The Scorpio was a smaller weapon, more of a sniper weapon than a siege engine, being operated by only one person. The Scorpio was basically a primitive giant crossbow, a 'catapult with bolts', probably first invented by the Greeks, then later adopted and used on a larger scale by the Roman legions. This catapult used a system of springs with torsion, making it possible to obtain very great power and thus a high speed of ejection for the bolts.

This is another war machine; this machine can be a good example of Maya dynamics. In this tutorial I create ‘T” Shape object and put 3 cube on each end and make two of them passive body. Attach two springs to third cube and set the value of spring. This is very simple and fun to create this machine

High res video 800X600

The onager was a post-classical Roman siege engine, which derived its name from the kicking action of the machine, similar to that of an onager (wild ass). It is a type of catapult that uses te nsional pressure, generally from twisted rope, to store energy for the shot (wikipedia.org).

I try to make that machine with the help of Maya dynamics, I hope you like it.
In this tutorial I first made arm with the help of cube and then arrange dynamic constrain to make it work. Spring played very important part in this simulation, you have to adjust it rest length to make it make properly.

and here is high res video (800X600)

This tutorial is showing how u can emit particle from biped. You can create very good motion with the help of biped and then with biped particle also move same way.

First create biped and give it some motion with the help of *.bip file or create by footstep mode. Create particle flow and change Position Icon to Position object, so that u can choose biped (all part of biped but not bip01).
Remove speed and add Delete operator, put particle life 1.Now change in birth operator and increase particle amount to 100000 or 200000 depending on your system.

this is the render output of this tutorial

High res video for this tutorial is here