Find a good receiver
Search around for a receiver that will fit the size of your robot. Remember that receivers are available in different sizes. Moreover, big receivers are more powerful and have a longer battery life. However, you might need to buy a smaller model that suits your robot’s size. Ponder the weight of the model when building the machine as well. It will add extra weight to your robot and in effect changing the robot’s needs for traction, centre of gravity and power. A few models of receivers promote their brands for being light, but know that the light receivers will come at a hefty price.
Get a suitable transmitter
Know that you will require both a radio transmitter and a radio receiver to get the thing working. You can buy them as a bundle or separately, that is totally up to you. Also find out the power of radio signal that you require. You will need a strong signal if you will be operating your robot from a good distance. Majority of the controls are available in 2.4 GHz, which is good enough to control a robot that you can see through naked eye. Furthermore, also choose the number of channels you desire for your controller. You can get a multi-channel control for various radio controlled robots. However, you might encounter channel interference so find a good transmitter.
See if you have to purchase a separate antenna for the robot to boost the power of your receiver. Know that both the transmitter and receiver require a power source. The best way to operate a transmitter and receiver is to make use of rechargeable batteries. Also ponder about used parts of radio controlled devices such as robot toys or remote controlled boats, planes or cars. A new transmitter will cost you hundred of dollars.