Jrk 12v12 pulse width control for a linear actuator with feedback

I have a 12V linear actuator with a 10K feedback pot that I’m driving with a Jrk 12v12 controller. The feedback mode is analog and I can move the actuator to the mechanical limits in each direction to identify the feedback values for setting the limits of travel. My control signal is a 5V pulse varying between 1 and 2 ms, with a 50 Hz repetition rate (20 ms period).

The problem is that the Jrk only follows the control signal sporadically and sometimes exceeds the mechanical limits (I have the load disconnected for testing) and sometimes will not travel as far as the limits. Do I possibly need to restrict the control signal to a value between 1.5 and 2 ms, since the actuator position is always “positive”?

I’ve read the notes about each value corresponding to 2/3 micro sec, but using values according to that scheme based on my mechanical limits doesn’t give the desired result. The learn mode on the input tab of the Jrk Configuration utility doesn’t seem to help either.

The controller seems to be in good working order. The feedback pot is giving a reliable signal…

I’m stuck. Thanks for any help you can offer.

Here’s a link to the typical control signals that I’m sending to the RX pin.

Here’s a link to the plot of the actuator following the target setting.

Here’s the configuration settings file:

Thank you.


Thank you for including pictures and your settings file. From your plot from the Jrk Configuration Utility, it looks like your jrk thinks it is working fine (e.g. the feedback is changing after the target does until the error is reduced to zero), so I suspect there is a problem in the way the jrk is configured.

From your description of your problem, it sounds like you might not have correctly configured the input scaling and feedback scaling settings. You mentioned finding the feedback values that correspond to the mechanical limits of your system, but I noticed that they are still set to the default values in the “Feedback” tab of the Jrk Configuration Utility (e.g. Minimum is 0 and Maximum is 4095).

Could you try setting the minimum and maximum feedback scaling values to the values that correspond to the extremes of the motion that you recorded? Also, once you do this, you should be able to change the Target Min and Target Max values to 0 and 4095 respectively in the “Input” tab of the Jrk Configuration Utility since those values should map to the newly configured feedback scaling values. The values you have in the Input Min and Input Max look fine to me.

If changing that does not help the problem, could you post a video that shows the behavior you are describing?

By the way, it looks like there are three signals being shown in your oscilloscope capture, but the jrk only accepts a single pulse width input; are the signals shown just examples of the range of signals you are sending?


Yes, that was the issue. I hadn’t realized the distinction between “Input” limits and “Target” limits. When I set the target limits to match the values discovered by manually setting the target to the physical limits at each end of travel, I got limits of travel that I needed.
I’m still not sure what to about the feedback limits, but that’s a problem for another day. I also get full mechanical limits at less than 100% of the potentiometer setting (my control input.)

I’ll think about it more later, we have enough control now to try flying our hydrofoil boat. There’s only an hour till sunset.

Thanks for your help.