Irratic Blade 120 SR

Splitts · Hover Master Joined: 29 Sep 2011 Posts: 13

I'm back again. Checked and tried may thing to correct irratic hover. It lifts off the starts osscoilating fore and aft and sideways. If I have enough room to let it go it goes into what I have seen termed and the toilet bowl effect. Round and round till it crashes. No amount of trim fixes it. I have been able to momentarily catch it with the controls. In all of this it maintains good heading.

All the links are tight and the the swash plate in intact. All the guides are tight. I did find a cracked rotor head and replaced it to no avail. It does have vibration on bentch tests. Installed new blades to no avail. I took it apart and the shaft is straight. I noted that the flybar is quite loose on the shaft. I guess it it gets off center it could cause an out of balance.

The the flybar have to be snug on the shaft?

What is the function of the flybar? Ut appears to me that it is some type of centrifical stablizer?

Help[/b]

nick_onelove · Posted: Sat Oct 08, 2011 9:31 am Post subject:

You nailed it; it's toilet-bowl effect. If you Google that term you will find all the information you need and more. An extremely detailed explanation can be found here: http://www.rchelicopterfun.com/toilet-bowl-effect.html

It's talking about co-axials, but the concept is the same because the 120 SR sports the 45° flybar which lends it its amazing stability.

You say the links and flybar are tight, how tight? What do you mean? You actually want things loose around the flybar so that it can rock freely and easily.

When I got a new upgrade flybar from MicroHeli, I had uncontrollable TBE and absolutely nothing was wrong. A member here recommended dry-type (evaporating) silicone spray, and that cleared it right up:

http://www.amazon.com/Silicone-Spray-Dry-Type-Lubricant/dp/B000MQX7K2
_________________
Align: Trex 250 3GX + Trex 450 Pro with Vbar
Blade: 450 X, mCP X, 120 SR, mSR X, CX3, mCX2
Esky: Belt-CP X and V2 - Futaba: Heli-Max Axe 400
Walkera: V500D01, M120D01, V100D08, DEVO 8
Spektrum: DX8 - AMA #967873 - IRCHA #4095

Tom Lauten · Posted: Sat Oct 08, 2011 9:43 am Post subject:

Hi Splitts.

Toilet Bowl Effect (TBE) is generally caused by the flybar being "out of phase" with the blades. That is to say that because the two are linked and the flybar acts not only as a gryro for the flight attitude, it also translates the movement of the swash (as determined by you as the pilot) into movement for the rotor head and blades. The fact it is 45 degrees offset to the blade position (when you look down on the heli like a clock) is very purposeful and important. The offset makes up for a delay or "micro-time-lag" in the movement of the swash,flybar and head "chain of command".

When parts are too tight or bind in ANY way, this can throw off the speed or timing of the "chain of command" movements... this is the "out of phase" bit, or TBE. The blades get the command to move that bit too late so the compensation is like a delay or echo and it keeps building until it is swinging around endlessly trying to catch up with where it thinks it should be.

TBE is the manifestation of this delay in the mechanical linkages caused by friction or binding.

The cure ususally is to make sure that all of the various pivots, links, sliding bits (etc.) ALL are balanced and move without ANY friction or binding. A tap on the end of the flybar should cause it to bounce down off it's lower stop, up to the other side's stopping point and some way back again without any hang up (with the balanced blades fully extended).

Here is a brilliant description of TBE as it applies to coaxials but the effect and issures are much the same with single rotor helis as well.

http://www.rchelicopterfun.com/toilet-bowl-effect.html

Hope this helps.
_________________
If only I could fly as well as I spend money I don't have...

All Blades, all the time...
MSR
MSR X
MCP X
120SR
Blade 400

Splitts · Hover Master Joined: 29 Sep 2011 Posts: 13

Hey thanks guys. This gives me something to shoot at.

Splitts

Dumb Thumbs · Posted: Sun Oct 09, 2011 9:40 am Post subject:

Sounds like you ruled out most of the common problems that cause the dreaded TBE. One more thing I'd check is blade balance. Yea, I know the 120 blades are small, but ANY inbalance in any size heli is trouble.

A blade balancer for a T-Rex 250 might work well for 120 blades and only costs a few bucks, but I haven't tried myself.
_________________
Next Level 650 Quad Copter, T-Rex 500, 450SEv2 & 250
HK 450
Blade CP Pro (deceased), CX3, MCX, MSR,
MCP X, 120SR, MSR X, MQX
Pro Boat-Miss Geico & ShockWave, a few planks & a HPI Baja 5B SS gas buggy.
AMA#900889

Splitts · Hover Master Joined: 29 Sep 2011 Posts: 13

Thanks. I think I do have a blade balance problem and will check it.

A question concerning the blades. I had a cracked rotor head so I replaced it. I also got a new feathering spindel. It came with a bushing and O ring for each side but when installed them the blade was in a bind. Not good if free movement is needed. I also did not find any o rings when I tood the broken one apart. What are the O rings for?

