learning the ropes

All of the pieces for a single assembly are together. I’m happy with the way the unit looks and feels. I’m a little dissatisfied with the way it turns, though, so I’ll need to do a bit more sanding to make sure the wheel spins as freely as possible.

Today I etched two test boards for the pulley encoders: the RJ-45 breakout board and the emitter/detector pair board. I wanted to make sure that the board design worked correctly before ordering multiple copies of the boards. After soldering the components onto the boards, I connected a CAT-5 cable between the newly fabricated boards and the interface board I made last week. Before plugging anything in, I checked continuity on the various traces to make sure things were wired properly — or so I thought. When I plugged in the unit after testing, I found that it didn’t detect rotation. I inspected the infrared LED on the detector and found that it wasn’t glowing (I used my digital camera to check). I wasn’t completely surprised; when I hacked apart the mouse circuit board, I found that the X- and Y-axis LEDs were wired together. To fix this problem, I soldered the second IR LED onto the bottom of my interface board. Still no luck. Double checking things, I found that copper traces were bridged on one of the the circuit board I etched. After fixing the bridged traces, I found that the circuit still didn’t work. From prior experience, I figured that either the LEDs, the phototransistors, or both were probably blown, so I decided to try again with another mouse.

So I goofed — maybe. When I modeled the pulleys earlier this week, I somehow messed up the dimensions. I drew the model too small — and only caught the mistake after I purchased my materials. Remember measure twice — cut once? Well, I didn’t cut yet, but I definitely didn’t measure twice.

I was not thrilled about correcting my mistake, as it will take some time to correct it. Further complicating matters is that obtaining the correct material dimensions will become more difficult, too. I will need to go to Dimension Lumber to get a custom piece milled — and I prefer not to do that now because of the time involved. I was also somewhat concerned about the aesthetics of the pulleys, but maybe the smaller pulley looks nicer. It’s going to be hard to say without seeing it build. The point of these remaining weeks is to develop my performance — not to sweat mechanical details.

I’m going to sleep on it, consider the feedback I’ve received from friends, and then decide in the morning.

I want to be able to work with two pulleys simultaneously, so I’m adding the rotary encoder to wooden pulley I started building last week. The PS/2 mice have turned out to be quite a clever hack because each one gives me two rotary encoders and three switch inputs in exchange to two pins on the Arduino. I’ve started thinking a bit more about multiples — and while this may be a little premature, I want to work out a bit of the technical end of this before getting too heavily into final fabrication.

I’ve invested rather heavily in this for the past two days. Perhaps because this is more comfortable for me than other things that need to get done now — like preparing for the mid-term presentation.

What this does mean, however, is that I have the pieces for a much more modular system. I’m envisioning a hub that I can plug each pulley into using a single CAT-5 cable. This makes the performance setup clean — and won’t require any soldering.

It’s time to step away from the prototype and move towards a finished-looking product. Since I’ve also discovered that driving the mouse ball from the outer rim of my pulley causes the ball to spin too fast, I’ve decided to track the rotation at the shaft instead. This means I need the shaft to be attached to the pulley rather than spinning freely through its center.

I built another model in sketchup to understand how the pieces were going to fit together (and also to beef up my sketchup chops — bad idea, but I have a nice illustration now). [ later realization: one thing that's important to remember about these exercises is to continually question major time investments --at their outset and throughout the process... Is this the real problem that needs to be solved? Is there any easier way to get the effect I'm going for? Is this essential to the project? Is this part of the essence of the project? ]

Now that we’re getting down to the wire, I’m committed to cardboard as a building material, mostly as an aesthetic choice, but also because there is not enough time for me to learn the AMS laser cutting process. Prototyping in cardboard can be fast, but constructing in cardboard can be time-consuming.