View Full Version : Blades Won't Track (random wild oscillations)

Gary JP4
06-09-2006, 12:17 PM
By blades won’t track very well. I have the HB CP2 with wood symmetrical blades. When I adjust 1/2 or one turn at a time sometimes nothing happens and when I continue to adjust they switch to the opposite blade high. Some times they switch on their own after changing to negative pitch and back again. They are out close to 1 cm at the tips. I have just lived with this.

Now, after several small crashes, bent main shaft, bent feathering shaft (all replaced or repaired), I occasionally get a flutter. I have not crashed because of this but it does not fly very well when this happens. Looking from the side when checking tracking I have been able to reproduce this and it looks like a wave up and down that moves around with rotation. E.g. I think blades are tracking up and down randomly. I assume this is due to something loose. After the last crash I used my best straightened main shaft but the hole for the pin was a little oversize. I get a little backlash when turning the drive gear and holding the rotor head. Also my S-75 servos have a few mm of play at the end of the arm. All about the same. I think they have always had that much play. I found I had a bent feathering shaft and replaced it. That didn't fix it. The blades have some minor repair (CA in a short crack and bare wood on each blade. I had the same tracking problem on previous blades but not the flutter. I have always balanced them with matching CG's.

I have blades, main shaft, and mast head on order.

Can anybody tell me if they have any play in their servos?

Any body else have this happen?

06-09-2006, 01:33 PM
Sloppy servos will definitely cause this. At first i was going to ask if you're balancing them, but as I read, you said you are. I would at least pick up some new S75's if you don't want ot put out for something better. I don't know how many flights you have on you rbird. The S75's don't have an outstanding record for longevity.

Gary JP4
06-09-2006, 02:42 PM
Thanks for the reply.

I was just looking at the new servos (I think they are S-75's) that came with a Spectrum DX6 I have. They have about the same slop.

I have about 20 flights, 3 crashes (one took a pretty good hit). Mostly hovering, some forward flight. No aerobatics. All indoors.

I have a DF4 and I put GWS Narrow servos on it. They are tight.

Are there better gear sets for the S-75's.

06-09-2006, 05:02 PM
if the tracking goes inand out randomly, it is not the servos, it's the spindle.
check that before you waste too much time.
You may want to look at the head block for play between it and the mainshaft.

06-09-2006, 06:11 PM
He already replaced the spindle but you may be right about the head block as a problem, especially if he bent the spindle first.

As far as I know the only gear set for an S75 comes with another servo attached :) Mine also had a unique stamped on them, they said HS56 for some reason :D

Gary JP4
06-09-2006, 10:42 PM
Ri...ght. I think I got it about the servos. I'll check the head block. Thanks.

You are talking about the center hub (the piece that the pin goes through and into the main shaft) right? Like I said there is a little play there either in the head plastic or the shaft. That is the area I have parts coming for.

06-10-2006, 01:55 AM
My gut feeling still says look at the servos, but Wayne's a lot higher on the food chain than me :wink:

06-10-2006, 05:06 AM
Food chain don't matter, especially when someone's trying to resolve a problem. I have been wrong before, but I'll stand up on this one.
Tracking issues are generally going to be from the swashplate up. After re-reading your origional post, try different blades as well, you could have a cross chord fracture in them.
Yes, the center mast hub, goes on top of the shaft is the block I meant.

Gary JP4
06-14-2006, 09:37 AM
Thanks guys.

It looks like it was primarily the blades at least for the wave action oscillation. I said the blades had some minor repair. They were a little worse than I described. On closer inspection they were pretty smooth on top but one was cracked at the tip longitudinally about 1/2 inch long and not lined up perfectly and pretty rough where I CA'd the tip. I smoothed it out with a file where it was rough on the bottom side of the tip and flew it. This seemed to fix the oscillation problem. Still tracks badly. When I adjust one blade either tracks high or low but not in-between. And after cycling from positive to negative and back it sometimes switches from the high blade to the low. I have always had trouble with that even before I flew it for the first times and on previous blades.

Haven't installed the new parts yet.

I rechecked my new S-75 servos and (3) out of (4) have similar (almost as much) backlash to the ones I am using and one is tight.

Gary JP4
07-02-2006, 08:48 AM
As a follow up. I replaced the blades and things seemed better for a few minutes then the ossolations started again. I checked everything for play again and everything in the head is pretty sloppy compared to a Trex. I tightened the screws that the arms connected to the head pivot on called control arms or wash out arms on some heli's I think. They seemed a litle loose. This did the trick.

07-02-2006, 11:42 AM
They do sell a rebuild kit now for the S-75's for three bucks. Don't know if they're better gears or not, but at least you "can" rebuild them now.

I have the HB2 B/H head on mine and it's got a lot of slop. Disturbs me but it flies fine. I don't 3D with it so basicly once it spins up I geuss everything just lines up. I did set the pitch while holding the head so I think that helped, but it tracks OK. I'll definitel have to replace it as I get better. I like to experiment with the blade before I try things on the rex.

Gary JP4
07-03-2006, 09:17 AM
I like to experiment with the blade before I try things on the rex.

Me too!

I warm up on it if I have it togather then fly the Trex.

Gary JP4
07-04-2006, 09:24 AM
Mine is very loose too. I have to take an average on blade to fly bar angle with the pitch gauge. Looks like about +/- 3 to 4 degrees. I swing the blade back and forth keeping the fly bar level and set the pitch gauge to get the same degrees of slop on either side of nominal.

I put a new set of blades on and it flies really well, sweet. I had a couple of crashes one diving into the hangar floor and didn't pull up enough and scrubed the blade tips off a bit, glued, filed off the burrs, and reblanced and it still flies great. Just wish the tail would hold like the Trex.

I seem to have settled down on the controls a bit too. After reading some of the flight training thread http://www.littlerotors.com/flyinglessons/ I backed off from fast foward flight. Thought I was getting ahead of myself. Now doing symmetrical figure eight’s through nose in, 360 degree circles, and hovering nose in. Still a bit intimidated and jerky on the Rex, especially nose in. Scared to crash my Trex SE.