TheHindmost

Hi folks,

My crash repairs (see my [link=http://www.rcuniverse.com/forum/m_4047709/tm.htm]crash report[/link]) have not yet been successful. I've got the motor mount replaced and the motor soldered. Now, the problem is that I'm getting severe surging in motor speeds when bench testing (with rotors mounted) and I'm blowing fuses. At this point, I think the left/right motors are Ok, and the front motor and/or rear motor are the suspects. The rear is the one I replaced, but it's actually the front motor which I think is causing most of the problem.

Something must be binding somewhere...but I'm not sure where. I'm going to do more work on it and will report back. Meanwhile, if anyone has any ideas, helpful suggestions or a shot of really good single malt Scotch for me , please post back!

Thanks,

Will

TheHindmost

Problem found, I believe...The front main gear bearing got trashed as well. Very interesting, given that, generally, the front of the DF showed very little crash damage...The rotor was even intact.

I found this using the following simple method, rather than manually removing and checking all the bearings: Bring up the DF, hold it down by the canopy, and arm it. Then, goose the throttle, and immediately cut it. All four rotors should take a revolution (at least) to stop, assuming you goosed the throttle far enough. Try it a few times. The rotor which stops almost immediately probably has a bad bearing. Obvious, I know, but little ideas like this are sometimes not obvious in the heat of debugging!

To verify (and this is a little tricky with one person!), command stick opposite the suspect rotor and do the "goose" test again. For example, if you suspect the front bearing, command full back pitch and goose the throttle. This ensures that the front motor is commanded to go to high RPM...If the rotor still stops almost immediately, you know you've got it. Removing the bearing and check it. If it's Ok, then the motor is probably bad.

I think the surging I was seeing in the other motors was due to the front motor drawing highly varying amounts of power (including overload power draws). That must have messed up the power system pretty well! But I guess I won't know for sure until I replace that main gear.

BTW, if you blow a fuse during this test, then you can be pretty darn sure you've got an issue!

(If anyone has better ideas for this kind of diagnosis or sees a problem with the method above, please post back...I'm still very, very new at this.)

So...my DF is down until I get another main gear.

Will

TheHindmost

Darnit!! Okay, retract that last posting...The bearings are Ok. Back to the drawing board!

Will

TheHindmost

Well, hopefully this blow-by-blow monologue I've got going here (this is the last entry for a while) will be helpful to someone in the future!

I removed all the main gears (which, due to one which just wouldn't come off, resulted in another broken motor mount, grrr... [:@]) and did the "goose" test with just the motors, no gears and obviously no rotors. The front motor is toast. It runs, but it stops almost immediately after power is removed, whereas the other three all take several revolutions to stop. The opposite stick method confirmed it (much more handy to do that test when you don't really have to worry about holding the DF down!).

So, I'm going to replace that motor, at least, and of course the broken mount.

Will

yvesOttawa

Will, sorry to hear about your problems. Have you checked if a magnet has slipped down on that front motor? sometimes when a motor takes a hit, the magnet inside it slips down and covers the hole. You can use a small screwdriver to push it back up inside there.

Hope this helps.

TheHindmost

Thanks, Yves!

Yeah, I checked the magnet...It's Ok. I think either foreign debris (namely, mud) got into the motor, or in-flight or impact forces just toasted its bearings. It is likely the DF lost radio contact with the transmitter before crashing, so the (remaining) rotors were still turning when it crashed. The only thing I can say for sure is that the motor is fried and needs to be replaced.

I'm starting to appreciate what a hobby I've gotten myself into here...I think I'm going to enjoy it, though. I'm actually looking forward to flying the DF after having made significant repairs to it...first step toward home-building your own!

Will

Sky High

Did you check to see if the motor's shaft was bent. That's what happened to me with my first nose dive into the ground. It wasn't evident at first but the next time I flew I noticed less lift from the front rotor. Then after hand spinning each rotor like you mentioned too, I noticed that the motor that took the impact had a slight wobble to it. That's what was causing the problem. It didn't cause a blown fuse though.

TheHindmost

I didn't check the shaft specifically, and I will. But I think a bent shaft would have been evident during my "goose" tests, showing up as a wobble in the rotor, and then as components were removed, the main gear/bearing and finally the motor pinion gear/shaft itself. I didn't see any wobble at all, just a reluctance to turn.

