i had made an airsoft tank and wanted it both to freeroam and be controlled by rc. and found it to be quite simple actualy using the ping code. this is just the begining of the code but the robot will nagigate with ping and when the rx is switched on will stop the arduino. and when switched off will let it continue. i did this using an unused channel on the rx. when the rx is swithed on but the tx is not it sends out no pulses but when the tx is switched on its send pulses high then a servos range. using the ping code it reads at 17 inches. so modding the ping code.