Quality Motors

Forrest Frantz January 20, 2013 at 12:26pm

10.5 kg? What are you carrying?

I'm custom building an octa camera platform large enough to carry a huge lens and full-body format Canon camera (about 8 kg total payload). To gain experience, first I used an off-the-shelf hex as other suggested to gain some experience and knowledge. Now I'm going to build one that will easily carry half my target load (standard lens and camera) and barely carry the other. After I gain the experience then depending on stability, vibration ... is it worth going larger or do the vibrations make long-lens unfeasible?

My approach was as follows:

Chose a battery size based on AmpHr/Weight efficiency. 3C was the best.
Reviewed test results on over 2,000 motors to narrow that down to the best 10. Bought those for testing.
Got props of all diameters (8" to 14") and pitches for each and types (slow, electric, carbon, etc.). Came to about 50 different props
Set up a scale to measure net lift force (net of engine and prop weight because it has to life the prop and motor first) to appropriately determine the best combination for a copter. Also added a structure penalty for prop size because larger props mean larger frames. So net lift was in fact a comparable net.
Controlled voltage and amps via a DC Power Supply (to determine watts)
Calculated motor efficiency by dividing net lift/watts for net lifts of 100g from 200g - 1200g per motor (for 9.6kg total net lift)
Also recorded motor temp at 800g net lift running for 2 minutes. Quick way to eliminate some motors.
Chose the best two motors.
Ran both for 4 days continuous paired with the best prop using the power supply at various loads from 200g to 800g lift to ensure they were durable.
Then found the best CW CCW props and tested those.
Then tested various ESCs with the best motor-prop combo

So that is one approach to selecting your lift system.

Developer

John Arne Birkeland January 10, 2013 at 1:01am

I'll be brutally honest with you. If you are new to this, a DIY heavy octo lifter will only burn a lot of money and cause you grief. So start simple with a RTF (Ready To Fly) quad kit to get your feet wet. Then progress from there.

If you absolutely must have a heavy lifting octo NOW! The alternative route is to spent big money and get a pre-tuned "Professional RTF" kit with matched hardware that will fly well from the start. But then you are just throwing money at the problem instead of learning the required steps. And be prepared to throw a lot of money on it...

Søren Kuula January 9, 2013 at 11:35am

Hi,

Well you start by determining how much thrust you will need. A rule of thumb is twice the all-up weight of the copter.

Then you decide on a battery voltage, in your case it looks to me like an almost certain 6S.

Then you find several motor/prop combinations that claim to have that thrust / 8, and where the prop is available as CW as well as CCW. The current should be specified then; you can get BECs for that current (more won't harm).

You can now chance it and get 8 of each of all, or get one set to test run and see if you like it and if it is all up to spec....

Maybe there is a decent fellow somewhere who got the wrong size of something and can tell you honestly if it might suit your project better, and possibly sell it for a resonable price.

PS there is also this great propeller calculator to play with: http://ecalc.ch with a multicopter tool.

Try punch in 8 motors, 6S 12000mAh, 100A BEC, Axi4120/20 motors, APC slowfly 16x6 props (which don't exist but OK for starters).

The Axis are great motors and expensive too. Remember to get the rear mount option.

Regards

Soren

elad orbach January 1, 2013 at 3:45pm

define best?

what size weight is the octo? batteries? ...

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