Radio Controlled (RC) aircraft have been around for the better part of a century. The hobby originated with the creation of the RC model airplane. The RC model airplane was satisfactory for a long time, but it had many limitations such as its inability to make abrupt directional changes. As the hobby progressed, RC model helicopters were introduced. Helicopters provided much more control than their fixed wing counterparts due to their ability to hover and strafe. It wasn't until just recently, with the popularization of UAV's in the media, that the construction and flight of multirotor aircraft was introduced to hobbyists.

The first multirotors were very basic with marginal control and lots of failure. The equipment used was for airplanes and helicopters, which, while fine for those, lacked the special needs for multirotor operation and control. The electronic control systems improved, specialized firmware for electronic speed controls began to develop, motors and propeller choices and availability for the unique multirotor needs became more available. The latest generation of electronics and hardware now allow the complete novice, with little or no flight training or experience, to successfully fly a radio controlled multirotor. While this has greatly increased the number of interested fliers it has also resulted in many people making poor decisions in how and where to responsibly fly their shiny new 'toys'. The goal of this lesson is to ensure that members of DASL are well informed on the proper practices to make sure that they are operating both safely and legally for the sake of both themselves, and everyone around them.

Safety should be the number one concern of every pilot when operating their multirotor aircraft. Multirotor aircraft can be very dangerous if operated incorrectly. Because of their small size and range of flight, multirotors can both injure civilians on the ground and interfere with the operations of full sized aircraft. It is no surprise that the misuse of Small Unmanned Aircraft System (sUAS) has brought about the need for government regulation. An excellent guide has been put together online to educate pilots on the responsibilities, guidelines, and requirements to operate an sUAS either recreationally, or commercially. The following points are important guidelines taken from the text, the entirety of which can be found at Know Before You Fly.

• Follow community-based safety guidelines, as developed by organizations such as the Academy of Model Aeronautics (AMA)
• Fly no higher than 400 feet and remain below any surrounding obstacles when possible.
• Keep your sUAS in eyesight at all times, and use an observer to assist if needed.
• Remain well clear of and do not interfere with manned aircraft operations, and you must see and avoid other aircraft and obstacles at all times.
• Remain well clear of and do not interfere with manned aircraft operations, and you must see and avoid other aircraft and obstacles at all times.
• Contact the airport and control tower before flying within five miles of an airport or heliport.
• Do not fly in adverse weather conditions such as in high winds or reduced visibility.
• Do not fly under the influence of alcohol or drugs.
• Ensure the operating environment is safe and that the operator is competent and proficient in the operation of the sUAS.
• Do not fly near or over sensitive infrastructure or property such as power stations, water treatment facilities, correctional facilities, heavily traveled roadways, government facilities, etc.
• Check and follow all local laws and ordinances before flying over private property.
• Do not conduct surveillance or photograph persons in areas where there is an expectation of privacy without the individual’s permission.
  

Users of commercial and recreational sUAS should be aware that in remote, rural and agricultural areas, manned aircraft, including fixed-wing aircraft and helicopters, may be operating very close to ground level. Pilots conducting agricultural, firefighting, law enforcement, emergency medical, wildlife survey operations and a variety of other services all legally and routinely work in low-level airspace. Operators controlling sUAS in these areas should maintain situational awareness, give way to, and remain a safe distance from these low-level, manned aircraft.
Here are a few other things to take note of in order to fly 100% safely.

You might not believe it, but a first aid kit is the most important part of your flight box. It may sound silly but it's true. Accidents should you be ready for:

1. Burns
2. Cuts
3. Prop bites
4. Insect bites

An instant ice pack goes a long way. You should always have paper towels or napkins, and at least a bottle of water with you. Other items to consider is protection from the elements, sun glasses, sun block, hat, shade, etc.

When choosing a flying site for practice, it is best to choose a place free from obstacles and void of people. New pilots tend to lose control of their aircraft fairly frequently. If this happens, we want to ensure that the stray aircraft does not hit any person, car, building, or other property. The best places are where no one will bother you. If there are people present, always be sure to be flying away from them. Your sUAS should never be between you and another person.

