FRC Motor Selection for Disc Launcher

Selecting a motor for the disc thrower will need to account for:

The necessary output speed of the wheel launcher

The torque applied to the wheel.

System:

The disc weighs 0.18kg (http://www.andymark.com/FIRST-Choice-p/fc13-141.htm)

Field = 50' max

Speed of Launcher:

Our team did several trials for how fast a disc must be thrown to not drop over 50feet (~15.4meters) to cross the game field. 

The trials results ranged from 1.2seconds to 1.5seconds. 

We use the 1.2seconds as the time to cover 15.4meters.

This provides a linear speed of 15.4m/1.2s = 12.82m/s

A wheel travels it's circumference(pi*diameter) every revolution (distance/rev).

This provides Pi*Diameter/Revolution

Our team examined 6", 8" and 12" wheels

(39.354"/meter)

Now determine how fast the launcher must spin to achieve a linear speed of >12.82m/s

Then convert inches to meters for units

If there is any gear ratio between the motor output and the launching wheel then that must also be included in the rpm to the motor.

The actual excel sheet is a little easier to see the diameter linked to the output:

The spinning objects are measured several ways. 

Cycles per second = Hertz

Radians per second = 2*pi*Hertz

Revolutions per second = RPS = Hertz

Revolutions per minute = RPM = Hertz*60

Motors are usually rated in Revolutions per minute (RPM)

The units for linear speed is meters/second