I am a student of BE taking Mega-Quadcopter as my final year project.Can u please help me with the total hand calculations of the mega-copter i.e its procedure and formulaes? . I wanted to know how to calculate the dimensions of frame,specifications of motor and propeller,the rating of ESC's and the power rating of the batteries and its total no.s.I do not want direct answers but its procedure and formulaes.I want to lift aload of around 20-30 kgs .Please feel free to help.
What is BE? Bachelor of Engineering? I feel like you shouldn't need our help if you're in your senior year of an engineering degree, but briefly:
It's all about the specifications. Pick a vertical acceleration you want to achieve, then calculate the total force (thrust) you need with $F=ma$.
Divide the total thrust by the number of motors you want to use for the per-motor thrust required.
Define a rotation rate you want to achieve then calculate the torque required to achieve that rate with the torque equation $\tau = I \alpha$.
Use the torque from this equation with the per-motor thrust from earlier to determine the motor radial distance with $\tau = r \times F$. This spacing will impact your moment if inertia, so you will have to re-calculate the required torque - this is called iterative design.
Define a top vertical speed, then calculate the required motor power with this speed and the per by $P = F v$. Then define a top rotational speed and calculate the power required for rotating by $P = \tau \cdot \omega$. The actual power you need will be the larger of the two power terms you calculate to ensure you can meet all of your performance specifications.
Using the calculated motor power will give you a ballpark to start shopping for motors. Contact sellers and give them your power and thrust requirements to see if they can provide something that meets your needs, but the motors are going to weigh something substantial, so you need to basically re-calculate everything from the moment of inertia down again to refine your design. Again, iterative design process.
You will be better off empirically testing motor/prop combinations than trying to calculate thrust from blade design, but again, your base calculations should give the class of motor you need by output power required. Also, use sales engineers! It's a LOT less work to give a sales engineer your spec and have them do the legwork than to do this testing yourself. Give them your spec, then ask to try their recommendation to verify before purchase.
You should find your motor power requirements in line with this guide posted by TobiasK. Using the moderate flight estimate of 250W/kg, you're looking at over 6kW just for your payload. When you add an airframe, motors, and batteries, you could be looking at 7.5 to 10kW - this is not a small project!