Feedback jitter

[nknotts]

Hi,
I'm getting some jitter in my feedback signal from the AX-12. I know this is to be expected from any electrical sensor but the problem is the readings will sometimes jump beyond the acceptable range of output values.
I am commanding the wheel turn speed in continuous rotation to roughly 500 counts. As expected, the average feedback value is close to 500 counts. However occasionally, the value jumps close to 3900 counts, a number I wouldn't expect to see (I thought the maximum was 2047). 3900 maps to -828 if using the first 10 bits as the magnitude and the 11th bit as the sign. The manual says bit 12-16 should always be zero but clearly that is not the case here.
Is this a known problem or am I experiencing something strange and unheard of?

Thanks,
Nate

[JonHylands]

I don't believe you can reliably use the encoder counts in the 60 degree "dead" zone. I've taken apart the AX-12, and it uses what looks like a fairly standard potentiometer, which means there is most likely an actual dead zone where it doesn't count. That is most likely why it is limited to 300 degree rotation while in servo mode.



- Jon

[limor]

Dead zone is one issue. Another is speed reading. I assume you are referring to jitter in the speed feedback value. this value is calculated in software on the servo board and it doesnt seem that they use a kalman estimator or something to smooth out the noise. it also seems that the speed value is updated around 7 times/sec. You are better off reading the position value a few hundred times/sec and calculating the speed yourself. The position value can be read at 400 times/sec.