Unfortunately, UNLV is not an ideal place to practice flying. When flying within 5 miles of an airport, you must contact the airports air traffic control tower to let them know. While it is not illegal to fly in these areas, there is a possibility of interfering with manned air traffic. It is recommended that future students do not practice at UNLV to avoid any issues with the airport or law enforcement.

The authors of this course have had luck practicing at the soccer fields just east of Sam Boyd Stadium on Tuesday mornings. When flying at parks or fields it is very important to be aware of any sprinklers as they can severely damage the equipment.

Always make sure you are using tested and reputable equipment when flying. Though in many industries it can generally be assumed that inexpensive hardware may not be adequate for certain applications, in the RC multirotor industry, there are many inexpensive DIY frames that have proven to be reliable and sometimes on par with name brand products.

The batteries powering your sUAV are high quality, yet they still require care and attention. The misuse and mistreatment of batteries can not only hinder the performance of your vehicle, but could also pose a physical threat. The chemicals used in the batteries are caustic and flammable and therefore the batteries should be treated with great care. Always follow the manufacturer directions and specifications for charging, discharging, storing, and disposing.

Many people seem to lack this trait. If something doesn't “feel” right something is probably wrong. If something seems wrong while flying, land and find out what doesn't feel right. Stick to the common sense rule when attempting anything with R/C equipment.

Recent federal regulations require all sUAVs between 250g and 25kg in weight be registered and the sUAV marked with the registration number. The registration fee is minimal and good for several years. The registration is really for the pilot, not for each sUAV. Each and every sUAV the pilot operates will have the same registration number affixed. More information on registration can be found here: FAA Registration.

The majority of motors used are brushless out-runners. Brushless in that there is no physical connection between the stationary and rotating parts of the motor, other than the bearings. Out-runners have station wire wrapped stators in the middle of the motor and the outer diameter, the bell, rotates around the stators. The bell has permanent magnets installed around its inner diameter. Energizing the winding in sequence creates an eletro-magnet force that attracts the stationary magnets in the bell which results in the rotational force needed to spin the propeller.

There is no set conformity in motor size listings. Most indicate motor size by the diameter and height of the stator. Some are listed by the physical outer diameter and height of the bell. The size listing is normally a set of four numbers, where the first two numbers are the diameter and the last two numbers are the height. For example, a 2212 would be read as a 22mm diameter stator/bell with a 12mm stator/bell height. Unfortunately the manufacturers don't always describe exactly how they measured the motors and some extra research by the purchaser may be required. For example, a motor with a 2208 (stator size) listing could be the exact same size as a another manufacture's 2812 (bell size) listing.

Motors are also listed in kv. Kv is the rated RPM of the motor per applied volt with no load (no propeller). A 1000kv motor connected to a 10v power source would spin at 10,000RPM. A 2300kv motor with the same 10v power source would spin at 23,000.

Multirotors require motors that spin in both Clockwise CW and Counter-Clockwise CCW directions. Some motor sets come with both CW and CCW motors. The motors themselves don't care what direction they spin. The CW/CCW motors are based on the thread direction of the motor's prop shaft. You want to place the motors in the positions that would produce a self-tightening tendency of the prop shaft nut when the motor is turning. It is recommended to use a nylon-insert lock nut for motors with all normal rotation prop shaft threads. The lock nuts great reduced the chance of a prop loosening/coming off in flight.

The required motor rotation direction for each motor is determined by the firmware in the flight controller. It is imperative the rotation of both the motor and propeller matches what the flight controller is expecting. There are two common ways to change motor direction; a) swap any two of the three motor wire connections to the Electronic Speed Control, b) via a change of firmware of jumper setting on the speed controller.

