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DrakeAnubis

Inverse Spinning LED Display

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I saw a demonstration of a very large Spinning LED display. The type of display that spins a bar of LEDs fast enough that the bar "disappears" and only the floating LED message remains.

From my understanding these are simple to make (you see a ton of them on MAKE), wouldn't it be simple to just inverse the entire thing? Ff the bar revolved around the viewer it would, or at least should, create a surround image.

I mocked this up in Visio while making waffles.

Inverse_LED_Display.png

The only problems I saw where:

You need to over come centripetal force (either with a brace or by spacing the LEDs accordingly)

Antiquate speed is slightly challenging (although as long as you keep it as light as possible and weight it correctly, you should be able to whip the bar around fine)

Powering and controlling the LEDs becomes difficult since direct wires can't easily traverse the spinning axis (however, you could use a small controlling computer in place of the counter balance. And there are some simple ways to run power over a spinning axis)

Also, it would probably be amazing with 3D glasses. Think floating images.

Any comments?

Edited by Drake Anubis
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Awesome idea!

I might suggest instead of a counterbalance simply replicating the display on the other side of the arm too. This means it wouldn't have to spin as fast to keep the "image" in front of you.

Also if you flip the drive motor so the main unit is also on the arm, the arm can be a self-contained unit requiring no wires to the outside world.

*thinks about this on the way home*

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Also if you flip the drive motor so the main unit is also on the arm, the arm can be a self-contained unit requiring no wires to the outside world.

What about power?

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Also if you flip the drive motor so the main unit is also on the arm, the arm can be a self-contained unit requiring no wires to the outside world.

What about power?

Could use brushes like in a motor, to send power to the thing.. Or find a motor that has a hollow shaft and let a 'jack and plug' spin around each other until they burn up..

What happens if somebody moves and gets whacked in the head with it? Should a position sensor be included to shut it down if someone gets too close?

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This is an awesome idea!

You could counter the centripetal force by turning the LED bar into a shaped piece, rather than having it be just a bar. Perhaps a hollow triangle, to minimize weight. It could be done from fiberglass to keep it light.

Brushes would be the way to go for the power supply...the less weight on the moving bits, the better. I'd use the shaft from the motor as a "common" point (probably ground)...then place an insulated-from-the-shaft conductive drum in the middle of the shaft, and have the brushes (both supply and pickup) rest on opposite sides of it. Since the brushes would provide constant power, and there would be no make-break situations as in motor commutators, they should last a long time. Make them from graphite and they'd be self-lubricating.

You could probably make the drum from a piece of brass or copper tubing placed over a plastic roller scavenged from a VCR or something. Or, if you wanted to fab it yourself, you could use a piece of PVC pipe with endcaps.

If you wanted to send data in a wired form from a source not on the spinning piece, you could put several rings of copper/brass on the roller or PVC tube and add additional brush pairs...it would only take 5 rings (3 if you use common ground) for power + Ethernet.

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What happens if somebody moves and gets whacked in the head with it? Should a position sensor be included to shut it down if someone gets too close?

I don't know if that would make a better youtube video or a better comic... don't forget to add a stop switch for while being inside the device or make plenty of ducking room :)

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What happens if somebody moves and gets whacked in the head with it? Should a position sensor be included to shut it down if someone gets too close?

I don't know if that would make a better youtube video or a better comic... don't forget to add a stop switch for while being inside the device or make plenty of ducking room :)

Excellent point...especially if you were using 3D glasses with it. You could add an infared sensor somewhere on the rotating arm that would detect something close to the arm, and switch a relay from driving the motor to shunting a big power resistor across it, like a dynamic brake.

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What about power?

I imagined a good LiPo battery mounted at the center of the arm. keeping it as a single unit makes the project simpler to make in my opinion. Maybe massive magnets to induce current in the arms moving across their fields :P

On the way home I thought perhaps 4 arms would be needed to keep a constantly-refreshed image in whichever direction you're looking. And for data purposes bluetooth (sparkfun.com) isn't overly expensive.

For safety though I can't think of a sensor fast enough to detect an obstruction when the arms are rotating quickly. An accelerometer could cut power if the arms hit something but that would be somewhat late.

Unfortunately I've packed everything up as I'm moving apartment at the weekend. This is one of those rare moments I want to get the soldering iron out!

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For safety...

You don't need safety, it needs to be light to hit an applicable speed. Something like light grade pvc won't hurt no matter how fast its going...

