TLDR - Higher Volts & Field Weakening
Amps generate heat, limiting performance. Better cooling = sustained power-use Statorade, hubsinks, and temp monitoring. Higher voltage delays Back-EMF, sustaining torque and speed. Torque scales with amps until saturation; low RPM is amp-limited, high RPM is Back-EMF-limited. Field weakening reduces Back-EMF, increasing amps at high RPM. ONYX SPM hubs see ~30% higher top speed.
Kelly Controller Field Weakening Settings
- Field: Min Excitation
| Value | Result | Effect | |
|---|---|---|---|
| 0 | Diabled | Off | |
| 10 | Enabled | 20% | |
| 20 | Enabled | 40% | |
| 30 | Enabled | 60% | |
| 40 | Enabled | 80% | |
| 50 | Enabled | 100% |
Heat and Performance
Amps generate heat, and a motor’s performance is limited by its cooling ability. Better cooling = better sustained performance. Statorade, hubsinks, and temperature monitoring are key to maximizing power.
Higher Voltage
Higher voltage allows higher RPM by delaying Back-EMF effects, sustaining more torque at speed.
Torque and Amps
Torque and amperage have a fixed ratio (e.g., 1:1, 1:2, etc.), meaning more amps = more torque until the motor reaches magnetic saturation. At low RPM, amperage limits torque regardless of battery voltage. At high RPM, Back-EMF (the voltage generated by the motor) opposes battery voltage, reducing amperage flow and torque. Once Back-EMF equals battery voltage, top speed is reached.
Voltage and Back-EMF
At low RPM, torque remains the same regardless of battery voltage. At high RPM, Back-EMF (the voltage generated by the motor) opposes battery voltage, reducing amperage flow and torque. Higher voltage delays Back-EMF, allowing more amps to flow at high RPM, increasing speed and power.
Field Weakening
This alters motor timing to reduce Back-EMF, allowing more amps at high RPM, improving top speed and acceleration. IPM motors (like Tesla’s) gain massive benefits, ONYX SPM hub motors typically see ~30% higher top speed and improved acceleration.
Field Weakening Gains
With effective cooling, field weakening could increase performance by 60%, though efficiency trade-offs exist.
Amperage Torque Control
A motor goes through three stages of amperage (torque) control.
- Low RPM: Torque is limited by Phase Amps (controller to motor).
- Medium RPM: Torque is limited by Battery Amps (battery to controller).
- High RPM: Torque is limited by Back-EMF, which increases resistance as speed rises, reducing amps and torque.
At top speed, Back-EMF fully limits amps, preventing further acceleration. Controller peak amperage specs refer to either phase amps or battery line amps, with phase amps being higher.
Field weakening reduces motor resistance in stages 2 and 3, allowing more amps to flow at higher speeds.