As Matt’s post will explain to you in a much more in-depth fashion, our quad finally got air today. And we couldn’t be more happy. As badly as it scared the crap out of me to see this monster take to the skies on its foot long leash, it had to make me smile.
“Close is only good for Horshoes and Handgrenades,” and very good if you barely miss catastrophy.
Published December 22, 2009 Uncategorized Leave a CommentWhen I say I’m very lucky to be typing this, I mean that I was less than a millimeter away from not having fingers anymore. Last post I mentioned my near miss from flipping the polarity on the battery connector and blowing out everything on the board… a millimeter, the thickness between the plastic end of a female connector and the beginning of the metal female receptacle within the connector, was the leeway I had. This time, less than a millimeter, the thickness of tin foil, between me and my not having hands. Well, in all reality, this tin foil is probably a little thicker than normal.
Control board with Altimeter
Let me explain what happened yesterday. As we finished up with mounting the control board to our quad frame and other important goals, we decided it was time to mount our altimeter (pressure sensor). This is a very sensitive little instrument that measures the barometric pressure in the air where the copter is. Quite intuitively, as you go up in the earth’s atmosphere, the pressure goes down, and vice versa. This means we can tell approximately how high our copter is, based on a reference to what the ground pressure was when we began our flight. The only problem here is that our props are moving a whole lot of air really fast. We are measuring the force in air on a sensor, so we don’t want our prop-wash to create a high or low pressure vortex to influence our normally pressured air we need to measure. We decided that the best way to get the least interference would be to mount the sensor downwards (only place we could), and with a larger shield than is already on it. We drilled a hole in the frame of the copter to help shield horizontal wind, and basically mounted it near the center of the board, looking downwards through the hole. This way less moving air from the props will interfere with our reading.
New Battery Mount
Well, the main part of our story begins here. We were getting rather tired and ready to call it quits, last part to finish, so we had gotten rather careless. We just mounted the battery to the underside of the frame in a pain-in-the-butt way to remove it… so, we left it on. I found a good looking place to drill, and started… only to notice moments later that I was drilling directly into the battery mounts… not the bad part. I removed the drill, and found a new place. I began again, made it all the way through, and the removed the drill bit from the hole. Upon flipping the frame over, we then noticed I had just barely peeled the outer heat shrink layer from the battery, just exposing the lithium polymer cells. The drill bit had just touched the tin foil, leaving little dents in it.
Nearly Damaged Battery
For those of you who don’t know, lithium is a rather reactive element. It combusts in the presence of water, and is very hard to put out. By rather reactive, I mean it will suck the water out of the air around it. So, lithium, sitting on its own will, yes, spontaneously combust. Had I broken through the tin foil wrapping around the cells, I would have allowed water to be absorbed from the air, through the minute hole, by the lithium, and thus we would have not had a lithium battery but a burnt lithium battery, as well as a burnt frame, and burnt hands, and a burnt table I had been working on. That would not have been very good.
Luckily, after much testing and reviewing (by which I mean it sat in a waterproof box all night outside, away from the house, and we made sure it wouldn’t burn during discharge in other ways) we concluded it’s safe to use the battery still.
Frame and Board Under Construction
Cross your fingers and hope we still aren’t dead by next week.
~Will
quadcopter grounded test 2, originally uploaded by wimbot32259.
This is the second test we’ve conducted with the Quad powered up. This time, we used the battery (good news is it didn’t explode). We, again, grounded it by tying it to a foam board with zip ties so the prop-wash only created lift off the board and did not let the copter take off. This was just a test to be sure our connections were all working and we could control the ESC’s off the new board correctly (notice all four props are on the quad this time) since the new board fits within the open area between all the props. We never got the motors to full power off the remote in this video, which is amazing because they truly move the air. I’m a little scared to set this out on its own… but I guess soon the time will come… and by soon I mean probably nearly another year from now. Our new altered, changed, revised, re planned, recalculated time schedule is to hopefully start our balance testing next weekend. It’ll be Christmas vacation, so we’ll have plenty of time… right?
Our final accomplishment of the day was the attachment of the altimeter. It is to be placed in a hole in the bottom of the base board of the quad, so prop wash won’t effect its readings. Matt gets the fun part now though, trying to figure out how to test a sensor that measures altitude.
~Will
P.S. I seem to have left out a good story in my recent post, but am now correcting my error. During our recent meeting, I seem to have nearly made a $500 or upwards mistake. As we were getting ready for our test using the new board (which fits nicely between all four moving props and does not get any wires lopped off of) I was nearing the point of contact between our plug and our board which would completely power on the whole board and all of the hardware that was STILL ATTACHED TO IT! Please note: we have made all the hardware easily detachable so that when testing something that’s integrity may risk an accident, and so shorts or broken parts, we can remove them… Needless to say, we didn’t.
The near disaster that I came within millimeters… literally, millimeters of causing was due to the fact that when soldering two of the most important wires together (the grounds main, and power main) I carelessly chose two of the battery terminal wires, and two of the plug wires, and on a whim connected the two I felt like connecting to the two I chose. AKA- A to B and B to A… not the way it should be. The truly ironic part of this is that when we chose what plug to use for the board power, we made sure to use a three pronged one, not two even though two is all we needed. This way if we used the center prong for ground, and the outside prong for power, as long as the center prong went on the center prong of the male side of the connector on the board, it wouldn’t matter which way you put the connector. If you swapped it, it just wouldn’t power the board, and you would flip the connector, and it would work. This is rather than you accidentally flipping a two pronged connector, so the power goes to ground and ground to power, and instantly killing everything on the board. Well, anyways, this long winded story is all to say this: CHECK YOUR CONNECTIONS BEFORE AND AFTER YOU SOLDER THEM AND ALWAYS BEFORE FIRST APPLYING POWER!!! Because I distinctly connected the positive end of the battery terminal to the negative input on the board, and visa versa. Consequentially nulling the “stupid check” as we call them that would avoid a mistake like that.
As I drew the connector closer and closer to the board, I was literally seating the female end to the male end, only the plastic remaining between the beginning of the contacts on the female end and the tips of the male prongs, which when touched would spell disaster… and I said “wait, I may have done something stupid.” Which Matt will attest to, totally freaked him out, because whenever I say I did something bad… it’s really bad.
So let this be a lesson to always look before you leap… no wait, before you cross the road… no… plug in a connector, yeah, that’s right.
