Open Source Motor Control (OSMC)

The OSMC is a high-power H-bridge circuit designed to control permanent magnet DC motors. It was designed expressly as a motor control for robot combat in competitions such as BattleBots™, Robot Wars™, Robotica™, and the like. The attributes of a controller for such an environment are much different than normally found in commercial or industrial motor control units. A robotic combat controller must have very high short-term power handling capability along with light weight and simple interfacing. It must drive a wide variety of motors and be easy to mount and secure from the shock and vibration of combat. The ideal controller should also be low-cost and easy to repair if needed.

Unlike most motor controls the OSMC does not use a heavy heatsink to extract heat from the MOSFETs. Rather, it uses a cooling fan to blow air across the board. This removes more heat more quickly than a plate type heatsink as has lower weight. The fan itself is a commonly available 80mm square computer cooling fan. Either a 12V or 24V fan may be installed on the OSMC. Mounting holes are provided at the correct spacing to mount the fan directly over the MOSFETs for maximum cooling efficiency.

The OSMC is a "simple" H-bridge power amplifier. It does not have any on-board logic to interpret RC or other commands. An external logic interface is required to translate command inputs into the PWM signals needed to drive the board. This increases system complexity somewhat but also increases flexibility as the OSMC board may be driven by any microcontroller or other signal source that can provide PWM and Enable logic. The OSMC project has developed the Modular OSMC Brain board to complement and complete the OSMC power board. This microcontroller-based interface board accepts RC signals and performs the conversion to PWM for two OSMC boards. More information about the MOB may be found within the MOB information.

One of the major advantages of separating the power section of the controller from the logic interface section is to allow the power units to be paralleled for special applications. One exciting application of this is to use two OSMC boards on a single interface channel to control high-powered four-brush motors such as the Magmotor or Astroflight™ motors. By using a special interface cable the OSMC can control these 4-brush motors at twice the current of a single power unit. That gives a continuous current capability of over 300A! This image shows a µMOB controlling 2 OSMC boards driving a four inch Magmotor. Stall testing with this motor and 24V of Hawker batteries showed no appreciable heating of the OSMC boards.

The method used by the OSMC/µRRC is superior to using two R/C-based controllers such as IFI Victor/Thor or Vantec on a four-brush motor because with the OSMC the two power units are driven by exactly the same drive signals and they will switch in perfect synchronization. Two RC-based controllers connected using a Y-cable to will not have the controllers synchronized due to differences between them. Clearly the OSMC is the way to go for maximum power handling on these large powerful motors.

For some related downloadable files regarding the OSMC, see the download page.