Receiver, ESC, Motor, Battery and Propeller

Hello everyone! In terms of power systems, there are five essential ones in RC planes. As you saw in the title, they are the receiver, ESC or engine speed control, motor, battery and propeller. Let's talk about them all.

Receiver

I like to think of the receiver as the central piece of electronics on an RC plane. The engine speed control or ESC and all of the servos connect to the receiver. When you make a certain control input on your transmitter, the transmitter sends that signal to the receiver. Since all the servos and engine speed control are connected to this receiver, it allows your plane to function according to your control inputs. 

ESC or Engine Speed Control

For what I know, the ESC is just what it sounds like. A way for the motor to vary its speed. There are many different types of speed controls, so it is important to get the right one based on the amount of current that that motor/propeller combination is using. A great site for this is www.flybrushless.com.

Battery

This one is quite obvious: to provide power for the motor, but there is something important here that I learnt from my Dad. If you multiply the mAh of the battery by its maximum continuos discharge rate, you will get the maximum amount of current that can be drawn from that battery. To make things simple, say that its the type of battery that I use in the foam board plane that my Dad and I built. An E-flite 800 mAh battery with a 20C maximum discharge rate. Multiply 800 mAh by 20C and you get 16000 mAh or 16 amps as the maximum current. This is important because it ties into the whole motor/prop combination thing. If your chosen motor and propeller combination is using say 18 amps of current and you have a battery that has a maximum current of 16, then you need a bigger battery or a different motor/prop combination. Don't worry if your motor/prop combo is using the absolute highest amount of current that the battery can handle being drawn from it. Getting the maximum performance is a good thing. 

Propeller

The propeller is what makes all of this stuff amount to your plane soaring through the skies. So, it is really important to choose the right one! Propellers have a twist in them called pitch. The difference that pitch makes is in the speed or thrust that the RC plane will have. Pitch is the limiting factor for speed because the RC plane gets to a point where the pitch of the propeller is sucking the air in and pushing it out the back as fast as it possibly can, which limits the top speed in level flight. A larger pitch will have a higher speed because it is taking bigger bites of air but lower thrust, and less pitch will have lower speed and a propeller with a larger diameter will have higher thrust. Again, flybrushless.com is a great website to visit for this. There is a way to calculate the maximum pitch speed of the propeller. This could also be considered the top speed of the model, assuming it had no drag which is not true. Here it is:

Pitch speed = (motor rpm * propeller pitch in inches)  * 60 * 0.0000254
(example) Pitch speed = (15096 rpm * 7 inch pitch) * 60 * 0.0000254
                 Pitch speed = 161.04 km/h 

Disclamer first: Just remember that this is what I think and may not take some things into account. But I have compared this against several online pitch speed calculators and an experienced person's website so I think that it is correct. 

Okay now that I have that out of the way, let me explain it. If a propeller has a pitch of 7 inches, then, every time it makes a full revolution or turn, the plane will move 7 inches forward through the air (at full rpm). Then, if you multiply the pitch of the propeller by the amount of revolutions it makes per minute (RPM), then you will get the amount of inches that the RC plane moves forward through the air every minute. If you multiply that by 60, then that is the amount of inches that the plane moves forward in an hour. Multiplying that by 0.0000254 will convert inches per hour to kilometres per hour.

Of course, this cannot be the maximum speed of the model. The main reason that I know of is drag. Drag slows the plane down. So, how much is the question. After doing some research on the e-flite website, testing RC planes out on the flight simulator and typing some things into my spreadsheet, I have made an estimate for the actual top speed of a model. For a high drag, box shaped plane by comparison such as the E-flite Apprentice or Carbon Z Cub,  http://www.e-fliterc.com/Products/Default.aspx?ProdID=EFL3100 the actual estimated top speed should be about 60% of the calculated pitch speed. You can do this easily on a spreadsheet by multiplying the cell with the value of pitch speed by sixty percent. For a medium drag type plane such as the HobbyZone Sportsman S, you could expect a higher top speed closer to 65% of the pitch speed. For a low drag plane such as the E-flite Rare Bear, the max should be about 70% the pitch speed on a good day. This is a great thing to add to a spreadsheet if you decide to make one.



Motor

The motor is what turns the propeller of an RC plane. We already talked about the interconnectedness of the motor, battery and propeller so I will just end by giving you a useful tip for motors: The motor KV multiplied by the voltage of the battery connected to it will give you the maximum potential RPM of the motor (e.g 1800 KV * 11.1 volts = 19980 RPM). Remember, this will change depending on the propeller that you use. I'm assuming that a propeller with a large pitch taking big bites of air will slow down the motor RPM, which would then affect the pitch speed of the propeller slightly, since pitch speed takes motor RPM into consideration. You could then expect the pitch speed to be slightly lower than your calculation depending on the type of propeller you use. 

The E-flite Park 370 Motor. Motor on the left, spinner in the centre and motor mount on the right.