View Full Version : 90 deg. rotation on punch out
10-14-2008, 09:30 PM
About two weeks ago I developed a new problem.
Symptom 1. When ever I do a medium throttle punch out the heli rotates about 90 degrees CCW.
Symptom 2. Often when I am in forward flight and do a banking turn to the right (I have not noticed it ever happening to the left), the heli does not respond right away to the rudder input and tail continues to go straight. Then after a delay it comes around.
Symptom 3. When entering a flip the tail does not hold. This puts me in an unexpected orientation, and resulted in a crash.
I am measured my headspeed at 2800. Flying pro woodies, HS65s, GY401, Fut. 9650, DX-7/AR700. The belt, boom, main, feather, and tail shaft are all new. The tail slider moves very freely, the gyro moves the tail back and forth when I rotate the heli, the heading hold appears to work, I can take my hands off the left stick and it holds for ever. The tail pulley seems to be holding strong, the tail servo seems to have plenty of torque (I held resistance on it while slowly moving it with the radio),
That is all that pops in my head right now that I have tried, I'm sure there is more. But I am running out of ideas. Has any one seem this, or have any suggestions what else to try. I am running out of flying season and need to get this thing back in the air..
10-14-2008, 10:37 PM
Post your Throttle and Pitch curves
10-14-2008, 11:39 PM
i had a 502 gyro on a 90 and it did that. it was a bad gyro. i was lucky and didnt crash it before i figured it out.
10-15-2008, 09:04 AM
I only fly in idle up 2 (idle2, stick slightly less than 50%, turn off th. hold, let soft start spin it up, take off...)
10-15-2008, 11:58 AM
i had a similar problem, the only difference was i had 180 turns......
it turned out to be the belt slipping!
check for it's tension
10-15-2008, 12:08 PM
I tightened the belt and rotated the main gear slowly while keeping tension on the tail, just in case some of the teeth were not gripping. I could not make it slip no matter how hard I tried. I am thinking that "gone cold" might be right about the gyro. But if I hold the heli with the nose facing me, and move the tail left or right, the tail pitch changes accordingly. And if I hover, it seems to keep its heading?? So it looks like the gyro is working??
10-15-2008, 12:12 PM
Low headspeed due to bogging??? What motor and what pinion?
10-15-2008, 12:14 PM
2800 isn't that high on the Trex. The tail drive was changed to slow down the tail when headspeeds got into the 3K range.
Grab the main hub and tail hub and twist against each other with moderate force. It could be a pulley slipping.
Have you done the Chinese weight mode? A weak servo or too much tail force could show the same symptoms.
10-15-2008, 12:54 PM
I also thought of the tail pulley slipping. And did the test that you suggested main hub and tail hub. I put pressure on both all the way through the length of the belt in case there were theeth missing or loose that I could not see. Also grabbed the tail pully with pliers and tried to turn the lower gear and it would not budge.
I don't hear any noticable bogging of the head. It does not take full throttle to make it spin out. I am running 12t with the stock V2 motor. I used to run in normal mode as low as 2500 and I never had this problem, so my head speed is way higher than it used to be. Also I do not have to have any increase in head speed or pitch. If I am flying straight and go into a right bank, sometimes the tail will not respond to the rudder input. In that case I did not increase the pitch or throttle.
Thanks for the suggestions so far. And if you have others, please keep them coming. I have a friend that is willing to let me try his 401, I think I will give that a try too.
10-15-2008, 12:57 PM
Oh, I forgot to comment on the Chinese mod. I have not done that. But I don't think that is the problem. I have pressed against the servo and it seems to have plenty of torque. I am not a strain gage so I don't know exactly how much, but it feels very strong. And like I said, it happens on slow casual flight too, when there is not much stress on it.
10-15-2008, 11:49 PM
i just went through a similar issue. i had just upgraded motors (put on a scorpion HK2221-12) and overpowered my tail setup.
i moved the ball to the outermost hole in the servo horn and that did the trick. no more blowouts on hard punchouts. and, this with the 'antiquated' 401/9650 setup and no chinese tail mod.
10-16-2008, 12:15 AM
I had this problem on my 500, and the solution was the tail servo placement. I had a hard landing the flight before and the servo had moved down the boom. Check to see if the tail linkage geometry is as it should be.
10-16-2008, 05:53 AM
The tail servo is giving full travel in both directions to the tail slider, it goes as far as it can with out binding and then centers after a few quick back and forth strokes. So I think that is OK. And I have not changed the motor (stock V2 motor) or the placement on the servo horn. It has been flying like this since the beggining of last summer. Is it possible that a gyro just gets old and flaky?
Like I said before this is not just a punch out issue, it looses control of the tail in nice easy forward flight and a simple turn. So it does not seem to be a high torque or head bogging problem.
10-16-2008, 07:40 AM
If it looses it in slow flight I would say it is a Gyro issue....
