Hello dear Forum, I am new here. I don't have much knowledge of solar panels or motors... I was wondering how it would be possible to connect a small/medium solar panel (not too expensive) to a mirror ball motor (for a 50cm diameter disco ball).
I don't have any of the materials yet, that's why I would first like to know what kind of solar panel I need for what kind of motor. It's for an outdoor art project, so that the disco ball will only rotate when the sun is shining, and nothing else. I would like to think that it is something easy to produce, I have already tried it with a small solar panel and 5v motor and it works fine without weight, the motor spins when there is sun (see attached photo of my first miniature test run) but there is not much power when I put weight on the motor.
But for a large disco ball of about 4-6 kg I still don't know what specs I would need, could someone enlighten me the way please?

thanks so much in advance!
j.

 

A disco mirror ball is usually hanging from the ceiling. There is very little torque required as there is little friction to oppose. Even for a heavier ball, once the ball gets turning, it's moment of inertia will help keep it going.

A small toy motor might work but you need a reduction gear.

The first important specification is the rotational speed needed.
What is your desired speed in rpm (rotations per minute)?

 

What is your desired speed in rpm (rotations per minute)?

Thanks for you response MrChips.

I guess in the 1-3 RPM range

 

From pololu.com the lowest RPM I can find is 13 RPM.



https://www.pololu.com/product/1596

 

Search for Hankscraft motors. They are low rpm and high torque motors. They have a 4 rpm model. They are available from a variety of suppliers, including Amazon.

I’ve used them before in a variety of applications, including a disco ball.

Edit:https://www.hankscraftpop.com/motors

 

https://www.solarbotics.com/product/22050

 

This is a standard mirror ball motor:
https://www.electrovision.co.uk/public/template-product-details.php?product_id=G007NT
but don’t buy it, because it is an AC synchronous motor and won’t work off DC. You need a DC motor of similar power.

Use a nice long length of chain to suspend he mirror ball. This lessens the starting torque required, as small movements of the motor can place the chain under torsion, which will eventually build up to overcome the breakaway torque.

Make sure that the motor shaft is adequately fixed to the gearbox. It must withstand a pull of 10 times the ball weight in order to comply with Health and Safety regulations if members of the public are walking beneath it. Some motor shafts are just pressed in.Make sure that there is some fixing mechanism that will not allow The shaft to come loose under any circumstances, such as a circlip.

You might need a simple MPPT circuit, as at low light levels the load line will not be on the optimum power curve for a solar panel.

There are battery operated rotators for home-party mirror balls, but they will only manage small mirror balls.
https://www.electrovision.co.uk/public/template-product-details.php?product_id=G007NW

 

The one thing that stood out in my mind is the weight of the ball and the bearings it's hanging from. If it's hanging directly on the motor shaft or motor transmission then its weight WILL add friction that will need to be overcome, regardless of the hanging method. If the ball is hanging from some sort of bearing arrangement then all the motor will need to do is turn the ball.

Oh, and welcome to AAC.

 

Also; the amount of power for turning the ball will depend in part on how big the panel is. A tiny PVP (PhotoVoltaic Panel) will produce a tiny amount of power or force. A larger panel would be needed to support a larger electrical demand such as a heavier motor.

 

The difficult part will certainly be the drive motor and the ball suspension. As already mentioned, those small motors tend to spin at a few thousand RPM, so some serious speed reduction will be required. The idea of a bit of chain between the drive and the ball is a very good choice, not only for providing a gentle start but also to avoid axis alignment issues.
So you will need to find a low powered motor with an integral gear reduction that will work with a typical smaller solar cell array. Probably rated at 12 volts DC or less. Since the exact speed is not critical you will not need to maximize the power or speed.

Once you find a suitable motor, or at least the power requirements, then you can find the correctly sized solar panel.

 

The one thing that stood out in my mind is the weight of the ball and the bearings it's hanging from. If it's hanging directly on the motor shaft or motor transmission then its weight WILL add friction that will need to be overcome, regardless of the hanging method. If the ball is hanging from some sort of bearing arrangement then all the motor will need to do is turn the ball.

Oh, and welcome to AAC.

A thrust bearing on a mounting bracket with a set screw collar on the shaft taking the weight will leave th e motor bearings free to deal with the rotation rather than the load.

​

[EDIT: Typo of "chart" for "shaft" corrected.]

 

Yes, thrust bearings. Not bushings - too much drag with weight.

 

Thank you all very much for your kind responses. I will be looking at all these specifications in the next few days to see carefully what I can work with in the best way. There are many things that I still don't understand about the technical issues that have been written to me here... I'll check on all these with care, will keep posting the progress soon

 

Be sure to keep in mind that here you have access to hundreds of years worth of experience, all for free.

 

I learned another lesson when I was a kid. I built a toy boat from balsa wood and wanted it to go fast.
So I put a large propeller on the rubber band motor.

To my surprise and amusement, when I put it to the test it was funny to see the boat spin and not the motor.

 

To my surprise and amusement, when I put it to the test it was funny to see the boat spin and not the motor.

That's funny. Sort of the thing I would have to learn the hard way. But way back then I also thought if I could plug a lamp into an extension cord, turn it on, then unplug the extension and plug it back into itself fast enough I could get the lamp to stay on because the current would be looping back on itself. To this day I've not been successful at such an experiment. Only, today I know why that is.

 

this is why discussions of systems exceeding 100% efficiency are seldom allowed on this forum. I think that they should indeed have a separate space for themselves, along with a size limit. Some concepts are so lame as to be funny.
Folks could be educated about the laws of physics and thermodynamics there.

 

That's funny. Sort of the thing I would have to learn the hard way. But way back then I also thought if I could plug a lamp into an extension cord, turn it on, then unplug the extension and plug it back into itself fast enough I could get the lamp to stay on because the current would be looping back on itself. To this day I've not been successful at such an experiment. Only, today I know why that is.

Yes, because electricity travels near the speed of light and you couldn't possibly do it fast enough! Duh.

 

How about the tray motor from an old CD/DVD drive? That could also be a source of gears and pulleys.

 

That's funny. Sort of the thing I would have to learn the hard way. But way back then I also thought if I could plug a lamp into an extension cord, turn it on, then unplug the extension and plug it back into itself fast enough I could get the lamp to stay on because the current would be looping back on itself. To this day I've not been successful at such an experiment. Only, today I know why that is.

That's the same concept as a buck regulator - but for that switching speed, you need one enormous inductor!