Looking for a simple smart stepper motor

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Looking for a simple smart stepper motor

Postby Tarkon » May 31st, 2017, 7:20 pm

Hi!

I'm trying to update and recreate a project I did in the past. It's a weather clock, which pulls information from a weather RSS feed and then points a needle to a corresponding icon on a clock face. It was the first project I did, and things have come so far since then. For this project I used a 360° winch servo, which was loud and inaccurate - causing it to routinely point off-center of the icon. Now the servo has burned out, I want to update it.

Ideally I'd like to use a stepper motor - of course the problem is that I don't know where top-center is with a stepper. I've read about projects of using a light sensor or a Hall effect sensor to determine zero position, but this seems like a lot of work. Surely there has to be a stepper out there already with this built-in, or some other method of determining zero position.

Since it's just turning a shaft to point a needle on a clock face, it obviously doesn't need to be powerful at all. But it does need to turn 360°, which rules out a X25/X27 dashboard stepper motor.

Does anyone have any suggestions? Any help would be greatly appreciated.

Thanks!
-T

2012-11-24 19.44.15.jpg
Tarkon
 
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Re: Looking for a simple smart stepper motor

Postby void » July 13th, 2017, 7:42 am

It is hard to find a stepper motor with that already built into it, mainly because the type of sensors you are talking about would not be affixed to the motor, but to the thing your motor is driving, and the motor manufacturer does not know what that is. I think the simplest thing you could do here, would be to buy any decently powered stepper motor, buy a driver board for the stepper motor so that you can adjust it's position with your microcontroller. And then to determine the position at any given time, just fit a rubber stopper onto a potentiometer, and mount it so that the rubber stopper presses against the shaft of the motor. then you can measure the resistance of the potentiometer with your microcontroller's ADC at any time to determine the position of the shaft.

Here is a potentiometer that should do the trick, https://www.sparkfun.com/products/9939 just put a 10kOhm resistor on 1 lead, connect the other end of that resistor to one of your microcontroller's 5V or 3.3V pins, and connect the wiper to ground. Then just connect your ADC in between the resistor and the potentiometer and you should read a voltage between 0V and 1/2 of your microcontroller's voltage pin (either 2.5 if your microcontroller is 5V or 1.6V if your microcontroller is 3.3V) depending on the position of the rotary encoder. You can get rubber stoppers cheap on amazon like this one https://www.amazon.com/10-Solid-Rubber- ... 21&sr=1-15
void
 
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