Clu gravity balls (prototype)

After looking arround the web, there doesn't seem to exist any supplier for the nice looking Clu gravity (or baoding) balls, as depicted in the movie Tron Legacy.

Since I haven't had much time to proceed with my robot project, I decided this would be a much smaller project, that I could do in a relativelly short time (but I was wrong :).

The problem with projects like these, is that I'm a perfectionist when it comes to detail, and that's good and bad. Good because the final product will look and feel better. Bad because it will eat away lots of time just to get it right, but in the end I'm happier.

At first I did some research, but there isn't much info on the actual gadjet, in terms of dimmensions, material it was made of, etc...

To make the ball sturdier and have a nice heavy/metal feel to it, I decided I would make the ball from aluminium.

Since I want to have at least 2 gadjets (avoiding the term "balls" in there :), and since others might be interested in it too, I opted to make a design that would allow for better replication or future production in the long run. So molded aluminium is an expected target, to give some extra use to the Aluminum Furnace.

I started planning, and after a few iterations, I was already on version 3, and lots of changes in between prototypes. However, while progressing between versions, I did several test runs, with materials and shapes, just to experiment with possible solutions, and validate expected results.

The first problem that I got into was to determine the actual correct radius for it. First design iterations, were more or less conditioned by the size of electrical components, battery, LEDs, etc... and I kind of eyeball it from movie screenshots. My initial estimate was arround a diameter of 50mm (~1.96 Inches).
 However, I realized soon that a small change in radius, implies a somewhat massive change in volume in practical terms, which is relevant for handling it with your hands (smaller is better), but space is at a premium for electronics (more volume is better). So this could quickly become an engineering decision of balancing the pros and cons.

For the first tries I used 3mm LEDs and a 12V battery, for it's larger capacity, and higher potencial which would allow powering a few LEDs in series, depending on the LEDs.

Using LEDs on a ball of this size, has some serious drawbacks, because even the most wide angle LEDs usually have only 120º degrees of output, however due to the size of the ball, the LEDs are so close to the outer surface, that simply it isn't possible to have enough LEDs to cover the entire light ring in a reasonable way.
Another problem is that LEDs have a very intense but focused light, i.e. LEDs are not a good source for a flood light, which is what is intended in this case. What actually happens is that LEDs light shape can be clearly seen on the outside of the light ring, due to their bright concentrated output, which shows up as hard spot lights.

After these first experiments, it was obvious that: ball was too big, current electronics didn't fit the bill, and I had a light difusion problem to solve.

In order to not throw away further work on the subject, I decided to make a more accurate size estimate based on the movie screenshots, because if it will take me more effort to make it smaller, at least I want to do it the right size. This took me to a range between 40mm and 42mm, which is very cramped for the 3mm LEDs, cables and battery.

So a change in electronics was in order, and now I had a target goal for size. But I still had the light difusion problem to solve.

After some more research on the web, checking manufacturers LED specs, LED lights and solutions for diffusion of LED lighting, I got to the point to investigate how laptops LED backlights were being built, since they have a very even light output, which is what we want.

All this investigation/digging put me in the right track, for hunting the right kind of acrylic/plastic that would have the best characteristics in terms of light diffusion and transmission, and also on how to direct light and build a shape in the best possible way, so that total internal reflection could be used to conduct light for a better effect, but still provide enough diffusion to scatter light evenly.
I also did some investigation on plastics that were used backlit buttons, for example elevator/lift controls, media center boxes, and some other cool looking gadjets, using backlit buttons.

So next batch of experiments was to try different kinds of plastics, their light scatering/diffusion characteristics and how shape and angles affected light going throw it. In order to have a more visual exploration of this subject I started conducting tests using a red laser.

After finding the plastic that satisfied my intentions, I started experimenting with the ring shape and how light
should hit it in order to have a nice even light glow.

After I got the light source and shape nailed to the high standards it deserves, I started working on actual ball requirements and how the interior should be built in order to satisfy them all.
Minimum mechanic design goals:

• Sturdy metalic ball
• Weight balanced ball, weight should be equally distributed
• Even light glow
• Replaceable battery
• Must have simple but sturdy open/close mechanism (to replace Battery)
• Open/close mechanism MUST NOT be of screwing/threaded type

Some goals are somewhat obvious but the last design goal, from this simplified list, was due to a reasonable expectation that if a user rotates two balls in one hand, the ball might eventually open, i.e. unscrew itself. On another note, any threads would probably have an adverse effect on the light ring glow to become un-even, due to possible reflection occuring on thread surfaces.

Another factor that went into the decision, to not use a threaded aproach for open/close ball, was the fact that given a two part sphere (two semi-spheres) gadjet, almost everyone will immediatly try to unscrew it, it's just a natural reaction. If the ball does not unscrew, it can create some mistery/challenge on how to actually open it, and that improves the coolness factor :).

I designed a simple but effective lock mechanism, after trying several methods, but I'll keep it under wraps for now :)

Next steps will be:

• Shrink electronics, so they can fit inside the ball.
• Black anodize a prototype aluminium ball.
• Create two versions, a single color (fixed at manufacture time) and a multi color one (configurable light glow color).
• Integrate an acelerometer, to power on/off on motion detection.
• Add a microcontroller for configuration and support some cool features (tell you all about it later).

Update

Just to link this post to the next one, which contains some video of a self-contained ball rolling around