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. 

RC cars may be a hobby for some but knowing how to tweak the ESC to get the most out of your RC device is what distinguishes a true fanatic from a hobbyist. But even someone who is a professional RC driver may not know the nitty-gritty of its power system, like the electronic speed control or ESC. Don’t worry it isn’t your fault. It’s just the ESC manufacturers who don’t want to give you the inside scoop.

But what is an ESC?

Electronic speed control or just speed control is what differentiates a $100 RC toy from a professional RC racing vehicle. Basically, a speed control is what takes the signals from the receiver, decodes the signals and sends a power signal to your brushless motor. This is what helps in getting your RC vehicle moving. So, whether you are building your own RC car model or looking to make some changes in a pre-built model, having some information on the ESC might provide you with more insight to this mysterious box.

In this article, we will specifically highlight the information about ESC that manufacturers tend to hide from geeks like us.

BEC Voltage from ESC in RC cars

The BEC, or the battery eliminator circuit, is present on the ESC and it “eliminates” the need to use an external battery pack to supply power to the receiver and other servos onboard. The ESC has a circuit that utilizes the battery voltage of your vehicle and reduces it to the amount of voltage required for the receiver and servos. Simply, this would be a power source for an RC vehicle, just like the power supply found inside a PC or server room within an office. These power supplies convert the typical 120 volts to 5, 12, 24 volts. However, if the PC loads its power supply, it is unlikely that the voltage will sag significantly within this system.

The simplest way to understand this is by understanding the following scenario: A server room power supply for providing source power for an RC charger charging either a 6s pack or 2 6s packs at 10 amps each. No matter what the case, there is a negligible drop in the voltage going inside the RC charger.

However, this is not the case for an ESC. Why?

Manufactures don’t want you to know this but the BEC current as advertised by the manufacture of the ESC is not always accurate. When we tested speed controls at the mentioned continuous power, a 25% reduction in the voltage value was observed, however, this depends on the type of RC vehicle. Do be careful as this 25% drop can cause issues with receivers that we will cover here shortly.

Building your RC vehicle

Those who want to build their own RC vehicles by using an ESC must understand speed control’s BEC. That’s because modern-day radio devices have a minimum voltage level that needs a check and balance. If the voltage tends to fall below the minimum threshold, your vehicle might become unmanageable or even shut off. Following that, your RC vehicle’s receiver will restart and try to acquire signals from its transmitter to send them back to all systems onboard. This will take some time and even increase the chances of your RC vehicle crashing into something.

Key Takeaway

As long as the power onboard is stable, the radio system of your vehicle will be functional.  We also recommend checking the maximum threshold voltage on your servos as well as your RC car’s receiver. Next, set the BEC voltage on your speed control at the same maximum threshold. This will allow the servos to produce maximum torque within their operational range, and operate at a higher functional speed. If the voltage from BEC begins to drop, the voltage at the receiver may be below its minimum threshold. If this does happen, signals being sent to the receiver will be disrupted.

To help prevent this from happening, the recommended voltage for operating most systems is 5.5 to 6 volt or more. This is because most radio system begin to suffer from voltage loss between 3.5 and 4.5V.

Maximum Continuous Current Rating on an ESC

The maximum continuous current rating, mentioned on the labels of all speed control in boldface, is the maximum current the vehicle’s motor system can produce. All ESC manufacturers are mindful of mentioning this since it is a very important figure.

But what does it actually mean? Does it imply that an ESC with a 60-amp rating can sustain a continuous current of 60 amp?

Not necessarily.

This is because we are not sure if the ESC manufacturer has tested this rating based on their operating conditions. What are these operating conditions you might ask?

A certain amount of airflow could be one example. The airflow over the speed control will keep the ESC functional and stable to allow waste heat to pass. This is not always mentioned in the instruction manual of RC devices as it isn’t required for every speed control.

Another important figure for us is the amount of heat within the ESC. This will help us to determine what the actual continuous current is in our environment. Try to record the heat generated within the ESC. Measuring temperature is the easiest way to do this. If it exceeds the required amount, this will be the RC device’s new maximum limit.

Although a lot of RC drivers are running over the 60 amps limit, that is only recommended if you are fully aware of what you are doing and recording temperature changes within the ESC.

Key Takeaway

If you are not an expert, it is recommended that you run your RC car or airplane within the mentioned current rating or its maximum temperature. No matter which threshold is reached first, stick with that.

Partial Throttle of ESC

A lot of RC drivers out there might not know but operating your speed control at partial throttle is inefficient and can be detrimental for your device. The closer the speed control operates to just above the 0% threshold, the less efficient it is going to be. Beware, efficiency here implies the resultant mechanical output from the electrical input to the system.

From an experimental point of view, we have observed that the speed control is most efficient at 100% throttle, and at the 50% threshold or below, efficiency drops.

