Trex 500 help needed

[RotorBlade]

Guys, I bought a used (very good condition) Trex 500 running stock with nanotech 2650s. From the off, it did a very occasional tail bob - just one at a time, usually in straight flight and only one time, twice during one battery. Usually, it doesn't do it at all. Today, putting 3 batteries through it it did it once, after a couple of minutes of the second battery.

After the first few times, I switched the elev servo with the aile and it seemed to stop. Not trusting 'luck' I bought a new servo and fitted it to the aile (where the old elev had been) and flew a few times without issue. Then Saturday morning - bob was an uncle again, not Sunday or Monday, but again today. Couldn't tell for sure whether it's always the same battery (just thought of that) - but has anyone got any experience of this, or suggestions as to the cause.

Thanks in advance
Keith

[J-S-Q]

Possibly a slipping belt? Did you notice which way the tail kicked? If it went nose left than the slipping belt could be a possibility.

[Si Goodchild]

Nah, it's a definite nose up / tail down "bob". I thought it was a twitching rear servo, but Keith seems to have eliminated that. His radio setup is a 2.4GHz System by BuzzFlyer and I don't think that system indicates a temporary loss of signal like Spektrum does. I've seen a really bad twitch out of this heli and told him to get it on the ground asap. Beats me. Perhaps a static issue? Can't see how the Esc "coughing" would cause a twitch in the elevator channel.

[glenflyer]

Hi How bad is it it could be just low headspeed my 500 dose it sometimes in normal switch to idle up and its gone seen a few do it depends how bad it is Richard

[Si Goodchild]

Could be worth adding a few % to the throttle curve, but it's a very occasional "twitch" rather than a "nod"

[unwind-protect]

I thought nodding 500's was a common problem, generally related to low head speeds and/ or too tight (too loose) blades?

[Smoothound]

It is normally linked to too low headspeed. 500's seem very finicky about the "right" minimum headspeed. I'd try winding your throttle curve up a bit at a time to see if it improves before spending anymore money

[RotorBlade]

Thanks for the suggstions chaps. I don't think it's hedspeed though. I've had that problem with smaller helis including a 450 and I know the symptoms. This just happens once or twice in say 6 batteries, not as a symptom of every flight. The only extra factor I could add is - and I cannot be sure of this, it seems like it happens after a turn upwind. Today I flew upwind & downwind 8s for 3 x 4 1/2 minutes and it happened once - a snap, tail down 'bob' as Si says - full recovery and barely a noticeable flight-path disturbance: like a sneeze.
Mystified

[pgkevet]

Low headspeed, worn dampers, one grip tighetr than the other or a loose/binding seesaw screw

[rexflyer]

i had similar but it was bad found out the head bolt was loose on the main shaft and also discoverd a couple of ball links were loose on the mixing arms.that was my problem anyway worth checking yours though.

[RotorBlade]

Good thoughts again guys - thanks!
The one that sticks out is the differing blade grip tension. I'm using the 3D Pro blades from GCod and whilst they fly well, one does feel slightly tighter than the other in the grip, no matter how tight the bolt is - it binds slightly. I have the CY blades that came with the heli (didn't want to risk them - hence the 3D Pro) but I could re-fit them and see what happens. I'll revert. Keith

[sacko]

Thats pretty normal.

Sand a some of the gel coat off the root of the blade if needed.

[Smudgyboy]

I could be your one way bearing on the way out, I had a similar problem. Worth a look.

[sacko]

have you checked the head bearings and dampers? That is where I would start.

[RotorBlade]

Thats pretty normal.

Sand a some of the gel coat off the root of the blade if needed.

Root of the 'fat' blade is 0.5mm thicker. I'll deal with that - don't think the heli has seen enough action for dampers or bearings, it's almost new, but that's where I'll head if this doesn't fix it. Cheers, Keith