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Really Bad Bounce On The Bench

Old 10-30-2008, 04:17 AM
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wiggles
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Default Really Bad Bounce On The Bench

Have taken the leap and bought myself my first Chopper after 15 years of Planes. Bought a Walkera 68B. After 5 minutes of very careful, just taking the weight of the training balls, it flung itself back and on it's right side. Stripped the main gear and damaged the blades. A screw had come loose. Got the replacement parts today and put it all back together. Ran the it up on the bench to check blade tracking. Very slowly. At less than 1/4 throttle the whole thing started to bounce violently on the bench. The blades seem to be tracking perfectly. There was no vibration before it started bouncing. Can some one give me a clue as to what to try? I know zip about Choppers. Forgot to say, I was holding it down with my hand on the skids and I moved the motor back to mesh with the gears.
Old 10-30-2008, 05:25 PM
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robtangie
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Default RE: Really Bad Bounce On The Bench

First off that's a good way to cut the crap out of your arm. You should use something heavy through the skids (not your arm, lol) or actually screw it down to the bench.
Now that the safety lesson is over,,, check your servos. Be sure that one (or more) dosen't have a stripped gear. It's pretty common to strip those plastic gears and that would cause it to jump or bounce as you described.
Good Luck.
Old 10-30-2008, 08:35 PM
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Default RE: Really Bad Bounce On The Bench

That is actually ground resonance. Usually from a springy connection to the ground like the skids.

It usually won't resonate if you were to hold it down rigidly... however the skids aren't designed for to hold that much force and you could actually break the heli from the skids and then it would fly wildly across the room into your face...

Blade tracking should be done (saftey glasses/helmet on) while in a free hover without connection to the ground.
Old 10-31-2008, 03:11 AM
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wiggles
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Default RE: Really Bad Bounce On The Bench

Thanks for the replies. Have checked the servos, Apart from the rudder which doesn't center properly, it will be replaced, all servos are working correctly. The bounce isn't a gentle thing, it was almost like hanging onto a jack hammer. Throttle setting was not that high. Way less than 1/4. It got light on the balls closer to half throttle.
Old 10-31-2008, 06:39 AM
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Default RE: Really Bad Bounce On The Bench

Dose it do this everytime you spool it up or was it a one time deal? Are you sure it's a bounce and not a vibration from something being bent or out of balance?
A bounce that violent at 1/4 throttle sounds very strange.

Hi VulcanGrey, you and I haven't butted heads over anything for quite a while. Good to hear from you.
Old 10-31-2008, 03:34 PM
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Default RE: Really Bad Bounce On The Bench

It did it 5 times. Always at the same throttle. slowly increase throttle, for 1/2 a second it is fine the it starts. I shut it down immediately. Going to take the blades off today and see if it still does it. Can't be the blades out as they seem to be tracking perfect.
Old 10-31-2008, 09:22 PM
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Default RE: Really Bad Bounce On The Bench

I'm getting the feeling that you have bent something when you laid it over. You continue to say that the blades are tracking perfect but how do you know that,,, you need to be up around half throttle to assure they are tracking good. You may have well bent the main staft as it dosen't take much to do so. Also check the flybar, be sure it's centered and they are at zero pitch.
The 60 and 68 are very fragile (IMO) with the metal frames so also be sure to take a long look at the upper frame to assure it's not bent also. I'm convinced it's not bouncing,,, something is most likely out of balance or bent. It's just a matter of finding it. Again, I'd start by looking at the main shaft.
Old 11-01-2008, 03:05 AM
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Default RE: Really Bad Bounce On The Bench

Started to think that way as well. Took the blades off, reduced it to a bad vibration. To me this means it is somewhere in the main drive. Pulled the paddles off and got the bar out. Is this supposed to have a kink in it? Is there any way to check the main shaft without pulling it out? I know I laid it over but it didn't seem that bad.

Just ordered new fly bars and main shafts. Should of spent a bit more on my first chopper. 2 of the servos won't centre now so will swap them all out and having real bad glitches on the bench so the radio is going as well. Not happy.
Old 11-01-2008, 09:13 AM
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Default RE: Really Bad Bounce On The Bench

The best way to check the main shaft is to take it out and roll it on a flat surface like a piece of glass. And no there should be no kink in the flybar.
You must understand that with any quality of heli that the blades at speed are traveling at about 200mph. Any 200mph crash has to allow the force to go somewhere. I found that the weakest points of the 60 and 68 are the frames but the real trick is to not crash, lol. I own a Trex and a CopterX and if I lay either of them over at speed I'm going to break, bend, or otherwise tear something up. It's the nature of the game,,, if you make them light enough to fly, you can't make them heavy enough to take an impact.
As for the glitching, that too is common with the metal frame helis and there are ways to fix that too. One thing that helps is a ferrite ring on the ESC wire. The best thing I have found is to ground the upper frame and lower frames together. For this I took an old computer coax cable and stripped the coax wire from it. I used it as a grounding strap from the upper frame (hook it on a scerw) through the tail servo mount (be sure to scratch off the blue or clear plastic coating on the boom) and down to the lower frame. This grounds the whole unit together and eliminates any static discharge caused by the belt drive and should stop your glitches.
It's kind of a pain in the butt, but it's cheaper than a new radio. Also, look up a site called Radds School of Rotary Flight. It's a great teaching tool and will help to make sure you don't lay it over again.
Old 11-01-2008, 02:28 PM
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wiggles
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Default RE: Really Bad Bounce On The Bench

Thanks for all of that. Have looked up Radds School of Flying. It was the way I was doing it. Nice and slow. I don't have to get a whole new set, just a receiver. As it was glitching with nothing going, that is what I will be doing.
Old 11-01-2008, 05:52 PM
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Default RE: Really Bad Bounce On The Bench

As for Radds, he says to practice without training gear. That's about all that he says that I disagree with. There is no harm in useing the training gear.
I'm guessing the radio that came with you 68 isn't the 2.4ghz. I did upgrade my 60 to a futaba 2.4 but just prior to receiving it got my glitching to stop.
Good Luck to you and don't give up, sometimes it's a hard climb but well worth it when you reach the peak.
Old 11-02-2008, 02:46 AM
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wiggles
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Default RE: Really Bad Bounce On The Bench

No, wont give up. to damn stubborn for that. I have two of these choppers and they WILL fly right. Just annoyed that what started all this was a bolt falling out.

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