I have a DOIT TS100 tank with differential steer. It has two 12v 180 rpm motors with encoders. The encoders are 300 PPR, and the gear reduction is 75:1.
I’ve connected as the guide on the ardupilot site shows. After I have rebooted the system, I tried to debug the configuration with mavlink inspector. There, no WHEEL_DISTANCE is available, while on the Mission Planner status tab rpm1 and rpm2 show 0.
What helped me most was getting the WENC distances as in above figure, and having the total distances shown be the same as in an actual test (129/132m as shown). The red trace is for the inner wheel in a circuit lap with known length.