How does a brushless outrunner work

Brushless DC motors, as you may imagine, do not contain brushes and use a DC current. These motors provide many specific advantages over other types of electrical motors, but, going beyond the basics, what exactly is a brushless DC motor? It often helps to explain how a brushed DC motor works first, as they were used for some time before brushless DC motors were available. A brushed DC motor has permanent magnets on the outside of its structure, with a spinning armature on the inside.

The permanent magnets, which are stationary on the outside, are called the stator. The armature, which rotates and contains an electromagnet, is called the rotor.

In a brushed DC motor, the rotor spins degrees when an electric current is run to the armature. What is an Outrunner Motor?

Outrunner and inrunner torque motors. Differences between an outrunner motor vs inrunner motor. Advantages outrunner torque motor. Adventages of an outrunner motor, in short, are: Maximum torque achieved for minimal build volume No need for mechanical transmission or gearboxes Rotor can directly drive the application Highly accurate No risk of contamination.

Visual representation of how an outrunner motor works. Our assortment of outrunner motors:. Click Here. Small, low maintenance and low energy consumption. Contact us for more information. This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish.

Close Privacy Overview This website uses cookies to improve your experience while you navigate through the website. Out of these cookies, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website.

We also use third-party cookies that help us analyze and understand how you use this website. These cookies will be stored in your browser only with your consent. You also have the option to opt-out of these cookies. But opting out of some of these cookies may have an effect on your browsing experience. Thus inrunners run best at high speed but generate less torque while outrunners work best with larger propellers because they can output more torque, but spin at slower speed.

For the reasons described above, eVTOLs often use outrunners for vertical thrust due to their high torque. Inrunners are more commonly used for ducted fan jets or fixed wing aircraft and for horizontal movements requiring high RPM. This value determines at which speed the motor will spin if 1 V is sent through it. Therefore, an inrunner typically has a higher Kv value than an outrunner of the same size because, as stated above, the inrunner has a smaller rotor which spins faster for the same voltage.

You will often see the Kv value displayed first when browsing brushless motors. When talking about the performance of a drone, we often think about the flight time. The only solution is to carefully select the electrical components that will use the battery charge most efficiently.

Many factors can optimize the energy consumption of a battery. To demonstrate this idea, we present a comparison of two similar BLDC motors with different price ranges. To compare the motors' performance, we used the RCbenchmark Series test stand. It is capable of measuring thrust, torque, voltage, current, RPM and efficiency. The data acquisition is done using the RCbenchmark software.

The two motors tested are Ts of Kv and Kv respectively. Both motors spin the same 7-inch propeller with a pitch of 4. The first graph in figure 7 displays the efficiency of both motors compared to the throttle.

The second graph shows the efficiency at specific speeds. Clearly, the smaller Kv motor requires more throttle to run efficiently. The efficiency range is also better on the Kv motor, meaning the motor keeps a high efficiency at both low and top speed. On the other hand, the smaller motor can operate at low speed and would probably be more efficient with a smaller propeller.

A drone used for transport would use a smaller motor to be able to stay idle and stable at low speed, while for a racing drone, a bigger motor that would struggle to hover at lower speed would work just fine. To get a full comparison, we would need to know the purpose of the drone and the RPM it will operate at. It is possible that the Kv motor is more efficient with a different propeller suited for a different function.

Only through testing can we find out. The most important characteristic is motor Kv, which describes the rotation speed you get for the power input to the motor.

A motor with Kv will spin at rotations per minute for every volt sent to the motor. Size is closely related to the Kv. A wide and large motor will often have higher torque but lower Kv and use a bigger propeller, while a thin but longer motor will have high Kv, low torque and would be best suited for a small propeller. This makes sense when you consider that a larger motor operates at lower RPM while a small motor operates at relatively high RPM.

The maximum power of a motor is also something to take into consideration. Exceeding the motor's power restriction would result in the motor heating up and thus drastically lowering its efficiency or even damaging it. The brand can also change a motor's performance. For the same Kv value, a motor from one brand may perform better than others.

As a general rule, it is wise to use the smallest lightest motor possible without being in danger of overpowering and overheating it.

The reason for this is to reduce the excess weight of a motor that is larger than needed. We have compiled a list of large motor manufacturers with products suitable for heavy-lift and manned drone operations.

The brushless DC motor is a genius invention that has been a game changer in the world of electric propulsion. Simple and streamlined in design, they allow vehicles like RC cars and drones to operate at high efficiency with maximum control. We also covered electromagnetism and how an ESC controls the speed of the motor.

This background helps us understand how to maximize efficiency, and how the requirements are different depending on the use for the drone.