OpenServo.com

[HalloweenBob]

I am trying to use a wiper Motor (from a car) as a servo.

The motor I want to use is on the Monster Guts website. Search for 12VDC Wiper Motor.

Sorry, I'm new here and I am not yet allowed to post URLs.

I want to use the lynxmotion Single H-Bridge - HS-5745 Servo Amp to control the motor since I want to control it from my SSC-32 card.

I will be running the Motor on 5VDC because that will give me the speed I want.

It will be used in a Halloween project as an armlifter for a plastic full sized skeleton purchased from Bucky's Boneyard. You'll have to google that if you are unfamiliar.

I am concerned that the Single H-Bridge - HS-5745 Servo Amp from parallax or lynxmotion will burn up if I try to drive that motor with it because of the current needed to drive that motor. Is that the case?

If so, is there any way to use the positioning elements of that board and replace the H-brigde circuit part with a 4PDT relay? or maybe a LMD18200T chip from National Semiconductor?

I will be mounting an external POT that turns in sync with the armature of the wiper motor and will be using a pulley system to lift the arms.

Any wisdom you can share would be greatly appreciated. Also any alternate ideas would be great!

[guru]

Can you post some real numbers on the parts you will be using?

What is the current of the wiper motor? If you cannot determine the *stall* current, give the ohm rating of the coils at least.

What is the continuous current rating of the lynxmotion h-bridge?

About what kind of load will you be putting on the wiper motor? Will it be working hard or will the task be quite easy for it? The torque placed on the motor will determine how close the current draw will get to the posted *stall* current.

If the h-bridge looks like it will be ok, just be sure to give it a quick 5 second test...turn it off, check the temp of the h-bridge with your finger. Of its ok, try a little longer. Work your way up to 20 minutes or more of usage and recheck the temperature. For really sensitive testing of temperature I have been known to hold it up to my lips! Your lips have a lot more nerves than your finger. I don't use one of those sissy temperature gadgets.

As for replacing with servos or digital servos, that probably won't work. The PWM used in the h-bridge controllers would be too fast for the switching characteristics of the relay for sure, ...not sure about the digita relays, but probably them too. You would just need to make your own out of powerful MOSFETs. The older open servo schematics have an h-bridge design made of mosfets. You could use this as a replacement and wouldnt be very hard to wire up.

(If you go wiring your own MOSFETs repost on here. There are a few things to consider before beginning since you are using 12v. Like for one, using pre-drive transistors to turn on the MOSFETS to the *full* 12 volts if the input drivers are low-power 5v.)

C

[HalloweenBob]

I should be able to post links tomorrow.

I will try again then.