Brushless motor spec`s

If you want to drag race and you're still looking for the most suitable engine you will soon come to a brushless motor. Brushless motors have like the English word implies no carbon brushes. This makes them more efficient and they require less maintenance. This type of engine comes in all shapes and sizes. What kind of motor you may use you can find in the contest rules. In a car you generally use a inrunner.

operation of a brushless motor
Spec `s of brushless motors

For each engine there are properties. They are slightly different for each engine. The properties discussed in this section are the following:(Source of schema

2 pole / 4 pole
Max rpm

Kv of Brushless motors

You would never guess and have to search for a long time but Kv stands for "Konstant velocity". Forget this immediately,… please!. What matters is what it means when you have to compare the spec `s of an engine. It represents the amount of rpm per volt the motor runs without load. So if the spec`s say “3000 Kv” it means that if you put 1 volt threu that motor without any load 3000 rpm`s are made. a 2 volt supply would mean 6000 rpm, 3 volt 9000 rpm 3 etc.


The maximum voltage is sometimes just given in volts and sometimes in a cell number. As indicated above, the maximum number of volts `s have an influence on the speed range of the engine. Since youre`drag racing set up may have only 11.1volt it makes no sense to choose an engine that handles up to 22.2 volts (6S lipo). That kind of engine will never reach its full potential if it gets no more than 11.1 volts. In itself it does no harm to a 4s (14.8 volts) engine to only supplie it with 11.1 volts. The motor, however, will not come to its maximum speed.


This indicates how many amps a motor pulls / asks from you`re esc on a average level that a manufacturer has measured during testing. There may be peaks well over the given amperidge. Keep this in mind when choosing your electronic speed controller. The higher the number of amperes the stronger the motor is at an equal amount of volts.


The amount of watts that a motor is able to produce is simply the voltage X amps. It provides, for those who are less well in to "Electro sums", a good indication of the power of the engine. And yes, indeed 1pk = 736 watts.

Turns in a brushless motor

Turns is an expression that refers to the amount of windings that are used are per coil. So when you see 3.5 turn, this means that 3 1/2e windings per coil are used. That would be a motor with high kv value. To give an idea, .. crawlers engines have somewhere between 35 and 55 turns. The fewer windings the more revs per volt the motor will make and vice versa. The misery of the expression "Turns" is that it says nothing about the type of thread used. If the wire is thin, there will be more volts but less amps going through them. You would have o an engine that runs very fast but does not have very much power. Of course, manufacturers use thicker wire as an engine should have more speed and still must have a reasonable amount (pulling) strength. It is therefore better to watch Kv with amps.

2 pole / 4 pole brushless motor

In the explanation of speed controllers, we have already talked about 2 or 4 pole motors. A standard brushless motor has 2 poles witch means that there are 2 magnets in it. A North and a South. A 4 pole motor therefore has 4 magnets. North, South, North, South.

The advantage of multiple poles is that there are more moments in 360 degrees of rotation in which the magnets meet the coil at the a maximum magnetic field. Compare it with the difference between 4 cylinder engine and an 8 cylinder engine with 1:1 cars. The advantage is somewhat offset by the magnets taking up more space and the fact that the controller must be 2 times as fast in giving pulses to achieve the same speed in rotation. Manufacturers often solve this by less windings with slightly thicker wire so that the speed (Kv) remains at a higher amount amperes. This way, an engine is created with more power at the same voltage and higher amperage. Isn`t that what we're looking for in drag racing?


The maximum speed that a motor can run is indicated with max RPM. It is a mechanical limit which is determined by bearings for rotating parts and the materials used but also the result of the maximum voltage X the Kv number. If the maximum RPM number is not listed, you can find it by multiplying volts times Kv. A frequently occurring maximum is between 50,000 and 60,000 revolutions per minute. The best motors have an efficiency around 90%

Here are some way`s to calculate

Volts x Amps = Watts
Watts / Amps = Volts
Watts / Volts = Amps
Kv X Voltage = Revolutions per minute

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