Tennis Ball launcher motor selction...

Hi there, I'm planning of making a tennis ball launcher original link --> http://arduino.cc/forum/index.php/topic,110827.msg858362.html#msg858362

im having trouble as to how powerful should the motors be? hi speed? hi torque?

i found this motor on ebay...will it do? --> http://www.ebay.ca/itm/RS-550PH-Motor-12V-DC-14-100-RPM-High-Power-550-Size-DC-Motor-Nichibo-/270971721651?pt=LH_DefaultDomain_0&hash=item3f172c57b3

Full load (maximum efficiency @ 12VDC) performance characteristics: Speed: 14,100 RPM Current: 7.75 A Torque: 500 g-cm (49.0 mN-m) Power output: 72.3 Watts Stall torque: 4400 g-cm (432 mN-m) Stall current: 60 A

any help would be greatly appreciated. thanks in advance. SN

im having trouble as to how powerful should the motors be? hi speed? hi torque?

How will the motor actually launch the tennis ball? Trebuche style? Or like a pitching machine? How fast should the tennis ball be launched?

Picking a motor is a small part of designing a tennis ball launcher. It needs to work with the rest of the design.