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Sunday, September 23, 2012

Fixing the Blade 130 X (100% Vibration Fix)

Anyone who’s flown the Blade 103 X will tell you, the tail was botched badly. 

The vibration problem:

Horizon Hobby wanted to use a Z8RC mCP X boom truss to limit 130 X vibrations, but bad implementation decisions drove them down a wrong path to disaster.  In order to attach the truss to the boom, HH used a square cross section Carbon Fiber tail boom.  The square x-section was a rookie mistake, as most people know CF isn’t that great in torsion rigidity in the first place; go to a square x-section and you’ve built a real twisting fool.

This means that any rotor imbalance (in blade lift or blade mass) will be magnified through the end of the twisty tail, and certain frequencies will resonate.   HH made the rookie design error of attaching the truss mid-way down the boom, encouraging one octave higher harmonic resonance.

Before starting any fix, do a blade balance and see if the problem is reduced or eliminated.  I was able to reduce, but not eliminate the vibration with balance.  The rest went away with the fix below. 

Balance both the tail blades and the main blades.  There are two methods to balance heli blades.  One is to start adding small pieces of tape to one side and do the “better or worse?” test.  Repeat until it is as good as it gets. 

The other is to remove the blades and use a single screw to attach both blades together through their mounting holes, fairly tightly.  Do this with blades like they are on the helicopter, extending in opposite directions.  Now you have a seesaw that can be balanced pretty easily, using tape, by setting the shaft of the screw on two raised blocks or drinking glasses, etc.

To fix the boom design, first, I added longer CF rods, CA’d into ball links to fashion larger trusses, then I inserted a small section of CF tube in the middle as a tensioner and a 3-point stiffener.  The tail control rod needed to be bent a touch straighter, easy enough.

photo

An invisible fix, in the photo above, was to stuff an aluminum tail axle spacer tube (from a 130 X tail gear kit) into the boom itself, to eliminate resonance inside torque tube. It is a perfect fit.  Slide it almost, but not quite half way down inside the square carbon fiber tail boom.  It will get stuck in there, from the natural squeeze of the boom.   The torque rod passes through it perfectly.

The Blade 130 is a much more rigid flier with this Z8RC 100% vibration fix.  Handling, tracking, and hovering are much improved!  Flips are a lot more predictable.  Now if I could fit up some digital servos, this little copter would really rock and roll.

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