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Old Oct 16, 2006, 04:08 PM
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Help!
Need Help with MS CH-46 Setup!

Problem #1 - My instructions dont include a CG location.

Problem #2 - My Multiplex Evo 12 does not allow configurable mixes in heli mode. Thus I cannot program elevator/rudder mixiing

Problem#3 - It always wants to pop a wheelie at takeoff. I have never been able to hover it at all. It lifts up in the front and whacks the rear blades on the ground. I hope that is just a CG issue. Right now I have the CG set halfway between the masts. Where should it be?

I am hoping Meatbomber or Paul, or anybody can help!

BTW, I started this with the 3 blade setup. I never used 2 blades.

Thanks,
-Todd
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Old Oct 17, 2006, 12:59 AM
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SeaKnight setup

Todd,
I can help a little.
1) CG is midway between the two rotor heads. Check it with the blades OFF. Othewise you'll have a problem with the odd blade orientation.

2) I don't know how this will work. That mix is pretty important. I don't think you can "thumb" your way through it. (You will probably be able to hover it, but any significant ELEVATOR will cause some tail wagging. The little gyros that came with mine wouldn't even try to hold this kind of torque. A 401 in HH mode, might work though.)

3) The nose naturally wants to lift first (by a little). The front rotor is tilted forward and the back is level. When it comes time to lift off, the heli will need to "average" the two rotor planes by lifting the nose a little (about half the amount the front mast is tilted). If it's really rearing up, then it's because the front rotor has more pitch than the back. The trick in setting the pitch on the two heads is to remember that the masts must be VERTICAL to set pitch. When you put the pitch gauge on the back, the heli can be sitting on its wheels (back mast is almost vertical then). When you're setting up the front mast, you need to lift the front (maybe an inch or more) to make the mast vertical. I haven't set mine up with the three bladed heads yet, but I expect to use something like 5 degrees at mid stick on both ends.

From where you are now, you might just lower the front (or raise the back depending on which has the most slack) until you get it to lift "level".

Once you get it to hover, you can tell if they're "balanced" by watching the plane of the two rotor disks. If they're both parallel, then you're golden. If they "cross" then you have an imblance in front/back lift which causes a pirouette tendency which will be offset by rudder position (trim or thumb), but with the unwanted side-effect of having the two disks tilted opposite ways. It flies, but it acts funny and not very stable. You can probably even figure out which one has higher pitch by noticing which way the rudder trim is offset (and hence which disk is tilted left and which is tilted right).

Hope that helps.
...paul
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Old Oct 17, 2006, 03:39 PM
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Thanks Paul.

One thing I did not do was balance without the blades on. I had not considered this because this is my first 3 blade heli.

Also, I am trying to get some clarification from Multiplex on my radio's capabilities (or lack there of).

I did not get a paper "protractor" with my kit so I am forced to put the stadard blades on so I can use my pitch gage. The 3 blade ones are too skinny. I may have flubbed that part up.

-Todd
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Old Oct 17, 2006, 10:48 PM
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You could make a "plywood" blade blank (something that fits the roots and is wide enough to fit your pitch gauge) to use for setting the pitch. Exact pitch isn't too critical anyway (it'll fly when the forces all balance, regardless of what your pitch gauge says). I'd just cut a piece of plywood that would fit in the blade grip and use it for setting up one blade on front and one on the back. Then I'd just make sure that all the links are identical and check tracking with it flying. You can fine tune later.

I don't think that with the slop in those little heads, you're going to be able to measure with any accuracy within 1 or 2 degrees anyway. Just try to make it symmetrical around 5-ish degrees, and try to make it the same front and back.

...paul
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Old Oct 17, 2006, 11:01 PM
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Here is the answer to my radio question:

http://www.rcgroups.com/forums/showt...033#post623866

Not good as I suspected.

