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Old Aug 22, 2014, 07:31 AM
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leadfeather's Avatar
Joined May 2006
9,479 Posts
Half Mad; slack + spring

I've been playing around with tail surface control a bit and I finally have a system I like for the Mad Stab. Plenty of resolution and perfect 90. So far I have it set up for 90 up only. This is because the current build on has a single side servo arm. This may be good enough for me personally, but I will probably make it do 90 up and down since it is a simple extension of what I have already done.

This new spring and slack method is really easy to set up and give perfect 90's. You can also engineer in lots of resolution and mechanical expo too. With the "eye of the control horn" behind the stab axle, slack will develop in the lines especially as the stab movement becomes larger and one of the lines touches the stab axle; giving the large mechanical expo. The springs may pull the stab well past 90 so I use a wire as a simple mechanical stop.

To visualize, picture a standard pull/pull setup. In the neutral position the pull/pull lines are taught. Now add in-line springs to the pull strings so that if any slack develops the springs take up the slack. Note that the springs positioned any where in the lines (attached to the servo arms, attached to the control horns, attached to the pull string only etc.) so they could be hidden in the pod if desired.

By adjusting the angle and the distance of the "eye of the control horn" from the stab axle it is possible to adjust resolution; the degree of mechanical expo; and the exact stab deflection where the expo kicks in.

Using hard stops; to control 90 up and down; means that trim adjustments do not effect the the full up and down position, this makes set up a little easier.

I'm really stoked about this idea. Implementing the slack + spring is really simple, cheap and light weight. Test flying of the up only first prototype should happen in about a week or so.
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Last edited by leadfeather; Aug 22, 2014 at 10:17 AM.
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Old Today, 10:38 AM
Winging it >
leadfeather's Avatar
Joined May 2006
9,479 Posts
The cores showed up yesterday. Kudos to flying Foam for a nice job cutting these.

I glued the halves together and marked the spars and flaperons. I'm hoping to have this 3rd build done for flying on Sunday.
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