Friday, June 15, 2018

Guatemala, Day 26

Its over! We did our final hospital visit today and the students did really well. The program's first month has come to a close. In a couple hours, I'll be heading to the bus station to catch my 4 hour ride back to Guatemala City and then to the airport. The students head to their new assignments on Sunday afternoon and they all seem capable and ready to go. Its been a fun month, and even though I missed my family something wicked, I learned a lot, which is really all I could have hoped for.

So today we visited a dental school and clinic. The facility is associated with a local university and I believe is set up to train dental hygienists and dentists, as well as treat patients. The facility was a big open space which it appeared was owned by the Lions Club. The main hall was the size of a basketball court and filled with maybe 35 dental chairs, some desks, and an x-ray lab in the back.

We were asked to take a look at some of the dental chairs that were having various issues. A couple of them had problems with the control unit that you use to make the chair go up and down and a couple more had lighting issues. Given the chairs were a good 20 years old, it was no surprise that everything we looked at had been messed around with by some other engineers at some point, and some of that work was, regrettably, a bit sloppy. We got to work.

The control pedals were pretty interesting. It turns out that the four-way controller (up, down, recline, sit up) is just a knob that forces one of four switches to close. When the switch is closed, the appropriate motor wire is connected to power, and the motor turns causing the chair to move.
Inside the chair's control unit - just four switches!

One of the two units we looked at was just a bit loose and we got it working by tightening up the cover. The other one was a hot mess of short circuits and amateur soldering. I had the students take it all apart and resolder all the connections, testing them one by one as they went, and they did a great job fixing it.

We also looked at some lighting problems. One light had a loose connection and flickered on and off quite a lot. That turned out to be an easy (but very time consuming) fix. It just needed a few loose wires re-connected and soldered, but the wires were very hard to access and it took a long time just to get them sufficiently free to work with.

What should have been an easy fix wound up being very time consuming!

It didn't help at all that the Portugal-Spain World Cup match was on and people kept running to the TV when things got interesting!

While the students were working, I decided to teach myself exactly how a dental chair works. I got down on all fours (and then flat on my stomach) to see what mysteries lurked beneath. Turns out it's pretty straightforward. There are two motors, one for the up-down action, and the other for the recline action. Each motor is only connected to power when the user pushes the control switch. There were two especially cool parts. First: the up-down motor was connected to two massive start capacitors. Most AC motors need some sort of a start cap in order to get spinning. In this case, there were two 147uF caps connected - real monsters!
As capacitors go, this one is pretty big!

The second cool thing was the mechanism the chair uses to know when to stop going up and down. I found two little switches under the chair that get depressed when the chair gets too high or too low. Once the switch is depressed, it cuts off power to the motor and the chair stops.


Overall, it's a pretty simple design but elegantly done.

That was pretty much it. After work, we went back to our classroom so the students could reorganize their tools and supplies for their Sunday departure. Afterwards, there was a funny ceremony of sorts where I was presented with a plastic trophy cup that says "#1" on it, along with a photo of our group.  It was a wonderful gesture and also very goofy and we all laughed pretty hard.

Me and our outstanding TA, Paul.
I was really proud of our group: smart, resourceful, and diligent, all of them. It was really fun to work with them and they made the effort of teaching very much worthwhile. They're all going to make excellent engineers.

And that was that! Another successful EWH trip is in the books. All that's left to do is get home safely ... and start planning for the next adventure.

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