The project describes how to build a Radio Controlled lawnmower using Arduino, a cheap R/C transmitter and receiver pair, and a couple of electric-wheelchair motors. It uses Mosfet h-bridge (N-channel and P-channel Mosfets) to control motor speed.
To implement the Failsafe, John David, the designer, used another Atmega168 (or an Arduino), to control a normally-open 60amp power relay. The relay disconnects the power to the motor-controller unless receiving a “good” signal from the 2nd microcontroller. This signal is updated 2 times every second and is either ON or OFF. If the bot gets out of range, it loses power to the motors. If I flip the kill-switch on the Transmitter, it loses power to the motors.
Project Firmware, Schematic and Documentation