This little widget doesn't take much building, and will flutter across a room.

_{(No video because I ran out of bands in prototyping, and I need to get this posted before the deadline.)}

Step 1: Materials and Tools

The materials you need:

Three paperclips. I used large ones that opened out to 15cm long, but I see no reason why this wouldn't work with ordinary clips.
An elastic band, sized to match your clips (the ones I used were 6cm long).
Paper - stiff and light for preference.

Tools:

Pliers (two pairs could make life easier).
Glue or tape.
Scissors or craft knife.

Step 2: Making the Frame

First, carefully straighten the clips and measure to find the middle.

Bend one clip to an angle of 90^o - this will support your front wings.

Bend the second clip 90^o as well, but then bend the wire back 45^o on each side of the first bend, making a straight wire with a V notch in the middle - this will support the back wings.

The third clip is much more complicated:

Turn a small loop in the middle of the wire (I wound it round the handle of a small paintbrush).
Bend the straight sections so that, when the loop is held horizontal, the straight legs point vertically down.
Bend the ends of the legs into an L (on the same side as the loop) and then bend the bottom of the L into a small V.

(Check the images to see what I mean.)

Step 3: Building the Frame.

The back wing-clip is connected to the middle frame you constructed in the last step.

Place the V between the two bent parts of the L you made, and use the pliers to clamp the Ls tightly over the wing-clip. Make sure that the point of the V is pointing up into the frame.

You are now ready to add the band and the wings.

Step 4: Design the Wings

I was aiming for a butterfly style, but you might want to use different-shaped wings.

I lay the frame on the paper, and sketched roughly what I wanted the wings to look like. When I was happy, I firmed up one side of the butterfly in marker pen, allowing for tabs to fold over and glue.

I then folded the paper in half to cut it out, thus making two identical-but-mirrored sets of wings.

Step 5: Add Power

I discovered during prototyping that it is easier to add the rubber band before attaching the wings. If you have to replace the band later, because it snaps, you will discover how hard it is to stretch it over the wings without crushing them.

Attach the band to the rear wing-clip with a lark's head hitch, then thread it through the loop at the other end of the frame, and thread the front wing-clip through the band.

Step 6: Add Wings.

Fold the tabs over the wing-clips and glue in place.

Make sure that the wings do not foul the frame or each other when they turn.

You could, of course, decorate your wings, but I would use ready-decorated paper (if I had any), such as the colourfully-marbled origami papers you can buy.

Step 7: Winding and Flying

To wind up the butterfly, hold the rear frame in one hand, and spin the front wings round with the index finger of the other hand until the rubber band is as tight as you like.

Hold the butterfly flat between the palms of both hands, and toss it into the air as if releasing a dove.

Both sets of wings will spin in opposite directions (if one set is larger, it will spin more slowly than the other pair), and the flat wings will bend, forming a pair of crude propellers - they work together, even though they're spinning in opposite directions.

The loop you made at the top of the frame is like a section of a helix; the front wings might catch on it, so you might find that the butterfly works better if you wind it one way and not the other.

Step 8: Oh, No!

As I said, flying the butterfly is simple.

Unfortunately, accidents during prototyping reduced me to just one last band. After test flying the final model, I decided to wind it just a little tighter to make it fly really well in the video.

_{I snapped the band.}

Still, here it is, ladies and gentlemen, for your consideration - the rubber band powered butterfly.

_{Double oh no! - this isn't as original as I thought. I was just googling for some images of butterflies, intending to draw on my finished wings, when I came across an existing rubber-band powered butterfly make. It's not exactly the same as mine, but identical in the flight mechanics. I hope this doesn't preclude me winning, but if it does, it was a fun make anyway.}