Electronic Speed Controls, also called ESCs, are rated by the max constant voltage and amperage they can safely handle. ESCs operate on Pulse Width Modulation. What this means, is that there is a running clock that expects a pulse of 'on' signal before switching 'off'. The length of this pulse dictates how fast the motor should spin. By modulating the width of this pulse, we are able to control the speed of the motor.

When the ESC is 'on' the system will draw the maximum amps the system requires. When off there are no amps supplied. Contrary to what many think, there is no such thing as being only partially on. Amp draw is measured as an average of current over a given period of time. For example, the full throttle (full on) amp draw of a motor over 1 minute of time is measured at 20 amps. This is the maximum amp draw of the power system. Repeating the run at half throttle over a 1 minute period ( 30 seconds on/30 seconds off) may show a 10 amp draw. This does not mean the system was actually drawing only 10 amps of current. It means that the average current was half because the ESC was on half the time and was off half the time.

It is critical you know the max amperage draw of the power system to verify your ESC rating is sufficient. This is normally done via use of a Watt Meter that connects between the battery and the power system. Full throttle is applied to the motor(s) with a propeller(s) installed, and reading the actual amp draw displayed on the meter. This MUST be done with safety in mind as the spinning props can easily cut anything that may come into contact with them.

Many ESCs have a Battery Elimination Circuit (BEC) built in. The BEC provides a 5v output required to power the Receiver and Flight Controller. There are two types of BEC, a) Linear, b) Switch Mode.

Linear BECs are the most commonly seen. They have fewer components on the ESCs. They are always on, meaning they are reducing the input voltage down to 5v all the time. The higher the input voltage the harder the BEC has to work to reduce the voltage and the hotter the linear regulator becomes. A overheating BEC will either have a thermal shutdown or burn-out…either resulting in loss of power to the Receivers and Flight Controller. It is not recommended to use a BEC with greater than a 3S (12v) battery. Removing/unpinning the red voltage wire from the ESC 3-wire harness disables the ESC for use with higher input voltage sources.

Switch Mode BEC's are more efficient than Linear BECs. They turn on and off to an averaged regulated output. They require more components on the ESC, do not heat up as much as linears, and can safely handle higher voltage inputs. Like the Linear BEC, they can be disabled by removing/disconnecting the red wire on the 3-wire servo harness.

An ESC without a BEC circuit is called an Opto ESC. It may have 2-wire harness or still have the 3-wire harness, with the red wire being inactive. Using an Opto ESC requires a separate, external voltage regulator to supply the 5v required by the Flight Controller and Receiver.

ESCs on multirotors often need to be calibrated. Follow the manufacturer's instructions on how to calibrate the selected ESC. Calibration sets the ESCs High and Low throttle signals to equal levels. This allows balanced throttle control to the motors vs having some motors trying to spin faster/slower than other motors at the same throttle level.

Props also come in all shapes and sizes. They can be wood, some form of plastic, and carbon fiber. The most common is the plastic 2-blade prop. They are sized by the diameter and pitch of the prop. For example, a 15×4.5 prop has a 15” diameter and a 4.5” pitch. Diameter affects the thrust provided; the larger the diameter the higher the thrust/lift capability will be. Pitch is the angle of attack (twist) of the prop blade. It is measured in how far the prop would move forward in one 360 degree rotation in a perfect environment. Pitch determines the speed; the higher the pitch the faster it would be.

The diameter and pitch of the propeller affects the load applied on the motor. The load on the motor determines the amps the system will draw from the battery. Prop size must be adjusted to gain the performance desired and the amp draw restrictions of the system. Multirotors are more geared towards thrust/lift than for speed. Most props used on multirotors are only in the 4.5”-6” pitch range.

Multirotors require clockwise (CW) and counterclockwise (CCW) propellers. Prop rotation is as viewed from the front. The normal rotation for props is CCW. Most CW props are called Pusher Props and use a letter P post-fix on the size marking. A prop marked as an 8×4.5 is a CCW prop, an 8×4.5P is a CW/Pusher prop.

