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HelicopterMain Discussion › TRex 600CF tail bounce
05-25-2017 06:02 AM  31 days agoPost 1
_dloe_

Heliman

Winton, Ca - USA

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I have a TRex 600CF converted to flybarless. I have the AR7210BX with a satellite installed. It is still running the 600L original motor. It flew fine 15-20 flights then I noticed the tail bouncing up and down. I landed and checked it over, but did not see anything wrong with it. I took back off and flew a couple circles and it seemed liked it started loosing power. I kept adding pitch but could not keep it up. It went in on it's side and ended up stripping both of the front cyclc servos and damaging the tail boom. I've replaced the damaged parts. The battery checks out good. I have it all back together, but still have the same problem. My pitch curve is 0, 80%, 90%, 95%, and 100%. I have the Castle Talon 90 speed control on it. Until the tail started bouncing the last couple flights this thing was perfectly smooth! What could be wrong with it?

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05-25-2017 01:18 PM  31 days agoPost 2
dkshema

rrMaster

Cedar Rapids, IA

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My guess is that the tail up/down bounce is relatively slow, not a high-speed vibration that makes the end of the tail boom a blur when you look at it.

If so, this is usually an indication that you are running a head speed that is too slow.

Losing power in flight is not cured by adding pitch, this only makes matters worse as an already over taxed power train gets an even higher load to work with.

You say your battery checks out fine. What did you do to test it?

A pitch curve stated in terms of TX setting percentages means absolutely nothing, as no one knows the actual pitch associated with a given percentage number. That being said, if your pitch curve is as you stated - that is a bizarre curve and shows an improperly set-up heli. Too much collective pitch will lead to low head speed.

If you don't have or use a pitch gauge, now would be the time to own one and use it.

Unfortunately, your Talon 90 does not have a data logging feature that would help sort this out.

Low head speed can be caused by a sick battery where one or more cells discharges at a higher rate than its brothers in the pack. Terminal voltage quickly drops off under any appreciable load.

A slipping motor pinion can cause low head speed as can a slipping one-way autorotation clutch.

Incorrect ESC setup or improper TX to ESC calibration can cause low head speed.

The original 600XL motor - black, non-rotating outer shell with silver bands - is not an ideal motor. It runs hot, has a marginal power output, and is inefficient. Perhaps its bearings are shot. If run too hot, the enamel insulation on the motor windings may have been compromised and internal shorts may occur. I witnessed one seizing up in-flight many years ago from overheating.

Time to figure out which of these brought you down.

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

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05-25-2017 02:47 PM  31 days agoPost 3
Richardmid1

rrProfessor

Leeds, England

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Like Dave said, bad motor (bearings seizing or burning out) or battery. If you are sure the battery is good and it's charging and balancing well I would first put a few drops of oil on the motor bearings but it maybe past that now!

IF the motor checks out ok, the next thing is to look at the setup although that would require having it looked over by an experienced heli pilot. Taking it to a heli specific shop or heli specific club would be your best bet. You may have too much pitch and not enough HS, the gear mesh might be too tight etc etc.

60% of the time, it works every time!

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05-25-2017 03:15 PM  31 days agoPost 4
_dloe_

Heliman

Winton, Ca - USA

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Thanks for the quick responses! I mistyped that. That is my throttle curve not pitch. My pitch ranges from -3 to +12. The motor is the old 600L original that came with it I believe.

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05-25-2017 03:40 PM  31 days agoPost 5
Richardmid1

rrProfessor

Leeds, England

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My pitch ranges from -3 to +12.
But 0 at center stick though right?

60% of the time, it works every time!

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05-25-2017 05:41 PM  31 days agoPost 6
_dloe_

Heliman

Winton, Ca - USA

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Yes that is correct. 0 at mid stick.

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05-26-2017 05:29 AM  30 days agoPost 7
_dloe_

Heliman

Winton, Ca - USA

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So what could cause a vibration in flight? It started out flying perfectly smooth then toward the end of a 5 minute flight I noticed the tail bounce. I'm not saying I have a lot of experience but this helicopter flew especially nice. The guys with a lot of experience at our field even commented on it. Maybe the motor just getting weak?