Splitts

chopper54 · Posted: Mon Oct 10, 2011 3:03 am Post subject: post subject

I think the o rings are sometimes refered to as dampeners and are supposed to help with damping down minor vibrations in the rotor head.
The heli would probably shake badly without them. Bigger heli fliers can tune the response of their machine by fitting harder or softer dampeners depending on the type of flying they do.

nick_onelove · Posted: Mon Oct 10, 2011 3:19 am Post subject:

Yeah, you definitely need the O-rings, that's probably your whole problem.

They go on the feathering shaft first between the bushings:

You can't really see the O-rings in that pic because they're behind the bushings, almost in the rotor head.
_________________
Align: Trex 250 3GX + Trex 450 Pro with Vbar
Blade: 450 X, mCP X, 120 SR, mSR X, CX3, mCX2
Esky: Belt-CP X and V2 - Futaba: Heli-Max Axe 400
Walkera: V500D01, M120D01, V100D08, DEVO 8
Spektrum: DX8 - AMA #967873 - IRCHA #4095

Splitts · Hover Master Joined: 29 Sep 2011 Posts: 13

Nick,
I installed the O rings as you described and the blades are stiff and difficult to change pitch. I did not fly it because my flybar is broke and I'm waitting for a new one.

I know the parts illastration shows the O rings, the replacement parts came with O rings and as you said they should be there, but if all the links are supposed to be free and then the blades are tight.

By the way I broke the ball on the flybar be trying to take the link off with my fingers. I made a tool by taking aflat nose needle nose and ground a notch on one side that clears the ball and a round ball on the other about the side of the ball link. The fork goes behind the link and the ball pushes against the ball and pops it off. No pressuer on the ball neck.

I'll let you know how it works when I get the flybar.

Dumb Thumbs · Posted: Tue Oct 11, 2011 6:29 am Post subject:

Something is really wrong with the head if the flybar isn't free moving.
Take it one step at a time. Pop off the links at the rotor head then see if it is indeed the head binding, or is the binding lower down.
I'm thinking you might have the links misaligned. From the swash ball those links should be connected to the foward balls on the flybar as in relation to head rotation. Links from the rear balls on the flybar go to the blade grips.
_________________
Next Level 650 Quad Copter, T-Rex 500, 450SEv2 & 250
HK 450
Blade CP Pro (deceased), CX3, MCX, MSR,
MCP X, 120SR, MSR X, MQX
Pro Boat-Miss Geico & ShockWave, a few planks & a HPI Baja 5B SS gas buggy.
AMA#900889

Splitts · Hover Master Joined: 29 Sep 2011 Posts: 13

I don't have any of the links connected. The head has nothing connected to it. How tight should the blade pivot be? I'm guessing the O ring are to take the end play out of the mount but blades should move ealily.

Tom Lauten · Posted: Tue Oct 11, 2011 6:55 am Post subject:

The full blade grip assembly should flop freely when mounted on the rotor head. I think you need to totally strip down the head, check that every part is free from burrs, debris etc and slowly reassemble checking freedom of movement as you go. There are not that many bits to it so the problem will show up if you are boringly methodical.

The exploded parts diagram should make it evident where everything goes.

Just make sure the O-rings and brass washers are the right number in the right place. A bit of lube on everything after assembly should see it moving freely.

AHHHHHHHHH... how many brass washers/shims are you using? There should be 2. If you use more the fit can look better but it can also bind.
_________________
If only I could fly as well as I spend money I don't have...

All Blades, all the time...
MSR
MSR X
MCP X
120SR
Blade 400

lightning · Posted: Tue Oct 11, 2011 1:35 pm Post subject:

Hey there Splitts,seriously don't try to fly until you have done everything these guys have advised .Trust me they know .By the way, welcome Wink

_________________
amatuers built the ark,professionals built the titannic.

mjg44mjg · Posted: Wed Oct 12, 2011 8:15 pm Post subject:

I had the same exact problem with mine and after replacing damn near the whole entire helicopter, I found that constant input on the sticks, little corrections, and mostly forward on the elevator fixed the issue.. Its not just one part on the heli causing your problem... Its the nature of the beast.. You just have to learn to make the corrections with the sticks to even her out.. Hope that made sense and helped a little..
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BLADE CX2, 120SR, SR, Scout CX, ESky Big Lama, E500

Fly til you crash, crash til you learn...!!

Splitts · Hover Master Joined: 29 Sep 2011 Posts: 13

Hey guys I'm back flying. Biggest problems is breaking off balls and I have to mail order parts so it takes forever. I also make tools to I won't break balls, or less chanch to.

Freeing up all the links took care of the TBE, but it was still erratic. Hover good for a little then take off forward or sideways. Found end play in main shaft and eliminaated that. Also found control panel loose. Both could change trim.

Would now hover with lots of trim. Adjusted servo links and now trim close to neutral.

Just finished flying going through 3 batteries and not breaking anything. Not pretty but I'm flying.

Thanks everyone for the advise.

Splitts