I used a number of tips to increase the effective range of my transmitter from about 2m to 40m. I used capacitors to minimise motor noise, put the receiver in an aluminium box, used a separate receiver battery, used co-ax cable within the robot to carry the aerial signal, earthed the shield to the battery negative (but did not earth the chassis), extended the length of the aerial to ~1.1m, and used sprung steel for the aerial to hold it away from the chassis. Each one of these elements had a positive effect. When at a later time I had to move the on-off switch to make it more accessible I used graphite cores at both end of the wiring. Surprisingly the reception didnt seem to change with or without these cores.

Jeremy