Project Concentric - 20" High Speed Spinning High Power LED Sphere Build

First I want to give credit where credit is due. This project was inspired by FireMyLaser's led ball build.

http://laserpointerforums.com/f57/led-orb-2-0-a-50012.html

His project is awesome and in the spirit of innovation I wanted to give it a try with a few tweaks!

Project Concentric

Differences:

1.I am only using 2 axis instead of 3 for reasons I will later explain. (also because I am not a slip ring building genius like FireMyLaser)

2. I will use 4 leds instead of 3

3. I am using high power 3w leds in the colors of red green blue and white instead of smaller RGB Leds

4. I am scaling up to 20"! This is why only 2 axis as 3 would end up being very heavy and there is a lot of spinning mass at play already.

5. I will control everything with an arduino. It will have preprogrammed displays that can be activated with the push of a button...preferably a big red one.

At this point I have most of the parts and have begun building the basic frame.

Here is a rough mock up.


The top bearing will be 608 style skateboard bearings with a 5/16 shaft for the main cross to ride on. This assembly will be mounted on to a circular piece of wood which will have a turntable bearing mounted below. This will allow the entire piece to spin for the 2nd axis. I am waiting on my third turntable bearing to arrive as the last 2 were insufficient.

The specs I know at this point:

• 
  When spun a 20" multicolor sphere will appear and be programmable for countless types of displays
  
  The main axis will be powered by a heavy duty cordless drill motor
  
  The top axis will be powered by a hpi racing rc motor
  
  Will be really loud when running most likely
  
  Is going to look like some sort of spaceship weapon
  
  It will probably be dangerous to stand by
  
  Its going to be really bright

Many updates will follow as assembly continues and I will likely be asking the community for help as I run into inevitable problems

I wanted to share my fun with everyone

Helios

You will run into problems with this large size, if you're aiming for high speed to achieve the persistence of vision effect. Try spinning a bike wheel while holding by the axle, and you'll see what happens if you try to turn it. Basically you'll be forced to run it at low speed or it will try to take off, or destroy itself. The best thing you can do is using three LEDs instead of four to save some rotating mass, and thus get a bit more speed out of it.

FireMyLaser said:

You will run into problems with this large size, if you're aiming for high speed to achieve the persistence of vision effect. Try spinning a bike wheel while holding by the axle, and you'll see what happens if you try to turn it. Basically you'll be forced to run it at low speed or it will try to take off, or destroy itself. The best thing you can do is using three LEDs instead of four to save some rotating mass, and thus get a bit more speed out of it.

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That could be but this it much lighter than a bike wheel. I don't expect super high speed on the main axis but the top should whip around pretty good with a racing rc motor. You may be right that it won't hold up...I will find out I guess. As long as I spin the main axis with the natural direction of the gyroscope I would think I should be okay. If you have more info I'd be glad to hear ir though.

That were you using to power the bottom axis?

In the video it was free standing and I was running to at top speed before it would start to move around - it was limited due to being fully portable and not bolted down. Both axes totally balanced and the spinning direction does not matter.

FireMyLaser said:

In the video it was free standing and I was running to at top speed before it would start to move around - it was limited due to being fully portable and not bolted down. Both axes totally balanced and the spinning direction does not matter.

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You are right. I am thinking of when you apply a force how it wants to turn. This is interesting. I considered this a bit but maybe not enough. So when you turn the bottom axis you found that it throws off the top? As in slows it down right?

I cant put it to words well, but you can study on it by searching gyroscopic precession. TLDR: It naturally don't want to be spun in two perpendicular axes, because physics.

FireMyLaser said:

I cant put it to words well, but you can study on it by searching gyroscopic precession. TLDR: It naturally don't want to be spun in two perpendicular axes, because physics.

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Yeah I understand that. Theres a great video of an old man lifting a big spinning weight over his head. He has it on the end of a shaft and swings it around him. The gyroscopic effect causes it to rise almost effortlessly even though it's like 50lbs or something. I guess I just don't know how strong the effect is at this lower mass. When I turn it it will want to rise as well but obviously it can't so I would assume that energy goes into slowing it down and/or tearing it apart. If it's light enough and the motors are strong enough it should over come it like in your design...I just don't know how to figure out how light and how strong it needs to be.

Make the top axis (the LED part) as light as you possibly can without compromising too much strength. The bottom axis can be as heavy and strong as you like, as well as the base. There really is not a limit to how fast, or large, or heavy you can make it, it just gets more difficult to manage.

FireMyLaser said:

Make the top axis (the LED part) as light as you possibly can without compromising too much strength. The bottom axis can be as heavy and strong as you like, as well as the base. There really is not a limit to how fast, or large, or heavy you can make it, it just gets more difficult to manage.

Click to expand...

I will try to gear the top axis motor as low as I can while still getting enough speed to keep up the torque and keep the cross as light as possible. I will mount the bearing in the cross instead of the supports so that I don't add the steal rod to the rotating mass. I think my biggest problem will be the dowels flexing. I chose oak because it's ridgid and the are suprisingly strong but if there is a lot of force they might just snap off.

I really appreciate all the advice. For anyone interested in following I will make videos of the test runs so that even in the worst case scenario it should be a fantastic looking failure with flying leds and shards of wood! Haha

Having more mass near the center of the top axis is fine. It gradually gets worse the further out you go from it. But using three LEDs instead of four is a big help.