Stumbled on the learning curve

[Bob Johnson]

Ok, I could use a bit of help. I let all the magic smoke (and a bit of flame) out of my ESC. Here’s the story. I was trying to better dial in my setup (standard Brodak Super Clown system) Things were going well, but I thought I’d try a 10x5 pusher prop as was recommended. I swapped the prop and changed the wiring. The first flight was OK but too fast, so I dialed back the power a bit and it was then too slow (8 sec laps). 3 rd flight dialed it up a bit, still too slow. 4th flight up all the way, still 8 sec. laps, RPM was around 7500. So… I thought I’d switch back to the 9x4.5 to see if that would improve things or at least return to the way it was. Swapped props and wires. Set it off and then it happened, the plane nosed over on launch. Prop was stopped followed immediately by a short (2-3 sec.) high-pitched whine followed by no sound just smoke and flame. I was able to get the battery and what was left of the ESC out quickly. No damage to the plane or battery but the ESC was stinky toast.(see photo)
    My questions are: (A) What happened? I assume it was a shaft free spin that overloaded the ESC, though I thought such a prop strike would cause the ESC to shut down. No?
(B) I know I need to replace the ESC, but is there a way to test the other parts for damage. i.e. if I need to order more parts I’d just as soon do it all at one time. (C) Given the way it was acting was the ESC damaged/defective before the incident or was the timer responsible for the mishap and possibly damaged or defective.
    I did save all the pieces, though I don't think super glue will help. Thanks for input in advance.
Bob

[Wynn Robins]

prop strike would have caused a current spike - the ESC would have burnt out due to that


from, what you have said, it seems the larger prop was drawing too much current - and would not let you get to your target RPM - did you tach the prop? 

[Tim Wescott]

Not a free-spinning motor, but a stalled one with the shaft held still.

I fly RC electric and slime stunt, but I've heard of this phenomenon.  Besides, I design circuits like this for a living.  To prevent something like this happening, the ESC designer has to go out of their way to detect the stalled condition (or the over-current condition) and shut down the motor.  AFAIK, most ESCs don't do this well (I know this through hearsay -- take it with a grain of salt).  I think the assumption is that they only need to last long enough for the pilot to slap the throttle stick to 'off', since they're assuming an RC pilot is in visual contact with the plane.

(Note, too, that this is one of the cool features of the Kieth Renicle timer -- he detects the stall and shuts off the signal to the ESC, preventing all this excitement).

If the battery isn't puffed up it's probably OK.  I'd charge it up, paying extra attention to the "don't let your battery catch the world on fire" rule, check for puffing, and if my charger will do so, discharge it to 3.7V/cell (or maybe 3. and see what sort of capacity it has.  Then I'd check for puffing again, charge it up, make one last check for puffing, and then maybe I'd leave it in a spot where it could burst into flame without burning down my house.  I'm probably being extra-paranoid, but, one does hear horror stories about torched batteries.  I think I'd also mark it somehow so I know that it's the 'one', so that if it dies an early death I'll know why.

There's a small chance that as the ESC died it exposed the timer to too much voltage.  There's a lot of things in the way of that in a normal ESC circuit, but on the other hand there's a lot of random hot things and molten solder rolling around, too.  If you have another ESC and motor, you're not going to hurt it by plugging the timer in and giving it a whirl.  Better yet, if you have a  way to hook it up to a servo and watch it work that would be a good test.

[John Rist]

(Note, too, that this is one of the cool features of the Kieth Renicle timer -- he detects the stall and shuts off the signal to the ESC, preventing all this excitement).

I also would recommend the  Kieth Renicle (KR) timer.  I have tested it by grabbing a motor with a rag.  The KR timer shut down the speed controller instantly.  I have had 3 noise overs on takeoff and all is good.  Just recycle the battery and it was good to go.

By the way if the low RPM problem was a burnt motor the KR timer would have detected this also and shut down the speed controller.

[Bob Johnson]

OK, I’m back in business with a new ESC and timer (Brodak stuff), test flights A-OK. Motor was unharmed.
Checking the battery temp after flight = 114+ degrees. Used 2828 ma according to the charger. Now to tweek the time and line length.
I’d still like to try the 10x5 pusher prop again but I’m a bit gun shy. Thanks again to all for the advise.

Bob

[Tim Wescott]

What prop are you using that works well?

[Bob Johnson]

Currently the 9 X 4.5 APC that came with the original package (and it works well). But supposedly the APC 10 X 5 will work. I'm thinking may be 9800 - 10,000 rpm. I haven't tacked the 9 X 4.5 as yet. Next session.

[CircuitFlyer]

Bob,

A 35 amp ESC and a 10x5 prop may not be a good combination.  Best advice is to get an ammeter and see.  It sound like you may have fried the first ESC on that first flight with the 10x5.  I use a non-Brodack power system in my Super Clown and fly with an APC 9x6 pusher.  On the bench it draws around 30 amps.  You could also try the APC 8x6 pusher.

Paul

[Dennis Adamisin]

With a front mounted motor it is possible to lock it up IF the prop adapter bottoms out against the motor. When you tighten the prop you lock it up. The solution is to make sure it isn't bottomed out, slip it forward a little before tightening the prop.  Then flip the prop a few times to make sure the motor is spinning free.

[Bob Johnson]

Hello Dennis
The prop spins free, always has. No real problem with the 9 x 4.5 I was just wanting to try the 10 x 5 pusher you recommended.

Hi Paul
What size ESC would you suggest 40-45? What set up are you using?

Thanks
Bob

[CircuitFlyer]

Bob,

For what it's worth:

Exceed RC 3015 - 1450kv, 40A ESC, KR Timer, APC 9x6 EP @ 10,800 RPM, 3S - 2650mAh Battery, 60' x .012"

I fly it a little faster than most folks prefer and I think my power system is more than necessary and a little on the heavy side too.  If Dennis recommends the 10x5 then it must work fine, just use the RPM's he recommends.

Paul

[Bob Johnson]

UPDATE: Ordered and installed a 9 x 4.5 pusher from APC. Everything else the same (except rotation). Flys like a charm, overhead tension might be a bit better, certainly no performance loss. I'm happy for now. Need to practice.

[Bob Johnson]

OK, I spoke too soon. Last night while practicing it happened. I had one good flight, everything normal. I wait about 10 min. get ready for a second flight. Plug in the battery as I always do and snap, spark, nothing. No chimes nada. Hmmmm... plug it in again and can barely hear the chime. Press the button and get a faint blip and 15 sec. later a weak attempt to run. So the ESC is fried. Crap, I just bought the thing. It doesn't have 15 flights on it yet (nor will it get any more). Was this a lemon ESC (Arrowind) or am I doing something wrong? Any words of wisdom? I'm not a happy camper. Recommend a better ESC to go with my Hubin timer?