Play counterweight trebuchet...

[iacob alex]

.....is a more definite suggestion,than the old one ("Play trebuchet..."/apr.2008).

Let's take a look at:  http://library.thinkquest.org/05aug/00627/phy.html

Here,look at the "launch of projectile's diagram"...a true "short arm-long arm " design.

If we report,the length of the variable arm (sling arm) with:

  -position of the counterweight (fixed arm length)

  -the power ("via" velocity) to throw the mass from the position "short arm" to "long arm"...and nothing more...

...we can understand easy,that we can "untie" the only one "Gordian knot",of a possible simple gravity powered machine: to get a "self" (short to long arm ) in the top position.

     All the best! / Alex

[iacob alex]

.....if  you take a look firstly , at :  www.youtube.com/watch?v=zt4JQlSrpts
...then try to imagine a "modified trebuchet" , playing as a gravity motor ( a continuous torque difference/unbalance  on the same side of the fulcrum ).
Maybe , we must accept reality...before a lot of theory...because...a fact is a fact.
       Al_ex