In many applications of radio controlled vehicles, the brushless motor may come in contact with water. This could be as significant as being even fully submerged. Some manufactures of radio controlled vehicles advertise right on the box that the RC inside is waterproof. What does this mean? Is the brushless motor in the vehicle really waterproof?
First let’s understand that there are 2 different types of brushless motors that are important for our topic today. The first type is sensorless motors and the last type are sensored motors. Click the link to learn more.
Waterproof Sensorless Motors
The short answer here is that the sensorless brushless motor will indeed operate while being fully submerged, however not without wear and tear. Electrically there will be no issue at the lower voltages we typically run. Here is an example from my own experience when racing fast electric boats. Below is a picture of what the hull looks like. You can see at the back of the boat, that the entire brushless motor is exposed. This is known as an outboard motor as the motor is external to the boat. In the second image, you can see what the hull looks like when the boat flips. In the image, if you look closely you can see the small trail of disturbed water behind the path of the boat.
Fast Electric race boat
Operating a Brushless Motor Submerged in Water
I was operating the boat upside down in order to return it back to shore. The brushless motor was able to operate without any issue. However, mechanically wear and tear does occur within the brushless motor. Let’s look at how and where.
Water is very good at penetrating small openings. It’s only a matter of time before water can find its way in. The shaft found on a brushless motor is supported by using a minimum of 2 bearings found on either side of the motor. Typical RC bearings found in brushless motors are shielded against debris from entering the ball bearing. The truth is brushless motors are water resistant however they are not really waterproof. Water is never pure in a lake or puddle or even rain. Small particles will find there way in to the bearings on a brushless motor delivered right from the water itself.
Over time this is what can destroy the bearings. Worn bearings on the motor can cause the rotor of the motor to contact the stator causing near permanent damage to the motor if spun up.
Also, depending on how your rotor was manufactured, you may find bulging or bubbling of the rotor material. These areas can also scrape along the stator causing damage.
Waterproof Sensored Motors
It is not recommended to place sensored motors in to a wet environment. Sensored motors have these components known as sensors (who would have guessed that?) inside the brushless motor that are not waterproof. A brushless motor would have to be entirely sealed to prevent water from entering the motor destroying the sensors. If you are looking at turning a sensored motor into a sensorless motor, water may be a good way to get you there.
Waterproof Motor Conclusion
If you do plan on running a brushless motor in wet conditions, careful inspection is required to ensure optimal condition. Checking the condition of all the internal motor parts would be a good way to prevent complete destruction of your motor. Sensored motors are not fit for operation in water unless otherwise noted by the manufacture. The same precautions would then apply.