This is how you wake up early in the morning

“Every morning in Africa, a gazelle wakes up. It knows it must outrun the 

fastest lion or it will be killed. Every morning in Africa, a lion wakes 

up. It knows it must run faster than the slowest gazelle or it will 

starve. It doesn't matter whether you're a lion or a gazelle. When the sun 

comes up, you'd better be running” 

-Anonymous

My first answer on Quora!

Hello!

The question was:
 I want to make a Quadcopter but my budget is low. How to proceed?

My answer:

When surfing several RC hobby websites, one can find motors, frames, flight controllers, propellers, RC transmitters and receivers. Brands like Turnigy, Spektrum, Futaba, Hobbyking offer wide range of the above parts. Do not import them from international websites. Shipping and customs charge you extra. You can buy all the parts from local hobby websites. Refer to http://www.rcindia.org for links. This is a great forum for RC lovers.

If you plan to make a quadcopter whose rest mass is below 300 grams, please go for coreless DC motors(I will come to this category later). Brushless motors(BLs) are preferred for quads of 300 grams and above. To run a BL, one needs electronic speed controller(ESC) which is essentially a 3-phase oscillator that runs the former. 

For a quadcopter, you need four propellers. So, you need four BLs and four ESCs.  On Ebay the lowest range is about Rs.700-900 for a BL, Rs.600-800 for a ESC, Rs. 500 for good ABS propeller set(2 CW and 2 CCW). Flight controller starts from somewhere around Rs.2500 and the cheapest Radio control Tx and Rx is around Rs.2500. LiPo battery of  2000mAh(good flight time) costs Rs.1500-2000. You can either buy a frame or make one using aluminium channels with fixtures and base plates for motors and electronics. Overall it costs well over Rs.10,000. 

The best way to cut cost is to compromise on weight(below 300g). This way you can go for much cheaper parts like coreless motors of Rs.200-300 each. (No ESC required, driven by PWM through high current MOSFETs like IRF150), 3.7V LiPo battery costing Rs.1000 which can give 15-20 minutes of flight(you can even try button cells), tiny and sturdy frame which can be made at home, tiny propellers of 5-6 cm length of Rs.200-300/set and the same flight controller and radio set mentioned above. All this costs below Rs.7000. Note:Above costs are just estimates. You can get the parts for much cheaper prices by doing some research on hobby sites, Ebay and even visit some shops if in same city(to avoid shipping costs). It took me atleast a month to assess all these details. You can bring down the net cost to about Rs.5000.

To see how small a quadcopter can be search for "Husban H107L", "Micro Aerial Vehicles by DARPA, MIT, University of Pennsylvania's GRASP lab flying swarm robots".

However, there's a catch:
Coreless motors and short propellers are a bit hard to get. If you can, buy four small vibration motors(ones you find in mobile) and remove the uncentered masses from their shafts if you can(those cling on tight). Propellers....... searching is only option(make sure you buy perfect ones made with good quality plastic). There is good chance that motor's shaft may not fit with propeller's hole size, so buy propellers with hole adapters that help you to insert shaft tight enough.

Talking about flight controller, if you are really serious about 'how quadcopters fly' you should learn the theory behind its stable flight like motion algorithms, embedded control, sensor data acquisition and flight dynamics. You can make a flight controller with self-written firmware and add your own choice of sensors(apart from accelerometer, gyro) and even GPS at bare minimum cost. 

Obviously, I cannot explain the working and circuitry here as there are many websites you can look up to. Just google what you want.

Please comment if you want to say or ask something.

Goutham