Brushless Motors the Truth About Waterproof – Sensorless Sensored

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

Fast Electric race boat

Operating a Brushless Motor Submerged in Water

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.

Can the E-Flite 2.1m Carbon Cub Take off from Water on 4s?

The carbon cub was designed to run 6s. After all, this thing has a 2.1m (84in) wingspan. However, the airplane is also designed to operate on 4s and as such is advertised as 4s-6s. With this said, does 4s have enough power to get the E-Flite 2.1m Carbon Cub off the water?

While on 6s the power system is able to generate enough power for about 130 watts per pound. However on only 4s LiPo, there is only enough power for approximately 50 watts per pound. The difference is huge.

Here’s the video:

Can the 2.1m Carbon Cub take off from water on 4s LiPo?

Most important tool every RC Electric Hobbyist must have

Temperature Meter (temp gun)

Temperature Meter (temp gun)

The most important tool that every RC Electric Hobbyist must own is a temp (temperature) gun of some sort! You ask why? Well it will save you lots of money, that is why.

It doesn’t matter if you build your RC models or don’t. Having a temp gun in your toolbox will certainly help out. Heat is the worst enemy for any part of our electric power system. Managing the heat that is generated by our RC components is what will help save them. Too much heat that builds up in any electrical part of the power system can certainly destroy that component.

There are many temp guns out there that you can pick up. I have been using the Duratrax Flashpoint infrared temp gun for so many years. It is very easy to use and very cost effective.

 

How to use a Temp Gun Effectively

Periodic spot checks must become a standard for you as you run your RC vehicle. What you will want to do is every 5 runs of your RC vehicle, check the temperature of the brushless motor and electronic speed controller. To get an accurate reading, the measurement must be completed within 30 – 60 seconds of the RC vehicle coming to rest. Waiting too long may allow your heat sinks to remove heat providing you with a false reading. Next, you will want to use the temp gun as instructed in its manual. For best results, take measurements of many different locations on the motor and ESC. Allow the temp gun to read and retain the maximum temperature as you are taking readings from multiple different locations.

As your LiPo batteries begin to age, you will want to make certain that you are measuring the temperatures once every few runs. LiPo batteries will produce more heat when their internal resistance begins to rise as they age.

Factors that influence Temperature Readings

Keep in mind that there are many influences on the temperature of these components. These factors will skew your readings. What you want to watch out for is any sign that the power system is under higher then normal load. Here is a list of factors that can influence your running temperature.

  • Higher Ambient Temperatures (outdoor temperature for example)
  • Increased load on motor with aggressive throttle use
  • Binding of Driveline Components
  • Aging LiPo batteries
  • Length of Run Time

Using a Temp Gun for the First Run of a New Build

When running your setup for the first time, you want to be certain that you have selected conservative gearing or prop sizes. In RC Airplanes it is much easier to bench test your system. You are able to run up your motor and take measurements every 45 seconds.  For an RC car or boat build, you will have to run bring the vehicles in after 45 seconds. At this point take measurements of the motor, ESC and LiPo batteries.

If all  components are well under 140F/60C, run the vehicle for another 45 seconds and return to take measurements. Keep increasing the run time by 45 seconds if all components are under 140F/60C up to the maximum run time for your system.

If the temperature exceeds the safe limit, either the maximum allowable run time or maximum continuous load has been exceeded. Reduce the load and or run time and check the system again.

Determining Maximum Run Time

In the process described above, determine your total run time that will drain 80% capacity of your LiPo’s. Each time you run the vehicle for the 45 second period and reach about 3 total minutes, it would be a good idea to record how many mAh is placed back in to the LiPo Battery. Determine the amount of mAh that is placed back in the battery by charging the single battery and recording the value on the charger.

For example – If you were to get a 4 minute 15 seconds run time and replace 4000mAh from a 5000mAh battery, this should be considered your maximum run time. 80% of the batteries capacity has been drained. This is to ensure Long LiPo life while getting the better part of a batteries discharge curve.

To the run time calculator to help calculate run time based off of elapsed time and capacity placed in to the pack.

Application of using High or Low Motor / ESC Timing

Most hobbyists who operate electric RC vehicles understand that motor timing can be controlled. The questions is how many actually change the timing of their setup? If you haven’t already read the article on timing, click the link to view the article.

Applications of High and Low Motor Timing

Applications of High and Low Motor Timing

Do you have to change timing?

The short answer to this question is you generally don’t need to. Many ESC’s whether sensorless or not have a default setting that works well with most brushless motors. Performance of these ESC’s are already operating in a range that is suitable for many applications. Years ago I was messing around with timing a lot more than I am today. In fact it is very rare that I will change the default settings of an ESC in terms of timing.

When should you change Timing?

There are a few reasons why you would want to open up the software for your ESC and make a change to the settings. Here are those few key reasons listed below:

  1. Your brushless sensorless motor is not operating correctly
  2. To squeeze more RPM out of your brushless motor setup.
  3. Setup is operating with high temperatures.

Application of Using High Timing

If your RC car, boat or plane is not operating at the speed you are hoping for, changing the timing may get you there. Changing motor timing is not going to add a significant amount of speed. It is something you are able to adjust if going up a prop size or pinion gear size is too much. Or it is something you can adjust since it’s quite easy to do and does not cost anything other than time.

Before changing the timing, you will want to be certain that your power system is not operating at its maximum thermal potential. If so, you do not have the room necessary to increase timing. Increasing the timing will certainly add heat to your system. Upon an increase to timing you will also want to re-check the temperatures of your power system components. This will ensure that you are still operating within spec.

