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| Need help with motor sizing calculations for solar panel mount |
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| cbc02009:
Hello all, I have a 50W solar panel (Datasheet here:http://grapesolar.com/docs/GS-STAR-50W.pdf) that I am trying to build a solar-tracking mount for, and I am having trouble figuring out how to calculate the power of the motors I need. The solar panel will need two motors, one for movement about the vertical axis, and one for movement about the horizontal axis. I have approximated the moment of inertia for each axis of the panel using the formula --- Code: ---I = (1/12)*m*(h^2+w^2) --- End code --- and I know I can use that in combination with the necessary angular acceleration of the panel to find the required torque of the motor. My problem is, I have literally no idea what kind of acceleration is necessary (or even reasonable) for my project. It really doesn't need to move very fast, since the sun doesn't move terrible fast in the sky, but that's velocity, not acceleration. In fact, I don't know that I care very much about the actual acceleration of the panel at all, it's more that I don't want to buy an under-powered motor and have it stall. Any advice on where to find calculations, or even just where to start my search for the answer would be greatly appreciated. Thanks! |
| IanB:
I think you may be barking up the wrong tree. My guess is that friction in the gears and bearing system is likely to be the most important load on the motor. |
| CM800:
--- Quote from: IanB on September 16, 2018, 04:15:08 pm ---I think you may be barking up the wrong tree. My guess is that friction in the gears and bearing system is likely to be the most important load on the motor. --- End quote --- I'd strongly suggest calculating it all out. Calculate out a 10 second (you don't really want to wait a day to move it to the position you want, should you want to change. move 180* Using a movement curve without constant velocity gives you 1 rev / 20 seconds. (0.05rps) So find a motor that's pretty slow. For the acceleration, it will be twice the velocity (as you need to move half the distance in half the time) so 0.1rps /s (convert that to radians) The torque you will require is going to be the Inertia, multiplied by the Acceleration in Radians. |
| rstofer:
Have you considered the wind load on the panel? Around here we would design for 80 MPH. No, we're not going to hit that number more than a couple of times per year but that's what the building codes require and it seems reasonable to consider it. These tracking projects are all over the Internet. Maybe Google can help. https://www.electronicshub.org/sun-tracking-solar-panel/ |
| cbc02009:
--- Quote from: CM800 on September 16, 2018, 04:21:52 pm --- --- Quote from: IanB on September 16, 2018, 04:15:08 pm ---I think you may be barking up the wrong tree. My guess is that friction in the gears and bearing system is likely to be the most important load on the motor. --- End quote --- I'd strongly suggest calculating it all out. Calculate out a 10 second (you don't really want to wait a day to move it to the position you want, should you want to change. move 180* Using a movement curve without constant velocity gives you 1 rev / 20 seconds. (0.05rps) So find a motor that's pretty slow. For the acceleration, it will be twice the velocity (as you need to move half the distance in half the time) so 0.1rps /s (convert that to radians) The torque you will require is going to be the Inertia, multiplied by the Acceleration in Radians. --- End quote --- Thank you, that's very helpful. That's exactly what I was looking for. --- Quote from: rstofer on September 16, 2018, 05:31:04 pm ---Have you considered the wind load on the panel? Around here we would design for 80 MPH. No, we're not going to hit that number more than a couple of times per year but that's what the building codes require and it seems reasonable to consider it. These tracking projects are all over the Internet. Maybe Google can help. https://www.electronicshub.org/sun-tracking-solar-panel/ --- End quote --- This is a proof-of-concept prototype for a school project, so out of pocket cost is kind of the most important factor. I've seen projects online using servos and stepper motors, but don't those both require constant input from the MCU to maintain their position, thereby reducing the efficiency of the system compared to a regular gearboxed motor? I was hoping to use a wormgear to both increase the gear ratio, and also keep the panel held in place when we stop the motor. |
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