desired speed. Another option for speed control is to
reduce the motor’s voltage. Most models will accept a
lower voltage, but I have encountered a couple of oddballs
that required the full 12V. I have used the units I reference
above and been successful with voltages as low as 3.3V.
Reducing the voltage will also reduce the torque, but
depending on your application, that may not be a problem.
Wiper motors are power hungry beasts and require a
supply that can deliver sufficient amps. When choosing a
supply — regardless of the voltage — be sure and get one
that provides at least five amps.
Monster Guts carries an adapter plug which is a handy
accessory and offers a speedy solution for wiring up your
motor. I heartily recommend these plugs; they are a cheap
investment for the setup time saved.
Giving Your Motor a Performance
One possibility to further improve your control of a
wiper motor is to use a Picovolt controller from Fright Props
(see Resources). This unit allows you to adjust the speed
and direction of your motor and to record your desired
movements, and then replay them. It also allows you to
make the effect respond to a trigger input to further dial in
the timing of your effect. If your motor comes with the
park option, this controller will permit you to take
advantage of that feature and have your motor return to its
Are you ready to take it to the next level? Well, if you
are searching for even finer control, I may have a solution
for you. I came across an especially interesting hack for a
wiper motor that would correct what I feel is its biggest
drawback. It would allow positional control of the motor,
allowing it to work much like a servo while still providing
the power we enjoy from a wiper motor.
The concept was discussed on a robotics forum that I
am a member of. It was originally proposed by member,
ihnoblegnome who had been working on the idea but he
was running into some reliability issues. A solution was
offered by BinaryBedlam which seems to resolve the
problems encountered with the initial version. A link to his
post which has his comments, diagrams, and a video link is
included in the Resources. His video also includes some
footage of the circuit in use. It is worth checking out!
The concept of the design is to send your servo a PWM
signal which directs the position of your motor. By using a
comparator connected to a MOSFET based H-bridge, you
are able to send the proper signals.
In addition to building the circuit, you will also need to
do a little simple surgery to a servo for this project. The
modification requires you to remove one of the gears and
to disconnect the wires from the motor. You will need to
drill a small hole in the servo, lengthen these wires, and
extend them to attach them to the PCB in order for it to
provide the necessary positional feedback.
The servo shaft will then need to be attached to the
shaft of the motor. For preliminary testing of my motor
which has a 6 mm threaded shaft, I replaced the retaining
nut with a coupler. This allowed me to connect a bolt
which I hot-glued to the round servo horn. ServoCity carries
the hardware I used once I was pleased with the design to
make this a more solid and permanent connection between
the motor and servo (see Resources; Figure 9).
I was anxious to give the circuit a try and ordered up
the necessary parts. It did not take long before I had it
breadboarded up and I was ready to test it (Figure 10).
Success! It fired right up and we were off to the races. I
have incorporated a simple PICAXE board I often use into
the design, and was soon playing with the code and
running the circuit through its paces. The MOSFETs can get
a bit warm, but this issue was quickly resolved by simply
adding some heatsinks.
Everything was working well on my bench, but I
wanted to do some further testing. I went ahead and
designed a PCB and sent it off for production so that I
could more easily get additional input from a few fellow
builders. The new board makes putting the circuit together
a quick and easy process (Figure 11).
Brian Lincoln was the first to get the new boards and
SERVO 05.2016 27
Figure 9. ServoCity parts
make a secure connection.
Figure 10. It works great on the