Key Takeaway

To utilize your RC vehicle’s full potential, and if your primary concern is efficiency, try to operate its speed control at 100% throttle. For most general RC applications this is obviously not practical. We don’t recommend using a pylon racer at 100% throttle and operate the device at 3000 miles/hour in a circle. Not all that practical indeed.

However, your RC airplane’s cruise speed must be at 100% if you wish to get maximum range for an FPV long distance build. This also points to the discussion towards PWM switching.

PWM Switching Rate within ESC

An RC vehicle can make use of partial throttle, by reducing the signals sent to the motor. If the RC device operates at 100% throttle, its motor will reach its maximum rotational speed, however, to reduce that speed, the ESC will introduce PWM switching.

But here’s the catch.

ESC manufacturers don’t want you to know that by increasing the PWM switching rate, your speed control and the motor would become more efficient.

Why are they hiding this useful piece of information? ESC manufacturers don’t want you to know this because increasing the switching rate would burden the speed control. The speed control will introduce more heat in to the system, but the motor will become more efficient. The net result is efficiency gain as the motors gain is far more than the loss from the speed control.

Key Takeaway

Therefore, you want to make sure that you experiment with the PWM switching to attain maximum efficiency. However, be cautious about the temperature of the speed control.

Final words

Being an RC driver is about experimenting with speed control to get the most out of your RC device. However, take all precautionary steps to ensure proper operating temperature of your vehicle’s system.

C Rating of a LiPo Battery

In a previous article we talked about how the highest C rating has so many benefits that it makes it well worth it. However, because of all of these benefits, some LiPo manufactures use the C rating as not just a performance specification but more as a marketing tactic. This can make it very challenging for users such as us, to make a good selection for our true requirements. Some manufactures are recognizing this and try to provide the market with extra performance metrics that are not so vague. Also, the metrics provided by some manufactures are a lot more easily proved by consumers. Examples may include a simplified load test or using the internal resistance of the batteries cells.

What can you do about inaccurate C Ratings?

There are a few things that you would be able to do to help reduce chance getting stuck in these claims. The biggest and easiest method to avoiding these risks is to simply review the product reviews. Check what others are saying to see if the pack lives up to the standard you expect. Similarly, it is a good idea to check the forums to see what kind of reputation the LiPo manufacture has. Not only that but you may also run in to seeing what the popularity of the pack is. If many are using the LiPo and happy with it, chances are, it’s OK. Last item is to see if you can get any information as to the internal resistance of the pack. Using this data to compare against another pack, can tell you what performance to expect, Lower internal cell resistance will provide better performance. Check out this link to help determine the actual C rating of a LiPo.

Capacity of a LiPo Battery

There is no set standard to how a LiPo manufacture determines the capacity of a battery pack. Due to this, there is some variability in this performance specification. Some LiPo’s may not be able to deliver anywhere near their rated capacity. Now fortunately for us, the modeler, we can more easily prove and confirm these specifications just with the modern computer radio!

Capacity Varies Under Load

Yes, it’s true. Your 5000mAh battery may have just accepted 5000mAh that your charger put in to it. However, if you load the pack with a very light load you may get the full 5000mAh back out. Now if that load were to increase, you would get less total capacity out of the LiPo pack. This relationship is true based on how much load is placed on the pack up to a certain cutoff voltage.

This occurs as the minimum voltage of a LiPo battery comes in much quicker under significant load due to voltage drop. This is something to consider depending on the total amount of power that you RC vehicle will pull.

Soldered LiPo Battery Connectors

Many of the LiPo battery packs deliver some impressive numbers in terms of discharge current rates. Some of these rates easily exceed 100A continuous. However, In many cases you could see a high performing battery use such small wimpy connectors. Yep, it’s true. LiPo manufacture may choose to place small connectors on LiPo batteries for a few specific reasons. These reasons are primarily due to the market demand and cost. Some smaller connectors are more widely used. When a manufacture supplies a battery pack with a smaller more commonly used connector, less hobbyists would have to unsolder the connector only to replace with one of their own. The second primary reason manufactures may place smaller 60A connectors on a battery that can deliver well over 100A is purely due to cost. Smaller more popular connectors are inexpensive by nature. Reducing cost allows the manufacture to sell the battery more competitively and we in return get the pack for lesser overall cost.

In general, I replace the connectors on more than 75% of the LiPo battery packs I purchase. This is because primarily, I use an old connector that is rarely used these days. I also prefer a beefy connector for minimum voltage loss.

Wire Gauge used On the Battery

Very similarly as above with connectors, it may be possible that a manufacture chooses to use a gauge of wire that is smaller than what would be expected. However, the big difference here is that if you are going to be pushing packs extremely hard and want top performance – select a battery that has the wire gauge you are looking for. Otherwise what you may find yourself doing is re-soldering cables.

As for my setups. It’s rare that I run in to a situation where the wire on the battery pack is not large enough for my application. in general for most hobbyists out there, it really won’t make much of a difference at all. Wire gauge is a topic for the experienced hobbyists, otherwise run what you have.