Chassis_model.forward(1) only gets partial power

try to use the chassis skid model to drive user control.

use: chassis_skid_model.forward(1)

then we use: motor.getVoltage() to read the voltage on each of chassis motor.

We expect to read 12 volts
however we only get 4 volts or 7 volts when checked by .getVoltage() . It means the motors are not drinen in full power.

how do we get full power to drive chassis.
do we have to drive each motor separately?

.forward is open loop function. we believe pid setting has nothing to do with PID setting.

are you setting motor velocity?