In need of some assistance for BATMAN pov graphics

[MrDEB]

Am building a tandem recumbent quad bike (4 20" bicycle wheels) and whild in the process of designing and welding the frame I got the BATMAN bug. Why not add a SOF (skin on frame) body in the shape of a Batmobile and ride this in the day after Thanksgiving / Christmas parade. Put a couple of kids in the co-pilots seat. This is a form of velomobile.
What I plan to do is add some blue and red LEDs for a halo ground effect and put an LED pov graphic on the two front wheels BUT have tried using Brads graphic program with no success. Any help on this is greatly appreciated as I have never done a POV graphic type device.
Following Brads great build on POV devices I think I can assemble the hardware but the pic programming end of it.

[brad]

Which software were you using? I have made a few different versions

I will soon be working on a new version to!

[MrDEB]

I have tried the first version you posted about a year ago?
Looking to try out the version on the indestructible unless you have a better version?
Was looking over the one chip RGB POV build and with the simple graphics I am looking at doing this may be the best choice. Using all SMD and etch a PCB I just might get it to actually work. Perhaps add more LEDs? for resolution but ??

[brad]

Sorry I should have asked, was that the excel version or the newer visual basic version.

both versions can only do basic conversions that would cause your image to get drawn around the wheel. I haven't even tried to venture into a version that could convert a graphic to display on a spinning pod on a wheel that would look just as you would see it on a computer screen. (if that makes sense)

I guess what I'm trying to say is that I haven't got a version that can achieve this effect:

[MrDEB]

yes display a graphic on side of wheel.

[brad]

unfortunately I dont have a version that can achieve what you are looking for.

Infact, it would probably take me quite a while to figure out how to make a conversion program that could achieve that

On another note, how has the hardware side of things been coming along for you?

[bitfogav]

Just has an idea..

Because the bike wheel will be variable rotation, you could use two pickups on two different spokes?, and use an interrupt and timer to calculate the time between the two pickups.
You could then calculate the speed of the wheel and if you wanted to set an average over time, and use that to trigger the graphics over a set time base (so that the graphics is spread out equally), and to align with the wheel speed.
The one pickup then could be used after you have a wheel speed caculation to trigger the starting point for the POV image.

Picture below to show what I mean by the position of the two pickups:

bikewheel.png (57.28 KiB) Viewed 24292 times

But on the other hand you could just use one pickup on the bike wheel and use a timer to calculate one rotation of the wheel and work out the wheel speed and at what speed the POV needs to be set at to draw the image.

So the main problem is the variable wheel speed, I'm sure at very slow speeds the POV isn't going to work correctly anyway!.

[brad]

You right Gav, you will certainly need to calculate how many revolutions per second the wheel is doing and then use that to trigger the interrupt to draw the graphics at the right time.

You will also need to be riding at quite a great deal of knots to make sure that you don't get flicker on the display - I have seen others get around this problem by adding extra LED strips, the monkeylectric version I think has four strips so each strip takes care of drawing 1/4 of the complete display (instead of 1 strip trying to do the whole 360 degree rotation.

[MrDEB]

One problem I see with the monkeyelectric unit is 8-15mph. I plan on staying below 5mph.
YES the 4 led boards would SMOOTH out the display and having multiple trigger pickups. Thinking of two pickups but 5 magnets on the wheel.
Need to get outside and finish building the actual quad bike then start on the electronics.

[bitfogav]

One problem I see with the monkeyelectric unit is 8-15mph. I plan on staying below 5mph.

I can't see that 5mph would be fast enough for the POV to display a good image.

[brad]

What is the rim size?

I'd like to figure out how many revolutions per second you would get at 5MPH

[MrDEB]

wheels are 20". I could add a bunch more LEDs to increase the resolutionm and allow a slower wheel speed.

[brad]

hmm, just doing a little bit of maths here (and converting into km/h and meters etc...)

20" wheels = 50cm.

circumference = 157cm (so one rotation means you would have travelled 1.57 metres.)

5MPH = 8KMH = 133.3 Metres per Minute = 2.2 Metres per second

therefor you would be doing 1.4 revolutions per second. This is certainly to slow. You would only be drawing not quite 1 and a half images per second (rather than - i think - the 25 per second to get a nice flicker free image)

The monkeylectric version uses 4 sets of LED's which means you get one complete image every 1/4 of a revolution of the wheel. so at 5MPH you would get 5.6 images per second.

Could you increase you speed to maybe at least 15MPH or get really really small wheels!

[MrDEB]

If I added more sensops to imitate a smaller wheel and add more LEDs. Perhaps cover one half of the wheel or the entire wheel but then it would be defeating the purpose of POV.
Will ponder but need some insite on opening the code?

[bitfogav]

Why not strap a motor to the side of the wheel then you wouldn't have to worry about what speed the bike was going?