CX3 setup and troubleshooting guide

[Cheetah62]

I've assembled my scattered notes taken over the last ten months of banging my head and cursing e-Flite over this little heli. Today I am the proud owner of a CX3 that flies beautifully, is easy to troubleshoot and repair, and has to date almost 600 flights on it. I've seen a lot of heartache and frustration in these forums about the CX3 and it's a shame because I do believe there's hope. Here is my attempt at a setup checklist that may help some of you with your troubles. There is always more to say, and I know this doesn't cover everything. If anyone wishes to add to it or take issue with my method well, heck, it's an open forum so go for it.
For what it's worth... it's worked for me.

BTW - my CX3 did NOT fly well right out of the box. I learned to GROVEL before I learned to HOVER.


Many thanks to the R/C helicopter community on HeliFreak.com and my friends at my LHS who have helped me get the most out of my CX3. Long hours of frustration and trial-and-error have been spent learning the ins and outs of this little bird, but in the end I have enjoyed my CX3 immensely. Nearly every part of the heli has been replaced, either broken in a crash or worn out by over 60 hours (!) of flying. Today it flies beautifully and I am out burning batteries nearly every day that the weather permits.
Additional credit goes to John Salt in Canada who has published an excellent review and tutorial on CX3 performance and troubleshooting at http://www.rchelicopterfun.com/blade-cx3-tips.html. His explanation of Toilet Bowl Effect (TBE) and its solution are spot-on and should be checked out by anyone who experiences this insidious and aggravating condition.

Set-up checklist:
Note: When first setting up the helicopter, such as after a major overhaul, this checklist would be performed from the bottom up starting at the servos, linkages and swash plate, then the lower rotor, and finishing at the upper rotor and flybar (in the order of assembly). The idea is to make sure the static set up is square and true. In most cases a new heli will be properly set up right out of the box unless there is shipping damage. The top-down approach below is for troubleshooting a heli that has already been set up or one that does not fly properly out of the box. When doing my "C-check" overhauls I do this in a round-trip fashion, going up from the bottom during build and then down from the top during flight test. The result should be a smooth and stable helicopter that performs well.

Mechanical setup:
Start at the top of the rotor system and work down, finishing with the swash and cyclic linkages. Most mechanical stability problems start at the flybar and upper rotor, as these are most susceptible to damage and imbalance.

• Flybar:
  • Check that the flybar is perfectly straight - no lateral or vertical displacement. When viewed end-to-end from one weight to the other across the rotor head the weights and bar should align perfectly across the head. The importance of this cannot be overstated - failure to remedy a bent flybar will throw all your other adjustments off and make trimming your heli virtually impossible. A bent bar will introduce vibration, upper blade tracking issues and possibly TBE instability.
  • Check that the flybar pivot and linkage are perfectly free with no binding. The pivot should not have any sticking or "trick" points in it. With the linkage disconnected the flybar should teeter freely and settle randomly to rest (not necessarily level, but most likely). The linkage should be free, ball links should be very loose but no end-play. The link should hang loosely from the flybar when disconnected from the upper blade ball.

• Upper blades and rotor disc:
  • Check for blade balance by spinning up the rotor and noting any wobble. Bent shafts are not the most likely cause of rotor imbalance unless damaged in a crash. More likely the blades are not matched. Find a matching set of blades that minimize rotational vibration. Some people like to balance blades by using clear tape on the lower surface of the lighter blade, but I have found that with a little patience a reasonably matching pair can be found in the package. Mark matching pairs with a silver sharpie marker for future reference.
  • After the blade pair has been matched, adjust blade tip tracking by turning the flybar link a half-turn at a time, noting whether the tracking gets better or worse. Continue adjusting in the appropriate direction until both blade tips track. Two or three half-turns should do it.

• Lower blades and rotor disc:
  • Lower blade balance can be optimized the same way as the upper rotor, by matching blades. Imbalance on the lower rotor is more difficult to test because of the stiffness of the shorter shaft, and is of less consequence for the stability and handling of the heli because it is lower and closer to the center of gravity. Check for blade damage and smooth operation of the lower rotor. Because the swash linkages are fixed in length the tracking of the lower rotor blades is not adjustable.