[include pictures of propellers and pitch/diameter examples]

There are many battery types/chemistries available. The current batteries used are Lithium based with the Lithium Polymer (LiPo) being the most common. Other types are LiIo, LiFe, LiMh, LiHV. Each chemistry type has different maximum and minimum voltage levels. It is important to use battery charges that can charge the specific battery used. Over charging or excessive discharging of a battery can affect battery longevity or cause a catastrophic battery failure. The max voltage/cell for a LiPo battery is 4.2v, the minimum is ~3.3v, and a storage voltage is ~3.8v.

LiXx batteries will have the main battery leads and, normally, a set of smaller wires with connector. The small wire harness is the Balance Lead. It is used to test the voltage of each individual cell as well as when 'balance charging' the entire pack. Balance charging is discussed in the Battery Charger section.

LiXx batteries are sized by the number of individual cells in series, and capacity (measured in milliamps) of each cell. A 2S 3000mAh battery is two 3000mAh cells in series. A 6S 3000mAh is three 3000mAh cells in series. The max charge voltage for a LiPo battery is 4.2v per cell. Cell voltages are added in series. A 1S LiPo would have a max charge of 4.2v, 2S of 8.4v, a 3S of 12.6v, and a 6S of 25.2v.

Occasionally there may be the need to connect batteries in either series or parallel configuration. If needed, do this with great care or you could damage the battery or have a catastrophic failure/fire. The guideline is: For series connection: Cell count can be different, but the capacity MUST be the same. A 2S 3000mAh battery can be connected in series with a 4S 3000mAh battery to get an equivalent 6S 3000mAh battery. For parallel connection: Cell count MUST be the same, but the capacities can be different. A 3S 3000mAh battery in parallel with a 3S 5000mAh battery is equivalent to a 3S 8000mAh battery. So for series connections, add voltages; parallel connections, add capacities.

So why the need for different battery sizes? For capacity it's simple, for added duration…basically a larger electronic gas tank. For voltage it's efficiency; higher voltage will provide the same power at lower amps than lower voltage. So let's talk power.

We don't really fly based on amps, we fly based on required power. The simple formula for Power/Watts (W) is Applied Voltage (V) times current/amps (I); W=V*I. Let's say it takes 100W of power to maintain hover of a multirotor. A fully charged 3S battery be 12.6V. How many amps would be needed to produce 100W or power? Using the above formula, solve for I; I=W/V or I=100W/12.4v for a ~7.9A current draw. Take the same power requirement with a 6S (25.2v) and you get; I=100W/25.2 for ~3.96A current draw. Wow, same power for less amps means you can fly longer with the same available battery capacity. Unfortunately nothing is free. A 6S battery will weigh more than a equivalent capacity 3S battery. The added weight will require more power to sustain hover, the more power required means the higher the amp draw will be. So a higher voltage battery may provided more power and longer flight time, but not necessarily a linear increase.

The key is to the proper size power system is knowing the current draw and desired operational parameters of the multirotor. A small race quad will likely use a 4S LiPo with smaller, high kv motors, low diameter and higher pitch props. A multirotor designed for longer flight duration and increased lift capability will be a larger frame, using 6 to 8 motors, a 4S-6S, high capacity battery, with larger, low kv motors spinning large diameter, low pitch props

WARNING: Only charge batteries with an appropriate charger based on the type of battery being charged. Using the wrong charger and charge logic could result in reduced life-span of the battery to burning the entire neighborhood down. Follow your charger's instruction manual and do not leave batteries unattended while charging.

Since we are using rechargeable batteries we need a way to charge them after use. The variety and capabilities of available charges is vast. In general most chargers can:

1. Charge different battery types
2. Have adjustable charging rates (current)
3. Charge and discharge batteries
4. Have the ability to Balance Charge LiXx batteries
5. Have the ability to Storage Charge LiXx batteries

The most commonly used methods for charging LiXx batteries are, a) Charge, b) Balance Charge, c) Storage charge.

