On Sat, 09 Aug 2003 15:10:03 -0400, Silvan
wrote:

You need to account for the beam inertia too.

I have no idea how to calculate that, so we'll just skip it.

Download the programs WinTreb or TrebStar

I wonder how you'd factor in the roller bearings when calculating arm
inertia. I gather these things aren't usually built that way.

My one started with an axle of 3/4" tube, then bent that during
testing. Nw it runs with solid 3/4" steel. Don't underestimate the
forces around that pivot ! (like they did on Scrapheap Challenge)

there's only one like this
one, and I designed and built the thing myself, and it kicks ass, no matter
what anybody else says.

Absolutely !

BTW, the last couple I made were mangonels, not trebs (twisted rope,
not a weight) One had a 9" arm, for my 8 year old, and the other had
a 12" arm for a friend's birthday.
http://www.jarkman.co.uk/catalog/random/onager.htm