Well, maybe if you shot it out of a gun or something :P

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4 arms would be needed to keep a constantly-refreshed image in whichever direction you're looking

I don't believe you would need 4 arms, let alone 2. If you get the single arm moving at sufficient speed (which shouldn't be difficult, the human eye can't detect anything major over 60-110 frames per second anyway) then it works in all directions.

Because it's moving at a constant speed around a circle, if it works in one direction, it will work in all directions.

Yay Circles :D

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I don't believe you would need 4 arms, let alone 2. If you get the single arm moving at sufficient speed (which shouldn't be difficult, the human eye can't detect anything major over 60-110 frames per second anyway) then it works in all directions.

Because it's moving at a constant speed around a circle, if it works in one direction, it will work in all directions.

Yay Circles :D

:D

You're right, maybe my design is too sluggish and heavy. I don't fancy a thwack on the nose by something at 3600rpm though.

If it's that light could it be mounted to the user's head/hat/cap? Wearable computing with 360deg 3D vision, guaranteed only to thwack other people

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If it's that light could it be mounted to the user's head/hat/cap? Wearable computing with 360deg 3D vision, guaranteed only to thwack other people

The hat idea is neat, but it needs to be at least 18 inches away for your eyes to focus comfortably on it. Unless you wanted to do something that was only like 3-5 inches away and very small. Sort of like a Heads Up Display so you could just glance up and see information.

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I think you'll find the LEDs will have to be moving too quickly to get any meaningful POV. This means you'll need absolutely perfect balance and stability as well as a pretty strong motor. This will be exceptionally difficult because of the long LED bar, which will wiggle because of air resistance and throw the whole things off balance. It just doesn't look sturdy enough. It also means it's practically a decapitation or de-facing risk, so be careful.

You can take any of the existing POV clocks, scale it up and invert it. The code and designs already exist. You can take power from the motor with a brush and use a small filtering circuit (just a few caps) to smooth out the power for the microcontroller.

It's a neat idea, but I don't think it'll work.

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This means you'll need absolutely perfect balance as well as a pretty strong motor. This will be exceptionally difficult because of the long LED bar, which will wiggle because of air resistance and throw the whole things off balance.

Well, fortunately I have a friend in the aerospace industry, and I could actually achieve "perfect" balance out to 7-12 decimal places. However I don't think you need perfect balance, in fact you could be off balance, even significantly, and the effect would still work... it would just break down fairly quickly.

Now I could be wrong about this, and I'd have to check, but I believe in this case stability is proportional to momentum. I think you can demonstrate this effect by tying a small object (keys, pen, coin) to a string and twirling it around with your hand.

As it gets up to speed your hand motions get tighter and it becomes fairly stable.

Edited by Drake Anubis
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I still think you're going to have problems with stability. Maybe something like this would work better.

Instead of this:

+-----------|
| /
|/
|
|

Do this:

----+--------|
\ |
\ |
\ |
\|

The point is to keep the bottom from wobbling as much as possible. If it wobbles, it'll either shake itself apart or the image will be messed up. The POV toys that use a similar design (like the POV clocks) are much smaller and wobble is not as much of an issue.

Someone mentioned 4 arms. This is a good idea, the toy would only have to spin at 1/4 the speed. That solves the wobble problem, but I think there would be two arms in the field of view at the same time. Perhaps 3 arms would be better. The thing to making multiple arms simple is only driving one arm at a time. This is as simple at 3 transistors to sink the current from either of the 3 arms, and it only needs 3 more output pins. Erm.. come to think of it, you may as well just drive all the LEDs on all arms at the same time, it won't matter because 2 will be out of the field of view at any given time anyway.

Edit: It's formatting my diagram wrong, but I think you get the point.

Edited by Ohm
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I saw a demonstration of a very large Spinning LED display. The type of display that spins a bar of LEDs fast enough that the bar "disappears" and only the floating LED message remains.

From my understanding these are simple to make (you see a ton of them on MAKE), wouldn't it be simple to just inverse the entire thing? Ff the bar revolved around the viewer it would, or at least should, create a surround image.

I mocked this up in Visio while making waffles.

Inverse_LED_Display.png

The only problems I saw where:

You need to over come centripetal force (either with a brace or by spacing the LEDs accordingly)

Antiquate speed is slightly challenging (although as long as you keep it as light as possible and weight it correctly, you should be able to whip the bar around fine)

Powering and controlling the LEDs becomes difficult since direct wires can't easily traverse the spinning axis (however, you could use a small controlling computer in place of the counter balance. And there are some simple ways to run power over a spinning axis)

Also, it would probably be amazing with 3D glasses. Think floating images.

Any comments?

*koff koff*

Make sure it has a safety cylinder so nobody loses an arm or a head.

:P

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