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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Correcting for unequal throw on either side of 0* level head?
08-02-2007 10:28 PM  13 years ago
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darkfa8

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Brick, NJ - USA

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Correcting for unequal throw on either side of 0* level head?
I'm setting up a Trex with a microheli frame, again...

anyway, in the radio: 50% at all points in Normal mode, servo arms were set by eye to be perpendicular the mainshaft, all links from the servos to swash are the same length, at 50% collective I get 0* pitch on the mains and all mixers, flybar, main grips are level.

when i switch to my idle-up (0-100% pitch curve) and I go to low stick I get about -6*, at full stick I get 11* and the washout base is butted up against the bottom of the head yoke.

How do I get this equalled out and have 0* at mid-stick/50%?
- Dan Goldstein
Team Revolectrix
Lynx Heli Innovations
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08-02-2007 10:34 PM  13 years ago
Rodney

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St.Cloud,Florida

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Make sure the pitch trim knob on your radio is either set to center or disable if possible. It will only work in normal mode so that may be your problem.
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08-02-2007 10:53 PM  13 years ago
darkfa8

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Brick, NJ - USA

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hov-thr & pit are disabled and null

no other mixes are active.

subtrim: ail +4
ele +15
pit +37

I tried to get the servo arms as close to 90* to the servo case as possible.

I've had this problem before and I just can't remember what was done to correct it.
- Dan Goldstein
Team Revolectrix
Lynx Heli Innovations
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08-03-2007 12:28 AM  13 years ago
oldboldpilot

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Southern California

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darkfa8,

Sounds like your slide block is too high.

At minimum pitch (idle-up), see that the guide pins are still engaging the slide block about 15%, then see what your maximum pitch situation looks like..
Helis are Man's Defiance of the Laws of Nature - OCHC
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08-03-2007 12:56 AM  13 years ago
z11355

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New England

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the problem is that you set everything up using incorrect rod lengths.

you have a total of 17* of throw so you should have 8.5 on each
side of zero.

adjust either the short final mixing rods (that go to the blades)
or the long ones from the swash so that you have 2.5* at midstick.

then set the collective so you read zero pitch and go back and reset all of the servo arms to be 90 degrees etc etc
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08-03-2007 02:26 AM  13 years ago
darkfa8

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Brick, NJ - USA

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math and fixin'
ok, did some quick math to figure out if the balls on my servo arms weren't in the right spot...

optimally they should be 12mm out on the arm based on my measuring 17mm of total swash travel on the main shaft.

((total pushrod travel/2 / sin(servo rotation angle(45*))) = how far out the ball should be

They had been at 15mm out, but there is a hole at 11 and 13mm, I put them at 13mm.

After doing that and using a HelicopterJohn Trex450SE swash leveling tool to get the swash level at 50% Pitch/ half-stick and adjust all the links from the servos to the blades to get everything level/90* and 0* pitch on the mains I now have +10/0/-10 using a Swash Pitch AFR of -37%, all my servo ATVs are 100/100.

I have the numbers I want and mechanically everything centers/levels at half-stick and I don't appear to have any binding at low or high stick. But, is my Pitch AFR to low?
- Dan Goldstein
Team Revolectrix
Lynx Heli Innovations
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08-03-2007 02:44 AM  13 years ago
SSN Pru

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Taxachusetts

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the only thing that will adjust uneven throws is adjusting the control rods that go from the servos/control arms to the swash plate.

Its funny when ever anyone comes in here and asks this question, everyone says to adjust the rods in teh head somewhere. that will only give you more or less unequal pitch. the only way to get equal pitch is to adjust the rods mentioned above.

basically, if you have 17mm of swash travel, then you want to have 8.5mm on either side of neutral. that is where the swash leveling tool came in. it centered your swash in its travel...

your pitch afr is what it is.... every radio will be different from the others.
Stupidity can be cured. Ignorance is for life!
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08-03-2007 02:49 AM  13 years ago
darkfa8

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Brick, NJ - USA

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thanks you!

this isn't the first ccpm heli i've built but I ALWAYS run into this sort of problem. i just forget what the heck to do to resolve it.

