Providing Power, Direction and Speed Control
Wiring the Motors, DPDT Relays and PWM to the MOSFET
The diagram above shows how I wired four of the DPDT relays (on my eight relay board) to control the direction and speed of the motors for the Rover's wheels. NB the circuit for controlling the relays using an Arduino pin is ready made on the eight relay board - here.
A logic level, power N-MOSFET switches high current to provide motive power at 12vdc vdc. The gate is controlled by an Arduino PWM pin so speed can be adjusted accordingly. However each individual relay is only capable of switching 2A at 12vdc, but that can give me 24watts, per wheel in theory.
When the Arduino PIN V1 is set to logic 1, the motor goes in one direction, and when set to logic 0 the the DPDT relay switches it to go in the opposite direction. Fly-back diodes (D1 and D2) are used to reduce emf spikes from the coils in the relay and motors. D1 is an integral diode in the MOSFET package.
I decided to make a perf-board version of the Mosfet PWN driver circuit x4 using this free design app.
Mosfet PWN driver circuit x4
I could have made it more compact, but I wanted to keep the symmetry of the design:
Perf-board Mosfet PWN driver circuit x4 with heat sinks
I glued aluminum heat sinks to the Mosfets using epoxy-based thermo-paste, and used Schottky power diodes for fly-back [those are the big black monoliths].