You are trying to power the Trex from the Arduino's 5V supply. There are 2 problems with this. First, the Arduino +5V line can probably not provide enough current to start the motor. Second, the Trex is specified for a supply of 6V minimum.
You are trying to power the Trex from the Arduino's 5V supply. There are 2 problems with this. First, the Arduino +5V line can probably not provide enough current to start the motor. Second, the Trex is specified for a supply of 6V minimum.