I have Been flying for about two weeks. I had it outside and was doing loops and rolls. Well i have a few trees in the yard and i thought that i was going to nail it. I cut the juice off and realized that i was behind the tree. I powered up but it was to late. It landed perfect but hard. Well I replaced the main shaft, blade grips, bearings in the main shaft, center hub, tail motor, and tail shaft /gear. There was nothing wrong with the tail motor but i replaced it anyway. When you bring it up to a hover it is ok. Well if you throw it fowards fast and catch it, when it changes from foward to reverse it starts bouncing or wobbling. I am hovering tail in. This may not make any sense. I don't really know how to explain it. The tail boom starts bouncing up and down. Before i crashed it was solid. You could throw it foward and then bring it back and it never wobbled or bounced a bit. I have tried everything. That is why i put the new tail motor on. Someone mentioned that the headspeed was low and the tail was pulling to much juice. It comes up to hover fine and it flies around ok but the wobble causes it to be unstable and dangerous. Please help before i set fire to this thing.

It's probably your dampers too tight.
Where the feathering shaft goes thru the hub there are some o-rings and some tiny shims and some step washers. All this stuff has to be assembled correctly. The tiny shims can make a big difference. I have seen replacement hubs that needed only 1 shim per side, and up to 5 shims per side is not unusual. If the damping is too tight, that is too many shims, or if the step washers are not in correctly, it will "nod" or "twitch" like you are describing.
Also severe blade imbalance will do that but I doubt if that is your problem.

Well it has two shims. I took one out on both sides and the problem gets worst. As i was trying to take it back apart i broke the ball off of the paddle control frame. Going to get one today. I will let you know if that fixes the problem. Thanks for the info. Forgot to say that it had two shims per side. When i fisrt put it back together it didn't have any shims at all. It done the same thing. The tail boom bounces up and down. When i have it in a hover, I push the stick foward and back really fast and the thing starts bouncing. If i barely even breathe on the controls to move it around it does not do it quite as bad. I wish i could video this because i feel like i don't make any sense.

That's weird. Never heard of that happening, did you get the step washers in the right way around?
The shims go next to the o-rings, the step washers go next to the bearings with the step towards the bearing.


And I am realizing that many people don't seem to know that the link sockets are one-way, especially the paddle control pushrod sockets. They will bind and require excessive force to be removed or installed if they are put on backwards.

Yes they are in the right way. I think i need to burn it.

Is it really cold where you are flying? Mine is really sensitive to temperature, if it is below about 45 F it really will nod, it's the material that the o-rings are made of. On really cold days I can even notice it warming up and cooling down at various altitudes in my apartment...It'll nod in the cold layers and stop nodding in the warmer air near the heater.


I'd try some softer o-rings before I threw it on the fire...

Since i put it back together i have only flew it in my room. It is about 70 degrees. The bounce is kinda slow, it looks like a sesaw. I also tried the old o-rings. It acts the same.

Ahh, a slow see-saw like bounce. THat's not dampers, that's most likely a servo going bad. Those s75s will fail in such a way as to lose their sense of "center" and they will wander a bit. I almost lost control of my MX400Pro on maiden hover because of one of those things doing that (they came with the DX6, I was just using them to set-up, never again will I make that mistake).


This diagnosis also explains the fact that it got worse when you _removed_ a shim, not better. THe heli is more responsive with tighter damping, so you are seeing it respond to the bad servo more.

Since the nod is in the pitch direction (nose up and down) I'll bet it's the front servo. If it were one of the others the motion would be a pitch-roll couple.

But first eliminate all binding and/or play in the links to that servo, before you go and replace it.
If you do need to replace a servo I recommend replacing all three with HS55s.

Thanks for info. I am heading to the lhs in a few minutes. I will let you know if it works. Thanks alot!

If you get hs 55s they will need to be reversed, it is an easy mod, choppersrule/dave posted the directions on the main BCPP thread.

Man, Finally this thing flies like it's supposed to. Thanks for the help!!!!!

You are welcome. When you have a chance let us know just what you did.
--John

(now that i think about it I might be wrong about the servo/damping relationship, but at least we got it straightened out.)

