Please double-check the wiring connection of the foot motors.
The wires going to “LM” on the MeccaBrain™ should be connected to the robot's left foot motor.
The wires going to “RM” on the MeccaBrain™ should be connected to the robot's right foot motor.
If that does not resolve the issue, please double-check the instruction manual to confirm that the feet have been built correctly. For more assistance, please review our instructional videos here:
www.meccano.com/watch?vid=43 and
www.meccano.com/watch?vid=51