Elevator 'seesaw' effect?

[trillian]

I have been flying with a BeastX rev 2.0 on my Trex 500 now since the middle of the summer last year and in general if works very well but something still annoys me a little bit.

What it does is that there is a strange feeling on the elevator at times where it's like a seesaw back and forth type oscillation. For example when flairing to slow down from forward flight it will seem to over cook the flair and then the natural reaction is to counter it and it ends up in an un-natural springy movement. This also shows in hovering. It's like it gives too much in one direction and then when you compensate you get too much in the opposite direction and the result is something a bit like the way people look riding a unicycle.

It's not easy to describe.

In forward flight it doesn't happen and it is a minor thing regardless but it is annoying.

I have the BX in transmitter mode and use 30% expo in the TX (DX7) 93% travel adjust.

The gain pots are at the default 12 o'clock settings. I did try once turning the swash gain down slightly but that didn't help.

Any ideas? Should I try increasing the gain pot?

[Steve]

FAI chaps (with flybars) get rid of this porpoising effect by adjusting the position and shape of the horizontal fin.

[trillian]

FAI chaps (with flybars) get rid of this porpoising effect by adjusting the position and shape of the horizontal fin.

It's not a porpoising as we usually know it, ie; in FF flight. When flying the aero stuff this doesn't happen, it's only in a hover or low speed or slowing down into a hover from FF flight. I don't know how else to describe the sensation.

Maybe I should reduce the elevator expo and then reduce the travel if it's too quick. It's like a spongy springy thing where for a sec you're fighting it a bit, like it's moving too much and in compensating you end up getting it swinging back so you have this nose-up then nose-down when it should have been a gentle return to level. It can happen in a hover as well making it almost impossible to sit still.

[Dan22]

When i first converted my ESP to FBL i had found the elevator was very twitchy an similar to what you are describing, i had the standard Align carbon flybarred blades on so then swapped to the 3G's and haven't had a problem since.
By the way i'm not impressed with my standard Align tail blades and you mentioned you changed yours for the KDBB ones, did it make a big difference?

Dan.

[Varelco]

What is the headspeed and dampening in the model?

If the dampers are too stiff then you will get this rocking effect as the lift produced by each blade differs as it spins parallel over the boom. Is amplified by lower headspeeds, it may be this?

[trillian]

When i first converted my ESP to FBL i had found the elevator was very twitchy an similar to what you are describing, i had the standard Align carbon flybarred blades on so then swapped to the 3GX and haven't had a problem since.
By the way i'm not impressed with my standard Align tail blades and you mentioned you changed yours for the KDBB ones, did it make a big difference?

Dan.

Yeah one of the first things I did was change the tail blades. I had the stock black plastic ones when I first got it and the KBDDs were a big improvement. At first it was flybarred and I was using a GY401, the tail servo is a DS650. The tail has always been rock solid.

I have the Mavvrik G5 blades right now and before that I had the regular flybar version Align 425Fs and the Mavvriks felt just that bit more stable and just seemed to work so I haven't tried anything else.

[trillian]

What is the headspeed and dampening in the model?

If the dampers are too stiff then you will get this rocking effect as the lift produced by each blade differs as it spins parallel over the boom. Is amplified by lower headspeeds, it may be this?

What you're describing sounds like nodding from stiff dampers at too low a headspeed, this is not nodding. It's an RJX head and I got it 2nd hand so I don't know what the dampers are but in any case I think this is something entirely different.

[Dan22]

Trillian
I have just been looking in the BeastX manual page 21 and it says that if you alter dial 1: Swashplate-cyclic Gain, if gain is too high then helicopter will feel soft in flight and tend to oscillate on the elevator axis. I thought it was Dial 2 that needed altering but as you say though as its not effecting forward flight then you could try altering Dial 1?

Dan.

[trillian]

Trillian
I have just been looking in the BeastX manual page 21 and it says that if you alter dial 1: Swashplate-cyclic Gain, if gain is too high then helicopter will feel soft in flight and tend to oscillate on the elevator axis. I thought it was Dial 2 that needed altering but as you say though as its not effecting forward flight then you could try altering Dial 1?

Dan.

Yeah I also just ran across this thread; http://www.rcheliaddict.co.uk/beastx...x-2nd-pot.html I'm not sure if what they were describing is the same cause and effect as what I'm seeing but it's worth trying a few variations next time out.

The thing is most of the time it doesn't appear to be happening so I have just ignored it but recently it has started to bother me more and if it can be cured with a setting or two it's worth doing.

[Dan22]

Elevator 'seesaw' effect?

Good find that. Let me know how you get on!

Dan.

[trillian]

Just to update this thread. Today I took the 500 out and tried it with the pot 2 turned down about two clicks (roughly the 10 o'clock' position maybe just a hair above 10).

This made it feel like it had too much expo so I brought down the expo in the TX from 30% to 26 which felt like not enough and I ended up at 28% on elevator and aileron. I did not change anything else. This appears to have done the trick. It was very windy so not the ideal conditions to look for subtle things but I was not seeing any of the over control / over correction seesaw that had nagged me before. It seems to sit much better in a hover and in the aero stuff the roll and flip rates seem just as good as before.

[Dan22]

Elevator 'seesaw' effect?

Glad you got it sorted. :-)