Response 2 of 2 (answering some technical questions)
Some of the screws are for fastening the box sides to the inside blocks of wood to hold it together. I thought that my choice of material for the box was pretty ingenious - I used fake wood flooring boards. Got a box of it for $10 on clearance. It's thin, light, smooth, rigid, and looks better than other wood scraps in my garage. And they snap together.
3 things that took the most time: Encoder code, trackballs, and spinners. Months and months of trial-and-error and redesigns on the two latter.
Spinnersfound some homemade spinner designs on the web, but they really looked like a lot of over-kill - relying on a lot of mechanics to detect rotation. I found online a simple chip that puts out an analog voltage in response to the orientation of a magnet in 360. I got some cheap casters from the hardware store and broke off the wheels. What you're left with is a base for a spinner. Just screw the top onto a dial, and glue a magnet on the bottom.
The dials themselves are the result of melting gluesticks with crayons in cat food cans. I did this 'cause I wanted colors matching the trackballs.
The dials work well for driving games or rotating tank turrets, stuff like that. Not so well with pong-type games like Arkanoid. Not sure if it's just my MAME configs or problems inherent with transforming rotation into lateral movement. Or maybe I just stink at Arkanoid.
Drawback - I have to admit the dials don't "feel" right - they feel very loose and light. But hey, they work. I saw some dial designs where pennies were put in to add some weight.
Anyway, the analog voltage goes to the Teensy where my program keeps track of the rotation changes and sends a keystroke for clockwise or counter-clockwise as needed. And I wrote the code to be self-calibrating since you might get different mins and maxes from different chips.
TrackballsThere were many good homemade trackball designs on the web that I stole from. Also my 9 year old son figured out some parts around the house that accidentally snapped together. He also helped with a lot of the troubleshooting. And it was his Raspberry Pi I was borrowing.
I thought it would be neat to use pool balls for the sake of the 1 & 2. Some posters were very insulted by this. For which I am extremely sorry. How dare I do that?
But, I didn't know what else to use for a ball in my price range, anyway. And everyone else was using cue balls, so I wanted to try something different.
Most of not all designs on the web used optical mouse guts. So I did that. Big problem was that some mice had trouble with the colors of one or both pool balls. Lots of trial and error with different mice. Eventually found some cheap ones t the store that worked with both balls. There are even cheaper ones online, but I have not tried them yet.
But how to mount the ball just perfectly above the sensor? 3 wood screws hold it up and allow for adjusting the centering and height. Used a dremel to smooth the heads to avoid scratching. Rolling is very smooth and feels good to the hand. My son and I found a way to keep everything together:
1. Cut piece of thick scrap wood into a "U" shape so mouse guts can fit in the center.
2. Screw 1 of 2 mason jar rings into the wood with the 3 screws at an angle.
3. Push the ring up through the big whole in your panel.
4. Get a small tupperware-type food container whose diameter is just the right size to snap firmly over the first ring. Cut the bottom off the container.
5. Snap the top of the tupperware on top of the first mason jar ring. Like magic, the ring is just tall enough, and the tupperware is just snug enough, that this trackball base holds on tight (with my choice of box material). But I use some how glue on the underside - just in case.
6. Put the ball on the screws and adjust.
7. Put another mason jar ring on top to keep ball from rolling out. In fact, the top ring fits so snuggly over the chopped off tupperware that you can even turn the panel upside down and the balls will not fall out. But I don't recommend it. You could glue it, but I leave it as is for future maintenance.
I forgot to power on for the photograph I posted earlier, but you get a nice red glow around the trackballs thanks to the mice LEDs and the translucent tupperware.
The mice plug into the USB hub (also in the box) that goes to your computer or the internal Pi.
Make sure you reverse either the X or Y in mouse configs in MAME.
OK, that's the high-level how-I-did-it. There are a lot of details I'm leaving out, but I hope to make time to put together a web page with a better walk-through.
Encoder was first an Arduino (cause I already had one), then I switched to Teensy for the lower price and need for a few more inputs. It's so teensy that you can't even see it in the photo unless you know where to look.
Below is the seedy underbelly.
Oh, before I forget, DO make sure you take the cat food OUT of the can first.
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