How to choose the correct Electronic Speed Controller (ESC)? – Part 6

RC Airplane Series – Part 6

In this article, we will learn how to perform ESC Calculations. Also, we are going to study the control systems connections (basically, how the electronics are connected)!

1. What is an Electronic Speed Controller (ESC)?

ESC stands for Electronic Speed Controller. Its job is to provide a set appropriate voltage across the BLDC motor according to the throttle given on the transmitter. 

• For example, suppose I give 25% throttle, so to get the speed corresponding to 25% throttle, what should be the voltage applied across the motor -> this is the job of the ESC! (speed is controlled by controlling current)
• The main thing to understand is that we will be controlling the voltage across the motor with the help of the ESC. We are already aware of the motor kV relation:

$\text{motor } kV = \frac{\text{RPM of motor}}{\text{Voltage across the motor}}$

• So, according to the relation, varying the voltage will vary the RPM of the motor, which will result in speed variation as well.

From the example itself, we can understand that choosing a proper ESC is very crucial so that everything is under control and also safe at the same time. 

Wiring connections for ESC:

2. How to choose an appropriate ESC?

Let’s understand the procedure using an example!

Suppose we finally choose the motor for our model: 

A2212 10T 1400kV BLDC motor

Step-1: Find out the maximum current that the current draws. If this value is not directly given, it can be calculated from the relation.

 $P = V \times I$

(‘P’ is max. power of motor, ‘V’ is the nominal voltage of our battery used, and ‘I’ is the max current from the motor.

From the datasheet:

In our case, the maximum power of the motor is 180W, and we consider that we are using a 3S LiPo battery, which gives us 11.1 V voltage

$P = V \times I$

$180\,W = (11.1\,V)\times I$

$I = 16.2\,A$

Step-2: But we should choose an ESC such that this maximum current value should just be 75% of the actual ESC current, which we will be buying. (Read it again !). We call this current ‘Actual ESC Current.’

Calculating 80% of ‘Actual ESC Current’ (this value needs to be on the ESC we would be finally buying) would give us the ‘Maximum motor current.’

$80\% \text{ of Actual ESC Current} = \text{Max motor Current}$

$\frac{75}{100} \times \text{Actual ESC current} = 16.2\,A$

$\text{Actual ESC current} = 20.25\,A$

This implies that we need an ESC that has a rating of 20.25 A. But in reality, there is no such ESC with this current rating being manufactured. So we need to go with an ESC that has a bigger value than 20.25

We can go with a 30A ESC or a 40A ESC, which would also be perfect in our case.

3. Connections of all of the RC Electronics involved

Now, by this article 6 of the RC Airplane Series, we already know about all the basic electronic requirements for an RC Airplane. Let’s list it down :

• Motor and Propeller
• LiPo Battery
• ESC (Electronic Speed Controller)
• Receiver (On board)
• Transmitter (Not on board)
• 4 Servos (1 for each aileron, 1 for elevator, 1 for rudder) 

In this example, let’s say we are using a 6-channel transmitter and receiver.

• Usually, in most of the cases, we have to attach the connectors to the 2 wires assigned for the battery in the ESC. For this, we can use the XT60 connector, which is very commonly used as well. They come in a set of female and male connectors. The female one is to be attached to the ESC, while the male one is to be attached to the battery

For more clarity on the above figure, you can also refer to the diagram below.

4. Why use Y-junction wire for ailerons?

• If you look into the connection diagram carefully, we can see that the servos attached to the 2 ailerons are connected to a Y-junction wire. This then goes on to connect to the receiver, and it uses just one channel on the receiver for 2 servos!

The reason behind us doing this thing can be learnt from the article – RC Airplane Series-2: ‘Understanding Control Surfaces.’

In the above article, the focus is on the aileron part to understand the reasoning behind the Y-junction cable. In short, we can summarize it as follows: 

To get a roll, having the ailerons deflect in the opposite sense helps even more. For example, if we need to take the right roll, then on giving just one stimulus through the transmitter, the right aileron will deflect upwards while at the same time, the left aileron also deflects downwards.

One Advantage and One Disadvantage:

Advantage :

• We can get a better roll due to 2 ailerons moving in opposite sense and everything is completed by using just 1 channel

Disadvantage :

• We can’t make the ailerons to be used as flaps since they will always move in the opposite sense. (i.e., flaperons are not possible)

Conclusion:

• So in this RC Airplane-6, we have learnt to do the ESC Calculations. Similar stuff is used while drone designing as well, since it also includes BLDC motors whose speed needs to be controlled. 
• Here, we have completed the basic design of the RC Airplane. Hope you enjoyed the Series and got to learn something new through this. But again, reminding you, this was just the Basics. 

RC Airplane Series (All previous Articles)

• Part-1: What’s in the Wings!
• Part-2: Understanding the control surfaces!
• Part-3: Designing your Airplane !!
• Part-4: Motor and Propeller Selection
• Part-5: How to choose a LiPo Battery?

Any suggestions from your side are welcome!

Keep Learning

All the Best