This lawnmower has forward - reverse - left - right commands, cutting height adjustment and throttle control. All this from my Hobbyking heli RC.
Using 2x 12Volts DC motors to drive invidually the back wheels.
1 electric jack for the cutting height
1 servo the actuate the throttle
The working principle is fairly simple as at the time my knowledge of programming was fairly low. I used servos to activate micro switches which then are read by a PIC. The PIC then outputs to couplers which drive the relays.
The two motors are driven through the relays by a brushed ESC for speed control.
Step 1: Mechanical side
Primary drive with toothed belt with a ratio of 8 to 24 teeth pulleys and final drive from 6 to 66 teeth sprockets which give me a speed of 1.21 turns per second which is pretty close to the speed you would push your lawnmower around the garden. I didn't have time to built a proper bearing housing for the drive shafts for each wheels so I used plummer blocks and it ended up working quite well I must say.
The electric jack has a strenght of 50kg push or pull. I had to add a spring to help it raise the height of cutting as it is quite heavy.
One end is bolted on the frame of the mower and the other is bolted on the connecting bar from the back to front wheels.
For the front wheels, I replaced the normal wheels by caster wheels to imrpove the turning.
You also have possibility to remove the chains on the back wheels and push your lawnmover by hand.