Timing Explained for Brushless Motor and ESC’s (Low vs High)
Brushless motor timing is critical to its operation. Without the correct amount, 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.
Also check out applications of using motor 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. Furthermore, advancing motor timing also can make it easier for a brushless motor and ESC to sync when operating in sensorless mode. This tends to happen most commonly with outrunners (Specific Motor/ESC Combination that does not work well together (simply put) ) where it may struggle to reach max RPM as it produces a very obvious screeching noise. Bumping the timing up can help with synchronization at higher speeds. 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.
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.
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.