Jrk 21v3 + wiper motor + feedback

I have a Jrk 21v3 connected to a wiper motor that I am using to steer a large bot via a standard RC radio. I am using a 5k pot for feedback and I am getting a solid 20 degrees of rotation (approx.) on the motor for each direction.

It all works but I would really love to have it rotate 45 degrees each direction so that I can get a tighter turning radius. Input settings are set to 0 to 4095, feedback set to 0 to 4095, PID is set to 2.

I thought It was possible to configure the range from within the configuration utility but I haven’t been able to figure it out. Got any ideas?


Depending on how you have your potentiometer connected in your system, you might be able to use the “Learn” feature in the jrk’s configuration utility to set the minimum and maximum positions for your steering. More information can be found in the “Calibrating feedback” step-by-step procedure under the “Setting Up Your System” section in the jrk user’s guide. You might find the “Learn” feature for scaling the input useful too. You can read about it in the “Input Options” section of the user’s guide.

- Jeremy

Tried that one. No go. I still have the same range of motion and everything is still operational.

Is there any combination of settings for signals, feedback, motor, that would increase the range of motion?

If not, then I suspect that the only way to increase the range of motion is to change the pot. Thoughts?

Your settings can affect the range of motion, but without knowing them, I cannot tell you if changing them will help. Also, without more information about how your motor and potentiometer are connected, it is difficult to determine whether the limitation is with your potentiometer. If you post your settings file and pictures of your setup, I would be happy to take a look at them and see if I notice anything that can be improved. Additional information about your motor and potentiometer would also be helpful.

- Jeremy

Screen shots attached.

JRk settings 7-2014 for wiper motor .docx (180 KB)

From those screen shots, it looks like the feedback scaling is the same as the default. If those screenshots were taken after using the “Learn” feature to set the “Scaling” values, it looks like you might be using the full range of your potentiometer; however, without knowing more about how you are using the potentiometer in your system, it is hard to confirm that. If you post pictures of your setup, it might help me understand your setup better, and I might be able to give better suggestions.

- Jeremy

I took another look at your settings and saw that your input range was still very close to the default setting. In RC mode, the input is in units of 2/3 μs, so for a normal RC transmitter with a signal that goes between 1000 us and 2000 us, the input should range between 1500 and 3000. You should be able to use the “Learn” feature to set the scaling values automatically.

- Jeremy

photo attached.

jrk setup .docx (521 KB)


Thanks much. That was what I was looking for. I ran learn on the Input screen and rescaled the input which gave me more travel. I also re-adjusted the max settings on the Futaba radio which gave me a little more throw.

Attached are the settings after running Input- Learn.

Pololu jrk settings for 45 degrees of rotation after learn.docx (82.4 KB)

Thanks for letting us know. I am glad you were able to adjust it.

- Jeremy