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Topic: Building a Winch. Stepper motor or regular DC motor. (Read 2334 times) previous topic - next topic

pdfmech

I am looking to build a winch and I need precise speed control. The winch needs to be able to lift about 40 pounds. I looked at just buying one but I need to be able to program two winches to work together. I have access to two wheelchair motors but I would have to buy a stepper motor. A stepper motor would be easier to control as a DC motor would likely need a feedback controller. Stepper motors are also more expensive. I guess my question is how difficult would it be to simultaneously and precisely control 2 DC motors? Any other suggestions/ideas would be appreciated as well.

Yankee

It's not clear from your description but I'm guessing you need to coordinate the 2 motors to position a load? DC motors would work if you could incorporate some sort of limit switches.
If you could give us some more specific information about the project it would help.

zoomkat

You will probably have to use rotary encoders on the motors and use their output to input a program to control the speed of the motors via an h-bridge (if not using stepper motors).
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sentryGun53

Like you said, position/speed feedback from the shaft would help a lot. But for simple, precise speed control of a DC motor, you can use an H-Bridge or MOSFET, taking a PWM signal from the micro controller.
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zoomkat

Quote
But for simple, precise speed control of a DC motor, you can use an H-Bridge or MOSFET, taking a PWM signal from the micro controller.


The speed of normal motors increases and decreases with the change in load, so more than this will probably be needed.
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pdfmech

Yes i am using the two motors to position a load. My group in senior design is designing and building a window cleaner.

MarkT

How precise?  If you use matched motors and reduction gearing so they are not heavily loaded you will get reasonalbe control just with PWM.  For more precise you need shaft-encoders and then close the loop to make two continuous rotation servo motors.

If the winch drum is not precise then your position feedback can't come from rotation, you will need linear position sensing of some form.

If all you need is to keep a platform level while winching both ends you just need an accelerometer to measure tilt of platform?  Or use one motor ;)

Stepper motors will be very slow and inefficient BTW and thermal issues may need addressing.
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jackrae

If the two motors are pulling in the same direction then you could use a single motor by feeding the rope from the winch drum over a pulley assembly at the terminal location then run the rope back to the location of the winch where it can be anchored. 

sentryGun53


Quote
But for simple, precise speed control of a DC motor, you can use an H-Bridge or MOSFET, taking a PWM signal from the micro controller.


The speed of normal motors increases and decreases with the change in load, so more than this will probably be needed.


Good point. But if the load was always 40 lbs, the motors would always move it at the same speed, right?
Build your own sentry gun! http://psg.rudolphlabs.com



Quote
But for simple, precise speed control of a DC motor, you can use an H-Bridge or MOSFET, taking a PWM signal from the micro controller.


The speed of normal motors increases and decreases with the change in load, so more than this will probably be needed.


Good point. But if the load was always 40 lbs, the motors would always move it at the same speed, right?


The window surface will also strain the window wiper in an unknown way... might not be enough to destabilize the system though.
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