Hi Andrew,

In addition to the .1uF caps (these should be X7R or X5R types), you should also add a 4.7uF or 10 uF solid tantalum capacitor on each controller. The output impedance of a power supply is only "near zero" at DC and can rise dramaticaly at higher frequencies. The object of the bypass caps is to lower the impedance. The tantalums do this for moderate frequencies and the ceramics "take over" at higher frequencies. Place them as close as possible to the ICs as possible, with very short leads to GND.

As an alternative to the MOV suggested you can place an RC network across the motor terminals, consisting of a film capacitor of 47 or 100nF in series with a 10 - 22 Ohm resistor. This network will suppress the electrical noise generated by the motor.

If you plan to use batteries, as described, the 7805 will not suffice. Use a low-dropout variety (like the LM2940) instead.

Regards,
Rob.