Problems with feedback on Jrk21v3 and Jrk12v12

Hi, I have some Jrk21v3 and one Jrk12v12 to drive som dc motors.

I purchased them some time ago and now I was going to try them. First of all I updated their firmware to last version on web page. Then I tried via usb connection. Motors run well both directions when I move slide bar on main page. The problem is when I try to control via some feedback. I set pid values, select digital (frequency) feedback and connected FB pin to a encoder output. Then, no matter what frequency is, both graphs (feedback and scaled feedback) never changes from 50% (they are stucked on that value). I’ve cheked output values from encoder and, as those were similar to 1V on low and 4V on high, I tried a different aproach: connected a pushbutton tied to ground and “manually” simmulated an encoder. But same thing again, the graphis from feedback are stucked on 50% and never move from that. A also tried to change maximum values for feedback (in your driver control program) but nothing different happens.

I did not try them before upgrading firmware, so I do not know if they worked before. Can you give me some help on how to proceed now or what more can I try?

In digital frequency feedback mode, the value of the Jrk’s “feedback” variable is 2048 +/- #(rising edges on FB line in last PID period)

What PID period are you using? If it is too short, you won’t be able to toggle the button very many times in that period, so the feedback will always be very close to 2048 (which is graphed as 50% by default). The default PID period is 10 ms, which is definitely too short.

The Jrk’s high and low thresholds for the frequency feedback are 1 V and 4 V, so you ultimately may need to add some component to your encoder’s output to fix its signal.


OMG, you are right, I did not think about pid period was very small to make sense. I tried now a very much larger value and graphis started moving. Thank you.

But, unfortunatly, that brings me a different (and worst) problem. I also bought a pair of pololu wheels with integrated encoders. I planned to use them for a fast line follower. Now I have to discard them as there is not enought resolution on them. I will have to buy an encoder with 100 or more cps.


The encoders for those wheels are intended for quadrature encoding, which can give you 48 counts per rotation. For a fast line follower, you’ll want 10 rotations per second or more, so you’ll be able to get over 500 counts per second. However, you would have to process the encoders on your own. If you’re just monitoring that and some line sensors, it shouldn’t be too much even for an 8-bit processor like the ATmega328P that is on the Orangutans and Arduino. The new Orangutan SVP even has an extra processor to handle the encoder.

- Jan