What screw RPM is recommended to push a medium-size sub? The 1/96 AKULA is 47" long witha 5.25" beam. My reason for asking is I just found some Maxon geardrive motors are on eBay. 1500 RPM at 12V DC, 900 RPM at 6V DC,and 175 RPM at 12V DC speeds are available. The motors can be used with lower or higher voltages and the output speed will be proportional. The output shaft is 3mm dia. Might be a good propulsion choice if I can match the output RPM of the motor to your recommendations.