Am I on the right track (Choosing motors/batteries etc)

[Borg]

Hey guys! I'm part of a college design competition where we're building a UAV that can carry as much load as possible for ~5-7 minutes while being able to maneuver through objects. One constraint is that it can not be bigger than 28" in diameter.

We were planning on having a coaxial octocopter to try to maximize the payload capacity given our size constraints.

So, what we were thinking is having 3-blade 10x4.5" propellers as shown here: http://www.goodluckbuy.com/1045-10x4-5-3-blade-counter-rotating-propeller-cw-ccw-blade-black.html

Then we were looking at having multiple 4 cell 5000mah batteries (either 2 or 4, suggestions?) as shown here: http://hobbyking.com/hobbyking/store/__15521__Turnigy_5000mAh_4S1P_14_8v_20C_hardcase_pack.html

And then we were looking at 900Kv motors as shown here: http://hobbyking.com/hobbyking/stor...s_28_30S_900kv_270w_short_shaft_version_.html

And then have 25A ESCs.

What do you guys think of this combination? Could we get around 6-8 kg of payload (including copter) and have it last for over 5 minutes?

Thanks for your help!

 

[PeteDee]

Easy way to get an idea of where you need to end up is to have a look at the e-Calc, plug in some numbers and see what happens.

Without having too close a look I would say that you might just get there with an octo to do that sort of weight lifting, I would say that at 6kg it might just fly but above that it is going to be a struggle.

Also keep in mind that 3 bladed props are less efficient that two bladed props.

Pete

http://www.ecalc.ch/xcoptercalc.htm?ecalc&lang=en

 

[Borg]

The e-calc is actually where I got the information to make these decisions, then I was just seeing if others agreed. Thanks for your input!

 

[PeteDee]

Given the constraints I would be looking at higher kv motors, that is pretty much the only thing you can play with to get more power.

You will also need bigger ESC's.

Pete