Application of Using High Timing – Synchronization Issues

If you have a motor that you spin up and it starts making a loud screeching type noise and slowing down, you should try changing the motor timing. The screeching noise is a telltale sign that the brushless motor you are running is losing its synchronization with the ESC. Increasing motor timing may help solve this issue.

Application of Using Low Timing

Low motor timing is commonly used on motors that have a low magnetic pole count and a hot wind. This may be something similar to a one turn, 4 pole brushless motor with a Delta wind termination.  These high strung motors do not like high motor timing. Other applications for low motor timing is to maximize run time, power efficiency and torque. If you need the most amount of torque in your setup, use low motor timing.

Changing Timing, Where to Start

Plan to experiment with motor timing and do not know where to start? The perfect place to start when adjust timing is on the low end. Low timing offers the least amount of performance. As you are increasing timing you will want to monitor temperatures to ensure that you do not exceed maximums. It is also best to monitor performance to understand how much of an increase you are seeing or not seeing.

Keep in mind, if you hear screeching from the motor while operating on low timing, try increasing the timing and try again.

In general motors with more magnetic poles tend to prefer higher timing settings.

Timing Explained for Brushless Motor and ESC’s

Brushless Motor Timing

Brushless Motor Timing

Timing is critical to a brushless motors operation. Without the correct amount of timing, a brushless motor may not operate efficiently or even at all. We will be exploring timing for brushless motors in this article. A few key focuses will be on what does brushless motor timing refer to, advantages of low and high timing, and lastly fixed timing vs variable timing.

What is timing within a Brushless Motor?

Timing is defined as the relationship of the position of the rotor relative to the exact moment when a stator winding is energized. Altering the position of the rotor at the moment the winding is powered up is controlling the timing.  There are 2 ways that you are able to alter the timing of a brushless motor. The more common and well known method of timing adjustment is done within the ESC. The second and much less common method of timing adjustment is adjusting the physical endbell of the motor. This method is more common with brushless motor for RC cars.

Advancement or increasing the timing is firing the stator winding phase earlier in the rotational cycle of the motor.

Advantages of High Motor Timing

Most would think that increasing your motor timing is specifically for high performance only. For the most part this is true, however, it is not always the case. When increasing the timing, the most general advantage that you may see is an increase in performance. Increasing the timing typically increases the amount of RPM that you will see out of your setup. Further advancing motor timing also makes it easier for a brushless motor and ESC to sync when operating in sensorless mode. Increasing the motor timing does have its share of disadvantages. These disadvantages are described below in the advantages of low motor timing section and vise versa.

Advantages of Low Motor Timing

A low motor timing offers the potential for a very efficient power system. Low motor timing tends to draw less current. When less power is drawn from the battery, you can expect lower overall temperatures and longer run times. In addition, low motor timing increase the amount of torque potential of your power system. If you are looking for more low end acceleration, adjusting timing to a lower amount will help get you there.

Fixed vs Variable (electronic) Timing

Adjustment of the end bell on a brushless motor is an example of a fixed mechanical adjustment. Once it is set, you can not change the timing when the motor is running, Motors that contain sensors also operate in a fixed mode of operation. Follow this link to read more on sensored motors vs sensorless. A fixed timing mode is limited as timing is best altered depending on several factors. Factors that affect timing include motor load, motor output RPM, number of poles, strength of the inductance within a motor and several more.

Sensorless motors and ESC’s do not use a known position of the rotor for timing purposes. Sensorless ESC’s rely on the back EMF that is produced in order to get the ESC and motor in sync. For this reason, the timing of the motor can actually be varied as the motor is in use. It is known that sensorless ESC’s are very efficient in the RPM range of a typical brushless motor.

ESC’s that are capable of handling timing automatically have significant advantages. Firstly, the decisions for any adjustments are handled by a complex algorithm. It is unlikely that the formula makes a mistake under normal running condition. Secondly, the user does not need to have any prior knowledge of the power system. Lastly, adjustments in timing are handled in order to optimize performance, efficiency and smooth operation. Fixed timing would not be able to accomplish this.

Setting the timing on an ESC that is capable of automatically determining the best range, allows the user to move up or down within this range.

Brushless Motor timing selection

Brushless Motor timing selection

ESC’s that run in Hybrid Sensored/Sensorless mode

Some ESC’s have specific modes that allow both fixed timing and variable timing. A perfect hybrid example is with a sensored motor and sensored/sensorless ESC. What happens is that the motor operates in sensored mode to get the car moving.  Sensored operation with fixed timing allows instant synchronization with the motor and ESC. Acceleration from 0 RPM is very predictable with no hesitation. Once a higher RPM is reached, the ESC automatically switches in to sensorless operation. Sensorless operation is most efficient at the high RPM end of the overall range.

ESC Boost  ( common for RC Cars only )

Boost timing is typically activated when selected on your ESC programming screen. On a Castle Creations ESC, it can only be selected while the power system is operating in sensored mode. Timing advance will start at a predetermined minimum RPM threshold. Timing will be added linearly until the motor achieves the high RPM threshold. From there timing will remain constant at its full setting.

Castle Creations CHEAT MODE

Castle Creations CHEAT MODE

ESC Turbo  ( common for RC Cars )

This is a type of timing when enabled will set a predetermined amount of timing advance at a specific trigger point. This trigger point can be either based on a specific throttle input such as 100%, an RPM value or both. These parameters are programmed in to the ESC. In some cases an ESC will also allow delay to be programmed in to allow a user to exit a corner before the “turbo” function kicks in.

Selecting advancement that is best for your Application

The easiest way to select the correct amount of timing for your application is by trial and error. To accomplish this, you will need to have measurement tools that are able to measure the power consumption and heat within the power system. We will get deeper in to this in the next article talking about the applications of brushless motor timing.

 

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