Any pre flights checks can do for heli under spool up load before taking off

[sleeperaus]

Had a bit of bad luck lately with my Blade 450x
Had about 4 crashes in a row where heli hardly even left floor without seeing it very rapidly again!

Last flight I had, did my pre flight checks, spooled it up on the ground, felt like everything was working fine, so slowly increased pitch to bring it up off the ground, then suddenly it pitched forward, basically flew a few metres forward and put itself into the ground on the head
I've checked the brain logs and there's no vibe issues and I can see in the log of inputs that I nor the tx werent giving any strange inputs.

When I took a look at the heli, the front elevator servo (h3050) was completely dead. Based on symptoms of previous crashes I'm hoping that that going progressively bad was what's been causing my issues.

when I was setting up the brain I checked all the Swash movements to make sure no issues and all servos behaving correctly. My best guess is that the issue with the servo was happening under spooled up load, ie. It not responding then suddenly jumping to a new position and sticking again.
In people's opinion, is this a reasonable theory?

So my question is, are there any tests I could do with the heli on bench or ground where i'd hopefully see any such behaviours before I planned to go fly? (IE. Maybe would have seen that under load, elevator servo doesn't respond properly)

[bundydeity]

not sure its a good idea to sit on the ground at high headspeed for too long. best to take off.

if you need to test it, remove mains and tails and go to your highest headpeed, move the sticks around and check for proper, smooth movement.
it is likely your elevator servo was failing and finally died.

edit: if they are MG servos, you could also apply a little bit of pressure with your finger to simulate a load whilst spooled up on the bench with main and tails removed and see how it responds

[macdad]

I don't do much when spooling up. However, I do move the collective and rudder after the heli has initialized. (Keep TH on) If the servo was already dead, this check would have caught the problem.

[myxiplx]

Do you check the swash and tail movements using the transmitter and by tilting the model to ensure FBL corrections are good?

After any impact servos are often damaged, so that may not be the cause of the crash, it could easily have been damaged this time.

It's important to check that all servos move smoothly with no notchiness or binding, and that they're also smooth under load (with the motor disconnected hold the head tight with your hand to add resistance).

Also check for lose wiring, or any worn wires. If a worn wire comes into contact with the carbon fibre frame that'll cause a loss of control every time.

Lots of preflight checks to do after a crash, but they'll all things you do on the bench, once you start spooling up all you can do is be prepared to hit throttle hold if you spot anything weird.

[bad007]

What ESC, BEC volts and Amperage? When you have a crash the FBL unit is still active and commanding movement to the servos that can lead to BEC and or Servo failure if linkage is bound up.
You need a BEC that can handle the load and after rebuilt you must apply load to the swash plate placing 2 fingers on it and pump the collective as fast as you can for at least 2 min and monitor with a DVOM for voltage drop if you have one and feel for rough gears in the servos or if there jittering from being damaged

[GREYEAGLE]

Four Wiffel Ball's and two stick's = SO What >>>>>> it stops a wadd up

Then you have the opportunity to remove them - CHEAP !!

Wasn't so foolish after all. Then you know

Allway's some thing their too remind me - Before you set it free.



The 1st skill set is How ?? too build them -

[gtrsteele]

I always check for proper movement on all control surfaces and from the FBL gyros with TH before taking of. If anything looks off I won't take it up.


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[sleeperaus]

Thanks for replies all.

As I said though I checked everything thoroughly before I even took it to field (and again on ground before turning off throttle hold), so am very certain the setup was fine and the servos were responding and moving correctly.

I'll try the Spool up with no Blades and giving tx inputs next time though to see how that works.

[ARM_Coder]

Servos can die out of nothing and without warning, and unfortunately no preflight will prevent this.

Years ago I crashed a brand new Trex 450 Pro V2 because of a swash servo failure. It had no previous crash history, the servo simply went nuts.

I also had a tail servo failure in a just-built 6HV, fortunately I managed to land it safely.

However, keep doing the preflight so you will still avoid most other problems.

Cheers!

[Fauropitotto]

After initialization, I physically push on the swash to make sure that the servos can hold under some moderate force. Many of our servo gears have a component that is press-fitted. A hard crash can cause that to slip, and once slipped, it will fail under load. A few Kg of pressure before a flight can help you spot something like that.

[Andy from Sandy]

It should be quite safe to have a tiny bit of negative pitch on the blades and be spooled up whilst on the ground. You may need to trim the rudder to stop it from trying to turn the model.

It is then possible to check cyclic to see the servos are working correctly. Then one final quick look round before lifting off.

Obviously the normal preflight check is carried out on the bench before the model goes live and then check fbl controller is working correctly with model live with throttle hold/motor off.

[wrench567]

It is important to keep the heli level while initializing the FBL. If it was tilted back a little it would take off forward on spool up.
After I initialize the heli with TH on I grab the head in the center of the head block with the grips in my hand and tilt the bird nose down, nose up and left and right. You can feel the grips move in your grasp and that puts pressure on the servos. I found a bad stripped out servo arm that way.
I feel your pain. I drove my 450 full speed into a dirt embankment because of a bad servo that was previously crashed. The worst part is that I always take apart and inspect the servos after every crash. I must have missed a cracked gear that finally failed in flight.

Pete

[bad007]

Originally Posted by sleeperaus

Thanks for replies all.

As I said though I checked everything thoroughly before I even took it to field (and again on ground before turning off throttle hold), so am very certain the setup was fine and the servos were responding and moving correctly.

I'll try the Spool up with no Blades and giving tx inputs next time though to see how that works.

What frequency do you have the servos set for?
Also make sure you read post 5
What Sat and binding procedure did you use. Do it wrong it may seem to work but fail to stay linked.

[im4711]

a servo failure after spool up is hard to identify upfront. If servos respond OK after arming the machine then I simply trust them to do so in flight.
Once you spool up there is not much room for tests/checkups. However during spool-up I do watch the rotor disk and swash plate as well as tail before I lift off. If an issue show's at spool up you have to have the finger on throttle hold.

[Chargersforlife]

When in doubt, do your usual pre flight checks; Make sure everything is tight etc.
Then, bring her to idle 2 (Mine is set at 100% throttle flat) and give it the beans! I like some pitch pumps, maybe some tic tocs, throw in a loop or two for good measure. If it can handle all that, you should be all set

PS Even with the most thorough pre flight check imaginable, anything can happen in the air. It's amazing these birds are reliable as they are

[bundydeity]

Originally Posted by wrench567

It is important to keep the heli level while initializing the FBL. If it was tilted back a little it would take off forward on spool up.

I didn't think that was true - i thought you could initialize in any orientation/angle and it would be fine

I thought the key was do not move it during the initialization process?

[seefest]

Originally Posted by bundydeity

I didn't think that was true - i thought you could initialize in any orientation/angle and it would be fine

I thought the key was do not move it during the initialization process?

You're correct. I know some guys that would initialize the helicopter on its side.

Some FBL units with rescue need to be level on initialization though.

[mqowen]

Originally Posted by bundydeity

not sure its a good idea to sit on the ground at high headspeed for too long. best to take off.

if you need to test it, remove mains and tails and go to your highest headpeed, move the sticks around and check for proper, smooth movement.
it is likely your elevator servo was failing and finally died.

edit: if they are MG servos, you could also apply a little bit of pressure with your finger to simulate a load whilst spooled up on the bench with main and tails removed and see how it responds

I feel that is good advice. Pop it up in the air a few feet a good distance away.