I've now gone around one full circle on the UAV wheel: I built her, flew her, and crashed her. It has been great fun so far and I can't wait to get in the air again. Before I do, however, I thought I would write something so that other beginners could learn from my mistakes.
Anticipation and Assembly
I decided sometime last April to buy an ArduCopter spent several months in breathless anticipation. I got home from Antarctica early this January to find the package had arrived and feverishly started building. A few little issues I encountered during construction:
- When connecting the ESCs to the power distribution board, the wiki guide advised me to solder them directly on. My ESCs had Deans connectors on them, so I chopped them off and soldered them on per the wiki instructions. Only later did I find the electronics assembly PDF, which advised soldering female deans connectors to the power board so that the ESCs could be disconnected. After finishing the copter, I found four female deans connectors in my kit which were for this purpose and wished I had followed the PDF rather than the wiki, so that I would have easily removable ESCs.
- The method for mounting the ESCs and dealing with the motor wires is unclear in the wiki instructions. This is probably because there are so many ways to do it, and also different types of arms. In the end, I velcroed my ESCs to the curved plastic supports of the protective dome, braided my motor wires, and wrapped them around the quad arms to take up the slack. In theory I guess the motor wires could go through the inside of the arms, but the arms that came with my kit had "half holes" i.e. they only have the slots for the wires on one side of each arm. Also, the slits for wire insertion are at the very end of the rods, so the motors mount right on top of the slits and it seems difficult to get the wires into the slits as the plastic motor screws are in the way. Not sure how this is supposed to work, it seems like maybe the "wires inside the arms" idea was abandoned during the design at some point.
- I cranked down too hard on one of the screws for the motor mounts, and cracked one of the thin clear plastic pieces below the motor and arm. This comes back to haunt me later in this blog entry!
- I forgot to solder 5 of the pins on the 6-pin header that connects the ArduPilot with the ArdIMU. This had the surprising result that the ArdIMU worked, but only in CLI mode. I was quite embarrassed when Sebastian on the forum suggested I check my soldering and it became clear why the ArdIMU was not initializing in normal mode!
First and second "flights"
Once I'd figured out my new Turnigy 9x and finished calibrations, I headed out to a nearby field with a couple of friends. After a good deal of testing I gritted my teeth and eased up the throttle. The hum whirred into a buzz and then... two of the propellers popped off, launched high into the air!
It reminded me of the Gemini test scenes in the movie The Right Stuff. I scratched my head for a while and eventually concluded that, unlike the motor mount screws, you really need to crank down on the propeller attachment chuck.
Props securely fastened, I tried again. This time, the copter got 3m up into the air and began to fly away from me quite quickly. Thinking I would bring it down and consider a recalibration, I eased off on the throttle. Cindi Lou (that's the copter's name) descended a few feet while still drifting away from me and then promptly flipped over at a little under 1m from the ground and attacked the grass! My friends tried to contain their laughter as I inspected the damage, which was disabling but not catastrophic: cracks in the top and bottom plastic sections of the forward motor mount. Here are a few photos of the damage, and a video of both attempts.
Recovery
Eager to get back in the air, I ordered the $30 crash kit from the Fah Pah store. I would have preferred to order from DiyDrones (since they're in the US, not Thailand) but it seems they only sell full replacement frames and replacement arms. Not content to wait for delivery, I picked up some plastic repair epoxy from Ace Hardware and set about mending the motor mount. It looks fairly solid, but I'm not sure if I would be jeopardizing the rest the Cindi Lou should I attempt to fly on the repaired mount. My impatience to fly again is competing with my better judgment here...
Lessons learned
I'm not certain whether the crashed was caused by my poor construction job, or my poor piloting. I wonder if the pre-existing crack in the bottom motor mount section contributed to the crash. Either way, the crack in the top section was certainly caused on impact with the ground. One take-away message is to tighten the propeller chucks hard, but not the motor mount screws. Perhaps a more important one is to make sure the copter's horizontal motion has stopped entirely before attempting to land!
Comments
Thanks for the recommendation, my charger and batteries are on the way! Now - do you all have recommendations for transmitter/receiver combos?
Just wanted to mention a technique I have been using for many years now. Saves your props a fair bit and often the motor shaft from bending. Usually if you just graze the prop on the ground, with a fixed prop adaptor you will break the prop. Little bit annoying on the quads as the reverse or pusher props are harder to source. Usually with a prop saver you can take a little hit and the prop will just shift a little. Remember with a quad, once one prop hits it will stop and the other props will work to flip it over very quickly!
Sorry about the poor focus, phone camera! No focus!
Jonathan, I got two Turnigy 2200 25C batteries, and one lightmax 4400 15C. I got the lightmax when i didn't know about discharge rates -- I hear you need at least 25C for flights. Combined with the extra weight of the 4400 I doubt that battery is flightworthy but maybe someday I will be cavalier enough to try it. I got a SkyCharger B6AC which is excellent (computer interface, temp sensor, balancing, works with lots of other cell chemistries) although not cheap.
John, there is no visible corrosion on the outside of my Turnigy RX, but when I opened it up (trying to figure out where the damn bind LED was!) I faintly remember seeing a little corrosion on the joints at the bottom of the board. I ignored this at the time, might have another look at it. In case anyone is wondering, the bind LED is on the top of the board inside the housing and does just about shine through the somewhat translucent black enclosure plastic when it's on (if you're not in bright light). Strange design there though.
Jonathan, I wish there were more sticklers like you out there. Stuff would certainly break less.
One more question for you: how do you ensure that the pin connectors coming off of the ArdIMU (inputs, outputs, power) are connected securely? Those seem to be the weakest link on my copter.
How did you tint the aluminum arms? Is that paint or anodizing? Looks great.
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