trouble with blade cx

[truthseeker]

i broke the top piece of the inner shaft on mine. no big deal, but when i replaced it with a new one, it got out of balance somewhere and now it does this eccentric wobble thing when you throttle it up. i checked the shaft and everything is straight, so i don't know what to try now. any suggestions?

 

[Candyman]

I don't know much about the cx, but in general, helis love symmetry. My first question is how did you break it? If it was a result of an impact or blade strike, check the blade balance. Even if you chipped a little piece off of a blade it can throw it all off. Check the main shaft to make sure it isn't bent (which it sounds like you already did). And make sure everything is mounted secure and centered. If it's wobbling, there's got to be a reason.

 

[truthseeker]

thanks for the input! the first thing is that the cx has counter-rotating blades and kind of a flybar with two weights instead of blades.
http://www.horizonhobby.com/Shop/ByCategory/Product/Default.aspx?ProdID=EFLH1200
the weights are equal and the blades are new. i broke it bonking the weights on a table. i can't think of what else would be out of whack. i know it's a balance problem but the cause is still a mystery. i think i'll have to part-swap and see if maybe i got a bad part somehow. i suppose it could happen. let me know if you think of anything after looking at the pics.

 

[Candyman]

I'm assuming the flybar is carbon fiber so that's probably not bent. But is it possible that the flybar isn't centered? Is one side just a touch longer than the other? If so, that can quickly send it shaking.

 

[truthseeker]

crap i didn't measure it! it's not CF so i was all worried about it being straight but i didn't measure. i'll try that and see what happens.

 

[rocknbil]

truthseeker,

I got one of these too for xmas and have learned soooo much about helis in the last month.

Yeah the stock flybar is metal and bendable, it should be as straight as you can get it but there are a couple things that can cause wobble:

1. Did you lose the camber link? There should be one link from the flybar to the upper blade, this is not optional, and is the most likely candidate, see pics below.
2. The flybar MUST be on the leading edge of the blade. That is, as the blades spin, it must be in front, not on the trailing edge. (It's only possible to get this wrong if you got the two-piece upper rotor head and it's rotated 90 degrees.)
3. Take off the flybar and make sure the rubber and metal are all the way out on the ends. Don't pull too hard, you will rip the rubber. grab it by the center plastic with two fingers and roll it in your fingers; if it's bent, straighten it as best as possible. Perfect is nice, but it doens't have to be. Now put a razor blade vertically into a piece of balsa wood or styofoam or something, get it as perfectly vertical as you can. Now try to balance the flybar on it without the camber link attached. It's OK for it to be **a little** out of balance, but if it's not, see if you can move the plastic dealio in the center one way or the other. They're usually very solid on there, but if it's bumped and slipped a little try and recenter it.
4. You can do the same with the blades, remove them and snap them together, you may have to put the screws in if you have trouble getting them to hold together. Put two razor blades in the styrofoam about as far apart as the ball ends, and balance the blades on the two razor blades. Sand equal bits off the leading AND trailing edge of the heavy side. I start with 50 grit for a couple strokes, then 100 grit for a couple strokes, then re-check for balance. See pic below.

If you do all that and it's still wobbling - it's a bend inner or outer shaft or both. Remove the upper rotor, then remove the two screws from the collet bottom of the shaft (under the BCX) and slide it out. Roll the shaft across a piece of glass with the head hanging over the edge, if you see any noticable wobble you can TRY to straighten it. If it's the outer shaft that's going to be a bit tougher to remove but same deal. It's not likely it;s the outer unless you crashed it hard and you'd have broken bits off the lower rotor head.

And a tip on the top rotor head: this has to be the dumbest part of the whole design (or smartest, if they want you to buy many many parts.) I've had my CX simply roll over in grass and it breaks off. So below is the coolest mod you'll ever find for the CX.

Next time it breaks (or try this with your old one!) find a piece of tubing that fits perfectly on the shaft. In the pic below, I used an old bearing from a rear axle of an AE truck or GT; the inner race fits PERFECTLY over the broken shaft. Now get some 5 minute epoxy and glue the collar on the shaft and the broken piece after that, be careful to perfectly align the broken peice with the top of the shaft. Let it set, and you'll never break another upper rotor again! The one in the pic below has been through five hard crashes now and the rest of the CX fell apart aound it.

Got LOTS more mods you can do to the CX, like folding blades, lights, etc. etc . . . this thing is flippin AWESOME and I love it.

 

[rocknbil]

A few more tips and mods -

You want to get the heat sink and cut out the top and bottom of your chassis to allow more air to pass through.

