Phillip's efforts yielded positive results, the most important one was the isolation of the sinews from the composite bow as his primary source of energy for his new weapon. He wanted to produce a torsion Katapultos; a engine that was powered by twisted sinew ropes. For next ten years, the Katapultos went through four stages of design.
The first design, devised around 340 BCE, consisted of two sinew ropes that were wrapped around a supportive frame at the front of the stock. Two arms, where a bowstring was attached, were placed through the ropes. After that, four wedges were placed underneath the ropes to increase tension. There was a disadvantage to this design, too little strain energy was produced.
In 343 BCE, the second design came about. It incorporated four holes in the frame, now called the hole carrier. The ropes were threaded through the four holes and held by in place four wooden or iron wedges. The wedges were meant to be turnable, at least initialy they were. After couple turns the ropes cause them to sieze against the top and bottom of the hole carrier.
To solve this problem, the third stage introduced a washer cup. This was used to reduced the amount of friction between the wedges and the hole carrier. But this provided another problem, the ropes would shift around in the holes, which cause them shear and making the engine useless.
The last stage and design consisted of four metal washers that were incorporated in the hole carrier. A counterplate, which the washers rotated on, was countersuck in the hole carrier. In the counterplate there were sixteen holes and they were twenty-two and a half degrees apart.
During the later stages of design, the hole carrier had some modifications done to it.