Mindboards

http://www.bricklink.com/catalogList.as ... &catLike=W

How is this piece a clutch? It seems to spin freely on the axle.
I tried looking at the instructions of sets that include the part, but I only see it spinning freely.

I would very much like to use this piece to feed power to another 16-tooth gear, but I can't figure it out.
Is there a second piece that fits inside it to provide a friction-slip function?
I suppose it could be mounted on a friction pin with a stop-bush
but, wow, that would be hard to use.

The back side has a recessed section with four teeth inside the outer surface. You have to use it with a transmission driving ring.



http://www.bricklink.com/catalogItem.asp?P=6539

There are two types of clutch gears now, the old ones like the picture you posted can be used with old 1/2 bushings with a similar tooth pattern on the face or side of them, to make a weak but simple clutch. The new version has a smooth ring on the side. Here is the old 1/2 bushing:



http://www.bricklink.com/catalogItem.asp?P=4265a

Here is an example of how to use the clutch gear and transmission ring from our friend Sariel:

http://sariel.pl/2009/01/10-speed-manual-gearbox/

Great!
That's two parts explained!

They won't work for me this time, but there's always next time.

And regarding the 10speed transmission... Wow.

Thanks

Another use is to transmit motion on a axle that is either locked or spinning in the wrong direction. I used this piece in the steering mechanism of my almost-life-sized model of the mars rover "sojourner". Here: (grey gear in the middle of the pic)



The bogie is rotating on a fixed axle, witch the clutch gear is on to transmit rotation to the two steering axles. This is used on both sides. I'll probably post a writeup of this model sometime soon. Even though it failed, it was still pretty cool.

Back to the topic: those gears are really useful, expecially the old kind. However, with the dawn of the smooth ones, the price of the old are bound to skyrocket. I wish I had many more