Note the chop on the 4-in-1-case - one of the problems with the CX is that it yaws right really bad, part of this is overheating of the 4-in-1.

You can see I've modified the landing gear, used a broken L.G. and copper tubes epoxied together, the wider stance is PERFECT and it doesn't want to tip over on sloppy landings.

You can also see the folding blades mod in this pic.

Did a custom paint job using regular RC body paint. It's not as glossy as model paint, it has kind of a sheen, but it's tough stuff and won't chip if you rough up the surface. I used the natural lines of the CX which are beautiful anyway and let the natural color of the fuse shine through as accents, so the only actual paint here is the red.

Then I added lights . . . . The headlight is OFF in this pic, when the voltage drops it goes out. Sucks. But the top red one on the tail feathers blinks. Tap it right into your main power leads. superbrightleds.com


I'm so hooked. LOL . . .

By the way the only mod here I didn't pic up from someone else is the landing gear, just giving credit where credit is due.

 

[truthseeker]

got it done. thanks man! it was the flybar all along. i had it on the trailing edge after all. see it fly [ame="http://media.putfile.com/heli-vid"]here.[/ame]

EDIT: oh btw, i saw an aluminum rotor head on horizon's site today. they got smart i guess. see it here.

EDIT2: just saw a police body kit too. now that's cool. not as cool as the custom paint, but still pretty cool. i think i'm gonna paint mine too.

 

[rocknbil]

S**T Man I can't fly half that well! I've been practicing though, going from L.R. floor to kitchen table to L.R. coffeetable. Total rush!


Yeah got mine pre-ordered. Dammit. All this work modding and NOW they come out with 'em. 'Sokay, having a loto f fun coming up with the mods.

<sigh> Guess I gotta get off it and do the vid thing. My digicam is video only though, will see if I can talk the wife into shooting one in the next day or two.

 

[truthseeker]

hey do you know of a bigger capacity lipo pack for it?

 

[rocknbil]

You can't. Won't fit and most likely be too much for the 4-in-1 unit, that's the word around the 'net on that one.

Hey one thing I found out - you definately want to shut it down as soon as it won't climb at full throttle. If you let it run until the motors stop, this will GREATLY reduce the life of the battery and even cause it to catch fire eventually.

If you have a digital voltmeter, at the end of a run put one lead on the CENTER post of the white charging jack and the other lead on either of the two leads in the red plug that plugs into the BCX. This reads the voltage of each cell, you should read at least 3.5 volts on one of those and -3.5 volts on the other. This is just about where it drops to when the BCX can't lift any more.

If you run it until the blades stop, this will bring the voltage under thre volts - which is actually very dangerous with lipos. The more voltage you leave in, the longer the battery will last. A lot of the vets are running for five minutes and shutting down, leaving their voltage at somewhere around 4 or 5 volts per cell.

Also after a run, the cells may be a little out of balance at first but let them cool and the voltage between the two should not vary more than a couple hundreths, like 3.59 and 3.61. If there's a half-volt difference betwen the two you would be very wise to retire the pack as it can blow or catch fire during charging, flying, or just carrying it across the room!

Lipos can be dangerous if out of balance or overdischarged. I always charge mine off a DC source (starter box battery) so I can set the whole deal outside on the concrete.

Important thread to read for ANYONE using a lipo.

 

[truthseeker]

yeah, i was afraid of that. well, you're right on about the battery stuff. i've read that thread too. there is a video there somewhere that will show you exactly what can happen if you don't respect those lipo's. if there are any r/c noobs reading this, PAY ATTENTION! these heli's are particularly easy to abuse the lipo pack with. i've seen a lot of people with zero r/c and lipo experience buy these helis and i feel like we're going to see a lot of fires and stuff before everybody gets up to speed on these things. i'm going to blame e-flite a little here, because they don't make a big enough deal out of being careful with the lipo's. i've seen at least 10 people run the packs down to the point where the motors won't even turn. THAT IS SO BAD I DON'T HAVE THE WORDS TO DESCRIBE IT!! so far i have seen one explosion right in the heli as a direct result of doing this. please, for yours and your family/property's sake, read the thread linked above.

 

[jmarzilli]

Just picked up a CX and love it. Rocknbil can you post up a link to the folding blade mod, cause I have been unable to find it on the web.

 

[rocknbil]

Here ya go. To be honest, it's not as great as you'd think. But it does work. Use your broken blades for the blade base and new ones for the actual blades. Tighten the screws snug but not killer tight. Make sure all your holes are drilled exactly the same, and when done balance the blades, this is most critical.