When you decided to build a quadcopter what do you need to know? Well the first thing you are going to need to know is how to do research, because you are going to be doing a lot of it; the second is going to be a basic idea of what general components are required.
Here is a list with a brief explanation to get you started on that.
You only need a frame that is sufficiently stiff and light, and doesn’t get in the way of airflow too much will do. So frame can be anything from an aluminium piece to artwork a stuffed cat with wood inserts, but for building a good quadcopter, you must be sure to research motor layouts.
Manufacturing depends on how the frame is designed, you can go with laser-cut or water-jet cut sheet metal (probably aluminium), plastic, or carbon fiber. There are plenty of low-quantity fabrication services that you can use to cut these for you. You can also go with vacuum-forming, the startup costs are quite a lot higher, but again, there are affordable fabrication services available these days (with setup-costs of the molding in the range of $1k)
(You can read this post how to choose a quadcopter frame?)
Power electronics system:
Power electronics system include battery, ESC, motor and prop.
Battery is any high power density battery that has the right working voltage and sufficient current supply. Lithium-ion polymer (LiPo) batteries are usually used because of their high energy density and lighter weight. Depending on the motors, your quadcopter will generally draw a lot of current compared to many other applications so this will need to be chosen after the motors and props.(Recomment quadcopter battery)
(You can read this post how to choose a lipo battery for your quadcopter?)
ESCs, is short for Electronic Speed Controllers, either off-the-shelf, or you can start looking into three phase bridge circuits, and motor commutation. It does a few jobs, first it takes the DC voltage from the battery and converts it to AC, then it gives the motors power as required by the flight controller, they communicate through PPM. Most ESCs have the BEC built in.(Recommend ESC)
Motors are generally motor with the right kv rating and power density three phase brushless motors. Higher KV motors will spin faster with the same voltage of a lower kv motor. Be sure to look at the wattage of a motor, along with max safe amp draw.(Recommend motors)
(You can read this post how to choose motors for your quadcopter)
Propellers will need to be matched to the motor operating speed/kv rating, and craft weight, and they’ll need to be fixed pitch counter-rotating pairs. Generally bigger props require lower kv motors, pitch is the pitch of the blade, and also affects the current requirements.
(You can read this post how to choose props for your quadcopter )
Flight controller and digital electronics:
Low-level stabilisation controller, IMU sensors, navigation controller, and radio receiver, (optionally telemetry). Generally on hobby or professional grade multirotors you have a seperate board to make stabilization and flight decisions. This flight controller can be as simple as to only have stabilization, or as complex to have stabilization, gps navigation and computer vision software for object tracking. A flight controller requires a minimum on an IMU, but for things like GPS you will of course need a GPS receiver. There are a lot of companies selling flight controllers, and a lot of open source flight controller firmware.
low-level controller is a microcontroller system dealing with sensor fusion, AHRS, and PID, probably with PWM outputs to the ESCs. processing power need not be high, depending on how much filtering you need, we used an ARM Cortex-M3, but others have used ATMEGA and PIC/dsPIC.
IMU needs to be at least MEMS gyroscope (you can kind of fly with just gyro), accelerometers needed for leveling and non-acro flight, addition of magneto will get you better heading lock, which is essential if you intend to do GPS autopilot. A barometer and ultrasound module is also useful for altitude hold.
Navigation controller is optional and can be combined with the low-level control, it adds a GPS module.
Radio Receiver depends on the transmitter and flight controller, needed to take input control, Most common output to the flight controller is PWM, but CPPM is also used, and the protocols vary from FASST to DSMX depending on the radio that the transmitter is made for, the flight controller really is not affected as long as it is getting input from the receiver. Protocols matter to the pilot, but not to the flight controller so be sure to find a good solid system that best fits your needs.
Telemetry (two-way comms) is entirely optional, we’ve used XBee mesh before, it’s very useful for debugging.
Flight control software: AHRS, sensor fusion, PID, navigation routines
AHRS and sensor fusion runs on the low-level controller, and combines the raw IMU sensors into an AHRS. DCM and Quaternions are popular for this. Sonsor fusion can be part of that, or can run through a separate Kalmann filter. Which you chose to develop will be based on your proficiency with maths, embedded development, and the processing power you have available. EKFs are awesome, but resource-heavy. We use quaternion without kalmann filters. Incidentally within our solution, there is need to re-derive some elements of the DCM anyway.
PID simply takes the calculated AHRS and compares with the attitude, heading and thrust demand from either the manual control, or the navigation controller (which itself is another set of PID loops, and probably a waypoint interpolator, depending on how you implement navigation).
PID tuning is a bit of a black art, there are established methods, but really once you’ve gotten used to how the gains behave, it’s not too bad. You’ll probably rely a lot on trial and error unless you add in HIL testing support and kinematic modelling.
Hint: AHRS and PID, though are the critical parts of the flight control code, make up only a few percent of the actual code. The rest is going to be glue logic and general useability code to deal with user inputs.
That’s pretty much it. If you understand all of the terms above, then you have all the knowledge that you need to build a quadcopter from scratch. If not, then you should probably begin by using kits or pre-built systems, and in the mean time search up all of the above concepts and how they fit together.
We’ve spent quite some time developing our own quadcopters from scratch, and let me tell you: it’s not something you should take lightly, we’ve spent a long time hitting dead ends and figuring things out: which hardware works and which doesn’t, and what algorithms work, and which don’t.
Notice the different mounts and materials:
Single blade that is made for a plane, and triblade carbon.
I’d suggest that you find a community to ask questions because you are going to get stuck at points and need advice, I am a bit biased but I really suggest Quadcopter Forum as it is a great place with many people from all skill sets who enjoy flying, prototyping, and building.
Next you want to make a build post to keep track of your ideas and get product/design suggestions from people experienced anywhere from structural design at Boeing, electrical engineers, or just 20 year hobbyist.
Try not to buy your frame or propulsion stuff before asking about it as this is where 99% of people mess us and end up paying 3x what they should have. So be willing to ask questions and learn and you’ll be fine.
You will be doing some soldering more than likely, a LOT of shopping, and after a long time of trying to get it off the ground your plane or multirotor (quadcopter AKA drone) will suddenly take off on one flight and you’ll wipe tears of joy from your eyes hahahaw.
Once you have designed a few or are immersed you can pretty much make a build log off the top of your head, or look at a build lon and know if it’ll fly. Just need to get started.
Please note that flying and FPV are very addictive.