A wheel can have an infinite number of revolutions
The future of our forum and a little treat
Since I read again and again that engines with
high specific speed (kv) have little torque,
But what is wrong, some technical facts about BL motors.
BL motors are classified according to kv, i.e. revolutions / volt.
Revolution / volt does not need to be explained, everyone understands.
The reciprocal of kv is km.
km = 9.55 / kv, unit Nm / A.
km is the unit of how many Nm per 1A current consumption the motor generates.
Motors with little kv generate more Nm per 1A than motors with more kv.
But that does not mean that motors with high kv generate less torque,
they just need more electricity.
That is the reason why motors with a high kv number draw a lot of current.
But so also high speed is associated with high torque.
This means that the torque does not decrease with increasing kv,
but the current increases.
And with the current, so does the torque.
These electrotechnical relationships between kv and km apply
for all types of BL motors, whether 100W or 10kW.
But just because of the simplicity, the specification of kv has become commonplace.
Considered together, kv and km belong together.
There is also no connection to the number of poles and torque.
A motor with more poles has no more torque than a motor
with fewer poles.
(with the same voltage, speed and current consumption)
As an an example:
Kontronik Pyro 700-45, current consumption approx. 13A, 10 poles, 0.3Nm approx. 16000rpm. Outrunner
Lehner 2230/40, current consumption approx. 13A, 2 poles, 0.3Nm approx. 18000rpm. Inrunner
Each with 10s.
The torque cannot be compared based on the number of poles
the torque arises in the air gap between rotor and stator,
because the distance between the lever ratios between rotor and stator is greater for external rotors than for internal rotors,
external runners generate more torque.
Taking into account the winding design.
With internal rotors, the force is created directly on the inside of the motor shaft (short lever)
with external rotors on the outside of the rotor bell. (long lever)
This is why external rotors have more torque depending on the winding.
Depending on the winding, because the Lehner 2230/40 at 13A in its
optimal efficiency, the Pyro 700-45 goes up to 80A.
External runners are rarely used in the automotive sector,
except for some 1: 5 self-builds with external runners.
In terms of torque, it does not matter whether you have a 2-pole, 4-pole, 6-pole, 8-pole internal rotor motor in your car.
Such motors differ more in winding, wire size,
Air gap, magnetic material, degree of filling of the winding, sheet thickness in the armature, length of the stator
than in relation to the torque and the number of poles.
Thin sheets in the armature increase the partial load strength (less heating with half-throttle)
and generate less eddy current losses than thicker sheets.
A high degree of filling increases the efficiency of the motor, i.e.:
The closer the winding is packed, the more magnetic field lines are cut.
And the more magnetic field lines that are cut, the higher the electromagnetic forces.
(i.e. how many windings are inside the housing
without leaving a lot of air between the windings)
Small air gap increases the torque.
German engines are top in terms of filling level, small air gap,
Magnet material, thin sheets, torque, efficiency.
(Hacker, Lehner, Plettenberg, Kontronik, Strecker)
American engines are a compromise on price
and quality based on German products. (New, Traxxas)
Asian products are solely committed to the price,
they cannot match the quality of American products,
let alone German products. (Turnigy, Scorpion, HK, Ezrun etc.)
That's not to say that Asian products are bad,
they are also powered by a model car or a model airplane, only there is better.
In other words, more efficient drives, where less battery power is consumed in heat
and where more battery power is converted into drive power.
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