Misbehaving encoders

[Jared Russell]

Originally Posted by Pikat

What if you're using VEX encoders, which, according to IFI's website, can only count properly up to 1000 rpm (it might be 1000 clicks per second, i can't remember off the top of my head. either way, there seems to be a limit)

That's a good point - many types of encoders (particularly those with bearings, and especially sleeve bearings) can fail mechanically long before they hit the Nyquist rate. Or an encoder might have additional filtering circuitry that rejects pulses that are too short (the wording of the Vex encoder Inventor's guide implies that this is the case).

But if hand-turning an encoder on the benchtop produces a square wave and hand-turning the encoder at a similar speed with the cRIO does not, this probably isn't the issue.

[AustinSchuh]

Originally Posted by Jared341

That's a good point - many types of encoders (particularly those with bearings, and especially sleeve bearings) can fail mechanically long before they hit the Nyquist rate.

I don't have the specs for the digital input module on me, but I seem to remember that a 256 count encoder attached directly to a CIM was about at the limit. 971 had a 64 count/rev encoder attached to the cim output shaft, and that worked fine. I think the cRIO module has a rated refresh rate of something around 7 us, which would translate to 14,290 samples/second. I ran the math ~6 months ago...