I want to build a quadcopter and I already have bought all the parts I need to build one.
My question:
How long should be the distance between two motors with 11''inch propellors, in order to fly efficiently and stably.
To clarify my question, I have uploaded a drawing.
Drawing: How long should be the distance a.
Replies
Here is a post that alternates the motors so one is up the next is down and they discuss overlap of props and the lose of efficiency. Hint...not much lost!
http://www.rcgroups.com/forums/showthread.php?t=2043858
What the heck? I'll nibble a bit at this one. Even though I don't have experience with these, I do have some engineering background.
That said, I'm pretty sure, from reading various forums, that your first multicopter should not be home-made. Your question, as posed, tells me that this will be your first because this info is among the stuff you'd pick up over time. Also, 11" props are mighty big, require very powerful motors, and should be considered lethal weapons. Everyone is strongly encouraged to start with equipment that is significantly smaller, and off-the-shelf. Preferably a kit.
As far as I can tell, the 'size' or 'class' of a multicopter is determined by the distance from the center of one motor across to the center of the opposite motor, not the distance between adjacent motors. Usually measured in millimeters. 11" props are almost 280 mm, so 300 mm to the adjacent motor is a good number to avoid prop overlap. Call it 425 mm across as a minimum. Some commercially available quad frames, designed for 10" props, are 440 mm across. Choose your scale.
Stability is a function of the flight computer. The entire exercise behind a multicopter is akin to getting a barn door to fly. The distance between motors should have no effect whatsoever on the stability of the multicopter, as long as the props don't crash into each other. [edit] Actually, I'm not so sure about this, there may be some reasonable minimum. or ratio/proportion.
There should be a rule of the English language stating that the word 'multicopter' (or 'quad') and the word 'efficiency' may never be used in the same article or post. It took the power/weight of LiPo batteries, inherent power of rare-earth magnet motors, and more compute power than all of NASA had when we landed men on the moon to get just one of these things to fly. If you want efficiency, build a motor-glider. 'Copters are strictly for fun.
Lastly, I get to the first line of your post: How can you have all the parts necessary to construct a multicopter and not already have a plan? Google 'ecalc' and do some analysis of your selected components to find out if they will even work. Going further, why a quad and not a hex? A hex might survive, without damage, the failure of one propulsor (my word for a motor with ESC and a prop) given a properly programmed flight computer. A quad won't, ever. BTW, an 'octo' is better than a 'hex', but that's getting into the area where, if you need to ask the price, you can't afford it....
Ok thats a real good reply, the only thing I'd say here is leave a little extra distance on your first build - you are bound to want to try out 12" props.
An old friend of mine once said there should be at lease half a prop distance between the tips of the blades on adjacent motors - I've found this not to be true and built quads with small and large distances between the adjacent motors - it makes little difference especially now auto tune seems to take care of the heavy tuning work on most frames. There's more to frame building than you think, look closely at the better frames and work out why they are better - or experiment and have fun.
Here's 2 years development work - all 'home grown' from experimentation
https://www.youtube.com/watch?v=vT9pUDkiLuk&list=UU3sTSpOMeln_P...