I'm trying to design a simple torsion spring catapult to launch a 0.15kg ball at a velocity of 35 m/sec at the moment of separation. The ball will be in direct contact with the unrestrained end of the spring. As a starting point, I'm planning a 0.3m length for that "arm" end of the spring as measured from the center of the torsion coil. I'm also starting with an assumption of 45 degrees of contact/throw for the arm. Can anyone help me define the torsion spring I need?