• Swash plate and linkages:
  • A common failure with e-Flite stock plastic swashes is separation of the upper and lower halves. This is a very subtle but damaging problem as the separation is invisible and very difficult to detect without disassembling the rotor system. The swash separation causes soft or erratic cyclic response and can cause the heli to drift laterally or roll completely over. Trimming at the transmitter is not enough to compensate. A separated swash can be repaired by pinching the halves together with a pair of pliers, but this is very difficult on an assembled system and usually the swash has to be disconnected or removed to fix. I replaced a swash that separated after about 500 flights because it wore out. The best permanent fix is to replace with the aluminum swash upgrade which is expensive and adds some weight, but it my mind the durability is worth it.
  • The stock plastic swash linkages are not adjustable. The only thing to check for is proper installation. The links should be vertical, aligned with the rotor shaft, and the slots in the links should ride on the alignment pins on the lower rotor head.
  • With the radio on and trims centered, the swash should be level. Adjustment is made by turning the servo links a half-turn in or out to shorten or lengthen. Before doing anything else make sure the servo arms are level when centered. The splines on the servo shaft and arm may not allow perfect level, but get as close as you can. Eyeball the swash as level as possible, then flight test for fine adjustment. If everything else is right the heli should hover in place with no lateral drift (forward, back or sideways).

Electronics setup:

• Proportional control:
  • The proportional adjustment on the 3-in-1 unit controls the balance of power output between the two motors. Power imbalance results in twisting or yawing of the helicopter that the heading-hold gyro will not correct. For persistent yawing issues turn the adjusting screw in very small increments until the yaw is eliminated. In older 3-in-1 units the manual says to adjust the screw in the direction of the correction, though experience shows that new units are reversed and the screw should be turned in the direction of the yaw rotation. As a starting point center the adjusting screw by turning in both directions to the endpoints, noting the full range of travel. Turn the screw to the halfway point and work from there (my proportional adjustment travels about 3/4 turn end-to-end).
    • Note: if your heli is older and has a lot of hours on it, this may not fix the problem. One of your motors may be on the way out, in which case the only fix is a new motor. I replaced both of my stock motors when one failed on the thinking that if one failed, the other wasn't far behind. Another consideration is that a failed motor may fry the ESC in your 3-in-1 unit, as mine did. The increased current draw on the failing motor burned it out, and both failed at once. Fortunately the heli was only five feet up, but it was still a $75 repair.

• Heading-hold gyro:
  • The HH gyro should be properly adjusted from the factory. The most common adjustment is made to "soften" the gyro authority by lowering the gain adjustment. This results in a slightly less precise hold but eliminates the twitching tail that is common in these helis. Note that the HH gyro will not compensate for yawing caused by skewed proportional adjustment, worn motors or rudder trim on the transmitter. Its sole purpose is to stop yawing rotation in the absence of rudder input. All of the above are interpreted by the gyro as intentional control inputs. Adjust the gain of the gyro in very small increments, low enough to stop the twitching but high enough to give crisp and solid tail-holding response.

• Swash settings: (Spektrum DX7 settings shown)
  • These settings are not possible on the stock LP5DSM transmitter that comes with the RTF.
  • Swash type: 3-servo, 90 degrees.
  • Aileron - 100%, Elevator - 100%, Pitch - 0% (zero).
    • NOTE: The swash will bind on the rotor shaft if travel is excessive. If you move your servo links to one of the outer holes for more cyclic travel you will probably encounter this. Reduce aileron and elevator travel limits in the transmitter until binding is eliminated. My links are in the second servo arm hole and my settings are 90%.

Troubleshooting:

The following symptoms are not listed in any particular order.
The causes are listed in order of likelihood.
The solutions are either self-evident or mentioned in the setup and inspection steps above.


Wobbling rotor shaft (noted at the upper head):

• Bent flybar.
• Un-balanced upper blade set.
• Upper bearing unseated from lower shaft.
• Bent shaft (after a major crash).

Yawing or spinning:

• Rudder trim not centered on the transmitter.
• Adjust the proportional control on the 3-in-1.
• Worn motors (reduced flight times or screeching bearings are a sure sign of this)
• Binding in the shaft bearings.

Cyclic response soft or erratic:

• Separated swash plate.
• Swash not level when centered.
• Binding servo or swash linkages.
• Improper travel (reversal) of cyclic servos (aileron and elevator).
• Improper swash settings in transmitter (if used).

Roll-over on takeoff:

• Skids caught in the grass.
• Landing surface not level.
• Wind.
• Swash separated or not level.

Moving to one side, forward or back:

• Aileron or elevator trim not centered.
• Swash separated or not level.

Tail twitching:

• Gyro gain too high.

Toilet Bowl Effect (one of my favorites):

• NOT caused by bent shafts, blade tracking or gyro settings.
• Flybar and/or upper rotor system is not balanced and free-moving.
• PERIOD.

