hmm, this could get slightly complicated for a beginner. You need to set up a circuit that controls the power to the rf device at timed intervals to only 'listen' for an incoming signal once every second/X, and to stay on when a signal is heard. This would be very easy with a PIC and some code. Otherwise you'll need an oscillator that charges and discharges a capacitor, and during each discharge will hold a transistors base to allow power to the RF circuit, then a seperate capacitor that is charged by the relay when a signal is received, that will hold the transistor on for as long as needed for the motor to do its job.
Does any of that make sense?