Motor Suppression in Robot Wars

Robot wars is a hostile place for motor controllers, and motor suppression should be given careful thought.

The main areas for concern are;

  1. Shock and vibration caused by collisions and weapon strikes.
  2. Electrical noise spikes caused by motors being subjected to rapid physical stops or shock loads whilst under full power.

Rotating weapons will be particularly susceptible to number 2. The main aim is to have the rotor spinning as fast as possible and then to transfer that energy instantly to the victim. When that happens there is a lot going on in the system not least of which is oscillation of the armature and possibly bouncing of the brushes in their holders. The physical energy hopefully goes into the victim but the built up electrical and magnetic energy has to go somewhere too. You also have a controller that is trying to drive full current across two brushes that are what…going forwards, backwards, stationary, across one winding, bridged across two?

This can lead to some pretty hefty transients being developed across the motor. To protect against these you should consider fitting a fast acting varistor transient absorber across the motor terminals as well as the capacitors and ferrites mentioned elsewhere. There are a number of suppliers of these e.g Littlefuse. or RS components.

Varistors come in a wide variety of ratings but we would recommend one with a varistor voltage above the battery voltage + any regen braking surge, but below the Vmax of the controller you are using, and with a current rating of at least 10x the maximum motor current. Typical part numbers would be Littlefuse’s V20P30AUTO for 24V systems or V20P42AUTO for 36 / 48V.

The same is also true [but to a lesser extent ] of main drive motors, that may get engaged in a pushing contest or are rammed hard.

This picture shows the protection fitted to the motor on one of our test rigs, in this case there is only a capacitor fitted but if this was for a robot I would fit a transorb in parallel with it.

motor suppression