What to tighten and what not to: my first baby steps with my ArduCopter

 

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!

 


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Comment by diego colonnello on January 19, 2011 at 9:02am
Hello Aaron..... where is the rest of the article?
Comment by Cliff Dearden on January 19, 2011 at 9:07am
Hi Aaron, Ditto the above, it was just getting interesting.
Comment by Ground Loop on January 19, 2011 at 9:39am

A cliffhanger!

 

The aluminum arms that came with my Arducopter were slotted on both ends, BUT I only used the motor-side oval cutout for wire exit.  It actually made a nice tight package, and really looks good.  the wires exit the side, and meet the motor on the mount above.  Like this:

[img]https://api.ning.com/files/rwropZPUhbg6TMC2iXf3ZYVp4mPs1YKu-*n7vnK7aEmAa-9fvmNlogZUhgTDwBSMqE*UR9L7spQOXuDYl-7l*A__/101225_1542418032.JPG?width=750[/img]

 

I did not use the side-port on the inside (hub) side of the arm -- the wires exit out the center of the channel and connect to the ESC.  Jordi posted a picture in another thread about how to mount the ESCs with zip-ties, but I think I like more "center-packed" design for durability.  It's not critical.

 

Make CERTAIN your motor-to-esc bullet connections are solid, and do not rotate freely.

 

Also consider excising the portion of the Arducopter RC2 code that DISarms the motors if you raise the throttle stick too quickly.

 

If you hard-wired the ESCs instead of soldering them, I wouldn't sweat it.  You saved weight. :)  Once you're stable and flying, your ESCs should last a lifetime. They're over-spec to boot.

Comment by Ground Loop on January 19, 2011 at 9:39am
Comment by Aaron Curtis on January 19, 2011 at 11:23am

Somehow this post went live when I tried to save it as a draft, sorry about that. It's finished now!

Great to see it's being read. Ground Loop, thanks for all the advice. Your setup looks great, I think I will try and re-configure mine to work like that. The ESCs are probably also better protected in case of major crash when they are central like you have them as well.

I'm jealous of your quad arms. You can see from my photos at http://www.diydrones.com/photo/albums/photos-of-my-quadcopter-after that the ones that came with mine are different and quite inferior.

One other issue I forgot to put in the construction section was that the included cable for the GPS was very short. I could only get the gps into it's little seat on top by careful placement and a little stretching. I'm looking for a longer cable now.

Comment by diego colonnello on January 19, 2011 at 11:50am
This Was a nice reading!!! my copter will come to life soon.....
Comment by Bart on January 19, 2011 at 12:02pm

Hi Aaron, I'm on youre tail!, just trying to calibrating the esc's. but can't arm the motors...still some reading to do.

hope to fly soon, keep up the blogging (and of course the flying!)

Comment by Aaron Curtis on January 19, 2011 at 12:13pm
Hey Bart, when I couldn't arm the motors it was because I had missed some soldering. Maybe you've already checked, and I know it's a pain to take it apart to have a look. Anyway, hope you get it working soon!
Comment by Cliff Dearden on January 19, 2011 at 12:13pm

Hi Aaron, really nice post, strange that you only got a short cable for your GPS, my kit arrived with 2 cables

one short and one long. Needless to say the long one was perfect. One small observation of the arms of

your quad, I hate to say this but they look like they are the wrong way around, length wise that is.I could

be wrong but it might be worth a check! The slots on each arm of mine are not of equal distance from the end.

Looking forward to your next flight. Cheers!

Comment by Cliff Dearden on January 19, 2011 at 12:40pm

Hi Aaron, Something told me to re-read your post and I can see I missed your point about the slots being on the same side and very close to the ends. My apologies for thinking you had made a mistake.

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