Tiger Moth Delight ... and DISASTER! - RC Groups
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Jun 13, 2002, 10:33 PM
Registered User
galloping gimp's Avatar

Tiger Moth Delight ... and DISASTER!

Tonight I had my best flying session EVER with my Tiger Moth. There was a very light breeze, probably 2-3 mph, just enough to help the plane climb when flying upwind.

My flying skills have improved to the point where I almost tried my first loop, but in the end I was content to meander around the sky. Big circles, figure eights, diving turns -- it was great -- everything I hoped R/C flying would be.

With two 150 mAH NiCad packs and one 300 mAH NiMH pack, I made three flights totalling about 20 minutes of flying time. Each landing was nearly perfect, and I taxied right back to my feet after each one.

It doesn't get any better than this. But then, everything went wrong ...

I decided to go for a 4th flight, so I put one of the 150 mAH packs on the Electrifly charger and switched the charger to its 600 mAH setting for a fast charge. About the time I finished with the other packs, the 150 mAH pack was ready to go, according to the blinking LED on the charger.

As usual, I ROGed the Moth, but uh-oh, she doesn't want to climb! The plane gets about 5 feet off the ground but is responding sluggishly -- not much air speed apparently. I can't maintain altitude, much less climb. Suddenly, she stalls, pinwheels to the right and hits the ground hard, nose first!

The grass in the field is cut short and does little to cushion the blow. The motor stick breaks, and I even from 100 feet away, I can see the prop is at a sickening angle. It's jammed against the fuselage and can't turn. Then I make a big mistake; I fail to bring the throttle control back to zero. By the time I got to the plane, the heat sink is too hot to touch. Arrrgh!

I suspect the motor (stock IPS unit) is fried because I did not zero the throttle. That's a rookie mistake, and I have learned something.

What I do not understand is why the plane did not stay in the air. Some possibilities that occur to me:

1. Perhaps charging the 150 mAH battery at 600 mAH was a mistake. Either it did not charge properly or charging at the higher rate damaged the battery. This was the first time I tried to charge a 150 mAH pack at the 600 mAH rate. I did this on the advice of someone who says he does it all the time without problems.

2. After 20 minutes of flying on 8.4-volt packs, could the motor have been overheating? If so, would that make it down on power? There is a heat sink on the motor, but this was the first time I ever attempted four consecutive flights. Previous sessions were limited to three flights.

3. ESC overheating?

Do any of the above make sense? Until the 4th flight, everything was working perfectly.

While I have your attention, what's the best way to re-mount the IPS on the Moth? I can't see digging out the motor stick, which is epoxied in place. Is there a better way?

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Jun 13, 2002, 11:00 PM
Live to ride... and fly!
Tres Wright's Avatar
Really sorry to hear that Jeff Doesn't sound like a very difficult repair though.

My vote is that something went wrong with your battery charging. It happens. I have a small voltmeter that I got at Radio Shack over a decade ago, it's the size of a calculator. I use it to check every single pack after every single charge, just to make sure. Sometimes if a pack gets too warm (from the weather or charging too soon after flying it, etc.) it will give a false peak and the charger will think it's charged and shut off. If you check the volts, you'll know right away not to put it on your plane. Usually I just pop it right back on the charger and all is well.

On the motor mount stick, how bad is it? If you've got all the pieces, try C/Aing it back together. If that doesn't work, try using an exacto to cut the glue joint between the stick and the foam and see if you can work it out. It won't be easy though!
Jun 13, 2002, 11:04 PM
Live to ride... and fly!
Tres Wright's Avatar
Just re-read your post. I think charging your cells at 4C may be the culprit. I was just reading yesterday that 1.5 to 2C is max charge rate on NiMH. I know yours was Nicad, but for a tiny pack like that I think the charge rate may be too high unless they are R cells. I don't think Sanyo makes R cells that small though!
Jun 13, 2002, 11:11 PM
an earth bound misfit, I
Basketcase's Avatar
GG, sorry to hear about your mishap, I think Tres hit the nail on the head. Sounds like a false peak to me. Especially at that high of rate. Some battery packs are more prone to it than others.

