Comparing the Approaches
| Scheme | How current is switched | Torque smoothness | Position feedback needed | FRC examples |
|---|---|---|---|---|
| Brushed (mechanical) | Physical commutator + brushes | Ripples with segment count | None, it's mechanical | CIM, 775pro, Mini CIM |
| Trapezoidal (six-step) | Electronic switching in 6 discrete steps | Noticeable ripple | Coarse (Hall sensors / back-EMF) | Older/basic brushless ESCs |
| Sinusoidal | Electronic switching, smooth 3-phase sine | Smooth | Fine, continuous (encoder) | Many modern brushless ESCs |
| Field-Oriented Control | Sinusoidal, but regulated in the rotor's own frame | Smoothest, most efficient | Fine, continuous + fast compute | TalonFX (Falcon 500 / Kraken X60 / X44) |
Notice that every row is solving the exact same problem posed back in Brushed DC Motors: keep the push pointed the right way as the thing producing it spins underneath you. A mechanical commutator, a six-step lookup table, a spinning sine wave, and a full FOC loop are four increasingly sophisticated answers to one question.
Tying Back to the Rest of Controls
Every commutation scheme in the table above is what a given motor controller uses under the hood, underneath everything covered earlier in the Controls section:
- Open Loop Control commanded raw voltage or duty cycle, the PWM idea from Brushed DC Motors, one level up, and its feedforward constants, and , turn out to just be this section's back-EMF and torque-current relationships, measured at the mechanism instead of at the bare motor shaft.
- Closed Loop Control covered the PID and PI loops that FOC's / regulation is built from, running on the motor controller instead of the roboRIO.
- Motion Profiling covered shaping what those closed loops are asked to track over time, moment to moment, rather than jumping straight to a single distant target.
No matter how far up that stack you were working, it all still comes down to keeping a magnet chasing a field that always stays one step ahead of it.
Where This Leads Next
Every scheme in the table above still needs to get a voltage or duty cycle command from the roboRIO to the motor controller, and a reading back, before any of it turns into a push. The Hardware Communication addendum covers how those signals actually travel over the wire.