I am using a 21V3 Jrk to control an off the shelf servo by removing the internal pcb and connecting directly to the 21v3 Jrk board. The servo pot is my feedback and I have another pot for the input. My loop tuning procedure requires knowledge of the filtering on the input signal or filtering via the microcontroller software. Is there any hardware or software filtering on the signal prior to processing by the pid algorithm? Is a copy of the schematic for this 21v3 pcb available? I realize Pololu may want to keep this confidential but I thought I would ask nonetheless. Thanks
Hello.
We do not make the schematic for the jrk available. However, there is no filtering on its RX pin, and there is a 10nF capacitor on the feedback pin to help filter that signal. As for software filtering, the jrk averages a number of samples of the signal each PID cycle. You can set the number of samples per cycle under the “Feedback” tab in the Jrk Configuration Utility.
- Grant
What signal is averaged the x number of samples every PID cycle, the error signal or feedback signal?
What is the time between each sample if the time for the PID cycle is variable?
For example, if I have it set for 128 samples and a 10mS PID cycle then is my time between sample = 10mS/128 = 78uS?
Or if I have it set for 4 samples and a 10mS PID cycle then is my time between sample = 10mS/4 = 2.5mS?
Thanks
Nick
It is the feedback signal that is averaged every PID cycle. During a PID cycle, the jrk takes the readings, does the calculations, updates the motor outputs, and then waits for the cycle to finish. The ADC readings for the input are taken first, followed by the ADC readings for the feedback. We don’t purposely add any delay between the ADC readings. Each ADC reading probably takes between 10 to 100 microseconds, and I can get a more accurate estimate if you need it. However, I don’t expect the exact details of the cycle to be that useful because the jrk is not meant to be used in applications where the feedback is changing significantly in a single PID period. The input could change very rapidly, but the exact timing of which PID period first sees the change in the input should not significantly affect the overall way your system reacts. The jrk also does not provide a way to synchronize a change in the input with a particular PID period, so if you do find that the exact details of the cycle matter, knowing them probably would not be very helpful.
- Grant
Grant
Thanks for you input.
Is it possible for the JRK controller to be put into a manual mode?
This would be a mode that allows the operator to drive to an output position(in my case) and not be automatically under PID control.
I have checked the datasheet and can’t find anything relating to a manual mode. Conversely automatic mode is the normal under PID control.
If I am using the analog input mode and change it to no input, my input signal jumps to 0V, I want to be able to set the input signal in manual mode to a specific value.
Thanks
Nick
Grant
Forget my last question I found the manual mode in the datasheet.
Nick