Electronic Components

In this section we will be covering the core electronic components and how everything connects together as one big working system. We've already covered most of the components that will be listed in this section, including: the motor, the servos and the battery. We will also introduce two new components: the ESC and BEC. This tutorial will be a little more technical than the others, but rest assured that I am not just trying to torture you with dry and bland material. If you choose to replace or upgrade components, you will need to understand this section, or you risk having a crucial failure during flight.

The Electronic Speed Controller (ESC)


The Electronic Speed Controller (ESC) is the device that regulates the electricity going from the battery to the motor. If there was no ESC, then the battery would just be directly to the motor, and you'd be stuck with only one speed : Full Throttle. Since you'd like to do other things with your aircraft, like land, being able to control throttle is a necessity. This is what the ESC provides for you.

You may be wondering how the ESC knows how much throttle you want to supply to the motor. To understand this, lets start with your transmitter. The Tx sends the information about your throttle position to the receiver. The ESC actually has a small 3 pin connector (like the servos have), and this connector plugs into the channel 3 slot on your receiver. The receiver then sends the throttle information over this wire to the ESC. The ESC now knows how much throttle you want to give to the motor, and it is able to regulate the power due to being in between the battery and motor. In case you are confused about how this works, lets take a look at how all the devices are connected.


As shown in the above diagram, the ESC directly connects to the battery. Its worth mentioning that when ESC's are sold by themselves, they are typically shipped without a battery connector. It is expected that you will choose what connector you want to use, and solder it on yourself. The battery connector must match that of your battery. All battery connectors consist of two wires - a positive (red) and a negative (black).


Aside from the battery connector, and the wire that goes to the receiver, the ESC has a set of wires running to our electric motor. Usually, these colors are red, black and blue. The motor will also have three wires extending from it, and they will often be the same color. Now, most of the time you can just match up the color of the wires and you are done... but the wiring can some times be inconsistent, and the motor will actually run in reverse. You can easily tell when the motor is reverse, as the airflow from the propeller is in the wrong direction. To fix this, you can simply swap the connection between any two wires. In other words if these connections cause the motor to run in reverse: red1 to red2, blue1 to blue2, black1 to black2, then swapping the configuration to this would fix it: red1-blue2, blue1-red2, black1-black2.

Since the ESC is connected to the battery, it will actually power all the other components on the plane. The motor is obviously powered via its direct connection to the ESC, and the receiver is powered via the ESC's 3 pin connector that is plugged into the CH 3/Throttle port on the receiver. Once the receiver has power, it will then pass some on to the servos that are spread out through the plane.


The BEC


The BEC is a "battery eliminator circuit" which allows you to power the receiver using the same battery that powers the motor. This eliminates the need for a seperate battery for the receiver. Its a necessity in most small planes, like the foamies you'll see us flying, because it eliminates the weight that would be present with a receiver battery. Most ESC's come equipped with a built in BEC (as shown in the picture above). This allows you to only have to worry about one piece of equipment, and not have to deal with additional wiring. In these cases, the wiring and the diagrams that we've already introduced do not need to be modified.


There are some instances where you'd probably want a standalone BEC unit. For one, high performance ESC's often do not come with built in BEC's. Secondly, your ESC may not have an adequate BEC to handle all of your servos. You see, the built in BEC inside the ESC has a separate power rating than your ESC. Your ESC may be rated for 50A, but its internal BEC might be rated for 2A. If you are using 6 servos that draw .75 A apiece, then you will need an external BEC. Its recommended that you buy an external BEC that supports the total amperage draw of your servos with at least 25% headroom. You should check your manufacturer's servo specifications to determine how much current they can draw. In the picture above, the ESC is in the lower right, while the external BEC is the small module towards the center of the image.


To wire the BEC, the red and black BEC wires will usually have to be soldered into the ESC's battery connector. Basically, both the ESC and the BEC wires must be electrically connected to the battery. There will also be a 3 pin connector coming out of the BEC, and this needs to connect into the battery (BATT) connection on the receiver. You will then have to remove the red wire from the 3 pin connector coming out of the ESC in order to disconnect its onboard BEC. This is done to prevent electrical issues that occur when the ESC's BEC and the external BEC are both connected. I recommened you just pull the pin out of the connector and wrap it with electrical tape. The above image is a good illustration of how the wiring will look with an external BEC.