Heli sinks when cyclic control is applied:

• (Note: some sinking is normal as the lift vector shifts, but it is very minimal and not a problem.)
• Swash binding on rotor shaft (travel is excessive).

[QueadlunnRau]

Good thread.

[Skyranger]

just got my CX3 back from Horizon and will not change anything anymore. I called and they left the alum swash and top O.S.bearing "alum", and top head, and put on a CX2 body. It is like a sewing machine and no shakes...PERFECT, just what I thought I was buying. My $100.00's of upgrades will stay in their old boxes. Fly this heli for what it was made for, Fun!!

[elmarco]

How much was it to send back and fix up? what was wrong with it before you sent it!
Is the aluminum swash plate worth it?
Thanks I just got mine and am looking to set up for better flying.

[Skyranger]

When I got mine it did not fly right. After all my calls to Horizon they sent me a prepaid shipping label. I took all my "upgrades" off except the alum bearing on the outer shaft, and the alum swashplate, which is worth $17.00. They put in new motors with heatsink on and a new 3 in 1. It is a CX3 with a CX2 fuselage. It does not shake or twich at all and flys perfect. I had heli-tec extended shaft on it, with bladegrips and EXteme blades and a boomtown tail. Also I kept the boomtown skids. I also had a heli-tec shortened flybar, now it is back stock. I will leave well enough alone.

[elmarco]

Thanks for the info .... I just sent for Superskids for my cx3 and am looking at
http://www.flyrcrivesud.com/index.html upgrades! did you ever hear of them and are they as good as Extreme?
Thanks for your help!

[bobbygee]

I just replaced the main frame on mine after breaking the swash plate bracket. Since I was going to have it apart, I decided to upgrade to the metal swash plate.
While setting up the linkages to have a flat swash plate at neutral, I noticed that the shaft and blades turned when I "stirred"the right stick to check for full movement of the swash plate.
I went ahead and tried to fly and the heli twirls to the right.
What can be causing this?
Thanks,

BobbyG

[Cheetah62]

If I understand what you're saying, it sounds like the swash is binding against the outer shaft at full travel. This would cause the lower rotor to turn slightly as you stir the stick. Check this - does the direction of rotation reverse when you stir in the other direction? If the swash is binding against the shaft then travel is excessive. You will not only experience a slowing of the rotor in flight at maximum cyclic deflection and a sinking of the heli, but eventually a wearing of the shaft and swash. Reduce your swash travel by moving the servo link to a closer hole on the arm (make both aileron and elevator links the same) or reduce travel in the transmitter swash settings.

[bobbygee]

Thanks Cheetah - yes, it does reverse when I stir the other way. I thought it might be the swash rubbing on the shaft, but wasn't sure of what to do about it.

I'll reduce the travel using the Tx.

As for the spinning, I followed your initial post in this thread and found the midpoint on the proportional at the 3 in 1. It now has some left drift on the nose which I'l take care of at my next session, I ran out of time today.

Thanks for your help - this is a great thread!

BobbyG

[eflight blade-3]

eflight blade-3 need help bab my cx3 wants to spin to the right facing from tail will not yan to left or try to lift off eny help app,

[Cheetah62]

Did you go through the checks at the start of the thread?

[Skyranger]

great thread....so true , all of it ..#1 was a perfectly straight and balanced flybar...#2 balanced blade sets...#3 aluminun swash...+10...Dave...I did it ..it works..like AA

[Cheetah62]

It only works if you work it.

[Skyranger]

Cat man..thanks, and I Am doing to everything to unF myself from my old self, + flying helis FUI is dangerous and stupid.....I am in treatment for alcohol addiction, got it from my dad an airline Capt. drunk...just starting to be truthful, it's not fun... Dave ....I can't believe I am saying this..treatment may be sinking in, lying all the time is harder than anything.............

[Cheetah62]

I've got 11+ years now.
I count my blessings every day for the opportunities that I've been given.
The things I have in my life today would not be possible as I was then.
You're right - the old way was a lot of work.
What a relief.

[Skyranger]

Again..thank you for your honesty in public. You make me proud to be like you... Dave....made my day !!!

[Flight Life]

18 years this August.

[LBCAK]

15 minutes for me... but I don't think a beer or two every month or so is over doing it.

Congrats guys...

BTW, I didn't know this thread existed. I guess now I have to get the CX2 back out and see what I can do with it. (2 HRS from LHS makes for an expensive parts run!)

[kaiser01]

great thread. i can't wait for my parts to arrive so i can go through the checklist and get some flight time.

i'm not giving up on the cx3.

[Luvmyhelis]

With a little work and some patience they are quite addictive!