Violent Cyclic Wobble after a minute of smooth flight

[ToddMcF2002]

Never seen this tendency before. I maidened my 250 today and all was well in normal and 80% flat. After about a minute it starts shaking hard enough to reset the Microbeast. I found this link that sounds very similar to my issue:

http://www.rcheliaddict.co.uk/beastx...th-wobble.html

Anyone experience something like this? My cyclic pot is sitting at 12 o'clock. They all are.

Thanks.

[myxiplx]

Sounds like too high gain on the main rotor. I've not worked with the Beast, but maybe dial the gain pots down a little.

[lahannsven]

Put the potentiometer 1 for swashplate sensitivity down (counter clockwise).

I had also extreme wobble because of torque tube front gear drive not fitting exactly with main gear drive.

Another failure is when the motor runs longer or hot. Then the frame vibrates more.

In total the 250 is a very sensitive baby and I much more prefer the 450 or bigger.


Sven

[ToddMcF2002]

I'll turn pot 1 down to 9 o'clock and retest. When its no wobbling it is extremely smooth and the tail/cyclic feels great.

[pgoelz]

Note that at least on some versions of the BeastX (for example, the Hobby King and BGL versions), the pots are described in the manual and marked BACKWARDS.... counter clockwise = HIGHER. Make sure you are actually reducing the cyclic gain when you adjust the pot

I have also found that slow servos or a controller configured for less than the servo's maximum frame rate can cause instability, especially at higher values of cyclic gain.

And of course, the deadband from any excessive slop will cause the system to hunt (shake).

Paul

[ToddMcF2002]

Thanks. This is a genuine MicroBeast so the it should match my AR7200BX's on my other helis but I'll double check the documentation and go through the setup again to ensure the frequency is correct. It has stock 415's on it for cyclic and an MKS DS95i on the tail.

[pgoelz]

If the clones have reversed pots, I'm wondering if what they cloned also does? It is consistent across two firmware versions and from two different vendors and if you aren't aware of it, you will think that "reducing" the cyclic gain isn't helping. .

Are you positive the issue is the controller? I have had massive vibration issues with my used 250 since I purchased it but they were pretty clearly main rotor vibes. I have now resolved them, but it was a struggle. At one point it abruptly transitioned from smooth flying to vibrating so badly the magnetic front half of the scale fuselage fell off

The key is frequency. Controller / servo / slop issues will cause shaking that you can see. Main rotor vibes, even severe, will just be a blur.

Main rotor vibes can contribute to controller shaking, but I suspect they will not if the rest of the system is stable.

Also, make sure that any significant mass is well secured. The battery in particular.... if it is able to wiggle it can add a pendulum effect that can de-stabilize the system.

Don't forget the tail. It is my belief that a sloppy tail can induce cyclic instability as it hunts around either side of center since its thrust line is not coincident with the main rotor.

Paul

[ToddMcF2002]

If the pot doesn't alter the behavior she is getting a full tear down and I'll probably switch to my IKON. I don't know if it is mechanical, but given if flies perfectly for 60 seconds before doing the shake routine it suggests the FBL is acting up. The link I put in the OP post is pretty dead on what I'm experiencing.

Everything is secure. I've got a bit of build experience so its not something super obvious like a bent feathering shaft, tail vibe induced FBL vibe, main shaft or blades out of balance.

Less drastic things I'll try first:
I'll move the Microbeast FBL out of the frame to the side and use a better mounting gel tape. If it still vibes I"ll swap out the servos starting with elevator in case the servo motor is failing, which would cause the Beast to go psycho trying to compensate.

[pgoelz]

I don't use vibration absorbing tape on any of my three BeastX installations. If the vibes are minimal, you don't need it. And with fairly thick tape, you can actually make things worse if the wires hanging off the end of the BeastX are inducing movement.

Either something is changing, or you are on the edge of instability and it falls over the edge during the flight. Kinda like tail wag.... it can be perfect and then something perturbs it enough and it starts wagging and won't stop. And of course if you moved the pot to a HIGHER gain setting thinking you were lowering it......

Try moving the cyclic gain pot to the 9:00 position. In my installations, that is a bit soft but far below the point of instability. Be careful on liftoff after changing the pot in case it is a little too undamped.

Also go back and go through the collective pitch range and then the 6 degree pitch setup..... in that order. They may interact, and it makes more sense to do the collective pitch range setting BEFORE the 6 degree setting in spite of the way they are arranged if you go through the steps in order per the manual. I don't know exactly what the 6 degree setting does, but it might configure some internal tilt error vs. servo movement parameter. Interestingly, on my 250, the BeastX does NOT confirm that my geometry is acceptable with a blue LED. I have not looked into that yet, but it flies OK. On my 450, the 6 degree point is about in the middle of the blue LED range.

Paul

[pgoelz]

I tweeked the setup on my BGL version BeastX and discovered a couple things that might help.

1. The zero pitch point on the throttle stick is set mechanically after setting the three servo neutral points. The max and min pitch settings in the menu do not affect the zero point. Took me a while to figure out why my zero pitch was always offset slightly from stick center. It was because after setting the servos to horizontal arms, I did not then adjust the three linkages to fine tune the pitch to zero. I thought that would be taken care of when I set the upper and lower collective pitches. Not

2. The six degree setting definitely affects an internal gain setting and interacts with the cyclic gain setting on the pot. This setting seems to be tricky to set correctly because you need an accurate zero pitch reference unless you are measuring directly against the mainshaft. I did not check to see if perhaps the setting starts out at what the controller thinks is zero pitch. If so, you could zero the pitch gauge and then drive it to six degrees.

3. After I was done, I had moved the zero pitch vs. servo arm position a couple degrees so that I actually got zero pitch with the arms level and now I get the blue LED at six degrees. Previously, I did not. A test flight showed that I now had significantly more cyclic gain than before and had to reduce the gain pot CW to the 3:00 position for stable flight.

Paul

[pgoelz]

Originally Posted by pgoelz

Try moving the cyclic gain pot to the 9:00 position. In my installations, that is a bit soft but far below the point of instability. Be careful on liftoff after changing the pot in case it is a little too undamped.
Paul

OOPS! I meant to say move it to the 3:00 position! Ie., LESS than midpoint gain assuming the pot is indeed reversed. Sorry.

Paul

[ToddMcF2002]

I moved the Beast to the side and remounted with Gel tape. Cyclic gain at 11 o'clock (a very minor adjustment) and all is well. Thanks for the help

[pgoelz]

Originally Posted by ToddMcF2002

I moved the Beast to the side and remounted with Gel tape. Cyclic gain at 11 o'clock (a very minor adjustment) and all is well. Thanks for the help

What was the original setting? I'm curious whether your pots are reversed like mine are.

I need to do some testing too.... I have wondered for a while whether the cyclic "gain" pot was in fact gain or perhaps response speed. It would seem to be valuable to be able to fine tune the system response speed.... smaller helis can move faster than big ones.

I saw somewhere that someone makes an auto-tune controller, don't they? That would seem to be the way to go. I can easily see how the controller could analyze transmitter commands vs. heli movement and develop all the proper timings and gains automatically. Like an auto-tune PID loop.

Paul

[ToddMcF2002]

Mine is an actual BeastX Microbeast and pot 1 is clearly documented as cyclic gain. Left to reduce, right to increase. I turned it left slightly.