Calculating The Requirements


Its actually very important that you choose an ESC and battery that is rated at a higher amperage than the current you will be using during flight. One of the biggest problems is that its very hard to estimate how much power your motor will use. Its largely dependent upon both the motor and the propeller you choose. Some times the manufacturer of your electric motor will be nice enought to tell you the estimated current draw with a few different propeller sizes. If not, you can try http://www.flybrushless.com/search to try and find the specs of your motor and prop combination. There are ways to measure your current draw, but that is beyond the scope of this course.

Once you find the amperage that your motor will draw, its important you get an ESC that is rated beyond that amperage. Leaving a headroom of 20%-30% is considered good practice, as you don't want any risk of overloading your ESC. If your ESC is rated at a lower amperage than the amperage specified for your motor and propeller combo, its highly likely the ESC will give out during flight. This could lead to total failure of your aircraft and cause you to crash.

Its also important to make sure your battery is rated to supply enough current to meet the estimated current draw of your motor. To calculate this, simply take the capacity (like a 2200 mAh ration) and multiply it by the discharge rate (like a 20C rating). Since 2200 mAh = 2.2A, and our motor is rated in amperage (instead of milliamps), its easier to use the units of Ah. So, in this case, we have 2.2A * 20C = 44A. If you expect your motor to draw 30A, this battery will do fine. If you expect your motor to draw 60A, this battery will not be able to supply the necessary power to the motor. This will overtax the battery and could damage it. Its a good idea to buy batteries with an extra 20%-30% overhead, just like with the ESCs.


Its also good to know how to calculate the expected flight times of your battery with your equipment. You will need only two pieces of information to calculate this: the amperage draw of your motor at full load, and your battery capacity. If you don't have the specs on your motor, use the rating of your ESC (it will usually be pretty close to the draw of your motor). Lets say you expect your motor to draw 30A at full throttle, and your battery holds 2000 mah (or 2Ah). This means that if you ran your motor for an hour, it would draw 30A. Your battery, however, only holds 2A, so you will not last anywhere near a full hour. You can calculate what fraction of an hour your 2A battery will last for by simply dividing by the 30A of your motor draw. To put this in laymen's terms - your motor draws 30A in an hour, and you have 2A. You have 2/30th of the power needed to run for an hour. This works out to be 6.6% of the power you need to last a full hour, and therefore you will only last 6.6% of time in that hour. Since 1 hour = 60 minutes, we can find 6.6% of 60 minutes through simple multiplication. 60 minutes x .066 = ~4 minutes.

Now keep in mind that you should probably not run your battery completely dry. You'll want to leave about 20%-30% of the power in the battery. This means that you should probably aim to be on the ground with 20%-30% of flight time remaining. In our previous example, we calculated a 4 minute flight time. We'd probably want to actually limit this flight to around 3 minutes in order to avoid draining the battery too much. Its also important to remember that we are assuming that full throttle will be used the entire flight. In reality, you might only fly at half throttle most of the time. This would greatly increase your flight times. You may have to experiment a bit to determine your actual battery life. Its a good idea to always err on the side of coming down too early. The last thing you want to do is run out of battery while you are up 250 feet in the air.


The Importance of Proper Cooling


If you know anything about electronic circuits, you should know that heat causes resistance and can damage or impede electronic components. Basically, everything electrical runs better when its cold. Your battery, motor, ESC and receiver are no different. The receiver will typically not generate much heat, but its still a good idea to keep it cool. The Battery, ESC and motor will often generate a great deal of heat when they are in use, and its utterly vital that they are constantly cooled by moving air.

Since your airplane will be moving at a fast pace, you do not need any form of active coolinmg (like a fan). Instead, you will rely on air vents on the front of the plane to let air in as the plane flies. Exhaust vents are equally important as they let air out of the plane. In order for the cooling to be effective, the air must travel in the plane and then out of it, otherwise the components will not be adequately cooled. Blocking either the intake or exhaust air canals should be avoided at all costs. If your airplane lacks sufficient airflow, its not uncommon for pilots to dig away at the foam in strategic locations in order to provide better intake or exhaust.

