ombudsman

I took my little 1/2-sized electric StickIt for its maiden flight. It has a Rimfire 400, 950kW, turning a 9X4.8(?) APC. The esc is a Grayson 30A. The battery a 3s 1350 LiPo. I launched and hit full throttle to get altitude to trim out the plane. I took it vertical about 100', turned down wind maybe 20 yards, started to throttle down when the motor stopped. I thought, "Certainly the battery couldn't be gone this quickly!" But no problem, I thought, I'll just glide down. I turned upwind and started down, when the I lost radio. Though I had checked CG carefully, I think the plane was nose-heavy and when I lost radio the plane dove absolutely vertically into the ground. Of course I pulled up, but the huge elevator had no effect (no radio.)

The carbon fiber boom broke just behind the motor mount. That's about the only significant obvious damage. I repaired the boom and all appeared well. This morning I hooked up the electrics to see that everything is working there. The control surfaces all responded, but when I tried the motor, it tried, in little jitters to run backward. Then a wisp of smoke came from the motor. Of course I shut it down immediately, but I fear the worst. Now, the motor could have been damaged in the crash, though there is no apparent damage and the prop turns freely.

I failed to check the contents of the battery (I was still shell-shocked,) but it charged back up successfully.

I would greatly appreciate ideas on what has happened here. Did I get a bad esc? Did I burn out the motor or esc with the6 or 8 sec. full-throttle run? The Grayson user's manual says that you can't use 4 servos @ 11.1 V (I have four servos), but the LHS said that the esc wouldn't even notice my four micro servos. Was LHS wrong? Why did I lose receiver power?

Help, please.
Dave

ombudsman

Well, a trip to the LHS and a lot of fiddling proved that the problem is the Grayson Hobbies esc. LHS tells me that there is no warranty. I couldunderstand no one-year warranty on electrical items, but 30 seconds? While there, another flyer told me that they all have used Grayson ESCs and have found that the little tube connectors supplied with the esc are no good. He said that they hard-wire the esc to the motor and have had no more trouble.

Would a bad connection at the motor cause loss of signal to the receiver? I don't understand this. As I said, after the motor quit, I had a few seconds of control (unless the plane coincidently moved in the way I intended.)

Can anyone enlighten me on this occurence?

Thanks,
Dave

toywizard

I suppose the bad connection could have caused a massive overdraw of power and drained your batteries below the rx control level although it does seem
strange. I have had stranger things happen.

I have used Castle Creations esc's (many) and Hitec rx units. Never had a prob other than my flying. lol

Its the most helpless feeling to see you plane taken over by gravity and have no control over it.

Grayson Hobbies is usually pretty good to me so far but I have not purchased that much stuff from them yet.

Remember when a bad connection happens it does not mean it does not get enough voltage, it can try to draw
so much that it would burn off the connection, over heat the batteries.

I think Red Scholfield could explain it better than I can but a bad connection can cause over drawing of power.

Dr Kiwi

I'd beg or borrow another ESC... and try that on the ground/test bench just to see if the servos and motor will run normally.

airdrew99

I really don't know much about electrics, but my brother had a fairly expensive electric motor that I believe had a similar problem. His flew good for a few flights, then just got to the point where it was jittery and wouldn't run correctly. He finally realized that the motor was grounding out (shorting out) inside the motor. Tried a different motor just to verify that all else was normal. So, if you have a different motor, esc, or battery to try, this could help you troubleshoot and eliminate problem areas. Hope this helps a little bit.

Drew

ombudsman

At the LHS, we determined that the problem was the esc. The motor ran fine with a different one. So, the LHS cut me a deal on another Grayson. I hooked it up, knowing that I might have to switch two of the wires. Soooo.... I soldered (hard-wired) one of the three wires and just twisted together the other two (so if I had to switch 'em I wouldn't have to unsolder.) No good- motor wouldn't run. I checked everything again and again, but no luck. With nothing else to try, I went ahead and soldered the other two wires. VOILA!! The motor ran perfectly - you guessed it - backward. I unsoldered two of the wires, switched them and resoldered. All is well.

What a wonderful sound in the dining room; the whine of the electric motor, the prop noise, the terrific pull on the plane, the sound of my wife screaming, "David! You're blowing stuff all over the house!!! YOU'RE GOING TO PICK ALL THIS STUFF UP!!!" LOL

Of course tomorrow is supposed to be rainy, with wind 15-30 mph. Naturally. I'm anxious, though, to fly!

Now I'm wondering if there is anything wrong with the original esc or if it just has ineffective connectors. I may just have an extra esc.

Thanks for all the help.

Dave

pilotpete2

Hi Dave,
If the ESC is not rated for four servos with 3S lipo, then there is a very good chance that the BEC overheated and shut down.
If the Grayson ESC has less than a 3A rating on the BEC, four servos will be too many. The best test before flying a new setup is to feel the ESC, while moving all the servos continuously, if the ESC gets very hot in one spot (BEC regulator) don't fly it.
I have all CC controllers that have a 3A rated BEC and they will handle 4 micros, like the Hitec HS-55's.
Good luck,
Pete

ombudsman

Thanks, Pete. I'll check that. Thinking back, though, I never used all four servos at once on that short "flight;" As a matter of fact, I don't think I ever touched the rudder.

EDIT: One piece of the puzzle that I forgot to mention is that when we tried to post mortem at the LHS, the original (putatively bad) esc would run the servos - it would not run the motor. I'm surely wondering if there was a bad motor connection that, as someone suggested, sucked the battery down to the cut-off point, thus no radio. BTW, my Grayson BEC is rated at 3A. My four servos are Hi-Tec, and are little ones, but I don't remember the model number.

Dave

ombudsman

I lied. My four little servos are Electrifly ES80 micros.

Walt Thyng

My Feedback: (9)

LVC (low voltage cut off) should not shut now the BEC, only power to the motor. I suspect that you hit thermal shut-down due to too many servos (or a stalled or high drag linkage). Micro servos often draw far more power than standard sized ones (I have several ESCs that reduce the number of servos by one if they are micros). Your post-mortem test at the LHS was invalid if the motor wasn't running. Also, it doesn't matte whether or not you were actuating all four servos during the flight; they still draw current at idle which increases as they fight to maintain neutral against air loads.
Walt

ombudsman

That's interesting, Walt. I wouldn't have thought that the little servos would take much power.

In any case, I installed a new Grayson esc (hard-wired to the motor) and flew last night. Everything went well. Immediately after landing I felt the esc and found it just warm.

Walt Thyng

My Feedback: (9)

well, sometimes an electric component just isn't up to snuff. glad you're back in the air.
Walt