Sudden Pitch Changes -> hit the wall

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Home › ✈️Aircraft › 🚁Helicopter › Helicopter Main Discussion › Sudden Pitch Changes -> hit the wall

03-15-2014 04:10 AM 6 years ago

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fly_slowly

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Terrebonne, Quebec - Canada

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Sudden Pitch Changes -> hit the wall

Something strange happened after I installed my new Futaba GY520 gyro on my Blade 450 3D. On the first flight, with some wind, the helicopter occasionally jumped up and down by a foot or two. I was able to land it safely, took it into my workshop, removed the blades and tried to reproduce the problem on my workbench. Everything was normal. First I deduced it cannot be a servo because all three move together for a pitch change. Cannot be the gyro as the tail was acting normally.

Checked the transmitter for bad internal connection. Nope. Ruled out the throttle potentiometer because a) the monitor on the transmitter showed nothing abnormal b) can't reproduce it on my workbench without blades.

So I am left with : receiver. Switched receivers (from Hitec Optima 6 with SPC to Hitec Minima) and went outside with blades. Still strange behavior, now even before takeoff : no liftoff at usual position of throttle stick but uncontrolled left cyclic. Now, maybe it's the cold (-14 deg Celsius) ? Wasn't a problem before I switched gyros.

Anyway. I take it inside on the floor of our bedroom and spool up (have done short hovers for testing purposes in there before; not recommended, I know :-P). So I spool up and slowly increase the pitch. No takeoff yet at the usual point. But then, all of a sudden, the Blade jumps off the ground banking left and crashes into the wall a fraction of a second later. No one hurt and no serious damage (blades, one blade grip, two servo gears).

I am out of ideas here. Before I changed to the GY520, I used a RadioLink GY100 which wasn't too bad but had a tendency to short random tail moves. Also switched to a JR DS290G tail servo. Except the strange tail behavior due to the gyro I had no problems at all. (Why I used the GY100 and not the stock G210 is another story).

My last idea is the possibility that due to the better performance of the GY520 there is so much current draw from the tail servo that I am experiencing brownouts from the stock ESC BEC. Could it be ? How can I check for short current spikes ? I could always go back to the GY100 or the G210 but at this point, I am not sure I want to spool up again before identifying the root cause.

Sorry for the long (first) post. I thought context might be important.

Any ideas ?

Aurel

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03-15-2014 05:05 AM 6 years ago

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RM3

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Killeen, Texas - USA

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check your end play on the main shaft by pushing it into and outof the heli from the top...sounds like your main shaft is loose and suddenly pulling loose a bit when its running...other than that I would suspect the RX is going bad on you in some way or another...try a different Rx if you have it as well...in that case you need to set up a fail safe just in case the RX detects a power problem to shut power down to the motor AND bring the swash level at 0 pitch.showing a preference will only get you into trouble, 90% of everything is crap...

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03-15-2014 05:37 AM 6 years ago

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enerko

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Melbourne, Victoria-Australia

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Seems to be cyclic servos malfunctioning. When the servos are jittering badly in hover the heli jumps up and down.

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03-15-2014 06:03 AM 6 years ago

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JKos

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Redondo Beach, CA

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And you changed nothing the gyro?

- JohnRR rules!

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03-15-2014 07:25 AM 6 years ago

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Zbawer

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Singapore

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Blame it on the wind !
That's all there is to it...

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03-15-2014 01:00 PM 6 years ago

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VANHELI

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Omaha,Nebraska

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I would check the head assembly. Inspect thrust bearings. Under load if one or both are seizing it could cause what you are explaining.Dave V.

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03-15-2014 01:07 PM 6 years ago

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fly_slowly

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Terrebonne, Quebec - Canada

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RM3 : I'll program the fail-safe in case it's a power problem. Good idea.

JKos : Well, now that you ask, I changed the gyro *and* the tail servo at the same time. Will try to check the current draw of the tail servo.

If I can't identify current spikes, I will try powering the servos from a separate battery.

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03-16-2014 12:32 AM 6 years ago

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AirWolfRC

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42½ N, 83½ W

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I had a similar problem way back. Turned out to be a bad wire entering the servo to the board.

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03-16-2014 03:38 AM 6 years ago

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fly_slowly

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Terrebonne, Quebec - Canada

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Thanks for all the ideas!

I just finished the mechanical repairs and setup, taking the whole head apart and reassembling and balancing it. Swashplate is straight, servo travels perfect.

Before flying, I will look into the electrical side : loose wires, bad or weak BEC, etc.

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03-25-2014 11:51 AM 6 years ago

0Post 10

fly_slowly

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Terrebonne, Quebec - Canada

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Update : Solved

The issues have disappeared but it is not entirely clear to me why. This is what I did.

1. Installed CC BEC. My worry is the stock ESC BEC might have glitches because some melted snow got into it.

2. Made 3" long servo cables from the GY520 three way plug to the receiver (instead of 20mm cables I used before).

3.Installed receiver antenna vertically on the tail boom, above the tail servo.

4. Noticed that the signal wire connector of the elevator servo plug came out when plugging into the receiver. Damaged connector plug. Made sure all wires are well plugged into the receiver.

As I mentioned, not clear which of these four issues caused the problem, but I am glad it's fixed.

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03-25-2014 10:00 PM 6 years ago

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luz_husband

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Nancy, Kentucky

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I recently had a similar thing happen, I was hovering a newly built 450 and suddenly it went full negative pitch and hit the ground. after checking everything and trying to reproduce the problem everything seems to be working perfectly. Only damage was my landing gear, main blades, main & feathering shafts. I'm using a GY520 as well but the tail holds solid, even when it went full negative pitch the tail held. I could never reproduce the problem but I did relocate my electronics to get as much separation as possible between the receiver and any possible source of interference.Impacting the earth one heli at a time

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03-26-2014 12:06 AM 6 years ago

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icanfly

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ontario

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I've experienced those problems due to a failing servo, and something binding in the linkages. Replace each servo one by one and retest the situation until the bad servo is eliminated. Sometimes it's static, a bad connection, broken solder within a unit, wire grounding out in the presence of water, minor things that will crash a heli to many tiny fragments in the blink of an eye.

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Home › ✈️Aircraft › 🚁Helicopter › Helicopter Main Discussion › Sudden Pitch Changes -> hit the wall

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