Pololu Robotics & Electronics
My account Comments or questions? About Pololu Contact Ordering information Distributors

Recommended motors for jrk controller?


The new jrk controllers look terrific, but the topic is sorely in need of some examples of successful hookups with motors that provide feedback!

In the old days one could find 12V motors with tachometers in the 5 inch IBM PC floppy disk drives, but surely you folks have some more modern examples in mind. What sort of bargains are there on the surplus market that might work with these controllers?

Finally, the description of the “feedback in” input is less than clear. What are its electrical characteristics? Would a sine wave tachometer be acceptable?



Hi, Jim.

We are quite excited about the new jrk controllers. I mostly think of the controller as suitable for making your own giant servo systems, and we already have customers integrating these into big servos (which we hope to carry, too). Something like servo city’s linear servo could probably be done better with a jrk 12v12.

I don’t see the tachometer input being used as often, but I know of several customers who used it with the older feedback controllers. Nexisnet had an application, and a others working with encoders tapped off of one line to have our motor control do a speed control loop while they did some position control separately. Given that some people found it useful, we wanted to at least preserve the feature in these newer units.

The feedback pin basically just goes to a PIC I/O line (with schmitt trigger), though there is a 10 nF cap to ground and 100k pull-up. The thresholds are 1V and 4V, so some extra signal conditioning might be necessary if your tachometer doesn’t get to those levels.

We’ll work on getting some examples up. In general, though, I think that we’re covering a broad enough range of motors that there shouldn’t be only a few motors that are just right for these controllers. We don’t have specific plans yet, but I would like to have a higher-power version out next year so that we can cover an even broader range of motors.

- Jan