Wheel Encoder Setup

Rover firmware supports up to two AB-phase wheel encoders, which sharpen position estimation and matter most when there is no GPS. An encoder mounts on the motor shaft or the wheel axle, one per side of the vehicle.

Wiring and setup

Phases A and B each take an output. Before wiring, those two outputs have to be switched from servo output to plain IO.

▲ A and B each take an output; yellow is phase A, white is phase B, green is GND and blue is Vcc

1. Connect phases A and B to spare controller outputs (the official example uses AUX OUT 3~6).
2. Set SERVOx_FUNCTION on those outputs to -1 so they behave as GPIO inputs. In the example these are SERVO11_FUNCTION~SERVO14_FUNCTION.
3. If those outputs are taken by relays, release them by setting RELAY1_PIN and RELAY2_PIN to -1.

Output numbers depend on the controller

The SERVOx number behind an AUX pin varies between controllers. Go by the silkscreen and the output list in the ground station rather than copying 11~14 from the example.

The two encoders are configured separately: WENC_ for the first, WENC2_ for the second.

Parameter	Set to	Notes
WENC_TYPE / WENC2_TYPE	1	Encoder type; 1 is an AB-phase quadrature encoder
WENC_CPR / WENC2_CPR	From the datasheet	Counts per wheel revolution; look it up in the motor or encoder manual
WENC_RADIUS / WENC2_RADIUS	Per vehicle	Wheel radius in metres; a 5 cm radius is entered as 0.05
WENC_POS_X / WENC2_POS_X	Per vehicle	Fore-aft distance of that wheel from the controller (centre of gravity), forward positive, in metres
WENC_POS_Y / WENC2_POS_Y	Per vehicle	Left-right distance of that wheel from the controller (centre of gravity), right positive, in metres

For the encoders to feed position estimation you must use EKF3. Configure the items below, then restart the controller.

Parameter	Value	Notes
AHRS_EKF_TYPE	3	Use EKF3
EK2_ENABLE	0	Disable EKF2
EK3_ENABLE	1	Enable EKF3
EK3_SRC1_VELXY	7	Take horizontal velocity from the wheel encoder
EK3_SRC1_POSXY	0 (optional)	Set to None when GPS is not used at all
EK3_SRC1_VELZ	0 (optional)	Same here: vertical velocity without GPS

Ground test

The WHEEL_DISTANCE MAVLink message reports accumulated distance for both wheels in real time. In Mission Planner press Ctrl+F and open the MAVLink Inspector to watch it.

Push the vehicle in a straight line over a known distance on the ground (5 m, say) and compare the two readings. If the sides differ noticeably, check tyre slip and WENC_RADIUS first, then WENC_CPR. If one side counts downwards, that encoder's A and B phases are swapped — swap them back.

Wheel speed control

A balance bot can use the encoders to close a wheel-speed loop around the left and right throttle outputs. The steps are in the wheel speed control part of the official Balance Bot tuning page.

Logging

Accumulated distance for both wheels is also written to the WENC message in the log, so a run can be replayed afterwards and the distance checked.