The recommended charge rate for batteries is 1C, where 1C means the capacity of the battery * 1. A 2000mAh battery 1C charge rate would be 1*2000mAh=2000mA or 2A. A 2C charge rate would be 2*2000mAh=4000mA or 4A. Man modern batteries can safely be charged at a higher C rate. 1C is the easiest on the battery, but will also take longer to charge.

The Charge method only requires connection of the main battery lead to the charger. The charger needs to be manually set to battery's actual cell count (1S, 2S, 3S, etc). It will then charge the battery to its max voltage level for the set battery's chemistry type. It is imperative the cell count is set right or the charger will (try to) charge the battery to the wrong voltage. A 3S LiPo battery set to a 2S will likely not charge at all as the 3S battery low voltage of ~>9v (3S*3v/cell) is greater than a 2S battery's max charge voltage of 8.4v (2S*4.2v/cell). A 2S battery set for 3S will result in the charger trying to put 12.4v into a battery rated for only 8.4v max. The battery will puff up like a balloon, perhaps rupture the battery casing, and has a high potential of bursting into flames. The Charge method also does not take actual cell voltage into consideration. Through use, LiXx batteries often become unbalanced, where some cell voltages are higher/lower than others. The Charge method would result 'high' cells being overcharged and 'low' cells from charging all the way up.

Balance Charging helps prevent wrong battery cell settings. The battery main lead is connected to the charge port on the charger, but with Balance Charging, the battery's balance lead is also connected to the charger. The charger automatically determines the cell count from the balance port connection. This greatly reduces the possibility of overcharging errors. The charger's selected cell count needs to be verified in case of an improperly connected balance lead or broken balance lead wire. Once the settings are determined good, the Balance Charge will charge the pack and monitor the individual cell voltages. As the battery 'fills up' the charger will start to discharge any 'high' cells while still charging the 'low' cells. The charge is terminated once all the cells are equal and fully charged. Balance charging takes longer because of the balancing action, but is the easiest and safest method for the battery.

Storage Charging will charge or discharge a battery to the recommended level of ~3.8v/cell. Storage charging a battery that will not be put into near-term use (within a day or two after full charging) will help extend the lifespan of the battery. Like Balance Charging, both the main and balance leads of the battery are connected to the charger.

The Flight Controller (FC) is the brains of the system. Without the FC we would never be able to control a multirotor. In its simplest form, the FC receives the command signals from the pilot via the radio system, determines the current operating condition of the multirotor via a series of sensors, and sends signals to the appropriate ESCs to either increase or decrease motor speeds to cause the multirotor to respond to the desired control input. So what are the sensors the FC uses to perform its magic?

Most all FC's have, at a minimum, an on-board Gryo and Accelerometer. The Gyro is the main sensor and is used to hold the current attitude (pitch or bank) of the multirotor. This is the main sensor for Acro flight mode, where the frame is put at a desired attitude and hold that attitude when the control stick is neutralized. The Gyro does not try to return the multirotor to level.

The acccelerometer is used to sense a change of force and return the multirotor to level from any given attitude when the control stick is neutralized. This is the primary sensor used when flying in an Auto-level or Stabilized flight mode. The pilot must apply and hold the desired control input to maintain the desired flight attitude when in a stabilized flight mode.

Advanced FC's will normally also have a build in magnetic sensor (mag) and barometric sensor (baro). These can also be external, add on sensors, but are normally on the main FC board. The mag is used to determine the magnetic heading. The baro is used to sense atmospheric pressure changes for more accurate altitude control.

A GPS receiver is used for autonomous flights, Position Hold, and Return to Home (RTH) capability. The GPS in nearly always an externally device that is connected to the FC. Many GPS units also incorporate an additional mag sensor. Use of the GPS and associated flight modes will be covered in more detail as they are introduced in the actual flight training sections.

