R/C Speed Controller

rcspeedThis is a really nice circuit that I use in my Tamiya RC car (I’ve also sold some of them). In short, it gets the servo signal from the receiver and uses it to drive the car electric motor. The hexfet H-bridge can handle more than 40 Amperes without problems. But the thing I’m very proud of is the “throttle” handling.

A little zone around the radio stick center position is the “dead zone”: the motor is free. All the “forward” zone is reserved to make motor go forward (its speed is of course proportional to the stick position). The upper half of the “backward” zone is the active braking position: the motor is short-circuited (sort of) and so the car stops in very little space. The lower half is obviously dedicated to make motor go backward.

The system is configured easily for any radio: just power on the car keeping the switch on the Speed Controller pressed, wait for the “beep” (No, it’s not a buzzer !!! My circuit uses the motor as a speaker :-) ) then put the stick full forward and press the button, put the stick full backward and press the button. That’s all. The configuration is written to internal eeprom and kept also if you disconnect batteries.

Another nice thing if you run indoor, or you’re learning the “art” of R/C car driving, is the “dummy mode”: with the car powered on you can press the button, and the controller reduce the maximum speed to about 1/4, keeping full speed proportionality and active braking.