MakeIt Labs "x666" Quadcopter

Quadcopters, or more generally "Multirotors" operate on the same basic principal and with very similar parts.  Each leg of a multirotor has a propeller (Prop), Motor, and an Electronic Speed Controller (ESC).  Each ESC is directly powered by a central Lithium Polymer Battery.  Each ESC is controlled by a central Flight Controller.  The flight controller will actively control the speeds of the motor based on your control inputs from the radio receiver and other sensors.  The following diagram outlines the systems involved.

(I'll generate a better multicopter Diagram, but here's one for reference for now)

If you're new to multicopters or R/C Flying in general, check out the Flite Test Youtube channel.  These guys are great, they have hundreds of entertaining videos, many of which involve quadcopters.  Click here to go to the Flite Test Youtube Channel.

Also, I would highly suggest you invest in a nano-quacopter kit if you plan on flying a bigger one.  They have the same flight characteristics, but you can crash them without breaking them and without hurting someone!  RC Buyers Wearhouse in Nashua has the Estes ProtoX, it works great and it's only $40.  Highly highly recommended for any novice.

The following "MakeIt Labs Quadcopter kit" is a set of parts known to be compatible with each other. 

View the online Bill of Materials as a Google doc Here: 

Almost everything doesn't have an instruction manual, so you'll have to read the technical articles I have posted to get an understanding of what you're dealing with until I have step-by-step instructions.  If you have questions, feel free to contact me at Ian.Cook@makeitlabs.com.

The Technical Stuff

Motor/Prop combinations:  It is important that you find a good combination motor/prop for your multirotor application.  Too small a motor and you will not get off the ground.  Too big and you are carrying around excess motor weight.  Knowing what combination to choose starts with an estimation of the weight you are to be carrying.  Generally, you want to be able to hover easily at no more than half throttle.    

Start by choosing a motor/prop combination and a battery voltage.  In this kit, we will be using an 18 amp 1100kv Motor.  We are also using an 11.1 volt(3 cell lipo nominal) battery.  The KV rating means 1100 rpm-per-volt.  At 100% throttle we will theoretically be turning the motor at about 12,200 RPM, and at 50% throttle, we're turning at 6,100

RPM. 

Not take a look at your prop.  We chose a 10 x 4.5 prop.  The "10"  is your prop diameter.  The 4.5 is your pitch.  In this case, the pitch is how far the propeller will travel forward per revolution.  More pitch = more thrust, but it's less efficient and more susceptible to stalling.  Typically we want to use "Slow Flyer" type props.

Now we have all the information we need to calculate thrust at 50% throttle, the easy way.  Take this information and plug it into this online calculator:

http://personal.osi.hu/fuzesisz/strc_eng/

Note:  Choose Standard Propeller, 2 blades, and 68 degrees Fahrenheit

Now, you should see that the static thrust has been calculated out, and we're getting about 1 lb of force per arm.  For our quadcopter, this means about 4 lbs of force at 50% throttle.  You should find that this quad weighs in at around 2-3 lbs, so we're all set here.  Not check the required engine power.  It should be around 0.050 Kw, or 50 watts.  If we check our motor parameters you'll see this one is capable of handling 18 amps.  At 11.1 volts, this amounts to about 200 watts.  Since this is more than the required power, the motor will be able to turn at 6,100 rpm and provide the calculated thrust. Now change the RPM to your 100% throttle value of 12200 RPM and take a look at the required engine power.  You'll see this is about 0.400 Kw, or 400 Watts;  well above the motor's limitations.  This means we will likely not reach the anticipated 12200 RPM (Or 16 total lbs force), we could potentially benefit from a slightly smaller prop or pitch, or a slightly larger motor.  In any case, the 50% throttle numbers are acceptable and we can proceed with other parts.

Electronic Speed Controls 

The electronic speed controls need to be chosen in accordance with your motor choice and battery voltage.  We are using a 3 cell LiPo which is 11.1 volts nominal, 12.6 volts max.  The motors will pull a maximum of 18 amps. It is very easy to burn up an ESC, so generally we want a larger amp capacity on our ESC than our motor will pull.  We're using a 30 amp ESC in this kit.  For better stability, you may want to get a multirotor specific ESC.  These ESCs have a higher switching frequency (so the respond to signal changes faster).  Some also have special firmware (Check out the SimonK firmware)  This firmware is also more responsive and makes for a more stable multirotor.

