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MacGyver

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Joined: 12/05/2009
Location: United States
Posts: 1329

Posted: 04:38pm 29 Aug 2010

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I've been at it again in the shop. This time, I built a little device that pitches the blade of a single-blade turbine in an effort to return its starting position to 40* but allow the pitch to get more shallow (15*) as the thing gained rpm.

I posted something to this affect several months ago, maybe even a year ago, I dunno. At the time, I was thinking it would be cool for a 3-bladed rig, but in retrospect, matching each blade's movement to the others using this method would likely be impossible. For a single-blade, counter-balanced blade, it's the bee's knees.

Oh, I should tell you: I've decided to build single-bladed turbines for a while. They look goofy when they spin, but are actually more efficient than any other combination. By placing weights equal to the weight of one blade and its pitching mechanism (if any) at 120* from the blade each side of the hub, the thing will yaw without trying to jump rope. I'm not sure if the standard furling will apply; I haven't taken things that far yet. When I do and have some results to report, I'll do so here on the 4m.

For now, here's what I've come up with:

This shows the mechanism ("Tool") mounted to the root of a 3" x 2" x 4'
Coroflute blade. The shaft of the tool pinches the blade spar with two
1/4" x 20 screws tapped into the shaft. An old drill bit is positioned
inside the shaft at its center and held in place with a set screw. The
flutes of the drill bit extend through a block that has a "pin" (another
set screw threaded into the block) inserted so it is housed within the
bit's flute. Atop that is a spring and another block (round) used to
adjust the travel as well as spring tension against the block.

Here's a tight shot of the spring and keeper. The spring pulls the drill
shaft towards the center of the hub and the pin is set in a position to
hold the blade at 40*. As the wind spins the blade, centripetal force
throws the blade and attached drill bit outward, away from the hub,
compressing the spring and causing the drill-flute-pin combination
to twist the blade into a new position at 15* where the mill runs.

Here's a shot looking down the blade from the hub. This is the static
or stopped position of 40*. In a perfect world, as the wind increased
the speed of the blade, it would twist smoothly into its final "run"
position of 15*. In the real world it's all or nothing. I spun it with a
drill motor and it's either at 15* or 40*. That's okay, because in reality
all I was after was a way to get the blade to a steep pitch so it would
start in low wind. It does what I designed it to do.

. . . . . MacEdited by MacGyver 2010-08-31

Nothing difficult is ever easy!
Perhaps better stated in the words of Morgan Freeman,
"Where there is no struggle, there is no progress!"
Copeville, Texas

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