Testing and Cause of Failure for Encoders and Hall Effect sensors

[eugenebrooks]

Chris,

This thread caught my eye, and I have a few observations:

1) You mentioned that you don't use a pot because of resolution
issues, and I am wondering if you have tried a 10 turn pot on the
drive shaft that turns 5 times faster to resolve that problem. By
hooking the feedback closer to the motor, so to speak, you can also
remove instability arising from the slop in the gearing between the
motor and the arm.

2) With regard to sensor testing, we have used led indicators as
part of the design, so that a quick look can determine if it
is "blinking," software running in the RC that prints a message
each time a sensor value changes, and finally, a scope. There also
relatively cheap multi-meters that have a "frequency display" for
a TTL input level, and you can use these to see if a high pulse
rate sensor is working correctly.

3) I am a little worried about triggering an input to the RC
at 17khz and expecting the RC to track it, although I have not
tested the limits of the interrupt based inputs on the current RC.

3) The electrical environment in a robot is very noisy, with lots of
spikes on the power lines. If a sensor requires power from the 12
volt line, we bring that power in through a substantial inductor, a
capacitor bypass, and then on board voltage regulation. We usually
ground a sensor at the RC, instead of elsewhere, to avoid
any ground loops that might introduce spikes into the sensor output.

Although we have had some fun with PID control systems running amok
when a collision knocked the analog connector to the RC loose, we have
never had a sensor fail electrically, and we tend to salvage the more
expensive ones by desoldering from a prior years custom circuit board
and putting them into a new custom circuit board made for each build
season.

I hope that this helps...