So, I'm out on a shoot with a cameraman this morning -- we're a fifteen minute walk down a river bank away from my vehicle. I'm using a standard RTF C8, standard config with QC6200 mAH. I calibrated the compass, calibrated the gyros. Got GPS lock. Motor start. Uhoh. Motor on boom 8 twitches, but will not spin up to speed. How odd.... Motors stopped. Disconnected QC6200. Waited five seconds. Reconnected. All motors chirp and twitched, including boom #8. Try again. Recaled gyros, motor started. No motor #8. Removed battery plate: Green LED on FC board. Too much sunlight to see whether the Green LEDs are all on on the BL-Ctrl's. (Note to self, if I ever build my own PDB, put LEDs on top of PDB! ) We abandoned the shoot and I drove home. Got the C8 on my bench. Removed all the props. Plugged the same battery in. Green LEDs on FC and all BL-Ctrls are all on. Recaled gyros. Motors started. All motors now spin up. Everything works normally! "Oh dear." (Approximation of what I said. ) Using MK_GPX, the flight log data shows that an Error 24 (BL-Ctrl limitation) was the cause of the problem, but, looking at the analysis of the data from MK_GPX (attached), and the raw data output from MK_GPX (attached) there is nothing to suggest that there is an overcurrent or overtemperature problem with the *possible* exception of the current to motor #1 which seems higher than all the others. (Could this be the problem?) Two things of note: 1. We were fairly near power lines, one row was about 20 yards away. Another, higher voltage, about 100 yards away. 2. It was early morning, so there was a fair amount of dew on the ground and the airtemp was a tad cool. I was wondering whether we had some condensate on the FC, PDB or ESC -- I did a visual check, but could not see anything. Anyone seen a failure like this? More to the point how do I fix something that (now) isn't even broken? Why did the system report a problem, when the raw data seems just fine? And how come the problem fixed itself? "Expiring" minds want to know. We're going to try the shoot again tomorrow, in the interim I think I will take the MK boards off, mask them, and spray them with some conformal acrylic coating just to eliminate the idea of moisture being the problem. Andy
Have had the exact same thing happen in moist environments. Did you spray your boards with conformal coating? It seems to happen at the WORST times!
Aha. So it was the dew. That would also explain why it fixed itself. Thanks, Tabb. Board spraying is this afternoon! Re-shoot tomorrow. Yeah...Murphy's Law still applies. Even more so when there's a client/DP/EP/shooter standing to one side of you when you do a motor start. Andy.
Classic! A few times now I've had the copter refuse to start any motors and/or the motors will start but only stay at idle. The first time it did that I thought to myself 'oh crap, what's going on here' as folks looked on. Nothing like not having the motors start to inspire confidence! Turned out to be EMI from rebar, underground power lines or something else and simply moving the machine a little allowed for normal operation. But there was some head shaking until that was figured out! nick
I've had similar experiences... so not fun... "Hey Look! Something really cool and expensive! Want to watch it fly? Ok here we.... wait... uhhh.... just a second guys...."
That's interesting Nick. I did notice, with failed motor #8, when I goosed the throttle ever so slightly that motors didn't spin up as usual. One thing I tried when I had the failure was, when we got back to the SUV, about 1/4 mile away, I tried again and the failure was still there, even though we were well away from the power lines, so I think in my case, condensate on the boards was the culprit. I'm in the process of putting silicone on the PDB MOSFET leads (as Arctic Silver recommends), then gluing some heatsinks on -- and then I'll spray the PDB with conformal acrylic. I'll be going back to the site on Wednesday so we'll see whether it's the Evil Power Lines Problem. But this experience so early in my copter flying has made me realize that there are Universal Laws at work. Therefore, I hereby humbly propose: Johnson-Laird's Copter Law #1: The probability of copter failure is inverse to (a) the distance to the client, DP, EP, or power lines and (b) proportional to the distance between you and your tools and spare parts. Johnson-Laird's Copter Law #2: Any testing you do before a shoot increases the applicability of Copter Law #1. Johnson-Laird's Copter Law #3: The probability of doing a crap landing follows Copter Law #1(a) and is compounded by having spectators. Johnson-Laird's Copter Law #4: Things that should waggle, don't. Things that should not waggle, do. Additional submissions, named after the submitter, are encouraged. Andy
Lambeth Copter Law #5: When you want the wind it's not there. When you don't want the wind it's always there!
Nice one, Josh. I was also thinking of a corollary to Law #3: You will always land hard or bounce badly on landing if your spouse, kids, or even distant relatives are watching. Andy.
Andy If you are running an MX-20 check to see that the mag deviation is not greater than the tolerance setup. That can stop any start, but not one motor. Basically what nick has said. You can see it on one of the MK screens on the MX20. Forget which one.
Thanks for that idea, Gary. I'll seek out the MX20 screen and check it when I go to the location on Wednesday. I did do a compass calibration and that seemed to work ok, but that doesn't in any way invalidate your comment. Andy.
Andy, the Mk blc are very sensitive to any moisture in the air. Holger noted this many times. Definitely use a coating to seal your electronics. Not sure if you're using the distro board or not but I've always been terrified about having my electronics exposed. One drop of moisture in the atmosphere and down she comes...ask me how I know all electronics are now coated and protected.
Thanks, Howard. Yeah. As a computer geek myself I'm troubled by exposed electronics and unshielded and untwisted wires. Fortunately, mine was a ground failure that didn't involve any plummeting..... While I had the C8 boards off, I thought I might as well put heat sinks on the MOSFETs. The potting component that's used to hold the caps on,encroaches onto the surface of the MOSFETs underneath the board so I cut it back with an Exacto knife to try and get most of the heatsink on the MOSFET. I've got about a 90% overlap. I'm going to mask off the heatsinks as I don't think they'll benefit at all from a layer of conformal acrylic spray -- and, of course, mask off all the connectors, pots on Smart OSD board etc. Tabb was recommending two light coats of spray -- what did you end up putting on? Thanks Andy
Well I use epoxy resin, been using it for years with no issue. Simply brushed on. My speed controllers are mounted on the booms therefore they are easily touched, fondled and bumped on occasion when packing in peli cases and during normal transport. I needed a hard durable coating that would protect from these minor abuses and also protect from moisture...after sealing, I heat shrink wrap the entire controller including heat sinks. Not recommending anyone to follow, these are just techniques that I've used over the years. Downside for using epoxy is, once it's on...it's ON to stay. No replacing any components after they're covered in epoxy. Upside, which is a plus for me, you have a very durable controller that can take some handling abuse.
Yeah, epoxy is the ultimate conformal "spray" (industrial strength too). Not sure how good it is from the point of view of heat dissipation. From what you say, you're not using the standard MK Power Distribution Board? What configuration are you flying?