Remote Control a Windshield Wiper Motor with a PWM Switch

PWM dual relay servocity wired h-bridgeA Windshield wiper motor or anything requiring up to 12 amps of current at 30 VDC can be controlled using this PWM switch from Servocity (PWM is Pulse Width Modulation, FYI).  12 amps is a pretty heavy load compared to hobby servos!  In my case, my goal was to drive 4 wiper motors for control of the legs of a “giant” hexapod that I’ve been building.

Although it’s not done yet, I’m pleased to report that the the switches that I’ve hooked up are working nicely.  Interestingly enough, these little relays can be wired so that each switch controls the on-off signal of one output, allowing each channel to control two outputs individually.  In my case, they are wired up to act as a h-bridge circuit as seen in the picture to the right.  This will reverse or stop your motors, depending on whether the RC transmitter control is at the top, bottom, or middle.  I haven’t hooked it up yet (not sure I will), but there’s also a place to wire in two limit switches for each relay set.  I’m assuming that these will cut off power to your motor when it reaches a certain point in it’s rotation regardless of RC transmitter signal.

pvc-hexapod-rc-testsAt around $50 each, these relay sets aren’t cheap, but they seem quite full featured, and work as I would expect them to.  One thing to note though is that they don’t come with a male servo connector.  This may be prominently marked on Servocity’s page under “add to cart,” but I still managed to miss this.  If you do catch this, Servocity has some stuff that should work in their male servo leads section.  Since I’d already placed the initial order, I decided to buy some off of Amazon*, but it would have probably been cheaper to go with Servocity.

testing-relays-pwm-switchAt the moment, I have the windshield wiper motors hooked up directly to these switches, but I may eventually use them as binary inputs to a PLC or Arduino to offload some of the tasks of moving the ‘bot around.  Instead of controlling the motors directly, I’d just give it a left/right/forward/reverse signal and it would take care of the rest.  This would take 2 channels up, leaving 2 more channels, or 4 binary inputs free to control whatever else I’d like to work with (lasers, lights, moving eyes, whatever).

In the case of some sort of semi-autonomous locomotion, though this may not be necessary.  A microcontroller should be capable of reading that input directly.  On the other hand, this may be a tricky programming solution, possibly requiring the processor to be tied up trying to detect changes in the PWM signal.  I may want to still use these relays after all.  Be sure to check out the intro post for this robot, or just check out little PegLeg, this guy’s “father”.

*link is to a search, mine a “Hitec 54607S Male Servo Connector Heavy” wasn’t available as of this writing.


  1. Nice! Can’t wait to see it in action!

  2. The Mountainbeest – Now with Four Legs! - pingback on March 8, 2014 at 11:02 am

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