signal ( for a few mS ) has comming
from the cuadrature decoder, then the stepper
is supply on the right coil to keep unmoved the whole anssemble.
A small push on the pedal it's enough to force the stepper one step and
decoder to generate a releasing signal for the stepper.

regards,
Vasile
http://www.geocities.com/vsurducan


On Wed, 12 Jun 2002, Joris van den Heuvel wrote:

> Hey everyone.
>
> Recently I obtained a very sophisticated piece of equipment. A linear rotary
> actuator with an optical quadrature decoder for feedback. In other words: a
> harddrive arm. I thought of making a foot control pedal with it, to be built
> into a MIDI controller pedal with preset buttons. The tilt is just about
> right, and the optical encoder has amazing resolution. The idea is to have
> the pedal assume its last stored position for each preset, and to provide
> mechanical resistance when moved by the user.
>
> I guess I'll hook up the "voice coil" to a PWM-controlled H-bridge. The
> encoder has TTL outputs. So I'm not worried about hardware. But how would I
> go about the software, to have the maximum counter torque, but also a
> position hold, when the pedal is left alone? Anybody know any links to this
> kind of motion control? I'm using a PIC16F874-04
>
> Thanks,
> Joris.
>
>
>
> _______________________________________________________________
> "Bass is the basis of all that is music"
>
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