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05-26-2017 01:02 PM  30 days agoPost 8
dkshema

rrMaster

Cedar Rapids, IA

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I gave you a laundry list of possibilities. Instead of eliminating them one by one, you ask the question all over again.

If what you see is a relatively slow, bobbing or nodding, figure out why your head speed has dropped off.

If the flight starts off OK and the nodding shows up as flight time goes by then the first item on the suspect list is the battery.

If it is a higher speed short amplitude oscillation, you most likely stuck the tail rotor into the ground on a tail first landing and bent the tail rotor shaft. The skids would most likely vibrate fast enough to be blurred when looking at them in a hover. This would be present throughout the flight.

But you say you're losing lift and compensating by adding pitch. Sounds battery related.

And since you're looking for even more reasons, check out your FBL controller mounting tape and decrease the elevator gain.

I suppose there is an outside chance your elevator servo is weird, but I think that would show up as other controllability problems.

The guys at the field "with a lot of experience" - if they really DO, should be able to help you figure it out quickly if you're willing to ask for and heed their advice. Otherwise, they may not be as experienced as you believe.

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

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05-26-2017 03:32 PM  30 days agoPost 9
Flyin for Jesus

Senior Heliman

Dana Point, Ca. 92629

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I agree with dkshema on this one. Its okay that you don't have a lot of experience. Your original post kind of shows that because of the lack of specific details. However, if you knew what specific details were important to note, then you'd probably be able to fix it without our help.
Anyway, What sounds like to me is that your headspeed has dropped which would cause you wobble you speak of. ( it would wobble in the aileron direction too but its not as easy to notice because the heli is narrow ) Then you mentioned it basically falling and crashing. So, my guess is low headspeed.
The most common cause of this is going to be your battery packs. With age, the Internal Resistance ( IR ) will rise. What this does is you'll fully charge your packs to 4.2V per cell then go fly. During the flight, since the IRs are high, when the heli needs a lot of power, the packs can't do it so the motor performance drops. You then land and check the packs and your meter shows that you have something like 80% left in the packs. So, most people then start looking elsewhere for a problem since the batteries seem fine.
As you get further into this hobby, there are gizmos that make troubleshooting easier, but everything costs $$$.

Easiest way to check your packs, switch packs with a friend that has a pack that works well. if your pack won't fly their heli but their pack will fly yours... then you need a new pack. I have a charger that tests IR while charging so I can know how my packs are doing long before they fail in flight.

If you don't know anyone that can give you a hand locally, send me your pack and I'll throw it on my charger.

Good luck with the troubleshooting.

Dan

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05-26-2017 08:29 PM  30 days agoPost 10
_dloe_

Heliman

Winton, Ca - USA

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I have the I-charger 4010. It shows an IR range between 1.9 lowest and 4.0 the highest on both of my packs (which are new, purchased for this heli). I had already tried different batteries on it with the same results. I've replaced everything but the motor and the flybarless unit. The guys at align already checked my esc settings too. (I sent them a copy from the Castle app on my pc). When I run it with no blades attached there is no vibration. I've balanced the new blades with info from this website. Weighed and checked the cg of the new blades. This was all done before I posted on this site.

Sorry guys, I didn't mean to disregard anything you all said. I'll get help somewhere else... I did not mean to waste anyone's time!

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05-26-2017 09:22 PM  30 days agoPost 11
Flyin for Jesus

Senior Heliman

Dana Point, Ca. 92629

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Blades out of balance will not show the tail bouncing up and down. It will show a vibration in the tail fin itself but going right to left at the bottom of the fin. It does thing because the boom is heavy and reaches far out from the CG of the heli. The fin vibrates because the heli actually rotates right and left a lot easier so the tail fin itself vibrates on that same axis.
Since your pack IRs are fine, 1.9 to 4 is good, Then the Headspeed had to drop possibly the ESC overheated and shut down. Just a guess.
Again, good luck getting to the bottom of it.

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05-26-2017 10:50 PM  30 days agoPost 12
Heli_Splatter

Elite Veteran

Silver Spring, MD by way of Sidney, Ne - USA

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It would help if you posted video, I would agree with the others... a low head speed is causing the problem. Have you measured the head speed?

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