Im beginner as well as of stream(CSE), but im so curious about making Quadrotor heli.(3 idiots ) that i came all the way finding this org.
Well asking anything will be stupidity without self workout....so i just ask u admin to give links which are beneficial for this project.

You will find everything in this sub thread http://www.rcindia.org/multirotors/

And use search function of the forum, search for multirotor, quadcopter, tricopter you will get lots of the discussion about the same.

My answer as to how long it takes to learn is, NEVER. That's the whole joy of RC, you never stop learning. As new flight controllers are let loose on hobbyists we often have to re-learn for new features, how it's tweaked and most importantly how we can make it work better. New ESCs arrive, new designs in motors, receivers, transmitters and everything else to build and run a quadcopter.

I've been building them now for only 18 months, planes for 58 years, (I started at age 8 ) I've built 10 Quadcopters, 2 hexcopters and 1 tricopter and purchased 3 ready mades. I still don't know it all and never will. I'm continually falling behind when it comes to technology. I finally had the KK2 FC under control and now everything's gone computer programmable. Now I have to learn how to do that, but to be honest I think I'll stick to what I know. I think perhaps I've crammed as much data between the ears as there's space for. My brain needs a newer hard drive and more memory. Maybe in 10 years you young guys will be asking how we used to build them in the "old days"

Put on your thinking caps, you're in for a long ride. Study the many posts made on your subject. If you get stuck, ASK, but you have to be seen to be helping yourself. If anyone comes to me and asks endless questions, I'll ask them if they want me to fly their aircraft as well. Helping others is good, helping yourself is even better.

Stu

hm162222 asks a number of questions. Gyros are used to tell other electronic components which angle the unit it's connected to is currently at. With the quadcopter, to keep itself level the Flight Controller has to know which way it's orientated. Gyros send signals at a very fast speed to the FC telling it when it's level and if it's not, which way it's angled. Gyros can be found in some digital cameras for anti-shake recordings. Unmanned aircraft, missiles and many other gizmos and gadgets.

Brushless motors are far more robust, faster and less complicated than the brushed motors. As the name suggests there are no brushes rubbing against the armature, this eliminates sparks and wear, therefore the only friction generated is in the bearings of the motor. You could use the brushed variety in a quadcopter, in fact most of the toy copters use them and utilize small gear boxes to step the speed of the motor up. Also the brushless variety  are cheaper to produce. Two bladed props are the most popular version used today. The 3 and four bladed props can be used, but aren't as efficient. A prop works by pushing air in one direction. it works best when the air in front of the blade is at rest. For optimum thrust a prop should be just one bladed, This ensures a cleaner air to bite into. Yes there are one bladed props. They were designed many years ago and worked with a counterbalance being where the 2nd blade would normally be. Some diehard hobbyists in Australia still use the on their control line planes. Such props were extremely hard to balance and fell out of favour. 3 and 4 bladed props are normally used multi prop planes where the pitch of the prop can be varied. Single prop planes and quads plus fixed pitch helicopters use the 2 blades simply because they give the best thrust to power ratio. Modellers usually only use 3 or 4 bladed props for appearance sake, although I did purchase a quadcopter a few years ago which had 3 bladed props. Because they were far too flexible and gave poor thrust I replaced them with 2 bladed props and it performs much better.

A quadcopter can be almost any size. As with anything some people always think bigger is better. In reality bigger is not only much more expensive but can get to a point where any advantage of size is lost due to disadvantages in flight characteristics. Hobbyists are always trying to push the boundaries and there's always someone to try to be bigger and better than anyone else. It's human nature I guess.  There are the tiny toy variety which measure as little as 100mm from motor shaft to motor shaft and the size rises to I think the largest I've seen was one meter and that cost over $5000 USD. Scientists are working on a monocopter about as big as a bumble bee. Then there's the biggest of them all and definitely out of reach of any hobbyist the Boeing V 22 Osprey. From prop tip to prop tip 85 feet. It can be classed as a Duocopter (2 props) when in VTOL (Vertical Take Off and Landing) mode.

Please note, some of my answers can be argued with. I only give answers from memory and prefer not to refer to search engines unless the question requires specific data. Although the answers to all your questions can be found by Googling. :-)

Happy Flying.   Stu