M-Series drives and motors were sold as a packaged set and specifically matched at the factory, where the M-drive is optimized for one motor only through internal resistors and other drive modifications. The particular motor size that a given M-drive is optimized for is specified in the model number of that M-drive. If the customer wishes to upgrade his M-drive to be compatible with a different motor, the circuitry within the customer's M57-83-E drive can be modified by Compumotor's Field Service Department as a custom upgrade. However, since an M-drive can only be upgraded to provide current for one particular M-motor, it can no longer be used with the previous motor once it is modified to be used with a different size motor - due to the changes made to the drive.
An ML drive can be modified to be compatible with any 57 mm Frame or the 83-62 size M-motor, but not any of the 106mm size M-motors, which requires the larger MH drive. The MH drive can only be modified to operate the M83-93, M83-135, or 106 size M-motors. Unfortunately, The ML drive cannot be upgraded to an MH drive. For example: If a customer has an M57-83-E Drive - the low power M-Series drive optimized for use with an M57-83 motor - and is looking for a larger M-motor to use with his current drive, he can upgrade his M-drive to accept up to the largest 57 or 83 frame M-motors. But he cannot use any 106-Frame M-motor, because he needs to have a MH-Drive in order to supply an adequate amount of current for it.
The M-Drive and motors are obsolete and can be replaced with the ZETA series or the Gemini series.