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Old Jul 25, 2012, 11:37 PM
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Well, by wrapping a towel around the screwdriver and pushing like hell while turning, I managed to get all the screws in...basically creating my own threads. A little more of a do-it-yourself project then I would have liked. I've been reading both good and bad things about the aluminum shafts...people either love 'em or hate 'em. We'll see which category I fit into as soon as I finish rebuilding and get a chance to put her through the paces.
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Old Jul 25, 2012, 11:53 PM
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Originally Posted by 1Pilgrim View Post
Speaking of which, I found a crack in the frame where one of the main motor screws goes through. Got a new frame and put everything back together as carefully as I could but now have a wicked case of tbe.

I have a fairly complete parts inventory; here's what I've checked and/or replaced so far:

New blades, balanced and tracked.
New feathering shaft and o-rings.
New fly bar, balanced and tracked.
New main shaft (found a crack in the old one).
New links w/fishing line mod

I kept the CNC hub and anti-rotation collar, Xtreme motor, stock main gear, swashplate, and both servo push rods.

At this point the heli is unflyable. I can get it a foot or so off the floor before it starts to swing around in classic tbe fashion. Ideas?
Ah yes, good old TBE. I used to have an MSR with a bad case of it...I tried everything in the book and never got it fixed...I finally had to retire the thing. But in fifteen months with the 120SR I've never had more than an occasional bout with the problem. With the 120, I don't mind a slight case of it now and then since I'm using it mainly for open-field blasting rather than indoor precision flight.

It looks like you tried all the usual suspects...I don't know what else to suggest. The wierd thing about TBE is that you'll always find someone on a forum who swears on a stack of bibles that he did ______(fill in the blank) and it fixed his TBE for good - then you try it and it doesn't do squat. I have a feeling there are many different causes for it and no single guaranteed fix.
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Old Jul 26, 2012, 10:47 AM
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United States, MA, Malden
Joined Mar 2008
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Quote:
Originally Posted by 1Pilgrim View Post
Speaking of which, I found a crack in the frame where one of the main motor screws goes through. Got a new frame and put everything back together as carefully as I could but now have a wicked case of tbe.

I have a fairly complete parts inventory; here's what I've checked and/or replaced so far:

New blades, balanced and tracked.
New feathering shaft and o-rings.
New fly bar, balanced and tracked.
New main shaft (found a crack in the old one).
New links w/fishing line mod

I kept the CNC hub and anti-rotation collar, Xtreme motor, stock main gear, swashplate, and both servo push rods.

At this point the heli is unflyable. I can get it a foot or so off the floor before it starts to swing around in classic tbe fashion. Ideas?
I have found that using "regular" nylon fishing line no good "especially" for the top links where the flybar attaches. I too was getting TBE until I snipped off the fishing line. I re-did the bottom with nylon sewing thread which is much more flexible. The fishing line on the top link was actually binding upward/downward onto the flybar. Hence, your TBE. I leave the top links alone.

Mike.
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Old Jul 26, 2012, 05:16 PM
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I recently bought a used 120 SR and found it to have TBE. Changed all the blades and no help. I held the rotor head and tried to turn the main gear and foumd some flex to it. Went to my LHS and had them pull out a new one and tried the same thing. No flex at all. Bought the new aluminum ones and found the holes to be a little small. Found a little pointed screw in my tool box just a little larger than the set screw that goes in it and turned it a couple threads into the hole, and now the original screw fits. I also used the screw that holds the gear in.
It is a little heavier duty than the rest and that worked too. Once I had it back together I took it out to my garage. Flies great now. No flex in the shaft. Finally have it flying like I expected.
One question though.. When taking apart the feathering shaft, the manual shows o-rings and a washer on either side of it. Mine has two brass washers but no o-rings. Still though it goes together without much of a space in there. Didn't see any o-rings in the new one they pulled from the shelf to look at.
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Old Jul 26, 2012, 06:07 PM
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My heli came that way, too. Rubber o-rings are inserted through the slots on the side of the head and the shaft is run through them. They are your dampeners.
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Old Jul 26, 2012, 06:22 PM
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I really can not stress enough the value of John Salts e-guide. If you want to know what causes TBE, read thru it. He hits it on the head.

http://www.rchelicopterfun.com/blade-msr-tips.html

BD
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Old Jul 26, 2012, 06:25 PM
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Originally Posted by rwek View Post
Didn't see any o-rings in the new one they pulled from the shelf to look at.
The o-rings are not visible untill you remove them from the slots.

BD
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Old Jul 26, 2012, 08:11 PM
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Originally Posted by BattleDude View Post
I really can not stress enough the value of John Salts e-guide. If you want to know what causes TBE, read thru it. He hits it on the head.

http://www.rchelicopterfun.com/blade-msr-tips.html

BD
Not knocking the John Salt guide for one minute. There's a lot of good information there. And I'm basing my comments on an older version - mSR only; I haven't seen a version that has anything about the 120.

But I really think he's grossly oversimplifying the TBE issue. In the version I have, he states that "worn pushrod guides are usually the cause on the mSR". Not buying it: A factory-fresh mSR rotorhead or anti-rotation collar will have considerable play in the pushrod guides, which doesn't seem to cause any problems. With the 120 it's even less critical; I've logged plenty of flight time on the 120 with severely bent guides and have never found it to be a problem.

As I said in my earlier post, TBE is a very complex problem with many different causes - any claim for a one size fits all solution should be looked at with extreme skepticism.
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Old Jul 26, 2012, 08:37 PM
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Quote:
Originally Posted by Mickmeister View Post
Not knocking the John Salt guide for one minute. There's a lot of good information there. And I'm basing my comments on an older version - mSR only; I haven't seen a version that has anything about the 120.

