What Causes A Brushless RC Motor To Fail

Brushless radio-controlled (RC) motors have doubtlessly elevated the game thanks to their numerous advantages over the more traditional brushed configurations. Of course, the elevation is not the same thing as perfection, as we will soon see. Even this advanced technology is not infallible, and several problems may impede performance or even total failure. Today we examine some of the more common problems that lead to said failure. 

While several factors may contribute to the eventual failure of brushless RC motors, it has been found that excessive heat is the main culprit. Most RC motors have an optimum operating temperature range of about 150-160oF. Exceeding this range may result in the gradual weakening of the motor’s rotor and stator magnets. 

We take a look at various questions that arise from this issue. We will learn how to detect problems with brushless motors and the underlying causes of said problems. The expected life span of brushless motors is another key thing to know when tackling such a problem.

Of course, we are hardly the type to leave you all alone with your problem. There are some DIY repair tips that you can easily do yourself to save you from the cost of purchasing unnecessary replacements. 

What causes a brushless RC motor to fail?

While brushless motors offer a significant step up in performance and complexity over the brushed variety, they are not immune to failure. Many people who have experienced problems or even total failure have blamed such events on many things. 

The first suspect on the lineup is good (or bad in this case) old vibrations. These are usually a result of physical instability stemming from several possible scenarios. 

Misaligned parts may cause the motor to sway unusually, resulting in the motor shaking. Loose screws and bearings are another potential problem area as far as vibrations are concerned. 

Funnily enough, though, despite the many factors causing vibrations, the most common is simply misplacing the motor on an uneven or unstable surface. Take great care not to fall into this avoidable problem, folks. 

However, it is now clear that the main cause of failure in brushless RC motors is heat. As a matter of fact, it has been documented that over half of all insulating failures in motors are a result of excessive heat. 

For optimum performance, brushless engines must have an operational temperature of about 150-160oF. Any more than that, and your motor runs the risk of severe performance issues and eventual failure. 

Please note that this temperature range is just an average of what most brushless motors have. If your motor’s instructions or packaging specifies a different temperature, you will need to adhere to it.

Dust is another factor that may lead to a complete shut down in a brushless motor. While it is a rare occurrence, dust can and will wreak havoc on your motor if given the opportunity. 

Dust normally affects parts like bearings, which is a problem because the bearings’ gradual depletion could leave your rotor exposed to the magnets. Once this happens, you can call it a night for your motor. To avoid this, you should take your motor to a professional and have it analyzed.

Atmospheric entities like dust, pollen, and more can also negatively affect a motor’s functionality and lifespan. One example of this is how easily parts like the fan can be disrupted, leading to further heat problems.

How long will a brushless motor last?

One of the key reasons behind the eventual invention of brushless motors was the somewhat limited lifespan of brushed motors. The latter, as the name suggests, feature brushes made from (in most cases) carbon-graphite.

While this material is great for saving weight, it does wear away rather quickly.

As a result, for a brushed motor, the limiting factor is the lifespan of the brushes.  

On average, modern brushed motors have a lifespan of about 1,000-3,000 hours. Not bad, but the brushless motor has greater longevity thanks to its lack of cumbersome brushes.

The limiting factor for this motor category is the level of wear and tear sustained by the bearings. These factors allow brushless motors to run rings around their brushed cousins. Brushless motors can remain fully functional for well over 10,000 hours.

How to tell if a brushless motor is bad

Unfortunately, numbers don’t lie. Sometimes you will fall victim to some freak coincidence and get a faulty RC motor fresh out of the box. Luckily there is a surefire way for you to identify a shady deal.

The easiest and most popular approach these days is to hook the motor up to a brushless electronic speed controller (ESC). This is an electronic circuit that dictates how fast an electric motor can run at a given time. For a brushless motor, the ESC does this by regulating pulses of current it feeds to the motor’s windings.

Test your motor using one of these devices to determine whether everything is in order. I recommend that you use a dedicated brushless motor electric speed controller such as the 30A RC Brushless ESC. You can check it’s price here on Amazon.

This sweet device delivers a continuous current of 30 amps and a burst output of 40 amps for 15 seconds. If there are little or no signs of life when the ESC is connected, it might mean that your motor is faulty. In that eventuality, you could use a second ESC device to rule out the faultiness of the first.

Can a brushless motor burn out?

Quick answer? Yes!

Brushless motors are not exempt from unexpected prompts for the yellow flag. As the heat builds up, the magnets lose their grip and…kaput. So goes the tragedy known as over-revving.

To avoid this, you will need some serious cooling solutions. I recommend the Hobbywing Ezrun 5V cooling fan. Ideal for 1/8 rigs, this super cool fan hurls even cooler breezes in your steaming motor’s direction. Measuring 1.7X2.5 in (44X65mm), the Ezrun is the perfect heat regulation tool. Easy to set up, zero maintenance hassle, and a high-quality design that ensures that you buy once. What’s not to love?

What happens when a brushless motor overheats?

Once temperatures get too high, the rotor magnets and the stator electromagnets within the motor are depleted of their ability to get the rotor moving optimally. Like vibrations, heat can be gained in a variety of ways. In most day-to-day scenarios, an increase in temperature will stem from high current and electrical load. As increasing levels of a current surge through the motor’s wiring, heat slowly builds up in the motor windings. 

The rotor magnets, because of their proximity to these windings, get heated up to a point where they start losing their magnetism. The winding themselves can also lose their protective enamel coating if things get too hot.

Can you repair a brushless motor?

If you are a little on the frugal with-a-lot-of-time side, equipping yourself with in-depth DIY repair knowledge might prove to be the best move you can make. 

The first step is to clean the motor. You will need soap and maybe some scotch-brite. Scrub until the motor is free from rust and all other stains.

Step two is where the fun begins. Disassembly. Using a flat-tipped tool to wedge between the casing and the drive gear is the easiest way to begin the process of stripping these motors down. After this, it is just a case of undoing a few tabs and pulling the mechanism apart.

Next up is some more cleaning but on the inside. Expect this to be a slightly slimmer affair. This is because of the molten gooey glop of copper salts that are splattered all over the inside of the motor. 

Use paper towels to wipe off the mess. Latex gloves might be needed for this task because copper salts (and sometimes beryllium salts) are somewhat toxic to the human system. Use a cleaning aid to wipe off the commutator armature as well as the shaft assembly. Again, scrub until all rust is gone. The bearings must be super smooth and shiny when you’re done with them.

The fourth step is to carry out some basic repairs and fixes. Replacement cables can be sourced almost anywhere, but if you are completely stuck, you can use some old ribbon cabling or something similar.

Once you have made the necessary repairs, it’s time to seal up the motor again.

Paul Good

This awesome hobby has something for everyone, whether you like to build your RC from scratch and keep modifying till you've got it to just how you want it, to track racing. You might be out with a boat, or perfecting your skills with a plane. Are you taking some cool pics with your drone? I'm sure my site will help you on your journey.

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