Week 4

So on Saturday I was catching a few waves with an 8'2" longboard, and I thought that wasn't too bad. Come Sunday, I was feeling more confident (aka cocky), and so I went for a 6'4" fish. I caught nothing. And the one time I did, I nosedived. Stick with the longer board, son.



This past week has been quite interesting; I feel I've been working with sensors of sorts. The test for the second heat plate went well. This time we went for a peak of about 130 degrees C. I also tested one of LM35s to measure temperature, which went well. The LM35 give you a voltage readout, which converts directly to temperature (e.g. 0.31V ~ 31 degrees C).

I got the cheap temperature controller working as well. I hotwired it with the head of an old extension cord. The only thing about this controller is that it is not compatible with the LM35, so I used a K thermocouple to test it out. I also connected it to an opto-isolator, which isolates the circuit of heating resistors and temperature controller, so the temp controller doesn't suddenly receive too much voltage and explode. I'm currently working to integrate a triac into this circuit as well. A triac is essentialy a poor-man's solid-state relay. Supposedly, it can handle up to 15 amps, and we only need 8 amps. So far, I've attached it to a comically large heat sink.

The amateur thing of the week I did was confuse the triac and the LM35. They look identical, but are obviously not the same thing. So while trying to get a temperature readout of what I thought was an LM35, I ended up frying a triac. It actually started smoking. That's when I figured I should cut the power.

Unrelated to this project, I have also learned how strain gauges work this week. After lab, I'd head down to the SAE shop to help our chief engineer attach strain gauges to the A-arms of car 46 to get some suspension data (i.e. the compression and tension on the steel members). Strain gauges measure the strain on an object by measuring a change in resistance, just like the LM35 temperature sensors. This way we can get more accurate data and confirmation on the load experienced by the suspension arms. We've also managed to get our hands on a pretty expensive data logger, so we could start attaching temperature sensors on the tires (to measure dynamic camber), speed sensors on the hubs (to measure wheel slip), position sensors, and sensors of all sorts! So next time we go out testing, we can actually get some hard numbers to backup our design objectives.

Anyway, this past week has been pretty neat. I also started to play around with EagleCAD, so I could maybe draw up a simple schematic of the whole heatplate+temperature controller+LM35 setup. Now I'm going to go figure out how to use this triac, and hopefully keep my eyebrows.

Week 3

Flat surf this weekend. It was like a lake. Good paddling workout, though. And Central Park was beautiful to run in.

Anyway, the past week's work has been on fabricating a second, identical heat plate. Previously, when only one plate was used to heat the AR coats, there was some warping and deformation. Instead of having to flip the AR screen like pancakes, we can use two heat plates and bake the AR screen like waffles.

Drilling and tapping the holes for the power resistors was quite the excursion. We headed over to the SAE shop to use the drill press. Of course, using the no. 43 drill bit, which is tiny, I broke a couple. So we'll have to finish the holes sometime next week when the new bits come in. While I made the holes, Ross had the time of his life trying out the racing simulator. Who says the lab buddy-system has to be a hassle?



In tapping/threading these holes, I committed the amateur mistake of going too fast. I broke two taps in about ten holes. But I managed to get one out. I had only one left, so I went much slower; thread in, thread out, then thread in, then thread out, and so on. With that all done, I applied some silicone vacuum grease to the base of the resistors, and screwed them in. Then came the slow, laborious task of soldering each one in parallel and covering the terminals with heat shrink. It's a mundane task, but to quote Ross, "It's good for the soul," or, "It's like racing around the track, you've got to concentrate." After some time, I become less conscious of the soldering at hand, and more lost in my own thoughts. I lose track of time. Oh, the intrigue of soldering.

The cheap PI temperature controller and fancy LM35 temperature sensors also came in this past week. So while waiting for the new 4-40 tap and drill sets to come in, I should be playing around with relays and optocouplers, and learning about multiplexing for the next step in this project.

Week 2

I'm posting this the Monday after this last week, and I am exhausted from the weekend. Unrelated to work, this past weekend has been a blast. I hit the Rockaway surf in Queens both Saturday and Sunday, and caught a few waves in the east coast for the first time. Good thing the waves on Sunday were pretty gentle, so I was able to teach my friend. But on Saturday, boy, it was firing. They were four-foot sets at the max (I know, dinky, call me a kook if you like), but they were coming in incredibly inconsistent; there would be nothing, then suddenly two, three sets that push you back into the crash zone. I was getting pounded, and getting into the lineup took work. It was good fun nonetheless. The ride back into Manhattan on the A train was also quite an occasion. I had just met another surfer, Manny, who was also taking the A train back. While on the platform, we ran into a man and woman who recognized my new friend because he had been rocking the surf all day with his blinding fluorescent shorts. They thought Manny and I knew each other, and we thought the man and woman knew each other. After a good two, three stops on the train, it turns out that none of us knew each other an hour before. I thought that was pretty funny. The ride on the A train back into Manhattan is at least one-and-a-half hour long, so might as well get comfortable. There were good vibes all around, and pretty soon our half of the subway car had broken the ice, and everyone was just talking and hanging out. Strangers got on, strangers got off, but the ice was broken.

That was my little New York moment. I guess I haven't taken the subway enough to make any claims, but the subway has generally felt like a silent cave of motionless beings sitting and standing around ignoring one another, anxiously waiting for their stop. But going out to Rockaway, it seems like the culture of neurosis melts away, and the atmosphere just relaxes. And these immobile subway statues suddenly come to life.

Anyway, last week feels like ages ago. That's my excuse for not really remembering what I did. Well, the big accomplishment I remember was that I was able to successfully run a test on the heating plate. While debating whether it was safe to test, my lab supervisor Ross said, "What's the worst that could happen?"
"A small fire?" I replied.
"Yea, you'd die. Maybe get electrocuted."
"That's not too bad, I've already inhaled a ton of lead from soldering, and they're doing asbestos removal in the office across the hall."
"Yea, you had a great run."
After some debating and bantering, we decided that Ross would be the one to check if I had really grounded the base plate. On a side note, never test conductivity by grabbing onto the plate. Just tap with the back of your hand, otherwise you might grab onto the plate if you do get electrocuted.

Unfortunately, there were no shorts and I grounded the plate safely, so Ross still has his eyebrows.

The melting point of LDPE (low density polyethlyene) is about 110 degrees C. That was the goal, and the setup of the resistors on the heat plate got past 110, so it was a success. That's pretty neat, as we were able to boil some water on this plate I had made. Plus, this heating itself is going to take place in a massive vacuum chamber, so there is no heat loss via convection, and also nearly impossible to start a fire.

[Finally, just for personal bookkeeping purposes:
Placed order for the PI temperature controller and LM35 temperature sensors.
Decided to go with a triac and optocoupler instead of a Solid State Relay.
Begin working on fabricating second heating plate.]