Tuesday, July 27, 2010

ardWINDo: Update

The stand was anticipated to be the most painless piece of this project. Except, it's 0.22" polycarbonate and from the moment I unchecked the "bullet-resistant" box on the McMaster order I should have known it would be trouble. I thought it would be smelly to cut on the laser but I didn't anticipate it would catch fire. Or that it would be so hard to bend into shape. Functionally though, it works and I will use it. Hey, after going at it with a dremel and sandpaper it doesn't look half bad, Mike (Thanks for the laser time!):


With the mechanical end of things resolved I had some time to play with the electronics and software. The circuit is done and in the process of being transfered to a thinner prototyping board. A lot of careful planning is needed here because the 7-segment display takes up a lot of room. Other than that about the trickiest thing is the Red/Green LED. Maybe I'll post a schematic when it's all done.

As for the code, it does its job; it winds a watch as many times as you like. However, the current control structure for winding is imprecise. I'm not using one of the ATMEGA328 timers or even an external one. I simply use a for loop that decrements the winds and controls the servo per a delay calculated as the time it takes for the servo to complete one revolution. However, each cycle propagates a minute error when switching the servo from go (1400ms) to stop (1500ms). Not the end of the world but I'm going to synchronize the servo and display as well as the Arduino allows. Here's what it does so far:

High-pitched "PIZZAAAA" sound effect courtesy of Shane

Cost Update: $70.....

Monday, July 19, 2010

Axial Differential: Assembled

Looks like Shane beat me to it but here goes anyways...

The transformation from a live axle to a split one is a serious commitment. If one piddly gear is misaligned then all of the gears are misaligned. Nevertheless, with the bearing supports from the waterjet in and with the taste of finally driving the kart in our mouths, it was time to assemble the diff:

Does Ferrari lay out there parts with this level of OCD?

Through recklessless machining meticulous planning and attention to detail (Shane, I wrote this before yours and didn't get around to posting...not my fault that we write similarly), the diff went together seamlessly. The first hub was bored so that the 1/2" holes for the idle gear rods would be a couple thousandths greater in diameter than those of the second. This high tolerance is compensated for by the countersunk screws that hold the rods in place. Those rods were also hydraulically pressed into one hub and are not going anywhere soon. Here she is assembled:


There were a few last minute additions to keep the beast together; thrust bearings prevent friction between the aluminum hub and steel gears, and retaining clips keep the gears on the shaft. The bearings pressed into the hubs do not provide lateral support to the output shafts. However, the kart frame has bearings with set screws built in which will absorb all of the load. Shane didn't show you this:

video

Even dry, the output shafts spin with minimal resistance, which can be attributed to the - robust - weight of this thing. Similar shout-out to Charles for the concept. Stay tuned to see how it holds up once we begin road testing!

Monday, July 12, 2010

ardWINDo: Testing Arduino

I finally got a chance to mess around with the Arduino and test some sample code. Results:



Success. There wasn't much to be done but it's best to start from the very beginning. I will work on the actual coding soon but more critical at them moment is the mechanical end of things (SolidWorks license expires in 10 days!). As shown in the video above, the watch will be housed in an aluminum servo bracket...like those used in servo tilt-pans. It was $13 for two plus bearings and hardware, but that's a bargain when considering the time and money to make your own (as nicely).

The pursuit of simplicity has also inspired me to design a more elegant stand. The final product is going to be transparent, probably acrylic or polycarbonate. Fortunately I have a friend with a laser who can supposedly cut up to 1/4". Maybe I'm cheating a little on the pricing through this connection, but it's nothing that couldn't have been done with a drill and a dremel. Should look something like this:

Much Better. And the brick is a dummy Arduino-sized block.
Cost Update: $59.85

Friday, July 2, 2010

It Begins

This is it, my first D.I.Y. project to go public and to be finished (eventually)! It's about time a lowly MechE like myself got acquainted with all the fuss surrounding microcontrollers. After all, mechanical projects become a whole mess cooler when they're autonomous. So...
What does it all mean?

No, not a bomb. It's the shrapnel that with work, skill, and plenty of luck will become a watch-winder. Why a watch-winder? Well, I now own two watches, the primary of which is a self-winding Seiko Kinetic that does not like being neglected over the weekends. It's funny the concept of "self-winding" is misleading; the watch will wind itself only if it is clasped to your swinging wrist all day. And while I'm off enjoying my new Citizen with Eco-Drive I would like to know my Seiko is getting it's TLC. In essence I am constructing a replacement wrist that henceforward will be referred to as the "ardWINDo."

As shown above, the system will be controlled by the popular Arduino Duemilanove. These guys are very popular especially with the people at MAKE. It should be straight forward to program...or that's what I am told. The more I read about this highly capable piece of kit the less mechanical this project becomes. I won't give away all the details of the project but at the moment it will look like:

Subject to change!*

I'm going to try to cap this project at $70 but that will be challenging considering the Arduino itself runs for $30. This price was chosen because that looks like the going price of the cheapest decent watch-winder. It's time to start extracting parts from old projects...like a servo from an RC car? So the concept may be based on laziness but is that laziness then cancelled out by all the trouble I'm going through to construct an autonomous watch-winder? You decide...

*As I post this I already have three other ideas of how to produce the winding motion.