Jun 13, 2002, 11:22 PM
Registered User
galloping gimp's Avatar
It is a very ragged break in the motor stick. It almost looks like it was twisting as it broke. I don't think any pieces are missing, but it may be tough to fit it back together. I'll give it a try, though.

My brother, using the same type GWS 150 mAH NiCad packs and the same model Electrifly charger, routinely charges at the 600 mAH rate. I tried it for the first time and disaster occured!

It certainly behaved like a dead battery pack -- your "false peak" idea makes a lot of sense. The pack was slightly warm to the touch when I put it on the charger.

I have been an electronics experimenter for about 40 years, so I have all sorts of meters, including one of the little Radio Shack units. I will put it in my flight box from now on. Thanks for the suggestion, Tres.
Jun 13, 2002, 11:38 PM
Live to ride... and fly!
Tres Wright's Avatar
No problem Jeff! Glad we could help.

I've been thinking about the stick, if you can't C/A it together you might try clamping some lockjaws on it and work it back and forth to see how heavily it's glued in. Maybe you'll get lucky and work it out that way. If not, you could use progressively larger drill bits on it until you've basically drilled the stick out of the foam. You'll be left with an oversized hole, but you should be able to Probond a new stick in there. Some of the guys here have scratchbuilt surface mounted motor mounts and did away with the stick altogether. That might be Plan "C"

==The pack was slightly warm to the touch when I put it on the charger==

That could very well have been the problem. I've had that happen a few times, I thought the pack was cool and the charger didn't
Jun 13, 2002, 11:56 PM
Registered User
Stregone's Avatar
If there is enough stick left cut it off at as large of an angle as possible (so it is chisel shaped) to maximize the surface area. Get a new stick and cut it with a matching angle and glue it on with something really strong like 60 minute epoxy, and maybe give it a layer of light fiberglass for good measure.
Jun 14, 2002, 12:01 AM
Registered User
galloping gimp's Avatar
I've read here on the forum about drilling out a broken motor stick. Sounds like a rotten job.

Stregone -- not sure if there is enough of the stick protruding from the fuselage to be able to cut it at an angle. I'll take a look at that option, though.

I haven't done anything toward repairing it yet. I like the idea of doing away with the stick, though. I've seen pictures of a very nice adjustable motor mount.

What's really annoying me is that all this could have been prevented if I'd just flared and landed when it was obvious the Moth did not want to fly. Instead, I disbelieved what I was seeing and tried to force her into the air. Here's where my lack of previous R/C flying experience really showed.
Jun 14, 2002, 12:04 AM
an earth bound misfit, I
Basketcase's Avatar
I think too, that hi rate charging is something you have to work the packs up gradually. Give them a little more each time and eventually they should take 4C. But not a fresh pack.

I had to dig my broken stick out with a xacto chisel blade and an icepic. I put the new one in with a bead of probond at the firewall plus a tiny dab of it on the end in the fuse. It's in there nice and solid and will be alot easier to get out next time. Although, now that my flying has improved somewhat I don't crash as much anymore and hopefully won't need to.

Jun 14, 2002, 12:32 AM
Formerly Black96Z
Heli Slime's Avatar

This is what happened to the pack

It false peaked. Hre is probably why. You said that you were flying the other packs. At some point after you started charging the pack you closed the car door and then later opened it. The light turning on inside the car drew just enough power to fluctuate the car battery voltage just enough to false peak the pack. The Electrifly chargers are very sensitive to input voltage. If I start mine charging and close the door and set the alarm, 9 times out of 10 I get a false peak.

Jun 14, 2002, 12:44 AM
Registered User
galloping gimp's Avatar
David, that is quite possibly what happened. I opened the car door to put the pack on the charger and then closed it. I do not recall opening the door again, but maybe closing the door with the pack on the charger was enough.

I have opened and closed the car door many times in the past while charging battery packs. Was I simply unlucky this time? Or is a false peak more likely when charging at a higher rate? This was the first time I have ever used the higher charging rate on this charger.