Try the different 401 and let us know
10-16-2008, 07:46 AM
Probably already said before one of the following can be slipping:
- pinion on motor (I use a CD mark and draw a short straight line of 3mm across the centre of the shaft and pinion, if they are out of line then the pinion is slipping)
- one way slipping (stick in a spare main gear with new bearing and try, the new SE blue main gears are always round now and do not require the mesh to be set each time so it's an easy try)
- front tail pulley slipping (same straight line marking trick)
- Tail pulley slipping (no easy way to be sure but to replace)
Try also moving the tail servo ball in if possible. It may not have enough torque to fight the tail (possible that gears are worn too). I have play in my tail slider which I know is coming from a worn S9650
- Swash slipping (I had a the similar tail holding issues just before my swash came apart, no easy way to check unless you have a spare swash)
10-16-2008, 08:26 AM
OK, this first one is going to sound dumb, but I did it, and it produced similar symptoms. I flew 3 packs the other day, without figuring out that my gyro switch was in normal mode instead of heading hold. I came home to figure out what was wrong with my tail setup! It wouldn't hold under any kind of torque, and kept showing these weird heading changes that we're really messing with my flying. I figured it out later at home, DOH! I never touch that switch! I'm probably going to program it for HH in both positions! Anyway... sanity check. make sure its in HH mode.
Second, the chinese weight mod is a good thing. The force it eliminates is NOT just in high power situations. Its ALL THE TIME. whenever that tail rotor is spinning, your servo has to fight the CRM centering force, to hold pitch. Even if it doesn't fix your problem, its a good thing.
You said your tail servo: "... goes as far as it can with out binding and then centers after a few quick back and forth strokes."
A few quick back and forth strokes??? That sounds bad. Does it do that if you hook it directly to your radio (no gyro)? If so, it may be time for a new servo.
Edit: And, if it only does the centering "overshoot/hunt" when connected to the gyro, it sounds like your gyro has a problem...
10-16-2008, 11:35 AM
Trex888. I will try some of those test when I have a chance. Most of the items I have tried, but not the test method that you described. So I can retest them with your methods just to double check.
markb. No sugestion is dumb. (or sounds dumb). I did make sure that I was in heading hold. Both on the radio and I get the red heading hold light on the gryo. And I agree that the Chinese mod is probably a good thing and I might do it. But I don't think it is the root of this problem. These components have been working perfectly together for a year and a half now. So I want to fix what ever component has gone bad. And the "centering after a few back and forth strokes" is a function of the gyro. If you give it full left and right rudder three or more times rapidly, the 401 will center the servo when you let the stick return to neutral rudder. It helps you to know how to put on your servo horn at 90 deg and center the tail travel.
10-16-2008, 12:06 PM
any theory yet????
10-16-2008, 12:42 PM
My theory is that my gyro is going bad. But it was raining last night so I could not prove it. Tonight I am going to the LHS to see if they have a decent deal on a gyro. If not I will be ordering one. I still have the option of borrowing a friends, but that ,means him taking it off of his heli and since I am about to build a 500 any way, I might as well just buy one. Then if it is the problem, I will have to get one to put on there permanently.
10-16-2008, 08:42 PM
OK, so tonight I was able to borrow a 401 and try it out. Same thing. Rotates 90 CCW on punch out. And when making a right turn the rudder does not respond about 20% of the time for about 1/2 of a second.
Here is my thinking...
1. Forget the punch out.
2. Slow forward flight, only 1 out of every 5 passes, only when turning right.
3. Since it is slow and no sudden burst of throttle or change in pitch, it is not bogging the head.
4. Correct me on this if I am wrong.. looking down on the heli, the mail blades spin clockwise. So a right turn should be easier than a left, because you are asking the tail to resist the inertia of the mains less.
5. If a right turn is easier (by my theory) what would make the problem only show up on a right turn? Wouldn't that eliminate something slipping? Slipping would appear when there is more stress on the system not less.
6. That leaves what?? Binding in the tail shaft? It is smooth as can be, and the tail is brand new so I know it is not bent.
7. Binding in the pushrod, it seems free.
I just don't get it..
10-16-2008, 10:20 PM
Bad tail servo?
10-17-2008, 02:16 AM
Right turns are harder. The clockwise main rotor causes the heil to yaw left (Newton's 2nd law). The tail thus has to push left (i.e. apply right yaw) to fight this.
I still think your servo hole needs to be moved in (unless the servo is crapping out). Or that your gain on the gyro is too high and is fighting the servo too much on right turns.
On my Protos I had to replace the S9257 with a much stronger S9254 to eliminate a shudder that appeared in right hand turns only. Moving the hole in one and reducing the gain on the S0257 did help but not enough to eliminate completely.
10-17-2008, 05:58 AM
I have a new tail servo (9257) on the way from RedyHeli. But in the mean time, I could move the ball in. I have nothing to loose by trying it. But it has been flying perfectly where it is for 2 summers now. So maybe it is going bad. I can use the 9257 for diagnostics, but it is supposed to land in my 500 that I picked up last night.
Has any one tried the servos that come with the DX7 kit? I have 4 of them just sitting there.
10-17-2008, 06:51 AM
Try any servo. In slow flight it will be fine. It should tell you something and not swing out 90 deg.
Make sure of the mode you are in with the gyro
10-17-2008, 02:41 PM
Does the tail servo and gyro seem to work normally on the ground?