Hi.
Here's a small info about my experiments with the rcxplorer.se tricopter.
I had it build as to the plans, but during a rebuild after e huge crash, i had to replace the arms, here i desided to do some testing, i streched the arms a bit, in my mind, this would create even more stability. I mesured the lenght of my wires, and added an extra 5 cm, (app. 1,5 inch) to the arms. No big deal.
But, to dial the settings in. Ohhh!!!!
It had so much ocilation, wobble and unstability, i could not understand what there was wrong. I then got it dialed in at the best i could, and in a tail in hover, i studied the yaw and rear arm...
Surprice, BIG TIME.
A breif rudder input made the tail/yaw/arm go crazy. Wobble and shaking out of control, but yet the tri was maintaining it's hover??? Uhhh.
Some more investigation, and i realize that the flexing of the used pinewood is getting bigger and bigger as you strech out the arm.
Longer arm = more flexing
Shorter arm = less flexing
So the 48 cm (18,9 inch) is about the max lenght of pinewood arms.
You could though experiment with some reinforcement with carbon etc.
But then the entire plan of using wood goes down the drain.
But her's the video.
I hope this answered some questions, and spared some experimental time and hair-pulling.
Rene'
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I think the only way to strech the arms are by using Carbon Fiber rods.
So stick to the max 48 cm, unless you wanna "Rock 'N Roll"
That lenght is also enough to make a fairly stable platform.
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I know that carbon is stronger and more ridgid.
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Also, to save weight in the future, you can use soft light wood in the core of the arm and use harder/stiffer woods on the outside surface of the arm. You can also vary the cross sectional area of the arm. Start with a thick section at the base and narrow it down as you get towards the motor. This will give you the highest stiffness to weight ratio. It also gives you the highest strength to weight ratio.
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That would be an option, if you need the bigger reach/longer arms.
Mine was a "experiment" so it took only a few minuts after locating the problem, to move the motors inwards, and chop of the excess 5 cm.
Not that big a deal, the tri still flyes really stable and well.
But thanks Dirt Pilot for sharing your solution and thoughts.
Rene'
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Keep up the great work!!!!!!!!!!!!! ;)
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I will continue.
Rene'
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Ensure you use a non-stretch cable like wire or kite string such as 'Spectrum'. Also ensure you have balanced tension between all three. Don't over tighten the cables so you don't promote a catastrophic failure in another plane.
Here's a simple illustration of what I'm referring to.
http://img.photobucket.com/albums/v606/Cyberdactyl/tricopterstrut.jpg
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But some is also a rotation in the wood.
And the size it have now, the 48 cm arm length, is also a really great size for a Tricopter.
It almost draws a circle of 1 meter.
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