Figure 2. Controller schematic.
transmitter rather than a pistol grip style because
it was easier to implement. I took my transmitter
apart and rotated the left stick so that both sticks
moved up and down the same to give me a good
tank drive feel. You can certainly do this using a
pistol grip radio but you would then have to
interpret the steering and throttle signals to give
you the differential drive action.
Figure 3. MOSFET/relay motor driver.
14 SERVO 03.2010
This is a very simple project. In fact, the
controller uses things I’ve discussed in other
articles about creating high power PWM motor
drivers using a MOSFET and a relay rather than the
more complex, completely solid-state MOSFET H-bridge. This particular board set was designed to
be a special effects controller for Halloween spook
houses so it needed to be simple and robust.
Figure 1 shows what the board looks like. Note
that there are lots of parts on this controller that
have nothing to do with the motor controls!
Figure 2 and Figure 3 show my controller board
and motor driver board that use this program.
These motor controllers were 7. 5 24V maximum.
Creating a fairly high current motor controller
is easy with a relay, but you need to pay attention
to one really big caveat – DON’T change directions
while you are driving the motor! The relay is what
handles the motor direction; the MOSFET handles
the motor speed. Make sure that you have
stopped driving the motor (PWM = 0) before you
change direction or you’ll get a big fat inductive
kick when those contacts break! Sure, it’ll
probably handle it a couple of times, but