Nasty "bobbing," possible causes?

[warpspeed]

While I'm waiting for more Trex parts I've been trying to get my previously unflyable Rotofly working, with some limited success. It finally has enough power to get off the ground into a hover, but right from spool-up the heli starts to "buck"-kind of like a wag, but vertical, and it looks like the whole thing is pitching up and down rather than just the tail. (Not up and down in altitude, but the nose dips/tail comes up, tail dips/nose comes up type of movement) Hard to describe, but it's pretty violent and within seconds is bobbing faster than Monica's head at the Clinton hotel. I've completely disassembled everything and the main shaft is true, the flybar is balanced and paddles are at 0 deg, there's no binding or excessive slop in any of the linkages, and while the main rotor blades aren't perfect (couple of small nicks in the trailing edges) they seem to be tracking well enough.
Has anyone experienced this sort of behaviour before? Is there something else I should be checking?

Thanks!

[wren1702]

Sounds like the headspeed is too low. Is that a fixed pitch Heli?

[warpspeed]

Yeah, it's fixed pitch, about the size of a BCX. Like my Trex the thing has given me nothing but problems but size-wise it's ideal for indoors so I keep plugging away with it- even though I've been tempted to introduce it to my friend Mr. Sledgehammer.
I think the headspeed is ok since it seems to have more than enough power, but I suppose it could always use more!
I'll see if I can't get video of it this afternoon, maybe that would help with the diagnosis....

[Jermo]

:( don't sledge your T-Rex just yet. Have you heard of RADD? http://www.dream-models.com/eco/flying-index.html , do you have a simulator? learning on a sim is ALOT cheaper than trying to learn with a heli. There's still a difference between flying a sim and the real thing, however, most crashes by inexperienced pilots are likely a loss of orientation (basically you don't know what to do with the heli pointing certain ways so it crashes).

You'll want orientation and control to be reflex/2nd nature before you really get out and fly... just my 2c your results may vary, void where prohibited, not valid in the state of MD. ;)
Jermo

[warpspeed]

Hee hee, if the Trex ever had any idea just how close it's come to being stuffed into the meat grinder it would have packed up it's parts and moved to a friendlier climate long ago!
Anyway, I've gone thru Radd's, the EHBG, and seen most of Bob's vid's at least 3 times. I may invest in RF G3, but I'm still up in the air about that. I most definitely get disoriented though, 'course in my case that's normal. :oops:
I do have hovering pretty much down pat in all directions, but this Rotofly has got me stumped. When you see the vid you'll see what I'm talking about.
I'll have it posted here in a bit....

[Jermo]

mmm.. $200 for G3.5 or $200 in frustration and repairs.. of course you could just fly FMS and spring for the $30 tx interface...you can learn the same orientation/leveling without all the frills. Had my lovely bride not surprised me with the G3.5 I was already searching for the FMS interface online.
Jermo