If you have been an avid radio control racer for a while now, you must have heard the word “brushless motor”, if not a gazillion, then at least a hundred times. Especially when doing online research or browsing on different components required for speeding up your RC device, you might have come across the term “brushless motor”.
A little bit of context for those who are unfamiliar with this term, electric motor, as you might know, is for converting electrical energy into mechanical energy, to power your vehicle or any type of machinery. Over the years, one such type of motor, known as the brushless DC or BLDC motor is different from the conventional brushed DC motor but does the job of working your machinery or RC car with much more efficiency and control. In this article, we would, in fact, talk about five facts that you may or may not know about brushless motors.
Brushless motors come in different sizes
Brushless motors come in a wide range of sizes and are fairly compact for the amount of power that they can deliver. Due to the large range of sizes available, there is more room for the brushless motor to be used for a variety of different applications machinery. Anywhere from the size of 28 mm to a larger diameter of 56 mm, brushless motors, specific to your need can be found in the market.
RPM value of Brushless Motors
Most brushless motors in the 28-40mm diameter range can rev up to 60,000 rotations per minute (RPM). However, some brushless motors can even rev more than 60,000 RPM, or even more than 80,000 RPM. Despite these features, most users don’t really bother to question why a tiny motor with the attribute of delivering such high RPM is being offered in the market. Keeping in mind how RPM is related to power output – it is easier to attain more power out of a higher number of RPM – the internal combustion engines used in racing cars are a good example to begin understanding this.
Racing cars that we have nowadays, particularly F1 cars, or even sport bikes, typically rev at 10,000 or more RPM. Whereas a regular family car outputs up to 6500 RPM. This is true as it is more efficient to extract power from a lighter, smaller engine spinning at higher speeds.
Same applies to our motor scenario. It is easier to get more power from a motor that has a maximum value of 60,000 RPM at a 45,000 threshold, as compared with the same motor at 25,000 RPM.
The key point here is to understand that a motor with a maximum RPM of 60,000, must not be operated at a maximum of 10,000 RPM to get the most out of it. This would only underutilize the motor and not give enough potential output from that motor.
Magnets inside the Brushless Motor
One of the biggest perks of the brushless motor is that it uses a magnetic rotor and has a rotating field, unlike the traditional brushed DC motor.
If you have ever closely examined the brushless motor inside any of your RC vehicle, you might have noticed a rotor inside it. The rotor contains a rare Earth magnet, called neodymium. Neodymium is an extremely rare and strong magnet. It is perfect for the brushless motor as we need a strong motor to produce the right amount of power.
However, there are a few drawbacks to this magnet.
Replacement can be damaging for the magnet
First of all, since the magnet is very strong, it can be quite dangerous to remove it causing damage to the rotor or you. Though replacing it isn’t a bad idea in itself, how you insert it back can be a tough job.
When inserting the magnet back, make sure that you don’t pinch your fingers. Instead use a cloth or rag to avoid pinched fingers. Use one hand to fill the gap between the channel lock pliers and the rotor. Try resisting the rotor from snapping abruptly.
Ensure that the rotor does not snap back aggressively or the neodymium magnet might chip. A major down side to these types of magnets is they chip very easily. This is because they are super brittle. In fact, if the rotor comes in contact with any other object this can damage it quite easily. Click here if you would like to watch the below image play out.
Temperature sensitivity of the magnet
The temperature sensitivity of neodymium magnets is also an important factor. Neodymium magnets are vastly affected by temperature increases. With every 1 degree Celcius increase in temperature, the magnet loses about 0.1% of its strength. The magnet does not lose its strength when the temperature drops, therefore, just like every other component in a power system, keep the motor as cool as possible.
Brushless Motor Constant Kv may not be so constant
Considering how the strength of magnets depreciates as temperature rises, the same can be said about the Kv value of the brushless motor, implying that the constant values within the motor may not be as constant. When the temperature of the brushless motor increases, magnetic strength decreases, and Kv as a result increases. Although this effect on Kv is rather insignificant, it is still there.
Another area having even more presence for the Kv value of a motor is load. As you load a brushless motor the Kv value completely changes. A loaded motor will have the Kv value decrease relative to how much load is placed on the motor. This is one reason when making calculations using Kv that we must consider the changes that happens to Kv.
Internal Resistance in a Brushless Motor changes
The resistance value of the windings in a brushless motor is a specification typically provided by the the manufacturer. However, it too changes when the motor becomes heated. In fact, changes in heat within any electrical component will change the total resistance,. Whether that is the wire of a motor, speed control, or the battery pack.
BLDC Motors Do not Accept DC Voltage
BLDC stands for brushless DC. As mentioned earlier, brushless motors were created as an alternative to traditional brushed DC motors. But traditional brushed motors accept DC voltage. If you were to send DC voltage to a brushless motor, you would in fact blow the motor up.
Brushless motors actually need a commutated AC voltage to function properly. When the brushless motor is supplied with electrical power, it starts off as DC at the battery pack. Then Voltage gets converted into three-phase AC so that the brushless motor can operate smoothly.
Final Words
This sums up five facts that we think a lot of RC enthusiasts may not have known about brushless motors. Knowing these facts would not only help you in getting the most out of your RC brushless motor but take good care of it as well.
If you know any other interesting facts and insights, share them with us in the video comment section. Or tell us which fact surprised you the most.