To rotate the disc, it must be connected to a driving source, such as a motor. They are commonly driven by pulse-width modulation (PWM) generators (though modeled as if driven by linear-gain amplifiers) and provide position information via attached digital encoders. The Maxon Precision Motors Re-35 DC brushed motor meets all of the design requirements when geared to the disc at a load-to-motor ratio of 1:2, and has a form factor on the order of the disc radius.
|max (continuous) torque||105||mNm|
|max (stall) torque||493||mNm|
|damping coefficient||1.22||mNm / (rad/s)|
|torque constant||119.00||mNm / A|
|back-EMF constant||0.12||V / (rad/s)|
|armature inertia||65.5||g / cm^2|
We have modeled the motor as powered by a linear gain amplifier, which is uncommon due to power efficiency and cost concerns. Instead, we use a more conventional pulse-width modulation (PWM) generator. We treat the PWM output signal as if it were the equivalent output from a linear gain amplifier, since PWM generators that produce a high-frequency output have approximately the same effect, and mathematical representations of PWM signals are cumbersome.