Hi
I am rather a beginner in multicopter flying and I am planning to build a miniquad by myself. It should become kind of an allround quadcopter that is powerful enough for acro flying and carrying a lightweight fpv setup. But mainly it should have a long flight time (for a miniquad).

The motors I have in mind are
Lumenier rx2206 2000kv
Lumenier rx2206 2350kv
Cobra 2204 2300kv
mainly because of their high efficiency.

I am not sure about the battery: is 3S more efficient or 4S?


See my planned setup for the quad below:
Frame: DIY aluminum - OR - ImpulseRC Warpquad
Battery: ~2000mah 3S
ESCs: some 30A
Props: 5030 / 6040 (depends on motor)
Flightcontroller: Custom build (project still in planning)
RX: nrf20L01 module (fitting my diy FC)
Planned size: 230 - 250mm
Planned weight: ~500g

Are my suggested motors as efficient as I assume (compared to others)? And which one do you recommend?

Do you have any general recommendations on motors / props / batteries / ESC's?

I hope you have some time to answer my questions.
Thank you in advance

I think you probably need to do more of this research yourself as the answers to many of your questions are "it depends".

You say "long flight time". What do you consider to be a long flight time for a 250 class quadcopter?

A motor on its own cannot be rated for efficiency as without a propeller and some power it cannot do work and therefore has nothing to be efficient about.

Efficiency is a product of the motor and propeller combination and the battery voltage and is not a constant over the throttle range, so you need to do the research here and find test data for each of the combinations of motors, propellers and battery voltages you are looking at and make the appropriate comparisons.

In general terms, flight time in minutes can be estimated with reasonable accuracy from the following calculation:

time = density / (1000 * R / efficiency) * 60 where

"density" is the battery's energy density in Watt hours per kilogramme.
"R" is the ratio between the all up weight of the craft (including battery) and the weight of the battery alone.
"efficiency" is the efficiency of the motor and propeller combination at the chosen battery voltage expressed in grammes per Watt. The efficiency rating used should be that at the throttle value needed to hover the craft.

Here is a spreadsheet that will calculate flight time for you. Just enter the information in the yellow cells and the spreadsheet will work out the rest.


  GenericFlightTime.xlsx (Size: 6.04 KB / Downloads: 108)

Nice unseen! Did you produce that?

(28-Apr-2017, 05:02 PM)sloscotty Wrote: Nice unseen!  Did you produce that?

I made the spreadsheet based on the formula. I first saw the formula in a post by renatoa on RCGroups, but I doubt that he is the originator of it. It's a very basic calculation of how long an energy source of a given weight will last in a craft of a given total weight with a propulsion system that uses the power at the rate implied by the power system's efficiency.

As there's no magic involved in multirotors, it's actually quite accurate even though it is remarkably simple.

The hard part about using the formula is getting hold of an accurate g/W efficiency rating for the power system you are interested in. Very few manufacturers publish full data about their motors with various props at different throttle levels. T-Motor and Cobra are some of the few that do.

Rather than hide this info here, I'll make a post in the "Useful info" thread in a while so that it's more accessible.