Well it don't bounce around it seems to want to just fall out of the sky. Then all of a sudden it goes back up. What in the world could that be??h

That sounds like the famous "sticky collective" which I personally have never experienced. So it was working good for a short while then started doing this falling and climbing thing?
Did you replace all three servos or just the one in front?

I replaced all three. Before i crahed, it kinda would drop (1.5ft) then it would climb back to where it was. Now it seems to be alot worse. Do i need to take the one shim per side out or do i need to add more? I don't see why these things are so hard set up the way it was before.

Get the stepped washers in the grips properly, with the steps facing the ball bearings.
My CP started that crap; I found one of the washers was in backwards. I beat up the guy that did that.

hee hee where did you get that black eye tall paul?

The replacement parts all have minor variations, the head should be set up from the beginning after a major crash, especially if the center hub or the main shaft have been replaced.

Jellyson, Why is this thing so agrivating. The thin flew like a champ out of the box. Now it has all new parts and the thing is possesed! It looks like a yo-yo. With no input on the throttle, it climbs and is stable then it drops 2-3 ft. If it is a "sticky collective" how in the world do you fix that. This is turning into a bad expirence with helis. If i can't get this thing figured out i am going back to planes!!

Calm down, have a beverage, we have all been there or somewhere near there. I've got to go to bed, but we will get this thing sorted out, don't worry.
May need to disassemble the head yet again and double-check everything. But tomorrow, OK?
g'nite...
--John

I got to messing around with this thing and i think that i found a cure. The step washers that are closest to the allen screw, i turned the step away from the bearing. The heli flies great now. It doesn't drop , it just hovers perfectly,BUT now it seems to not want to lift. I have increased the pitch lengths alot just to get it off the ground. It's wierd because once you get it off the ground i am seeing the red light on the 3n1 stay solid. It almost seems like it is straining or something. I can't win for losing. At this point i am a click past halfway on the throtlle and you can give it more but it takes a few seconds for it to climb. Is the main motor bad?

Yeah those washers and shims must be in there correctly or it will bind. I made some pictures that show how loose the whole thing should be.

You should not be using the pitch control links to adjust collective pitch, these are for fine-tuning the pitch of each blade. The collective pitch should be adjusted mainly by the servo link pushrods.

Here is how it should be: take off the blades. pop the servo link rods off the swashplate, so the swash is dangling from the paddle control links and the Bell mixer pushrods. Now, if you lift up on the flybar control frame, you can see how the collective pitch works. This whole assembly should be free enough to drop of its own weight all the way from the top of the travel (full negative pitch) to the bottom (full pos pitch). If there is _any_ binding at this time, track it down and fix it before going further.

Look at the pics: side view and front view, up and down, just dropping it out of my fingers and it falls to full + pitch.
If it doesn't do this you will have a "sticky collective."

I am suspicious of your "cure." The steps are supposed to go toward the bearing. I think you should take it apart again and make sure that it is assembled 100 percent correctly, or we will be in uncharted territory and you will be on your own.

I see that the order of the pics got scrambled, the "up" should precede the "down" of course, since most things don't fall up.

It is waaay too early to blame your motor for any difficulty you might be having. To ease some of your fears, unplug both the motors, and watch how the green/red light responds to throttle inputs. You will see something interesting.

when my bcpp was doing the yo-yo thng I remedied it by getting a century products main gear with the one way bearing and a new head ( not the whole thing just the center )
Check how much play you have in your mainshaft/rotor assembly. Grab the main gear and gently turn the rotor assembly back and forth. I bet you can move it quite a bit. You can also try using a new slightly thicker pin to hold the head on or one with a bit of a "z" bend in it to tighten up the rotor/main shaft connection. Hope that makes sense

I don't understand why it flies so much better. I took it apart and put it the step washers the way they are supposed to be. It started to yo-yo again. I then put them on with the steps out and it flies fine. It don't seem to have nowhere near the headspeed it had. That is why i thought maybe the motor was bad. I had a spare so i tried it and it doesn't help anything. Could i have a problem with the 3-1?