Originally Posted by
coherent
Instability, loss of torque (each motor would get roughly half the current that the driver would normally supply to one motor), possible timing issues. You are doubling the reactance or inductance applied to the driver. This will likely cause instability and loss of torque of the motors at higher drive frequencies resulting in lost steps. This is a nonlinear function, meaning torque drops more rapidly with increasing drive frequency. This will severely limit the maximum speed of your machine. In addition, the back EMF from two motors under certain operating conditions may add up to the point where it exceeds the voltage rating of the driver which can result in damage to the driver.