I've seen a bunch of Instructables that describe how a radio-controlled car can be converted to a robot. Most of these require that the R/C car's receiver board be modified so that the RF section of the receiver is bypassed with the Left/Right/Forward/Backward signals coming from a microcontroller instead of the RF decoder.
That's a great idea but not something that everyone can easily do. Our approach is different. We decided to leave the R/C car's receiver intact and instead create a shield (an interface board) that takes the L/R/F/B signals from an Arduino and converts them to RF signals exactly like the ones coming from the R/C car's transmitter.
So we created a shield that mimics the R/C transmitter. We turned this into a Kickstarter project.
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Step 1: The Shield
This is the shield that mimics the R/C car's transmitter radio signals. It also includes a 9V battery and voltage regulators so that the shield and Arduino (and other circuits you might want to add) can be powered. Most R/C cars use either 27MHz or 49MHz as their radio frequency and either frequency can be supported by the shield
Step 2: The Arduino
The Arduino that we used is an Uno like this, but any Arduino ought to work. The four control signals that the Arduino generates are Left, Right, Forward, and Backward and they originate from the P2 through P5 signals of the Arduino.
Step 3: The Arduino Interface
Like any shield, the Arduino and the wireless interface board mate together using the edge connectors of the Arduino.
As mentioned, either a 27MHz or a 49MHz version can be produced. Some new (and relatively expensive) R/C cars now use 2.4GHz as their radio frequency. That radio frequency is not supported.
Step 4: Adding the Arduino/Shield to Your R/C Car or Truck
If you like, you can leave your R/C car or truck entirely intact. However, it makes it easier to mount the Arduino/Shield assembly if you take the body off. On most cars, the body is easily removed by undoing a few screws or taking off a few clips.
With the body removed, you can just stick the Arduino/Shield assembly on with velcro tape or whatever way you choose to fasten it to the body. Note that there are no wire connections between the Arduino/Shield assembly and the R/C vehicle - all communications between the electronics assembly and the vehicle are through the antennas.
Step 5: Demo of the Arduino Wireless Interface Shield
Here's a short video of the Arduino/Shield working. Note that you will probably want to add sensors, for example, ultrasonic or light sensors.
Step 6: Conclusion
If you think you'd like to try this board, see our Kickstarter page at https://www.kickstarter.com/projects/1366635924/wireless-robotic-interface-for-radio-controlled-ca