I'm not sure if the swash tool is the right height for this frame, but I did kinda compare how it sits on the 450sev1 frame it was designed for and this microheli frame and it's prolly within 1mm or so height difference or less, so in other words, it's close enough.
- Dan Goldstein
Team Revolectrix
Lynx Heli Innovations
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08-03-2007 03:10 AM  13 years ago
JAGNZ

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Auckland, New Zealand

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Do a Google Search for 'Finless Videos' and then download his CCPM setup videos. The best I have ever seen on the subject. Basically, when you originally set up the links from the servos to the swash you did not set them to raise the swash high enough at max pitch. The washout should almost touch the headblock at max pitch. From there you setup the rest...
Jason Greenwood

www.3dheli.co.nz
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08-03-2007 02:15 PM  13 years ago
SSN Pru

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Taxachusetts

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Basically, when you originally set up the links from the servos to the swash you did not set them to raise the swash high enough at max pitch.
That isnt correct. His problem centered around the fact that the swash was not centered in its travel range. The maximums and minimums have nothing to do with centering the swash first!

Everything else comes after.
Stupidity can be cured. Ignorance is for life!
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08-03-2007 05:58 PM  13 years ago
Micro-Maniac

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Pasco,Washington Formerly: Captain Chaos

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Some helis I work from the top down - I start by fixing the head in the center of it's available travel range then level all the mixing arms with 0° blade pitch and level flybar then finally size the servo links to the swash plate making sure the swash is level and the servo arms are all 90°

Simpler heads I make sure the servo arms are all 90° then adjust the servo links evenly raising/lowering the swash levelly until the head itself is centered in it's available travel range then adjust the the pitch control links to 0° blade pitch with the flybar level

Notice that I pay no attention to the position of the swash plate as it usually doesn't matter - Only that it's level - Other things usually determine it's position
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08-03-2007 07:15 PM  13 years ago
SSN Pru

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Taxachusetts

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Other things usually determine it's position
Yup, you are correct. But, by adjusting the linkages in the way that you have, you are centering the swash...
Stupidity can be cured. Ignorance is for life!
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08-03-2007 07:32 PM  13 years ago
z11355

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New England

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I thought I had read that he centered the swash.

oh well.
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08-03-2007 07:40 PM  13 years ago
Micro-Maniac

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Pasco,Washington Formerly: Captain Chaos

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Point is that the position of the swash plate is usually irrelevant unless the links between the swash plate and control/mixing levers are all adjustable which usually they are not

In the Trex' case the swash position is determined by the centering of the washout base on the main rotor housing pins and the non-adjustable links between the leveled flybar control levers and swash plate leaving no choice as to the position of the swash plate

Some people make the mistake of focusing on the position of the swash plate then wonder why everything else doesn't work out right - If you forget about the position of the swash plate and only concern yourself with it's levelness then it'll fall into it's proper place on it's own as more important things are set in thier proper place
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08-03-2007 08:44 PM  13 years ago
Micro-Maniac

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Pasco,Washington Formerly: Captain Chaos

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I'll walk through a Trex head setup real quick

1 - Neutralize radio collective (50%)
2 - Adjust servo arms to right angles (90°)
3 - Adjust servo links so the washout base is centered on the main rotor housing pins with the flybar control levers and swash plate all level (may require also adjusting or just disconnecting the flybar control links to achieve center/level here)
4 - Adjust the flybar control links to equal lengths so the flybar cage is level
5 - Level the flybar and adjust the SF links to equal lengths so the SF mixing levers are also level with the flybar
6 - Adjust the pitch control links so the blades show 0° pitch to the leveled flybar (tracking should be adjusted here as well - bad things would occur if blade pitch adjustments were instead made from the sf links)
7 - Confirm that everything is centered and leveled all at once

Setting up everything centered and leveled like this should provide complete linear control
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