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Quick arduino question

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Thread replies: 20
Thread images: 5

Hello! Is there any motor that allows me to move about 0.3 degrees per day?

A servo might be good, but I've heard that those have a minimum movement of half degree. I need it to move both ways, so I don't think a stepper could work.
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Use gears?
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>>903254
>I don't think steppers can rotate in two directions
Sounds like you need to git learn't, sonny.

Do you need a smooth rotation or is stepping what you actually want? What's the application of this?
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>>903264

I want to follow the sun from south to north and the other way around. I dont mind if the movement isn't too smooth.
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>>903260

I would rather code a motor, i need to keep the machine as little as posible
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>>903270
In that case, you could get a stepper with an attached gearbox. The steps could be well within the increments you need, and you definitely can drive steppers in both directions.
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>>903276

That was pretty quick, thank you man, I don't work with electronics so I was having a hard time.
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>>903271
you can't code around physical limitations.
Ya gunna need a reduction gear to get to 0.3
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File: feedback.jpg (24KB, 912x214px) Image search: [iqdb] [SauceNao] [Google]
feedback.jpg
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>>903271
>>903293
Sounds like you need a feedback loop then. Potentiometer on the output motor for position feedback to the microcontroller.
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You could get a stepper with 0.3 degree resolution, but that's a bad idea. Cause you might skip steps and to get any torque at all you need a beefy ass stepper motor. Go with a gearbox with an encoder or pot for feedback.
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>>903311
Or you can turn 1.8 degrees in 6 days.
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>>903359
You mean per 6 day interval. Stepper motors step. Still risk skipping steps over long time periods
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File: 20130727_001547.png (1MB, 942x819px) Image search: [iqdb] [SauceNao] [Google]
20130727_001547.png
1MB, 942x819px
>>903254
Yes, camera gimbals can do it... they use a PWM to rapidly alternate power between two adjacent phases of the motor, so the motor holds a position *between* steps. Most gimbals use 3-phase brushless motors with only 12~24 steps per revolution, but hold positions accurately to a fraction of a degree.
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>>903254
What is this thing supposed to do exactly, and how will it be powered?

Various thoughts, numbered to make arguing easier--
1. Servos and steppers can both turn both directions
2. I dunno about servos, but most stepper motors are either 200-steps (1.8° per step) or 400-steps per turn (.9° per step). Anything different tends to cost rather a lot of money.
3. If you use a larger stepper driver, it will allow a bunch of microstepping modes. Pic related--the green is the different microstep modes they typically provide.
4. To hit .3 degrees exactly, you would need 1,200 steps per turn, that none of the motors provides, and none of the microstepper modes provides.
5. If you used a 6:1 gear reduction on a normal 200-step motor, you would hit .3° per step. However...
6. Stepper and servo motors need constant power to maintain their positions; they lose their precision if you power them down and then up again. For something you want to run an entire year at a time, any stepper or servo may not be ideal.
7. You can't run a motor directly off an arduino anyway. You will need a separate driver for the motor.
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>driving a motor without flyback diode
I see disaster coming this way
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>>903254
buy a geared down stepper motor on ebay.
drive it with a uln2003 or something.

its easy, google it.
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>>903477
this.
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>>903475

It will be a suntracker powered by battery, or maybe powered by a solar panel attached to it.
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>>903529
>It will be a suntracker powered by battery, or maybe powered by a solar panel attached to it.
Various thoughts...
1. We don't know how much weight this thing will need to move, so it's still kinda hard to make any specific recommendations
2. You can use a stepper but you wouldn't want to keep it powered all the time. So that means two more things, #3 and #4
3. The mechanical drive needs a worm screw in it, so that the motor can drive the load, but the load will not drive the unpowered motor
4. If the motor can't be kept powered all the time, then the motor needs a separate tracking method--some type of rotary encoder. Stepper motors lose their positions when powered down and over time that error would build up.
5. If you build the mechanical drive so that the motor is spun in {some number of complete turns} to move .3°, then you only need an encoder that signals once every rotation of the motor.

There are some small camera steppers on the China sites--pic related. This one has a work screw and a plastic cam on it that could maybe work... (the plastic cam would operate a microswitch once for every turn) It still needs a driver but that isn't difficult.

It depends on how much load (weight) this thing needs to move and what tools you have.
Not much tools means buying parts ready-made, that cost more.
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>>903601
(continuing my posting)
the problem you have here is that pretty much all the tiny cheap gear reductions I've ever seen didn't have brushless motors on them--they have DC motors. And those could work, IF you could fit an encoder to the motor somehow,,,, but that is a pretty difficult task without machine tools.

There is also cheap small plastic gears and gear kits around you can buy--but the problem there is that the smaller ones are made for a smaller shaft than the larger ones are. So once again, it's hard to use them without any machine tools to make the shaft that could fit both a small gear and a large gear on it.
Thread posts: 20
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