Bosch 750W Motor Suppression

The Robot Wars construction guide suggests using 470nF capacitors to suppress motors, however 4QD suggest using 10nF capacitors as they have a higher impedance at the switching frequency 4QD controllers work at, and so will consume less PWM current. For this reason we used 1 10nF capacitor across each pair of brushes in the motor.

Here is how we fitted the capacitors:

Firstly remove the back of the motor by undoing the three screws with a star shaped socket. We managed to do this without having to take the motor out of the robot:

Now remove the brown bit, which the brushes are attached to (sorry it's out of focus - camera got confused ;o):

Get you capacitors (we used 10n Ceramic capacitors) and you will probably find you will have to solder a piece of wire onto the legs (we insulated the join with heat shrink tubing), as the legs are too short to reach between the brushes. Now solder the capacitors between the pairs of brushes - like this:

Now just reassemble the motor. You will probably require an extra pair of hands to do this, as you need to push the four brushes in all at once.

After we installed the capacitors, I read a comment that soldering might not be the best method, as at high currents the solder could melt. I don't know what the chances of this happening are, however we have decided to see how the solder holds up, and if the capacitor fall off then we will try a different method of attaching them. Perhaps it might be possible to poke the legs of the capacitors through the holes at the ends of the brushes and wind them round a bit....

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