Due to the fact that the plane's movement generates the cooling, its important not to run the motor too much while on your test bench. There will be very little airflow over the components, and its very common for the ESC, battery or motor to overheat like this. In some cases, even just testing the servos on the bench is enough to cause the BEC to overheat. These types of problems can be partially alleviated by ensuring that all of your equipment has adequate headroom. Of course, when you buy an "almost ready to fly" (ARF) or "read to fly" (RTF) airplane, you will often be using the components that come with the plane. Bundled components will sometimes have very little headroom, so don't automatically assume the manufacturer did things the "right way".

    

Manufacturers tend to do other strange things as well. One of the strangest things I've noticed is that ESCs are often wrapped in plastic, with a label attached to the top of them. This is especially strange to me because most manufacturers will make sure to put a heatsink on their ESC to help with cooling. What makes this so strange is the fact that they've wrapped their heat dissapating mechanism with plastic, an insulator. While I do not recommend removing all of the plastic, its usually a good idea to take an Xacto knife and cut the label off. This will expose the metal heatsink underneath, and allow air to better cool the ESC. The pitcure above and to the left shows the label in question, and the picture to the right shows what an ESC looks like without the plastic.


Diagnosing problems


Once the battery is plugged into the ESC, it will begin a short bootup process. You will usually hear several audible tones coming from the ESC. This is part of a very basic power on self test. If everything is normal, you should hear an uplifting beep tune as verification. Failure to hear the beep-tune usually means something is wrong with a critical component. This usually includes the motor or the radio equipment, but NOT the servos. Some times you will hear a slow steady beep, other times you just might not hear the tune. Most of the time, your radio equpment is at fault. Either the transmitter isn't on, or the ESC has not fully initialized due to throttle protection. In most ESCs, if you do not have throttle set all the way down to zero, it will fail to initialize. If you are still having trouble after checking these two common problems, double check every connection to your ESC. If you still can't figure it out, consult your ESC documentation.

Once the ESC is initialized, your plane should be ready to fly. You will want to do a quick pre-flight check before you actually take your plane into the air. We will have more on the pre-flight check in the "first flight" tutorial, but lets hit some of the basics here. Check that all the control surfaces are moving, and make sure they are moving in the right direction. If a servo is not moving at all, its probably not connected into the receiver correctly. If it is plugged in, make sure you don't have the servo wire in backwards (I do this all the time!). Having the servo wire in backwards will cause them to be completely unresponsive. Its important to note that if you use a Y-cable (like for the ailerons), then having any one of the three connections reversed will cause both servos not to work.

Once you get up in the air, you may experience a failure of the electronics. Most of the time, people assume the radio is at fault. While it is true that poor reception or interference can cause the plane to do very weird things, the BEC and ESC are often responsible for a lot of issues. This is especially true if you have not chosen these components carefully, and are pushing them to their limits. If you experience issues with your servos in the air, it could be due to the BEC or ESC overheating and/or malfunctioning. The same thing applies to motor cut-outs, as a failure of the ESC will cause a loss of power to the motor. In certain situations, a failure or short on the ESC will cause the entire plane to stop responding, and simply fall to the ground. Some times its very difficult to tell whether its the radio equipment or the ESC & BEC, and the only way to find out is through bench testing (or a post mortem :-P ). The best way to prevent such problems is to ensure that all the parts in your plane are receiving adequate cooling, and to make sure you aren't overloading your ESC or BEC.



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Supplemental Videos From the Web



ESC, Motor and Receiver Wiring


This video is actually made in three parts (links to part 2 and 3 are inside the video). It is a comprehensive guide to hooking up all of your electronic components. The only thing it does not cover is the connection of servos to the receiver, but we have a video for that in the radio training section.



Connecting the Servos to the Receiver


This video is a great illustration of how the servo wires plug into the receiver, and how the respective channels control the different surface (ailerons, elevators, rudder, throttle).




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