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Old 01-20-2020, 11:16 AM
homo ludens modelisticus
ron_van_sommeren's Avatar
Join Date: Jul 2005
Location: near Nijmegen, Nederland
Posts: 1,142

Originally Posted by dasintex View Post
... the higher Kv motor the larger the props that can be used?
Kv says very little about max.power or max. current a motor can handle, nor about max. torque. A 1:1 train motor and the motor in your toothbrush or in a bedroom appliance can have the same Kv.

Motors have only one Kv ,it is the velocity konstant, a physical property, expressed in the unit rpm/volt. Kv is not a rating, not a figure of merit (explanation).
A Kv=1000rpm/volt motor on 10volt and a Kv=2000rpm/volt on 5volt will give same (no_load)speed of 10,000rpm, provided the motors can handle the current and power.

It's all about what the motor wants to do versus what the motor can do.
Kv matches rpm and voltage, there's nothing more to it.
  1. Want
    Kv and voltage determine how fast motor wants/tries to run
    (rpm_noload = voltage Kv, or, in other words, Kv = rpm_noload / voltage.)
  2. Current
    RPM and prop determine torque, which in turn determines current
    (current = torque Kv, in SI units!, or proportional to Kv ).
  3. Can
    Max.current and max.power determine whether that battery/motor/rpm/prop combo can run without going up in smoke.
An engine tries to keep a constant torque: as load goes up, rpm goes down.
An e-motor tries to keep a constant rpm, no matter the load: as load goes up, torque must go up, and therefore current goes up.

Last edited by ron_van_sommeren; 01-20-2020 at 01:51 PM.
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