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

Home made Aluminum Furnace

In order to be able to build face plate discs (to hold the bearings of my H3 Robot wheels), while avoiding some heavy routing work (6 wheels = 12 plates) and lots of wasted aluminum during the process (if done from a solid block), I decided on building an aluminum furnace, so that I can make a mould and then just poor aluminum into it, to roughly produce my face plate discs.

I based my furnace on an old gas container shell. Using a gas container, can be dangerous due to residual gas that is still inside. In order to remove the pressure valve, I had to first remove any remaining gas and oil, very carefully. I let remaining gas escape for a whole day, by just forcing the valve to open slightly, making sure to not produce any spark during the process, due to the risk of explosion. In order to determine when all gas had efectivelly escaped, a small amount of water or other similar liquid (oil for example), can be used, to cover the valve openning. As long as we can see gas bubling through the liquid, it's not done yet. Simple, but efective.

After this process was complete, any remaining oil inside the container was removed by just unscrewing the pressure valve, and letting it flow out.

Once the shell was free of gas, and hence safe to work with power tools, it was time to cut it. To make a lid, the top was cut flat, as high as possible to maximize useful internal work volume. An extra hole was done near the bottom, to provide a viable source for heating the contents of the future furnace.

In order to be easy to close and open the furnace, a large hinge was adapted to the outer shell, allowing to operate the cut out lid.

In order for the furnace to withstand the heat required for melting aluminum (around 600ºC), and to make the melting process more eficient, the interior was filled with a heat refracting clay. Heat refracting concrete is also available and can be used instead of clay.

To accomplish this, first we need to define the required work volume so that this volume can be isolated, so that the clay can be poored between the outer shell and this inner shell that will limit the useful working volume available.

The inner shell, must be made from a material that can withstand the heat that will be generated. Any iron based metal sheet will do, since iron has a much higher melting point (above 1100ºC) than aluminum.

Before pooring any clay into the device, the inner shell needs to also have a hole where an iron tube will connect it to the outer shell, so that heating can be supplied from the outside. The main ideia here, is to slant the heat/flame admission tube, so that it will be relatively tangent to the surface of the inner shell cylinder. The ideia behind this setup is to force heat to spiral it's way up, hopefully providing a better distribution of heat.

The heat admission tube, must be soldered, since it will receive lots of heat when the furnace is working. I arc welded mine, but it was somewhat hard to make it stick and weld well, because the tube was a very different metal from the one used in the container. But In the end it got welded good enough to withstand the furnace working conditions.

The ideal way to apply the clay is to make it as much liquid has possible, without becoming completely fluid. After pooring the clay, it takes some time to dry, since there is a lot of water in it. A possible option is to turn on the furnace, and hope that the clay won't crack, while cooking, which I didn't try because I expected it to form air bubble pockets, that would ruin part of the intended thermal isolation. Instead I opted to let it dry by itself, in the sun. Concrete might be better in this situation, since it "cooks" itself slowly while setting.

However, while pooring clay or soldering the tube, the inner metal sheet, shaped like a cylinder, got a little bit off center. But not enough to make the furnace fail. Something to account for, and correct if I ever refill the heat refracting material

It worked ok, apart from the fact, that all the clay that was placed in the lid, to protect it from furnace heat, just crumbled apart. I somehow expected this to happen, but didn't think much of it. To prevent this, I should have soldered a simple metal net/grid or similar to keep the clay in place.

When it crumbled, I just used the pieces to fill the remaining space that wasn't completely filled before.

Next time, I will show what happened when I fired it up.

Finally, Z Axel is complete !!!

The axel screw extra length has been cut off to correct size, and motor protection and cable support have been securely reattached.
It already passed, several function tests, but the ultimate test is to cut some stock material to see if the original problem is gone, with all the load on the axel, including spindle and vacuum setup.

