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Swash levelling - setting 0 pitch


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matelot
Extreme 3D
Extreme 3D


Joined: 09 Jan 2012
Posts: 331
Location: Back in Blighty

PostPosted: Sat Nov 03, 2012 5:24 pm
PostPost subject: Swash levelling - setting 0 pitch
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.
To try and level the swash, I initially used the zip-tie method, and it got pretty close. The problem was the servo to swash links: the link eyes can only be turned in complete revolutions because of the necessity to keep the letter A on the outside of the link.

What to do?

Firstly, I levelled the Tarot on both axes using small spirit levels. One is shown laid across the frame stuck to a ruler with double-sided tape - as photo below:



Then I attached another level along the top of the pitch gauge. I'd previously used the gauge without the level, and the blades were almost 0 pitch at mid stick. But the swash was clearly still out when I rotated the blades. The 'rabbit ears' method worked, up to a point, but still couldn't level the swash because of the link eye problem.



So, I plugged in the ZYX programmer, and set one blade at 0 pitch with the spirit level on the pitch gauge when the push rod for that blade was over the elevator servo.

In turn over the other two servos, I used the programmer to adjust each servo a couple of clicks to zero pitch the blade at that point. Then rechecked no.3. Shortly, at any point on the circumference, the blade remained at zero pitch. That told me that the swash was level. I even switched everything off and on again to double check, just in case the servos were slightly out. All ticketty-boo.

The next step was to put the pitch gauge on the other blade, and use the turnbuckle to zero it on the grounds that the swash was perfectly level.

It all seems to have worked, but I've ordered a Tarot digital pitch gauge from OOmodel anyway.

Why not use a swash tool? Having to remove the head, many advocate the zip-tie method, some swash levellers don't actually fit properly. And I like the challenge of finding an alternative method that works. Laughing

Any comments appreciated.

PS - the bright LEDs in the background of photo 2 is my homemade power supply. It's a 450 watt PSU fitted with LEDs and banana jacks to give me stable 12v, 5v and 3.3v. That powers my iCharger, and the 5v powers the receiver/gyro/programmer without hooking up the battery.
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Burgess
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Joined: 27 Mar 2012
Posts: 1098
Location: Wales

PostPosted: Sat Nov 03, 2012 9:26 pm
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The swashplate levelling tool needs to be on for checking mid, top, bottom and interaction while moving the throttle through its complete movement.

I first set up the head using these two jigs and invert the swashplate levelling tool, this way the mixing arms are at 90 degrees and the swashlpate is perpendicular to the main shaft. it's easy to see if the pitch link rods need any adjustments.

I use a spare main shaft drop in the bearings and pop in an M2 machine screw through the bottom of the main gear assembly and shaft, drop on a spare swashplate and pop servo link rods onto link-balls on the swashplate.

Well, I pop the link-balls into the servo link rods and screw them into the swash arms when levelled undo them and refit them into the swashplate on the head after fitting it into the heli, that saves popping them on and off.






I then use the flybar locking saddle to hold the flybar at 90 degrees while doing pitch setting.

Doing this sets the head assembly as it would be at zero degrees and the swash also, what do you think'Cool'

Burgess
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matelot
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Joined: 09 Jan 2012
Posts: 331
Location: Back in Blighty

PostPosted: Sun Nov 04, 2012 2:07 pm
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I don't have a flybar, of course, but looking at logical mechanics, it all seems sound enough to me.
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Burgess
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Joined: 27 Mar 2012
Posts: 1098
Location: Wales

PostPosted: Mon Nov 05, 2012 4:31 am
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Here is the engineering rationale for my jig and swash levelling tool system.

The datum line for any rotor head is the main axis.

Zero Pitch therefore must be perpendicular to that datum line.
When both blade holders are held at zero incidence, they are parallel to each other and perpendicular to the main axis.

********Applicable only to fly-bared heads************
When the flybar is perpendicular to the main axis
When the mixing arms are perpendicular to the main axis,
************************************************
When the swashplate is perpendicular to the main axis, -ascertained by fitting the swash levelling tool on inverted under the swashplate- the rotor head is precisely at the zero pitch configuration, just as it will be when fitted in the helicopter.

Using another swash plate and main shaft for the levelling procedures, saves taking an assembled rotor head apart.

The swashplate levelling tool uses an old engineering principle, in this case the levelling tool and any of the swash plate arms, any size of gap will be seen.

Now that's has far more engineering accuracy and logical mechanical application than anything I've seen out there.

Swashplate levelling tools, purchasing an up market brand will eliminate the chance of being provided with an inaccurate tool. 'Cool'
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