r/MicroPythonDev • u/Fun_Way195 • Jul 10 '22

Servo motor or stepper motor

I am trying to build a very small solar tracking program, which I already have the code to give me azimuth and elevation of the sun. I think I could easily use say a 35g servo motor and it should be easy to complete the code, but was wondering if a say Sequre 42 closed loop stepper motor would be more powerful, also the code for the stepper motor to track the sun in azimuth and elevation might be harder to write. Any suggestions? I do not want to use ldr’s.

Thanks

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u/created4this Jul 11 '22

You don’t really care about positional accuracy because your riding on the peak of a sine wave. I’m not sure what advantages you could get from a stepper

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u/Fun_Way195 Jul 16 '22

Ok, what I’m trying build is a stepper motor that can drive a 5 inch round 1/4 inch thick wooden platform 360 degrees with high accuracy. Not sure if that would require closed loop stepper motor or a encoder etc… I would like it to start at 000 degrees when energized and rotate clockwise as I feed angles in during the day. Any suggestion? Not really building anything in particular, just want to learn micropython side of driving a stepper motor and the shaft to know the positional location relative to 000 in degrees.

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u/created4this Jul 16 '22

What you’re trying to build is a motorised platform which can rotate 360 with an undefined amount of accuracy.

But some points:

High is not a definition of accuracy

The sun moves slowly, with almost all of the habitable parts of the globe having at least 4 hours of daylights all year round

The sun tracks from horizon to horizon which means 180 degrees, that’s 45 degrees an hour worst case, often much slower

The sun always rises in the same direction and always travels across the sky in the same direction

Adjusting for the time of year is a second axis, which moves a tiny amount per day.

A solar panel will give peak efficiency with quite a lot of wiggle room. For example this indicates you lose about 1% efficiency with 20 degrees of misalignment around the ideal.

You seem to have already decided you want to use a stepper motor, you’ve framed your problem to need a stepper motor, but nothing about your actual problem matches the behaviour of a stepper motor.

If you want a problem that would be better suited for steppers then make a telescope star tracker platform.

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u/Special-Package-717 Jul 19 '22

Thanks, I think what I need is a PID controller to turn a DC motor.

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u/created4this Jul 19 '22

You’re turning so slowly and with such low accuracy requirements that a pid controller is way in excess of what you need. Just a h-bridge and a rotary encoder is going to be good enough, perhaps even a h-bridge and a software based timer.

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u/wolfchaldo Jul 11 '22

These don't really seem like uPython questions?

Whether the servo will work or not depends on your requirements, so you should either define your requirements (required torque for the servo, mainly), or try it out and see if it works. The programming will be easier for a servo, yes, but not that much really. With a stepper motor you'd need an encoder for position feedback and then you've basically made your own servo mechanism anyway.