Battery

To get the best power to weight ratio, you will need a Lithium-Polymer Battery.  These are dangerous, very very dangerous.  If overcharged, and/or punctured, they catch fire and could possibly explode.  A quick search on Youtube and you will understand.  YOU MUST purchase a proper LiPo charger if you have LiPo batteries. Do not leave them unattended while charging or discharging.

Most hazards can be avoided with the proper understanding of the limitations of this type of battery.  If punctured, particularly with a metal object, the battery will vent, get hot, and possibly shoot flames from the puncture.  While this is may be the most likely of failures, it is usually caused by a crash and the battery is probably already outside.  If your craft burns to pieces in the grass, boo-hoo,  not a big deal in the grand scheme of things.

The absolute most dangerous time for a battery to have problems is while charging.  This is because the battery is likely inside a building or home and could start a much larger fire!  Overcharging easily leads to fires as well. To avoid this, you need to know a few things.

1) C-Ratings.  A C rating is what you will use to determine the maximum charge/discharge of a cell.  The C rating multiplied by the amp-hour rating will give you the maximum amps allowed for that particular use of the battery.  For example, if the above 2200 mAh battery has a maximum charge of 2C, you may only charge it at a maximum of 4.4 amps.  It may also have a 20C maximum rating for discharge, and an "burst" (Typically 10-second) rating of 30C.  This means the battery can be discharged at a maximum of 44 amps continuously, or  66 amps for 10 seconds.

2) Those extra little wires:  Yes! They are important!  You must plug those into the charger when charging.  Those wires go to the positive ends of each cell in the battery pack, giving the charger the ability to monitor and balance each cell in the pack.

3) Temperature:  LiPos heat up.  If they become anything warmer than 110 degrees F while discharging, you're abusing the battery and likely causing damage.  If they are getting warm during charging, stop charging.  You may have the charge current set too high or the battery is damaged.

4) Over/Under voltage:  LiPo Cells have a maximum voltage of 4.2 and minimum voltage of 3.0 per cell.  This is why I include a voltage monitor in the parts list.  It gives visual and audio alarms based on your battery voltage so you don't over-discharge your quadrotor. 

Onto the non-safety crap.  Each LiPo cell is 3.7 volts nominal, and 4.2volts max.  Typically batteries are purchased in 2, 3, and sometimes 4 cell configurations.  Typically we will use 3 cell configurations.  Be sure that the voltage of your battery never exceeds the maximum voltage of any of your components directly fed by the battery.  The batteries will also have a mAh rating and a C rating.  The mAh stands for mili amp hours.  A 1000 mili amp hour (1 amp hour) battery will last 1 hour at a 1 amp current draw.  More mAh = more fly time. 

In this kit, we recommend using a 2700mAh LiPo rated for 25C for continuous discharge, and 35C for burst discharge of up to 10 seconds.  This means that the battery can handle a 67.5 amps continuously and 94 amps for 10 seconds.  Keep in mind, our motors can pull up to 18 amps each or 72 combined.  This is only slightly over the continuous rating for the batteries but within the maximum capability of the battery. Therefore it is acceptable, but not advised to run your multirotor at full throttle. (Just don't do it for very long!)

Flight Controller:

This is where it gets interesting.  There are a few different multirotor control boards out there.  The control boards work by taking the the inputs from your radio (i.e, throttle, tilt, yaw) runs some calculations, and then sends signals to your ESCs thus controlling motor RPM.  The board also uses onboard sensors to make active decisions about the flight pattern.  Some flight controllers also have GPS inputs, altimeters, and other sensors imbedded or able to be added on.  In this kit, we will use the HobbyKing KK 2.1 board.  It is a fairly simple and cheap board and will get you in the air quickly.  Eventually you may want to upgrade/sidegrade to a MultiWii, Naza, or an ArduPilot board, all with interesting features.