There are many brands or FC's, each with their own features and capabilities. For this course the 3D Robotics Pixhawk FC will be used. The Pixhawk FC is a full featured system capable of basic through advanced autonomous flights. Discussion here will be basic. More detailed instructions and FC capabilities can be found here: http://ardupilot.org/copter/index.html . Specific features will be further discussed as they are introduced.

The primary control system used is the Radio Transmitter (Tx). There are many styles and manufacturers, each with their own range of capabilities. The Tx details will be discussed at a general level. The pilot must understand what their Tx's capabilities are and how to make adjustments to the Tx. Advanced FC's may also have the ability to be controlled from a Ground Station, be it a Laptop or Mobil Device via Telemetry Radios. This method of control will be covered in the advance flight training section of this guide.

The four basic flight controls are Aileron, Elevator, Rudder, and Throttle. These are mainly fixed-wing terms. For helicopters and multirotors these are called Roll, Pitch, Yaw, and Throttle. The four flight controls are channels 1-4. Different Tx's use different channel sequences for these controls. Likewise, FC's expect the flight controls sequence in a certain order based on their programming. You may need to change/remap the channel sequence of either the Tx or FC to match. Multirotors normally use a fifth control channel, Ch5, for Flight Mode selection. The user needs to know which switch on the Tx is tied to Ch5 and know how to change the switch used if/as desired. In this program we will be setting up an 8 channel control system for the Pixhawk.

The Radio Receiver (Rx) captures the control signals from the Tx and outputs them the FC or servos. There are several protocols for doing this. Many Rx's are larger and have one output pin for each channel of control they are able to provide. This type is called PWM and uses a lot more wiring for the control connections. This complexity is quickly fading in favor of more simplified connections.

The PPM protocol replaced PWM. PPM allows for all channels of control to transmitted over a single wire, with each channel of information in a stacked order, where each channel's information is transmitted one behind the other. PPM greatly reduced the wiring needed, but was a little slower in transmitting the channel information.

The latest protocol is Serial Communications. It is similar to PPM in that a single wire transmits all the channel information, but is faster and makes control inputs feel more responsive. Serial communications has different names from different manufacturers. Common ones are SBus and Spektrum Satellite. Refer to your individual radio's Rx instructions on what type of protocol(s) it outputs.

When holding the R/C transmitter it is most peoples nature to place their fingers around the back and use their thumbs to manipulate the gimbals. Although this would technically work, there is another technique that allows the user to have more control over their craft, and is the one we will be using in this course.

To hold the transmitter properly, place your outer three fingers behind the controller, and hold the gimbals between your pointer finger and your thumb. This may seem strange at first, but when used with a neck strap, the weight of the transmitter is negligible and so you can concentrate more on controlling the craft instead of holding the transmitter.

Radio Control Tx's normally come in a Mode 1 or Mode 2 configuration. The difference is in the control stick layout. Mode 1 uses the left stick for Pitch and Yaw control and the right stick for Throttle and Roll control. Mode 2 uses the left stick for Throttle and Yaw and the right stick for Pitch and Roll. Mode 2 is the predominant system used in the US and what this section will be describing.

Moving the right stick up will pitch the front of the multirotor down, resulting in forward flight. Moving the right stick down will pitch the nose up, resulting in rearward flight. Moving the right stick to the right will roll the multirotor to the right (right side low, left side high), resulting in sideways movement to the right. Moving the right stick to the left will roll the multirotor to the left, resulting in sideways flight to the left.

Moving the left stick up increases the throttle, the motors speed up and vertical lift is obtained. Moving the left stick down decreases the throttle, reducing lift. WARNING: Moving the left stick all the way down in flight will result in no/little throttle and the multirotor will drop out of the air like a rock. Do Not reduce throttle all the way down until landed. Moving the left stick to the right yaws the front of the multirotor to the right. Moving the left stick to the left yaws the front of the multirotor to the left.

Most flight controls come with coordinated, simultaneous movement of all the stick controls. This will likely feel uncomfortable at first, but will become second nature as your flying skills progress.

It is highly advised that students study this material for the test taking place the following class.