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250 Class Electric Helicopters 250 Class Electric Helicopters manufactured by Align, Tarot, SYMA, Airhog, Chaos, HK and similar.

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Old 10-31-2020, 10:22 PM   #1 (permalink)
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Join Date: Apr 2020
Location: Birmingham, AL
Default 300x oddity

I was working on a tune-up of my 300x last week. Fine-tuning the tail rotor. Went out on an absolutely dead calm day and had an "event."

Helicopter hovered almost hands-off, very little drift. Hovering over a 12" target was easy. Stray gust of wind came in over my shoulder and pushed the heli a few feet forward. I gently nudged it with back cyclic and it slowly returned to me. And kept going, and kept going. No cyclic control. no pitch/throttle control. No rudder control. No throttle hold. Thing just slowly (not crawling maybe a fast walking speed) back off the end of my driveway, into the back yard, and hit a couple of trees about 100 feet back.

This after less than a minute of flying. Went to pick it up, nothing worked (still). Took it into my shop, looked at all connections, everything OK. Unplugged receiver and turned transmitter off. Powered back on and all worked.

Can't figure out what might have happened here. I repaired (boom, feathering shaft, couple of ball links and blades of course). Several test flights have shown no problem, but I am a little hesitant to trust the thing. This is a ready to fly 300x with align's A10 transmitter which has been working just fine for 6-8 months.

Any ideas on something to look at.

After that, I had assumed (obviously) that there was a total communication failure. Decided to go in and set the fail-safe stuff, as I would at least like to reduce the throttle and pitch so that it won't maintain altitude and keep moving. But I still have not gotten that to work. I set everything to sort of "centered values" and then pulled cyclic and collective hard and turned off transmitter. Servos stayed where they were when I hit the power switch on the transmitter. Tried other tests. -nada-. Not so concerned with that, but the lock-up was any attention-getter.

BTW I found another glitch in the heli. I was working on a tail wag, and checked tail rotor neutral pitch and such. Started to test pitch linkage and found some slop. Checked the rotor gear pitch slider. Looked good. Pushrod looked good. Looked like the servo had some slop but when I looked carefully, the servo itself was rock solid. But the servo mount was moving. If you look, you will notice the two carbon-fiber side plates have small slots cut into them. The tail rotor servo tray has two ears that fit in these two slots. The slots were tight up and down, but could slide back and forth at least 1/16" or a bit more. Obviously that is not going to provide a stable tail rotor pitch since the servo tray can slide fore/aft which is exactly the direction needed to alter tail rotor pitch. I decided on a simple fix using a very tiny pipette and a tiny amount of thin ca, to lock one spot on each side. Solved that, and a test before doing this showed that the tiny amount of CA could be broken without damaging the carbon fiber stuff, should the frame need to be taken apart.

That's a bit sloppy design wise...
AMA #118235
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