How are teams mounting drivetrain encoders on WCD?

[AdamHeard]

Originally Posted by Nuttyman54

Just to make sure people understand here: Adam's example is valid proof that putting an encoder on an outer wheel axle will not inherently add too much variability to produce reliable autos.

I feel that it's worth adding that this is possible because 254 properly tensions their chains, which means the backlash/slop between the outer wheels and directly driven wheels is minimal. If you're using WCP sliding versablocks, you should be able to tension your chain/belt well enough to make this a viable solution as well.

As an aside, 254 and 971 gave a great talk at Champs 2015 which is recorded on Youtube about Motion Profiling and Control which is super helpful to understand how they get such reliable auto control. Worth looking at.

TLDR; If you have a reasonable tensioning method for your chains (esp sliding bearing blocks) you should be fine putting an encoder on one of the outer wheel axles.

I don't believe 254 ran tensioners in 2016 or 2015.

[Nuttyman54]

Originally Posted by AdamHeard

I don't believe 254 ran tensioners in 2016 or 2015.

Correct. I actually had a much longer post drafted up and then deleted most of it to keep it shorter and more straightforward. Tension your chains and you shouldn't have a problem.

I would consider a well-designed exact C-C setup to be "properly tensioned", such as 254 ran in 2015 and 2016 and 118 for the past few years as well.

Some quick math also shows that a few degrees of "slop" of the wheels relative to eachother will only result in a positional error of fractions of an inch (1 degree of slop on a 4" diameter wheel is less than 0.040" linear). While you may get some "noise" in your encoder values, you should be able to tune a PID loop to be stable with that amount of error and still give extremely precise auton navigation.