Blade 400 + JR DS3400G = tail flexing?

[BKF]

I decided to try upgrading my tail servo to the JR DS3400G on my Blade 400. Being bigger than stock, it was a little difficult to get mounted, but it's in there.

After reconnecting the linkage rod and firing it off, I see that in the extreme travel of the servo, it actually pulls & pushes the end of the tail boom. Basically the servo is strong enough to flex the end of the boom when the tail rotor linkage runs out of travel. I though the travel adjustment in the TX would allow me to limit the travel of the rudder servo, but it just seems to affect the speed of travel.

Figuring I'd just limit my rudder interaction, I took it outside to fly. When I cycled it up, the tail started to violently "wobble" the boom side to side while it was still on the ground. It didn't seem like a vibration wobble, but more the servo making the tail rotors pitch one way causing stress on the boom, then immediately back the other, etc... causing the tail rotors and the end of the boom to flex side to side. The main heli (http://www.rcuniverse.com/buynow/keywordclick.cfm?bid_id=4726) stayed put.

I figured maybe the gain was set too high compared to running the Spektrum DSP75 I had on their previously. I dropped it down from the 85% gain I had down to 66.5%. Same thing. Then I dropped it down to 55% and it got a lot better, but the tail isn't holding well... but it's not going out of control, either. I've got a GY401 servo I'll be adding next, but I like to add things one at a time so I'm not trying to figure out 50 things at once.

I previously finished mounting 3 HS65MG servos and those seem to be working pretty good now (during initial testing). Now I moved onto this JR tail servo and am having this wierd wobbling.

If I can't adjust the servo's travel in the TX, should I be doing something with the actual linkage? Making it shorter or something? Right now with no pitch to the rear rotors, it's sitting at 90 degrees, like stock. Unfortunately, this servo seems to have a lot more forward/backward travel than stock, so it's causing trouble.

What am I doing wrong?

[carlo_the_wonder_frog]

Your not doing anything wrong, the stock gyro is not a very good one. First have you set the gyro to digital mode? the 3400G is a digital servo and is capable of the faster digital mode the gyro can provide. If you continue to run the heli with the tail binding like it is then it will quickly burn up that nice new servo. what you need to do is limit overall travel. this can be accomplished by moving the tail rod link closer to the center of the servo horn. you will probably need to drill a new hole in the servo horn to accomplish this. doing this will also give it much better resolution as the total travel is smaller, but there is still the same amount of discrete steps on the servo.


You may also be experiencing some tail rod link binding, when you have it removed from the servo it should not take much force to get the tail pitch to change by moving the rod back and forth, if it binds that will cause alot of hunting issues.

[BKF]

I moved the linkage rod down to the innermost hole on the linkage. Now, however, I think I mounted the servo too low because it flexes the linkage rod downward on extreme forward/backward travel. I need to mount the whole servo up higher one hole.

Also, the GY401 seems to have a travel limit pot on it. I turned this down, and it seemed to stop the flexing issue... But a couple times for no reason the whole heli shook violently, starting with the tail. I'm wondering if I have the belt too tight. I tightened it, before mounting the gyro, thinking it might be the cause of my hunting issues with the previous gyro.

I took it for a few minute flight earlier this evening in between rain showers, but the wind was too darn bad. I was hovering between a few inches and a couple feet off the ground and it was holding a lot better than I've ever seen it, but I'd feel & hear the wind gust and the heli would drop a foot... but the tail held pretty well. There was a couple times it drifted a little bit to the right.

I still have to figure out the GY401. It's a lot more gyro than the G110. After flying, it started double flashing, which apparently means it lost the neutral position of the rudder. I haven't followed the step-by-step procedure for setting it, so that's my fault.

[sokal]

i had a few issues with the set up of the 401 .
carlo said that i should use NO subtrim just mechanical center on the slider and also rebind, after i falowed his words and like magic perfect.
i have 0 subtrim and 0 trim and my gyro rate is at 70%.
then adj the limit so each way you move the servo it comes with in a hair line of the end or when the servo binding stops
also 0 on the delay
make sure u do the limit check in standard rate
thier is a post i put up on that subject were carlo helped me may have more help

[BKF]

I went flying this afternoon in the fenced yard area at work and had a very slight right yaw issue. The tail, however, was a lot better than the G110 ever was... even with the yaw issue.

I took the bird home, moved the servo up, adjusted the linkage rod, switched the gyro into rate mode and centered the rudder. Then I adjusted the pot on the GY401 so it limited the travel so it wouldn't hit either side.

Then I took it outside, per the gyro directions and found the rudder's mid position. Then I landed, switched it into AVCS mode, and started bumping up the gain. No more yaw.

It was dark out, so I wasn't able to spend too much time with it, but I think it's getting pretty close, now.

However, I think my belt was too tight and causing some of the funky tail vibration. I loosened it up a bit and then took off the tail rotor housing and found the belt showing some odd wear on one side of each belt "tooth". Also, there appeared to be a bit of fiber like material massed in the rotor casing halves. I'm guessing this was because it was too tight and started eating up the belt.

Hopefully when I fly tomorrow (if it's not raining or windy), I'll finally see what I've been waiting to see... A totally stable and locked in tail.

[carlo_the_wonder_frog]

Replace your belt as soon as possible, don't wait for it to pull apart and cause a crash. Sounds like its going to fly well now that the gyro is upgraded.

[maxxteezy]

the b400 has a sloppy tail. No matter what g-ro you use, its gonna wag and chase. Leave the stock one on or slap on a trex tail if you want a better tail. If you put a better gyro on it, its just gonna wag more tryna adjust to the tail slop.

[sokal]

im sure u think that mine does not move at all no mater what full climb and desend wind or not solid