-Todd
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Old Oct 18, 2006, 12:26 PM
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For a 3-rotor head, this scheme should work..
Set the pitch on each blade so all three winding sticks are parallel to each other
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Old Oct 19, 2006, 12:46 PM
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Wannabe, phscott,

I am following this tread intently as I am approching that stage with my CH-46. I'm just getting all the servo's trimmed and located and figuring out what goes where.

But I had a thought that if the 'reverse' switch on the elevator gyro was set wrong (50/50 chance) wouldn't that cause your problem. On my T-rexs I get that switch (T/R) wrong about half the time and - everything is fine until whoops. Your description of the problem sounded similar.

Jim P.
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Old Oct 20, 2006, 01:02 AM
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You can always test the gyro direction by making sure that it makes the "correct" correction.

For a tail gyro, you first note which way the servo moves when you input a "nose-right" stick input (make sure that the tail moves the right way when you move the stick to the right, of course). Then while holding the heli in your hand (with the motors off) force the nose to go LEFT and note that the servo moves the same way as when you input the stick movement.

Likewise, you could check the Elevator Gyro by noting the deflection direction when you push the nose up or down and see that it corrects the correct way.

...paul
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Old Oct 26, 2006, 11:37 PM
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Hey Wannabe, I have been following the CH-46 threads with interest, id love ot build one of these.
Do you need to have the mixing in the radio or would the MS composit mixer handle these functions.

http://www.mscompositusa.com/electro...ml#description

I have an Evo 7 so if the 12 cant do it the 7 definatly cant.
Scott
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Old Oct 27, 2006, 10:38 AM
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THe MS mixer handles the pitch differential mixing. It expects your transmintter to handle the elevator/rudder mixing.

I broke down and bout the TechProducts mixing board. I have not had a chance to test it out yet...
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Old Oct 28, 2006, 09:36 AM
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Thanks,
I took a look and the Tech Products mixing board looks like it will certainaly do the trick.

Scott
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Old Aug 07, 2007, 05:19 PM
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tech products

where do you get a tech products mixing board?

why is it better than the MS board...

thanks

vertol
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Old Apr 10, 2015, 12:56 PM
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hi,
I realize this thread is ages old but I bought one of these like 8 yrs ago and built it but never flew it.was away working for all these yrs and recently came home to visit my parents and low and behold here are all my heli's sitting on a shelf like the day I left them.
using a futaba 7chp and all flight controls move correctly and gryo's seem to work right.
when I spin it up it wants to rotate ccw around vert axis(cant even stop it with full stick input).had to download the manual for the radio and found a copy of the assembly instructions.for channel 5 and 7 I set them to null in parameters and setup mixes(not sure if this is the right way).anyway think my problem is in the elevator/rudder mix.according to the documentation..
Code:
 The setting of the mix between elevator and rudder. The sequence of the attack angle change by the controlling of the elevator is the change of the power relation between rotors. This disturbs the balance of moment of torsion.modern start to rotate around vertical axis.  For this reason it is necessary to set the mix between elevator and rudder on the transmitter. Relation measure of mix depends on mix of opposing pitch to the elevator. The basic tuning of mixing: 100% elevator : 50% ruder -the elevator is in mix as a controlling function(master) and the rudder as An affected function(slave). It must be set when you push the elevator down must the front swash plate underlay to the right and rear to the left, when you pus the elevator up the opposite should occur.  If the model turns left when pushing the controller down it is needed to raise the relation of mixing rudder to elevator and contrary. The setting of this mix is ok if the model stays in the same course and does not turn when you put the elevator controller up and down.
but I think it refers to more of a in flight setting?
anyway if one of you people that have/had one and remember anything it would be great.
also its the 3 blade head setup.
read all the posts and cant figure it out(mostly due to not being around this stuff for all this time and forgot).
phscott..referring to the front rotor pitch setup and you referring to raising the nose till mast is straight.when I did mine I just went with +5 pitch at mid stick by referring to the slope of the body(wich the mast is perpendicular to and my swash is level with).think this gets same results as your referring to?
thks
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Last edited by Blackbear199; Apr 10, 2015 at 01:08 PM.
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