I am considering to buy the “Jrk 21v3 USB Motor Controller with
Feedback” to control these.
Is this controller appropriate for these motor/encoder combo ?
Can the output of the encoder be used as feedback in the “Jrk 21v3” ?
The manual says it supports "Frequency/tachometer digital input up to
2 MHz with 1 ms PID period."
as a closed-loop feedback option. Is the encoder capable of this ?
Edit: Most of this is wrong (see Jan’s reply below). Sorry for any confusion.
You could technically use the jrk with our encoder set, but for most applications I think it won’t work very well.
Here’s how I’m thinking about this: Our encoder set gives you a spacial resolution of 3 mm if your processor is reading both of the quadrature outputs. The jrk can only read one of the outputs, so that means it would get a resolution of 3*2 = 6 mm. Suppose your robot is as fast as a 3pi robot. That’s about 1000 mm/s, so the jrk would be getting about 166 counts per second. If you set your jrk’s PID period to 100 ms, you only get 16 counts per PID period and it’s hard to do accurate feedback with such a low number of counts. If you set the PID period any higher, then you would get more counts but your robot would have a slower reaction time.
All of our Orangutan robot controllers can drive two motors and read two quadrature encoders, so I think those would work better for you. But what is your application?
Edit: Most of this is wrong (see Jan’s reply below). Sorry for any confusion.
I forgot to account for the fact the Jrk tachometer feedback mode only counts pulses; it doesn’t count both the rising edge and the falling edge. So the spacial resolution you can get would be 12 mm, and all my numbers above should be worse by a factor of 2. --David
David’s answer is wrong and misleading: the jrk motor controllers do not support quadrature encoders. The frequency/tachometer feature only allows for closed-loop speed control without knowledge of direction or position, which is usually what you want if you’re using quadrature encoders. You can in general use quadrature encoder outputs as a tachometer input, which is what David was talking about, but if you care about position, you would have to keep track of that separately (that means his “spacial resolution” comments do not apply at all).
David’s comments about our particular wheel/encoder system being a poor tachometer for the jrk speed feedback option are still valid, so I absolutely do not recommend that they be used with the jrk.
