EVUL EMPIRE RACING · TOOLS

KV vs GEARING

Compare a stock motor on a big pinion with a higher-KV motor on a smaller pinion. Same cells, same top speed, same car. All outputs are EST from a simple model. The page shows what changes at the motor shaft, in current, and in heat.

Setup A: stock

Your current motor and gearing.

Motor KV Resistance (mΩ) No-load current (A) Pinion (teeth) Spur (teeth)

Setup B: higher KV

Higher KV motor, smaller pinion.

Motor KV Resistance (mΩ) No-load current (A) Pinion (teeth) Spur (teeth)

Estimate B's resistance and no-load current from A (resistance falls with KV squared, no-load current rises with KV)

Shared car and pack

Used by both setups.

Cells (S) Volts per cell Diff ring/pinion ratio Tire diameter (mm) Car weight (g) Tire grip (μ) Gear efficiency (%) Pack + ESC resistance (mΩ) Current limit (A) Drag area CdA (m²) Rolling resistance (Crr) Rotor inertia A (g·cm²) Rotor inertia B (g·cm²) Motor pole pairs Motor max RPM (0 = off) ESC max eRPM (0 = off)

Measure	A: stock	B: higher KV	B vs A

Shaft torque during the run

Motor heat built up

Speed during the run

EST: Pole count: 2 vs 4 vs 6

Same KV, same gearing, same car. This uses Setup B's KV, pinion and spur and changes only the pole count. Torque per amp depends on KV, not poles, so it stays the same. What changes is iron loss, which rises with electrical frequency (motor RPM × pole pairs): hysteresis loss ∝ f, eddy-current loss ∝ f². All results EST.

Iron share of no-load current at 4-pole (%) Eddy share of iron loss at 4-pole (%) ESC switching frequency (kHz, EST) Estimate 2-pole and 6-pole from the 4-pole values (iron part of no-load current scales with hysteresis ∝ f and eddy ∝ f², resistance held equal)

Motor	Resistance (mΩ)	No-load (A)
2-pole
4-pole
6-pole

Untick the box and enter each motor's measured resistance and no-load current once your test motors arrive.

Predicted	2-pole	4-pole	6-pole

Heat per 132 ft pass

Winding heatIron and friction heat

EST · 8S · 6-POLE

Pole count vs ESC switching

More poles = the ESC has to switch faster. Fewer PWM pulses fit in each turn of the magnetic field.

	2-pole	4-pole	6-pole
eRPM	73,920	147,840	221,760
Hz	1,232	2,464	3,696
Pulses / cycle	16.2	8.1	5.4
Pulses / step	2.7	1.4	0.9

eRPM = RPM × pole pairs. Hz = eRPM ÷ 60. Example: Setup A 2200 KV on 8S × 4.2 V = 33.6 V → 73,920 RPM. ESC switching 20 kHz is EST (E6 Max not published). A 6-step drive has 6 commutation steps per cycle.

Under ~10 pulses per cycle: choppy current, torque ripple

More heat in the motor and ESC FETs

More load on the ripple caps

Iron loss climbs with frequency (eddy ∝ f²)

Can lose sync or cut out near top speed

FIXES

Lower KV · gear to cap motor RPM · fewer poles · higher-switching ESC · get the real switching frequency and eRPM limit from the ESC maker and enter the limit above.

Higher KV makes it worse: Setup B (3100 KV) on 8S, 6-pole ≈ 312,480 eRPM, 5,208 Hz, ≈3.8 pulses (EST).

Lab verification: model vs measured

Run each motor on the same ESC, same pack, same car and same surface, then enter what you measured. The page shows how far the model was off. Within the tolerance counts as a match.

Match tolerance (%)

Motor	Measured 132 ft time (s)	Measured peak current (A)	Measured trap speed (mph)
2-pole
4-pole
6-pole

Check	Model	Measured	Error	Result

A mismatch is useful too. It tells us which assumption (resistance, no-load current or grip) is off.