Mammoth POV: an almost 5 metre, giant POV/squencer for Christmas displays etc

Tubular

This will be my entry for the Propeller Platform contest

Imagine a 5 metre long, 160 RGB led addressable rope light, being rotated the same way kids rotate long skipping ropes at primary school (one kid at each end with lots of kids jumping in the middle)

I am writing an editor based on Kye's 160*120 6 bit VGA driver to edit the sequence shown by the RGB LEDs as it sweeps around the arc. One pixel per RGB led, one row per sequence step.

Ultimately I'd like to have it read a bitmap off SD card and automatically display that bitmap, which involves syncing the rotation angle phase and speed etc.

What I really want from the forumistas at this stage is ideas for content you'd like to be displayed on this. If nothing else it should do a great job of displaying forum avatars!

TonyD

what a great project.

Imagine if it was hung vertically and turned by a small electric motor, the a great POV display you would get

Tubular

Tony thats a great idea. Looks like it might be useful as a giant easter egg as well as giant Christmas sled. It will be interesting to see how fast it can be turned.

This is as far as I got tonight -
* Made a cheap "bearing" using the belled end a 20mm electrical conduit and a bit of 4x2 with a 22mm hole.
* Bought a short length of 20mm ID tube to test passing the RGB strip through. Hose clamp to connect it together. All good!
* Applied 5V power and generated a test pattern just by touching the data pins. Probably not recommended due to static, but I was running out of time. Does this qualify as "digital" data?
* Found a good test location being a 4.8m wide roller door opening (with the roller door rolled out of way)

Couple of photos below of the "electronics end" where the propeller platform will mount - there will also be a similar arrangement at the "mechanical drive" end - whether its a manual crankshaft, electrical motor or wind turbine (!)

Looking ahead... I need to look at Matt Gilliland's new power pack to see if it could deliver 5V at about 3 amps, get a 5m length of protective tube, write some test code for some simple scrolling graphics, which should come out as a barber shop style spiral when it all rotates

WBA Consulting

You mentioned on the other contest thread about the boards handling the G-Forces. When we built addressable light beams for an LED lighting company (the same company that made the latest Times Square ball), the boards were laid into an aluminum u-channel and then the channel was filled with an RTV like coating/sealant. This made the finish product much more stable. For your project, you may want to look into filling the tube with mineral oil. This will aid in cooling the LEDs as well as provide some stability for the shock, etc. Just do a search for "mineral oil computer case" to get an idea of sites like this one.

Tubular

Very interesting, WBA. I had no idea such a product existed

During testing last night i was surprised at the lack of friction between the led strip and the outer protective sheath - so turning the sheath wasn't causing the inner strip to turn. My first reaction was that I would need to fill the tube with something viscous and clear... eg Honey! It was late, ok?

Actually first I'll just try clamping the ends and see if the middle bit stays facing outwards. I could also try small clear weights that the G forces would keep outermost (thus keeping the strip innermost but facing outwards, in theory)

kwinn

First, please be very careful. An assembly that size rotating fast enough for a POV display can cause a serious or possibly fatal injury if something came loose.

For powering the leds I would suggest using either slip rings or a permanent magnet motor on the stationary section rather than placing any mass on the rotating section. The pm motor could act as both the bearing and alternator to provide power to the circuitry.

Tubular

These are good points, Kwinn.

There are a couple of stages to this - initially I just want to get a feel for what the minimum speed required is - and I will be turning things by hand, a crankshaft or maybe a pull string wrapped many times around one end. I'll also be using 3 AA alkaline batteries to power the leds for whatever time they run for.

I've also been thinking of running a steel rope or two through the sheath - partly to support voltage droop but this could also be a safety feature for the higher speeds later.