Thread: Wiper Motor servo

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I made this monster servo from a wiper motor. Using an H-bridge amp from Lynxmotion and a Parallax servo board. The POT is not hooked up to the motor shaft yet for this test, and I am turning the POT by hand, controlling the speed and direction of the wiper motor. When the POT is coupled to the motor shaft, VSA will control it. With a couple of these I can animate arms and hands, as this servo has TONS of torque.

Here is a vid of the test:

powerservotest.flv - Video - Photobucket - Video and Image Hosting

I bow to the master! Well done, Dr. I'm a bit hazy on how the pot (i.e. resistance) will be controlled, though. Could you clarify? Thanks!

That looks great. I see a lot of potential in this.
I am definately interested in more information on how you set this up.
Please keep us posted.

I did developed a circuit for converting wiper motors into servos, the problem with the H-bridge drivers out of RC servos is that they can only handle a limited load, the circuit I developed could handle 40 amps.

It also included a feature which allowed you to tune the servo response and rig the servo as a stand alone two position relay controlled servo motor.

If there was much interest I could probably make up the board as self build kits for about $75, the only trouble is that one of the key components is a surface mount part and I would probably have to mount these myself.

Very cool, Dr. M. I too would be interested in learning more!

I see a TON of uses

Originally Posted by Phoenix_UK

I did developed a circuit for converting wiper motors into servos, the problem with the H-bridge drivers out of RC servos is that they can only handle a limited load, the circuit I developed could handle 40 amps.

It also included a feature which allowed you to tune the servo response and rig the servo as a stand alone two position relay controlled servo motor.

If there was much interest I could probably make up the board as self build kits for about $75, the only trouble is that one of the key components is a surface mount part and I would probably have to mount these myself.

There are many ways to do this, and I've investigated all of them. The most common is to use a standard hdriver from a standard RC servo and amplify it using MOSFETS. Those suckers can get expensive, and you also trash out a good servo (Which is why I was asking for burned out ones a while back on anither thread). Another way is to use Solid State relays in place of MOSFETS. Cleaner solution, but even more expensive and you still trash out a good servo by hijacking the H-bridge. I was turned onto the Power H-bridge over at Lynxmotion by another haunter, (Deathmaster over at HauntForum.com - Haunting's Home on the Web) and I'm sold on it. Here it is:
Single H-Bridge - HS-5745 Servo Amp

For all the parts so far, I spent under 40 bucks, including the wiper motor.

The cost/torque ratio on this you can't beat it. It has way more torque than the most expensive servo at Servo City (at least I think it does, if not it's still a crap-load of torque). The power Hbridge can handle twice as much current than a wiper motor needs at 5 volts at no load, which is fine for my application. If you need more current, then yea, a power MOSFET amp could be used in between the H-brisge and the motor. I still may do that later if I want a faster wiper servo to work at 12 volts.

Originally Posted by Otaku

I bow to the master! Well done, Dr. I'm a bit hazy on how the pot (i.e. resistance) will be controlled, though. Could you clarify? Thanks!

It's a 5K POT, and it will be coupled to the shaft of the motor like a regular servo. In the demo, I was turning the POT by hand sort of confusing the servo controller board into thinking the servo wasn't centered. Another idea I got from another haunter was to use a little servo to control the POT. This configuration would allow the wiper to operate at 360 degrees in either direction as you saw in the video, but I don't want to do that yet. For now, I just need a BIG ASS servo at 90 degree rotation. I'll mount a mechanical stop on the plate just in case so as not to overextend and ruin the POT. I just need to get a coupler of some kind to connect the shaft of the POT directly to the motor shaft. The POT will sit on a U bracket upside down suspended over the motor when finished...Oh and no, I am but a lowly apprentice it is YOU I bow to oh master! LOL!

Originally Posted by Regor

That looks great. I see a lot of potential in this.
I am definately interested in more information on how you set this up.
Please keep us posted.

Setup couldn't be simpler. Get a wiper motor. I mounted mine to a 4x4 post plate like Scary Terry describes on his site.
Buy this:
Single H-Bridge - HS-5745 Servo Amp

Get a 5K Potentiomter.

A powersupply, (I used an ATX computer power supply) or any comperable supply you would use with any wiper motor.

A servo controller like a PArallax, or Mini SCC or SCC32, or whatever you would normally control a regular servo with.

Wire it up as shown in the diagram:


Power it up. You will need to attach the POT to the motor shaft before you can control it like a servo first.

That's it, nothing to it really.

" I just need to get a coupler of some kind to connect the shaft of the POT directly to the motor shaft."

Is there enough thread on the shaft to mount a gear below the arm on the wiper motor? If so, you could mount the pot below and use a couple of gears in a 1:1 ratio. That would keep the package neat and solve the mounting question.

Just 2-cents worth.