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01-01-2014 | 09:52 PM

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TUTORIAL - How to build Multirotor from scratch9（1/2)

A tutorial From: http://www.multicopterclub.com/

Multirotor becoming very popular nowadays. It's real fun and pleasure to see them flying, however making them at home from scratch is tough job. So where to start and how to select parts for multirotor? Here i am trying to put everything step by step.

PURPOSE
Before you start buying parts you should have rough idea, for what purpose you want to make your multirotor? People make them for fun flying and hovering, stunts, AP(Aerial Photography), FPV(First Person View) and Heavy Lifting. You just can't make one multirotor that can do everything for you and if you are completely new to this thing you should first learn hovering and some basics of multirotor flying. So here we assume that we are making multirotor for beginner flying that can probably lift 200-300grams payload so you can hooked up light weight camera for onboard video recording(not FPV) in future.

TYPE, SIZE & WEIGHT OF MULTIROTOR
There are many types of multirotor people make nowadays. Some of them are Monocopter, Twincopter, Tricopter, Quadcopter, Y-6, Hexacopter, X-8, Octocopter. I found that less rotors more precision requires to build them. That's why FPV lovers use hexa or octocopters so if one motor fails, they can safely bring it down to the surface. But more rotors means you have to invest more money. As a beginner quadcopter is good to start. Tricopter is good as well but you will have to deal with yaw mechanism which is tricky if you are building it from scratch. So here we will start with quadcopter. Quadcopter or also called Quadrotor has 4 rotors and it has two flight configurations. X config and + config. In X config two arms will face front side while in + config only one arm will face front side. If you are making Quadcopter with plus config you can tune your quadcopter easily by single axis tuning method which we will learn later. Small and light weight quacopters can do stunts better while big quadcopters can lift heavy payload like cameras with gimbal and fpv gear. So here we assume we are making normal medium size Quadcopter with plus config and 1000-1100grams AUW(All Up Weight) for funflying. AUW includes battery and everything. Basic formula you should keep in mind that weight of multirotor should be half of the total thrust.
Total Thrust = 2x AUW
In short to lift 1000gram quadcopter we need 2000gram thrust. We will learn about thrust later.

FRAME
One of the most important part of multirotor is its frame because it supports motors and other electronics and prevents them from vibrations. You have to be very precise while making it.
ARM:
You can make arm from any material like CF, PVC pipes, Aluminium or Wood but make sure it has enough strength to withstand impact and rough landings. Frame weight should be around 200-250grams. I would recommend you to go with aluminium channels/beams as they are cheap, strong and easily available at any local hardware shop. You can cut, drill them easily at home.
CENTER PLATE:
Ceter plate holds the arms and supports FC, receiver and other sensors. You can use 2-3mm glass fibre, plywood, aluminium sheet or any plastic sheet material but make sure they are stiff, strong and light weight. You can put some holes to reduce weight.
LANDING SKID:
If you want to attach landing skid, buy any RC helicopter landing skid or you can build your own skid from scratch. It's all upto you.
FASTNERS:
Use M3 nut-bolts of different length to assemble frame and motor mount.
SIZE:
There is no thumb rule for size of the frame but for medium size quadcopter 450mm to 550mm motor to motor frame is enough. If your frame is too big compare to your power setup(motor-prop, esc, battery)it will add extra weight while if it's too small props will fight with each other.

Making frame is truly depends on your imagination, skill and availability of material. But it's fun building frame from scratch and you will learn many things from it. If you want to get rid of all these diy things you can simply buy readymade frame from the market but it might put big hole in your pocket. In our case we want to build quadcopter so make sure the angle between two arms is 90 degree and also check that arms are not twisted.

FC(Flight Controller)
There are many FCs out now in the RC world. Some of them are KK, MultiWii, Ardupilot, Naza, Naze, Rabbit, WKM and many other. Advanced FCs have more features and advanced sensors like gyro, accelerometer, sonar, GPS, Magnetometer. But as we know "more power comes with more responsibility and difficulties" so if you are newbie you should start with gyro only. Hobbyking v1, v2.1, v3.0 boards/KK boards have gyro sensor only but still they are best beginner boards in the market to learn and undestand science behind multirotor. So here we are assuming that we are going to use HK board. You can buy any board v1, v2.1 or v3.0. The only difference between them are ATMEGA chip. V1 has 4kb flash memory, V2.1 has 16kb memory while v3.0 has 32kb flash memory. One more reason to use these boards is they are cheap, reliable and easily available at any hobby store. It won't burn your pocket. If you crash and damage your board you can buy another and there are lots of posts and videos available describing how to use them.

MOTOR
One of the important part of multirotor is its motor. It's a part of power system. Infact whole power system depends on selection of motor so you should be very careful while selecting motor. We use Brushless motors for multirotor. Brushless motor comes with some important specifications. You will see these specifications on the page if you are purchasing it online. So it makes our job simple. For motor selection some important specifications are.
kV
Max current(A)
Shaft dia
Thrust
Weight
Lipo(3S-4S)
Suggested prop
For multirotor application 600-1200kV motors are good. Below 600kV even better. Low kV means you can swing big prop. Big prop means it can move more air and you will get more thrust.
kV = RPM/V
If you have 600kV motor and 3S battery to supply power, RPM of of motor at NO LOAD would be
600 x 11.1(3S battery) = 6660 RPM.
Max current rating is another important factor while selecting motor. Selection of ESC and battery depends on this value(we will learn it later). It should be able to run on both 3S and 4S lipo battery. Shaft diameter helps you selecting prop adapter. Now we are coming to the thrust. In most cases you will see value of the thrust motor can produce with suggested prop on the website. If you remember we learned that to lift 1000 grams quadcopter we need total 2000grams of thrust. And quadcopter has 4 motors, so each motor should be able to produce atleast 500grams of thrust to satisfy our need.
4 motors x 500grams thrust = 2000grams thrust.
One more thing is Watt.
Watt = V(Voltage) x I (Ampere)
More Watt more power so you should also consider that while selecting motor.
But when it comes to selecting motor you will notice that there are many options available for motor selection and it's really confusing, so which motor is best for multirotor application? Well you should consider few more things other than specifications. Some of them are
Motor Mount: Well motor mount is one more important factor you should keep in mind while selecting motor for your multirotor. Motor mount comes under tensile force especially when you are swinging big prop and if motor is not fitted properly it might come off during flight and i am sure nobody wants to see such things happen. So make sure that motor you are purchasing has good mount that can hold motor properly under heavy load and same way you can fit that mount easily on the frame. However you should always precheck before flight that all connections and fastners are properly fitted. Get one spare motor. So i hope i have covered everything for motor selection.

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