But I really think he's grossly oversimplifying the TBE issue. In the version I have, he states that "worn pushrod guides are usually the cause on the mSR". Not buying it: A factory-fresh mSR rotorhead or anti-rotation collar will have considerable play in the pushrod guides, which doesn't seem to cause any problems. With the 120 it's even less critical; I've logged plenty of flight time on the 120 with severely bent guides and have never found it to be a problem.

As I said in my earlier post, TBE is a very complex problem with many different causes - any claim for a one size fits all solution should be looked at with extreme skepticism.

TBE is only caused by either binding in he rotor head, worn dog bones, worm balls on the swash, grips...When mine gets TBE all I do is replace all the dog bones, replace the swash and blade grips...Flys like brand new and TBE is gone.
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Old Jul 26, 2012, 09:03 PM
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Originally Posted by Jake8131 View Post
TBE is only caused by either binding in he rotor head, worn dog bones, worm balls on the swash, grips...When mine gets TBE all I do is replace all the dog bones, replace the swash and blade grips...Flys like brand new and TBE is gone.
But, again, what fixes it for one guy doesn't work in another case. I replaced all of the above and more on my old mSR, and it's been sitting in a box for the past year, never to fly again.
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Old Jul 26, 2012, 09:40 PM
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Originally Posted by Mickmeister View Post
But, again, what fixes it for one guy doesn't work in another case. I replaced all of the above and more on my old mSR, and it's been sitting in a box for the past year, never to fly again.
You sure that you aren't experiencing the Pendulum effect and not TBE? Exactly what is it doing?

Pendulum Effect:
blade mSR pendulum effect (0 min 8 sec)


TBE;
mSR Toilet Bowl Effect (TBE) (0 min 18 sec)
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Old Jul 26, 2012, 09:47 PM
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If you don't fly it, you can give me the msr.....
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Old Jul 27, 2012, 02:02 PM
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You sure that you aren't experiencing the Pendulum effect and not TBE? Exactly what is it doing?
If you look at the video, when the cyclic is released the rotor disk is tilted to the rear (body ahead of the rotor). This results in rearward thrust from the rotor causing the heli to move backward. When the cyclic is released the rotor slows down first and faster than the body resulting in the body getting ahead of the rotor.

The main contributing factor is that in model helicopters and particularly small ones is that the CG is farther (lower) from the rotor disk than in larger models or in real ones. The increased distance improves the heli hover and low speed stability. However, sharp control inputs at faster speed will result in the CG of the helicopter moving out of line with the rotor shaft due to inertia (heli tilts). This can be mitigated by using smooth control movements.

In a real helicopter the heavy parts (engine, transmission) are mounted at the top of the fuselage right under the rotor. Because of component size and scale factors, a real helicopter built to replicate a model helicopter would have the engine and transmission mounted to the floor of the cabin not to the roof. This would induce some of the same pendulum effects in this real helicopter as seen in small models. This happens with real helicopters carrying large sling loads.

As you go up in model size, the weight fraction representing the motor and battery goes down compared to the rest of the helicopter. Also components can be mounted closer to the rotor as the size ratio of the parts also goes down.
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Old Jul 27, 2012, 02:49 PM
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Quote:
Originally Posted by Mickmeister View Post
Not knocking the John Salt guide for one minute. There's a lot of good information there. And I'm basing my comments on an older version - mSR only; I haven't seen a version that has anything about the 120.

But I really think he's grossly oversimplifying the TBE issue. In the version I have, he states that "worn pushrod guides are usually the cause on the mSR". Not buying it: A factory-fresh mSR rotorhead or anti-rotation collar will have considerable play in the pushrod guides, which doesn't seem to cause any problems. With the 120 it's even less critical; I've logged plenty of flight time on the 120 with severely bent guides and have never found it to be a problem.

As I said in my earlier post, TBE is a very complex problem with many different causes - any claim for a one size fits all solution should be looked at with extreme skepticism.
There are many different "indirect" causes of course, but the "direct" cause is the flybar being out of phase, for whatever reason, including wear, damage, missing parts, or mis-assembly.

The version of Salt's guide I have does cover the 120SR, and TBE is covered and mentioned in several different places in the guide.
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Old Jul 27, 2012, 08:38 PM
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Originally Posted by 1Pilgrim View Post
Got a new frame and put everything back together as carefully as I could but now have a wicked case of tbe.

...here's what I've checked and/or replaced so far:

New blades, balanced and tracked.
New feathering shaft and o-rings.
New fly bar, balanced and tracked.
New main shaft (found a crack in the old one).
New links w/fishing line mod (I use ordinary thread - easier to work with)

I kept the CNC hub and anti-rotation collar, Xtreme motor, stock main gear, swashplate, and both servo push rods.

At this point the heli is unflyable. I can get it a foot or so off the floor before it starts to swing around in classic tbe fashion. Ideas?
I lied - the "new" main shaft was cracked at the top. I may have overtightened the rotor hub retainer screw when I put it together the first time. After allowing a drop of ca to seep into the crack (taking care to blot off the excess and let it cure) I put the heli back together.

Et voila! No tbe. All is well with the world !

EDIT: Before attaching all the other "goodies" I pushed the main gear onto the shaft, fastened it with the retainer screw, ran the shaft up into the frame and gave it a spin. Huh. The shaft came to a stop with the head of the retainer screw pointing straight down.

After a few more trials I could see that the screw definitely threw the shaft out of balance so I tossed it - the main gear is keyed onto the shaft and is a very secure press fit so imho the screw is redundant. The shaft spins true without it, so we shall see what we shall see...
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