We should establish the NTSB of Draganflyers...maybe the DFSB? We've already got it informally here...but we could have formal reports/analysis on various DF crashes and causes. Just as in the real word, that helps us avoid crashes in the future. In my case, the cause would be pilot error, exacerbated by a design flaw. :-)

Meanwhile, I'm now waiting for an overnight shipment of various replacement DF parts...All I need right now is one motor and mount, but given the shipping costs from Canada (please don't ask), I'm stocking up! A frame stiffener is also on the way, and will be installed before the next flight. Hopefully by midweek I'll be airborne again!

Will

kuzer

Sounds like one of the gyros took a hit. I had similar problems and sent it to Spectrolutions for service.

intrim

hi guys my name is michael
call me intrim
i must say that i have learned an awful lot from some of you eg: skyhigh . the extra time it must take just so the rest of us can learn something or have our questions answered or watch a video is really fantastic. i dont do this too much because im a lousey typer but i have flown helis 20 years ago GMP (that should really date me) but i too am a draganflyer now and i have some issues with it but that i will get to at a later date. i had some jummpy moters and it ended up being a cracked capacitor, actually i think the shrink tubing was a little short and was shorting out against the bottom of the motor, also has anyone heard how david wife is doingwith the breast cancer scare? i bought some cf blades from him and in our communications he told me about it. god bless him and is family and all of you. i live in the wine co. napa valley and i cant wait for summer to fly in the valley
talk to you all again soon
michael

TheHindmost

Hmmm...Well, that's certainly possible. I have convinced myself that the front motor is having problems, so I'll replace it and do more bench testing before deciding whether a gyro is fried. It would be really nice if there were a "motor test" mode where you can command each motor from 0 to 100% individually to check them out. But the fast "spin down" behavior of the front motor (and I did get it turning pretty fast, and then it stopped pretty instantly after power was removed, even with a rotor [more inertia] attached) has me pretty sure that even if I also have a gyro issue, the motor needs to be replaced. So first things first.

What kind of turnaround time did you get from Spectrolutions? The optimist in me wants to believe that I'll replace that front motor and all will be well, but the realist in me understands the circuit board took quite a hit! So I guess I won't be too surprised to find myself dealing with Spectrolutions soon.

Does anyone know what kind of self-test the DF puts itself through during boot-up, if any?

I checked that...One capacitor is toast, and I just removed it completely for bench testing. (The lack of a cap shouldn't affect that test; they're just there to suppress RF noise, and at 2 feet of range, that's not an issue.) The cap on the suspect motor looks fine, but I went ahead and bent it away from the body of the motor (again, just for the test) to ensure that it wasn't shorting.

Obviously, I'll do extensive bench checking before I take the thing back into the air again! I really hope I don't find a bad gyro, but if I do, I do...such is the hobby, eh?

Will

TheHindmost

Hi Michael,

I didn't realize that was your first posting! Welcome to the board! I just got here a few days ago myself. Everyone's really friendly and everything's worth reading....I've got a lot of catching up to do. Fortunately for people like you and me, some prolific contributors (e.g., Sky High) have blazed the DF trail before us...so we have some guides!

I'm new to RC in general and the DF in particular...but I'm learning fast, and this board is helping tremendously!

Will

Sky High

Hindmost, you can get one motor to spin almost by itself by either removing the rotors and engaging extreme stick inputs for whatever motor you need get more power. For example, remove all rotors and then throttle up with a full stick in any direction. The opposite rotor should almost stop if not completely.

Sky High

For all of those that have made reference to it, I'm glad to be able to help and thanks for the complements. However, when I found this board I learned a few things from several of the existing members and still do. I'm glad to see that the activity has picked up recently because it was really dead for a while. Thanks to everyone for the info.

TheHindmost

Yep, I used that opposite stick method to confirm the bad motor...thanks! I was just saying a full-on test mode where you can command each motor individually through its entire range would be nice, too!

And regarding the compliments, you're welcome and they're very well-deserved!

Will

intrim

is it just me or does anyone else think that the df should have a port you could run a diagnostic to see what checks out. there are times when im not sure if the df is 100% or possibly this 4 channel hi-tec (ok but without dual rates it sucks). since everything is new ,now would be the time ot find out if there is a fly in the ointment.! seriously wouldnt that take a load off your mind when your trying to get answers and have to bug dfly. sometimes its hard just to make the time . and then i feel like a dork trying to explain whats going on
if you could ioslate the df right away. you could look elsewere. i realize intermittant problems might not show up. but as high tech sa this thing is. for all i know maybe mikes has some problem codes stored in memory to look at when he gets boards into repair.

mike