Every Flight controller is going to have PI or PID settings.  PID loops are a method of making corrections to an indirectly controlled variable to achieve a certain value.  For instance, the thermostat in a newer oven is controlled by a PID loop.  Based on the magnitude of the error and the rate at which the error is changing, the device will calculate an input to correct for the error.  This same loop is used to stabilize a quadrotor.  Because we are implementing the controller onto a craft with unknown parameters (eg, center of gravity, moment of inertia, etc.) we need to custom tune the Flight Controller to the quadrotor.  The math can become complicated, but here's what you need to know for PI. 

Your "P" gain is a multiplier that will be proportional to the error or "incorrect angle." The higher your P gain, the more aggressive the error correction will be.  Too much P gain, and the quadrotor will wobble and will be less responsive to your control inputs.  If you are of the mechanical mind, you can think of the P gain like a spring rate. 

Your "I" gain is a multiplier that will limit the rate of change of a correction.  Too little I gain, and your quadrotor will wobble with any input, and may wobble indefinitely.  If your P gain is also too high with your I gain too low, it may compound over-correct and crash on it's own.  With your I gain too high, the quadrotor will be sluggish with inputs and corrections.  If you are thinking of your P gain as a spring, think of your I gain as a shock-absorber.

Your "D".... well.... the HobbyKing KK flight controller doesn't have a D, so I don't actually know.  Yet.

I'll post my PI settings when I have mine totally dialed in..... ;)

Flight Methods

The easiest method to fly is where the board attempts to angle the copter relative to the pitch/tilt joystick on your controller.  It does this by 1) interpreting the position of your controller and 2) attempting to position the copter to the angle you specified using onboard gyroscopes and accelerometers.  This is known as "Auto-Level Mode"  where the copter theoretically returns to being level when you let go of the stick. 

Another common mode commonly referred to as "Acro" mode, is where the pitch/roll stick on the transmitter controls the rate of change of the pitch or roll.  In this mode, if you let go of the stick, the craft will attempt to hold it's current attitude.  While more difficult to handle, this mode allows for more freedom of flight and allows the craft to do flips, barrel rolls, extreme speed, and other maneuvers.

Should the Flight Controller have a GPS, it likely offers the ability for the craft to fly autonomously in GPS mode.  In this mode, no active controls are needed from the transmitter for the craft to reach it's destination.  This is where we cross the line from simple R/C quadrotor to a fully autonomous vehicle, otherwise known as a "Drone."

Radios

Most radios on the market today are in the 2.4 ghz band.  Even the cheaper ones have a range of a mile or so.  For a quadcopter, you need AT MINIMUM, 4 channels.  It is strongly recommended to get 6 or more, as you may be able to use the features to control extra features on your flight controller, or control servos for cameras, etc.  Radio transmitter/receivers can be found as cheap as $30 for a 6 channel.

Video and FPV

This quadrotor kit can easily carry a GoPro or similarly sized camera.  Cameras should obviously be attached securely to the quadrotor frame.  To get better quality video, you may want to pad the camera mounting with foam or similar vibration damping material.  The easiest way to get good quality video is to balance all of your motors and propellers.  This also makes the craft more stable as the flight controller has less "noise" in the accelerometers.

FPV  **I haven't ventured here yet, however my research indicates that you likely need a HAM radio license to transmit video on any of the frequencies that these camera systems work on.  FatShark offers a few 5.8 ghz systems that include everything you need including camera, transmitter, and FPV video goggles with built-in receiver.  The Teleporter kits run about $200, and Dominator kits run about $300. 

3D Printed Parts

Yes you can print parts for your copter.  No, you cannot print propellers.  At least, if you do, don't fly that thing around MakeIt Labs. For one, the forces are too great for such a small part, 3D printing is simply not suitable.  However, printing legs, motor mounts, and other adapters is perfectly acceptable and encouraged.  I have attached the current replacement leg I am using for my x666 Quadrotor.  I am always redesigning it, so if you like the one I post, keep it safe as I will take old ones down as I create new ones.  If you want to design parts but don't have a cheap copy of SolidWorks laying around, you may want to consider buying Cubify Invent from 3D Systems.  It is a fairly intuitive, SolidWorks-like CAD program meant for creating single-parts.  For only $50, it can't be beat.