Every Brushless motor has a series of windings that are an essential part of its operation. The windings in a brushless motor are considered a core item withing the motor. The purpose of the motor windings is to produce a magnetic field controlled by an electronic speed control to interact with the permanent magnets causing the motor shaft to rotate. Video Here.
Number of Turns on a Brushless Motor
When we refer to a winding, we are talking about a motor turn. This is where a turn represents the wire that is wrapped in full loop along the direction of the permanent magnet. A manufacture that sells electric motors, typically has a range of windings available for purchase. The availability of different windings or turns is what allows RC hobbyists to precisely select the best for their application.
Number of Turns vs Performance
We will investigate turn performance by stating that all other motor parameters are unchanged. As the number of turns increases within a motor, the Kv of the motor decreases. One can assume that the amount of current that the motor may consume decreases and the torque potential of the motor increases. A lower Kv allows a higher voltage to be used in order to maintain the same amount of overall output power. (watts)
The exact opposite is true when the number of turns is decreased.
How to select the best Turn Count
In our RC application, knowing the amount of turns is not all that important relative to the performance of a motor. However, understanding the amount of Kv that a motor has to offer is very important. The Kv value of a motor is the value that we must be using to select the correct motor.
A turn does not always consist of One Wire Strand
This is an important point to make as many months ago, I received a question. That question asked why someone’s one turn motor appears to have a million wires in it. How could it possibly be a one turn motor. Motor manufactures will typically wind a motor with not just one strand of a particular gauge of magnetic wire. What they will do is use a smaller wire consisting of a higher gauge number in order to create one turn.
The primary reason this is done, is that you can more effectively pack smaller wire in a tighter space vs having larger wire. A very important part of winding a brushless motor is making certain that you can pack in the most amount of copper as possible. Doing so will increase the efficiency of the motor. These smaller diameter strands of wire will allow the windings to be packed very tight decreasing the amount of voids in the windings. Take a look at this motor below. This is a 2.5 Turn motor. It looks like there is a lot more than 2.5 wires. In fact you can nearly see the groupings of each turn and how they are weaved.
Slotted vs Slotless Stator in a Brushless Motor
A slotted motor is a motor containing thin steel lamination that are stacked together. Copper windings are placed in the open slots and wrapped around the steel lamination’s. In a slotless motor, the windings are placed in to position and must be self supporting. There is no structure to help the placement of the windings in a slotless motor.
Advantages of a Slotted Motor
- Creates stronger magnetic fields resulting in higher torque
- Lower Kv motors
- Windings do not need to be self supporting
- Inexpensive to produce compared to Slotless motors
Advantages of a Slotless Motor
- No cogging torque caused by the permanent magnets lining up with the iron lamination’s.
- Best sensor-less low speed operation
- Reduced core losses at high speed operation
Difference between Wye and Delta Winds
There are two wiring patterns to terminate the windings on a brushless motor. One termination method is known as the Wye wind. The other termination method is known as the Delta wind. In a Wye wind, each motor connector is attached to the start of a phase. All three legs or loads are terminated together as below in the top diagram. In a delta wiring pattern, each motor phase is connected to two brushless motor connectors. Refer to the bottom diagram below.
Kv of a Delta Wound Motor vs Wye Wound motor
In general terms, a Delta wound motor would suggest the motor is of a hotter wind. This is of course when all else is equal. Kv of a Delta wound motor would be the square root of 3 or 1.732 times higher than a Wye wound motor. This is the most significant characteristic difference between the two terminations types. You can expect the current load of a Delta wound motor vs Wye wound motor when all else is equal, to be 1.732 times higher. This is exactly what is meant by a “hotter” wind. The motor is going to be more power hungry delivering a higher Kv.
Sensitivity of “hot” Delta Wound Motors
In my own personal experience, I have noticed that the electronic speed controls that I use are less sensitive to changes on a Wye wound motor. I have noticed this primarily when adjust the timing of the motor. Increasing the timing on a Delta wound motor can result in a lot more heat build up within the motor. I have noticed this more commonly with very hot setups running inrunner motors. More commonly 1 turn Delta wound motors.
Termination point of Motor Winds
In some motors, the wire termination point exists where the three leads exit the motor. It’s important to not cut or shorten these wires that are outside the motor case. in other words, doing so may cause your motor to become useless.
My Wind Preference
I don’t have a significant preference when it comes down to the type of motor wind for an application. I am more interested in finding the correct Kv for my application. However, with this being said, I am sensitive to selecting a Delta wind for a high performance race type application. I’ve had a greater amount of luck being able to dial in performance with a Wye wind. Just keep in mind this is my personal experience and there are many people out there who experience excellent race results using a Delta wound motor.