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Postby frazelle09 » Sat Apr 16, 2016 3:53 am

We've been working on a parabolic hot water heater (http://www.appropedia.org/Parabolic_Solar_Hot_Water_Heater) and have been unable to get it to work with a LED electronic circuit to seek and position the sun. So, we've switched to a Raspberry Pi B and a program to calculate solar position (pysolar) as well as a program which takes that info. as well as the info. from an IMU to move the parabola. Previously we had it working with a 12V 1Amp gearmotor which rotated at about 12 rpm and which was pretty powerful for such a small motor.

We've pretty much gotton to the stage where we have Jay Dosher's program (https://github.com/polyideas/Raspberry-Pi-Solar-Tracker/tree/master/Software%20(File%20System%20Root)/usr/lib/cgi-bin) integrated with some small scripts written by Joan on the Raspi forums (https://www.raspberrypi.org/forums/viewtopic.php?f=44&t=139584&p=927604#p927604) which are able to read our IMU (Jay's IMU was a different one connected to a Sparkfun something-or-other).

We have basically been told that we are going to need to change from our DC gearmotor to a stepper motor and are trying to figure out which one might fit our needs. Might you have any suggestions?

An idea of the travel required: The gearmotor rotates a long (1 M) rod which is threaded through an arm. As the thread turns, it makes the arm rotate which pushes or pulls a connecting rod attached to the bottom of the parabola - which means that the threaded rod needs to rotate several times in order to achieve one degree of movement of the parabola.

Hope this is enough info. If not, ask away! and have a great evening! :)

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Postby Jake » Mon Apr 18, 2016 9:22 am

Hello!

The only "beefy" stepper motor we stock is the following:

http://www.modmypi.com/electronics/moto ... 12v-400ma/

Datasheet here:

http://www.modmypi.com/download/42HS34-04A4.png

I don't think you need to be too concerned with the RPM of the motor, as you only need ~ 10RPM to move it at a reasonable rate. I'd be more concerned with the torque required to move the load. Realistically, if your current motor is 12V @ 1A, then an equivalent stepper should work just as well.

-- Jake

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Postby frazelle09 » Tue Apr 19, 2016 7:24 am

Thanks, Jay. i'm actually more concerned about the kg./cm. torque. The Granger unit appears to be about 35 ft./lbs. which is about the same in kg./cm. apparently.

i found this https://www.circuitspecialists.com/nema ... 310-d.html which, although is not 35, i'm thinking about trying in the application. If it works, it works. If it doesn't i'll just have to pop for the more expensive model - or better balance my parabolas. i actually don't know how much one parabola pulls, much less 5 or 6. Now that i'm writing about it, maybe there is some way i can check how much torque i really need for one unit... hmm...

Anyway, thanks again for answering and have a great evening! :)

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Postby Jake » Tue Apr 19, 2016 8:24 am

Decent torque converter here:

http://www.numberfactory.com/nf%20torque.htm

Are you sure it's not lb/in? As 35lbs/ft is ~ 480kg/cm!

I think your best bet is to overestimate, and just trial a motor like the one you suggested. Torque calculations are a massive headache, so I would personally avoid at all costs :D

-- Jake

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Postby frazelle09 » Tue Apr 19, 2016 4:13 pm

Thanks, Jake, you are correct, again! It is indeed in./lbs.

https://www.grainger.com/product/DAYTON ... late-2L009

Torque calculations are a massive headache, so I would personally avoid at all costs :D
- lol. Thanks for the heads-up. i'll try my best to do so. And again,

have a great day! :)

P.S. - this is not a double - post - lol. i'm just trying to increase my post numbers - lol.

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Postby kdeuler » Sat Jan 14, 2017 4:06 am

Frazelle09-

Just noticed this thread via google. May I ask:

1) What stepper motor did you end up with for this project?

2) What was the reason you were told to switch to a stepper motor? Was it because it could be positioned with more precision?

3) Any links to your project?!

I'm developing a solar tracking system for a parabolic solar concentrator, and I'm learning about what's worked for others.

Much obliged.

Kurt Euler
San Jose, CA USA

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Postby frazelle09 » Mon Jan 16, 2017 6:38 pm

Kurt! It's good to hear from you and your project!

1) What stepper motor did you end up with for this project?
i ended up with a Stepping Motor Type 57BYGH310-D, CW No. 2015.05.07

2) What was the reason you were told to switch to a stepper motor? Was it because it could be positioned with more precision?
The reason we were going to go to a stepper was what you just mentioned. Since we wanted to use an IMU and a couple of Python scripts, we eventually found out that the Python script called for a stepper motor instead of the DC one that we were using.

i never could figure out the Python readings from the IMU so was unable to connect the stepper. Went back to trying to correct the glare on the LEDs and just purchased the glass jar as well as the LED tracker and put a "headband" on it and now it seems to work just fine. Maybe someday i will find someone here in town who would be interested in helping implement the IMU/Python/stepper combo. i really couldn't find anyone who could translate the DC torque into stepper torque so i was never sure that the motor i had bought was going to be able to drive the parabolas or not. It seems strong enough for at least one parabola, but for a commercial venture i was looking for 4 - 5 ganged parabolas.

The links to the project are in the previous posts: http://www.appropedia.org/Parabolic_Sol ... ter_Heater

What are you making your parabolas out of? Wish you the best of luck with your endeavour and if you have any additional questions, please feel free to ask.

With warmest greetings and have a great day! :)

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