Encoder rate

[biojae]

What is the Jaguar's maximum encoder rate?

Would a K.O.P. encoder work well as a tachometer (only use channel A) for velocity control when driven directly from a CIM or FischerPrice motor?
Or would some sort of encoder divider (a few flip flops) be needed to reduce the input rate? (with the necessary scaling factors in place in the software to output the correct rate)

[Ether]

Originally Posted by biojae

What is the Jaguar's maximum encoder rate?

Would a K.O.P. encoder work well as a tachometer (only use channel A) for velocity control when driven directly from a CIM or FischerPrice motor

If anyone has successfully used the Jaguar's built-in speed control would you please share your experience here?

[MaxMax161]

Reading through the data sheet I got this;

The input frequency of the QEI (Quadrature Encoder Interface) inputs may be as high as 1/4 of the processor frequency (for example, 12.5 MHz for a 50-MHz system)

I double checked the specs of the jag processor just in case and it's 50 MHz.

I hope this helps!

[Bryscus]

Originally Posted by MaxMax161

Reading through the data sheet I got this;



I double checked the specs of the jag processor just in case and it's 50 MHz.

I hope this helps!

If you look at the datasheet for the black jaguar, it says 1e6 transitions per second. If you consider that there are 4 transitions used for quadrature encoding you get 250,000 lines per second. With a 100 click per rev encoder you'd get 2500 revs per second. That's 150,000 RPMs. The Jags should handle anything you can throw at them.

- Bryce

[biojae]

Originally Posted by Ether

If anyone has successfully used the Jaguar's built-in speed control would you please share your experience here?

Haven't tried yet, going to try method 2 first.
( PI loop)

Wanted to make sure that the Jag would be able to handle the high encoder rate before trying it.

Originally Posted by Bryscus

If you look at the datasheet for the black jaguar, it says 1e6 transitions per second. If you consider that there are 4 transitions used for quadrature encoding you get 250,000 lines per second. With a 100 click per rev encoder you'd get 2500 revs per second. That's 150,000 RPMs. The Jags should handle anything you can throw at them.

Cool. Thanks.

We are going to use just one output (channel A) of a 360 count per revolution encoder.
I don't think that there is a need for direction sensing on our mechanism.

[MikeE]

Originally Posted by biojae

We are going to use just one output (channel A) of a 360 count per revolution encoder.
I don't think that there is a need for direction sensing on our mechanism.

We are also investigating the same approach, using a Hall effect sensor to control wheel speed.

While this is working for cRIO control, it's proving difficult to close the loop on the Jaguar. I'm aware of the thread on Jaguar speed control http://www.chiefdelphi.com/forums/sh...d.php?t=100135 but we're seeing an even more basic problem with the encoder.

We hooked up the encoder to the Jag input using just 3 wires (+, A, -), and in software set the encoder type to kEncoder (cf kQuadEncoder).
Plotting the value of getSpeed(), we saw a useful signal when the shaft was rotating, but noise around 20kHz when the shaft was stationary rather than the expected zero speed reading.
Investigations continue...

Has anyone got a non-Quad encoder to work with Jaguar closed-loop?

[vamfun]

Originally Posted by MaxMax161

Reading through the data sheet I got this;



I double checked the specs of the jag processor just in case and it's 50 MHz.

I hope this helps!

I confirmed this too... but I am not sure if there are additional delays due to interupt processing. If I recall correctly, the pic used to have about 10 t0 20 us per interrupt for processing. Maybe a JAG engineer can chime in with respect to actual line/second limits.

[Joe Ross]

Originally Posted by vamfun

I confirmed this too... but I am not sure if there are additional delays due to interupt processing. If I recall correctly, the pic used to have about 10 t0 20 us per interrupt for processing. Maybe a JAG engineer can chime in with respect to actual line/second limits.

I suspect the jaguar is using the hardware quadrature decoder, rather then a software interrupt driven routine.

[Ether]

Originally Posted by vamfun

Maybe a JAG engineer can chime in with respect to actual line/second limits.

http://www.chiefdelphi.com/forums/sh...2&postcount=14