Refactored Motor Support

Since the new axel mount position only has an offset distance of about 12.0mm from original axis mount position, I opted to reuse/refactor the original aluminium motor support plaque, by re-drilling new mount and pass through holes. I also had to make a circular cavity, 3.0mm deep and 34.4 mm in diameter, in order to fit the motor in a secure configuration, that it also had originaly. The picture shows motor housing on top, attached to aluminium support plaque. And below we have a flexible coupling linking the motor shaft to the ball screw axel, just above the axel support bearing which is attached to aluminium L shapped support. Now I have to find a viable solution to fix the motor metal protection, that also as a handle, to drag the motor cables back and forth.

Checking for correct alignment

After making shure that the rail spacer was as flat as possible, I knew I had another problem to fix. Cutting down 0.6mm of spacer thickness meant that now I didn't have enought spacing for correct alignment. i.e. now it's parallel to Z-axel support bridge, but I need to increase the spacing, to get it on center again. As can be seen on the first image, after correcting for the missing spacing, now the support is correctly aligned with the z-Axel, since the axel goes through the bearing in perfect alignment. One solution to correct the missing spacing could be to replace the original clear acrylic part with a thicker one, and fly cut it to size, but I had ruled that out, once I decided to keep the original, and just make it flat by cutting it.

The reasoning for this decision is that this part is large, so replacing it would mean more weight on the Z support structure, due to the extra thickness, and more acrylic scrap leftover. Since I have another clear acrylic spacer, a smaller one, where the Z Rail Support is bolted to the bridge, it's easier, cheaper and faster to replace this part with a thicker one. Since I didn't have a thicker clear acrylic, hence I used an opaque one I had laying arround. In the second image we can see the rail support sandwhiched between a short opaque acrylic on the left, and a long clear acrylic on the right. On this image we can also clearly see screw shapped cavities in the clear acrylic, that were used to fix it for fly cutting.

Fixing Rail spacer thickness

Last week, I found out that I had a significant missalignment on the Z-axel rail. After checking the assembly, I found out that the support rail spacer, a piece of clear acrylic, was the culprit. Due to how the rail works, in the outermost positions of the spindle support, it was off center to as much as 2.0mm from the z-Axel. Reversing the rail spacer assembly, would give -2.0mm of center, wich proved that the spacer was the origin of the problem. I had assumed the acrylic board was flat and of even thickness, but that proved to not be the case. It had a diference in thickness that added up to ~0,6mm between both ends.

The solution was to remove the rail spacer, and fly cut it, until it was all of even thickness. To be able to fly cut the spacer, an already finished piece, I had to make two extra holes, to be able to fix it properly. I added a small cavity to sunk/hide the screw heads from the fly cutting tool surface area to be cut. While fly cutting plastic, it gets a static electric charge, making all the thin cut slices to glue everywhere, making me remember snow, specially when the plastic is floating in mid air.

Router Z-Axel Bearing Support

Since I couldn't find a supplier for a 80x80x75x8mm Aluminium L shape, I had to cut an Aluminium bilé that I had laying arround, for making molds. I cut it roughly to the required size, with some extra margin.

I fly cut it to an aproximate thickness size, and chanfered the middle section to give it more strength.

I had to reduce thickeness and chanfer to the correct size, so that the bearing assembly could lay flat, given the required center position. I also drilled 4 fixing holes.

Counter sunk the fixing holes, to provide extra clearance arround bolts heads, to allow enough room for the axel/motor coupling.

Made all required features to lock the bearing assembly in to place. Milled a main passage for the Z-Axel and bored it to size, and later drilled and threaded four M4 screw fixing holes.

Complete L-Support, with all required counter sunk and threaded holes, and counter sunk bearing alignment fixture.

L-Support with bearing assembly bolt into place.

Motor Winding PCB

After some more Design and CAD work, here is the latest version of the H3 Robot wheel, including PCB board, used to route the poles wiring. There will be a PCB on each side, i.e. one for each stepper motor phase. Each PCB will be used to wire a single phase, supplying solder points for both windings, clockwise and anti-clockwise. The PCB was designed in such a way that allows to make several cuts on the circuit, in order to make parallel phase windings, which will be useful if wire resistance is too high, or if current is too low.