"Over the shoulder" pitch / roll on liftoff?

[franklin_m]

After repairing a sheared mainshaft, and replacing the blades, I took my 300X out for a short flight yesterday. It spun up normally, but when I increased power to bring it up into a hover, it rose off the ground and immediately & sharply pitched nose up with a slight roll to the right -- cut an arc as if pulling into the first half of a poorly executed loop. I hit TH to limit the damage, but it hit on the tail breaking bladed grips, control arm, and who knows what else (haven't torn into it yet).

Any thoughts on what would produce that behavior? BeastX still solidly in place (even after this crash). Didn't see any noteworthy vibrations on spool up.

Thanks

[jypt01]

Check that your head is self correcting in the right direction. In other words when nose pitches forward does swash tilt back, when pitching left does the swash tilt to the right. I don't know how I got it wrong once but I did and the same thing happened to me on lift off. Goodluck

[franklin_m]

I just checked and the swash is moving correctly...

[Russell Harding]

Right roll of death: vibes.

You won't get off the ground if your sensor directions are incorrect, so it isn't likely that.

[franklin_m]

Ok. I've done the motor mod, so that's off the table. The blades were balanced. I found a crack in the landing gear, so I'm wondering if that I missed that and that produced enough vibes?

Frank

[Russell Harding]

Check the tail system if you've had a crash. The high frequency vibes are the worst for the unit.

[helidude71]

Originally Posted by franklin_m

Ok. I've done the motor mod, so that's off the table.
...
Frank

Not it's not.
It can still be a vibrating PITA.
The motor can is unbalanced, that will give vibs if you're out of luck.
Some stockers however can be fine.

Spool it up outside the frame and check for vibs!

[DoubleCH]

Motor vibes are high frequency and may not be visisble if run up outside of frame. The best way to check motor vibes is mount the motor on motor mount and tighten motor mount to frame but don't engage pinion to main gear and then run it up on a smooth level surface.
https://www.helifreak.com/showpost.p...12&postcount=5

[helidude71]

Originally Posted by DoubleCH

Motor vibes are high frequency and may not be visisble if run up outside of frame. ...

You will feel the vibs if you do.

[Uriah]

Any time you do a repair on a 250+ size bird that was a result of a crash (no matter how mild the crash was), I highly recommend that you take off the main blades and do a full power runup to check for vibes.

[helidude71]

Originally Posted by Uriah

Any time you do a repair on a 250+ size bird that was a result of a crash (no matter how mild the crash was), I highly recommend that you take off the main blades and do a full power runup to check for vibes.

+1

[franklin_m]

Originally Posted by Uriah

Any time you do a repair on a 250+ size bird that was a result of a crash (no matter how mild the crash was), I highly recommend that you take off the main blades and do a full power runup to check for vibes.

Parts due to arrive Friday. After I rebuild tail, I'll make sure to do that.

[DoubleCH]

Originally Posted by helidude71

You will feel the vibs if you do.

The stock motor from my 300X felt fine running outside of frame when I held it in hand and my fingers didn't even feel numb. When I installed it in the frame the whole heli will dance like cellphone on vibrate. Same goes for my friend's stock motor.

[franklin_m]

Well, after replacing the busted parts - tail rotor grip (1), tail case, slider, stripped servo gears, and blades, it appears that I have stumbled on the cause of the crash. The right rear DS76 doesn't move at all. This explains the up and over the right shoulder roll on liftoff. I must have missed it on my preflight (operator error on me) - and thus my earlier post that it was working was incorrect as well.

I suppose the good news is that I've learned how to replace / rebuild servo gears, tail grips, and do the locktite motor mod. The other good news is that a full power runup, minus main and tail blades, produces a rock steady machine on a smooth hardwood floor.

Back to the web to order a replacement servo...

While I'm at it, any recommendations on a better quality drop-in replacement - I'm not a 3D flyer - more scale flyer - that will hold up better? Also, what sort of BeastX reprogramming will be necessary?

[Russell Harding]

There are TONS of servo threads in the 450x forum, since this is a common problem, usually from stripped plastic gears. The gears are cheap and easy to replace, but will strip in a tip over or drop on the bench. Look for anything digital 450 sized cyclic servos with metal gears. Expect to pay $25-40 for decent servos. You will need to replace all three with the same type and redo the BX setup completely.