Stepper gen reborn!

[fungus]

Had all the parts lying around and had nothing else to do so decided to rebuild it. Its the same stepper motor as in http://www.fieldlines.com/story/2006/3/11/105413/187

I'm using a shaft adapter from a VCR motor,6mm, plywood hub with two bolts on each blade. The stepper motor has a 5mm shaft so to make it up I got an old capacitor that was the right size and hollowed it out :-P

Not perfect, but with a bit of balancing it works. I have tested it out the var sunroof before and it gives 4w or so, but the wind hasnt really been consistent enough to get some good readings, too gusty. When it gets going it really does rev up fast. Its using rich's 12" cnc blades, three of them. Great value at $14 inc. shipping to Scotland. I did find it hard to balance the prop, all teh little screws and bolts around the hub are balancing weights. I used some spare 4 core wire to bring the wire down the pole and made up a rectifier from some computer PSU rectifiers (4 wire stepper). I used an old bed post as the pole and lashed it to the fence. Hopefully I'll get something better rigged up.

Some pics:

[gotwind2]

Good start Fungus - 4 watts from a stepper is pretty good, a mini axial alternator might be the next step with those blades.

Ben

[richhagen]

Looks great!  I've used slightly longer bolts and added extra washers on the light side.  Not perfect, but it works out OK.  Rich

[Ungrounded Lightning Rod]

I did find it hard to balance the prop, all teh little screws and bolts around the hub are balancing weights.

A very slight change in the angle of one of the blades produces a large movement of the center of gravity.

You have a pair of close-spaced mounting screws for each blade crosswise to the blade's length, which means a tiny change in the mount produces a large change in the blade angle.

I suggest you use larger pieces of plywood for your hub - to go out as far as the flat mounting faces of the blades allow - and add a bolt as far out as possible, working against one as far in as possible, to maximize the inner lever arm and thus minimize the amount of angle error on the blade for a given amount of position error at the bolts.  (Spreading out the mounting bolts will also proportionally increase the mount's strength against movement of the blade against the mount.)

Similarly, a VERY slight change to the radial position of a blade makes an identical change to its center of gravity location, requiring a lot of counterweighting near the hub to balance out the error.  So you need to be very careful of your hole's radial positions to avoid injecting a large imbalance that needs a large correction.

[ghurd]

Looks good!

I have removed some hub material from the heavy side when the balance gets close.  Seems easier than adding more bolts sometimes.

G-

[Flux]

Try to keep the balance weights in the centre plane or at least split the weight at each point into halves with one bit on the front disc and one on the back.

With small corrections this doesn't make a lot of difference but with your big bricks on the thing you are introducing a couple that doesn't show with the static balance, but will cause a wobble or vibration when you run it. Blade tips not tracking also result in the same effect.

Correct blade spacing, correct tracking and balance weights added without producing a couple will get you there.

Flux