Batteries

[R_Lefebvre]

Well, it's non-linear, so there's not going to be one easy answer.

But considering the case of a 15" flat octo, you have 0.91m2 of disk area. To get the same disk area in a quad or X8, you'd need 21" props. But don't forget how much easier that is to do with only 4 disks. To make an octo with 15" props, it needs to be a 1000mm frame, bare minimum. But to make a quad with 21" props, it only needs to be 780mm.

 

[jdennings]

Ah, yes. Disk area of X8 = disk area of quad = 4 times individual prop disk area, vs 8 times prop disc areas on flat 8. Had somewhat mixed that up.
Quite un-intuitive to me, this X8 vs quad disk area of one ratio efficiency wise... I would've sworn the bottom props were doing *something* better ... (more than the possible 5% ...)

To really drive the point home I played with my X8 transforming it in a quad by comparing flight time, removing all bottom propellers and disconnecting corresponding motor ESCs. (And adding equivalent weight of propellers so that auw of quad and X8 was same).
Same battery, flight conditions, cut-off time, etc ...
Result: 17% shorter flight time with quad. Which is perfectly explained (within a couple percent)when looking at amp/thrust curves of the motors, given the loss of efficiency (g/w) of each of the four motors that were operating at much higher amperage and lower efficiency vs X8.

Great talk and discussion.

 

[Quinton]

There is a theory that using overlapping propellers, between 10-30% overlapping, could actually be up to 5% more efficient than the same two disks would be if separated. But it's never been proved out in reality. Even the guy who wrote a doctorate thesis on it, couldn't show it in lab testing. The possible 5% increase was lost in the measurement accuracy of his setup.

I rem you saying this a few days ago and it stuck in my head.
You may find this video interesting then which uses overlapping props..
http://news.msn.com/science-technology/video?videoid=f171f98d-556c-b6e5-16db-cfb6a4a0091b#tscptmf

edit* Actually this thing is on Kickstarter I just seen and finishes in 6 days time, its using Pixhawk controller..
https://www.kickstarter.com/projects/1524806320/hoverbike

"UK-based Malloy Aeronautics is preparing to test a manned quadcopter capable of out-manouvering a helicopter and presenting a new paradigm for aerial vehicles. A 1/3-sized scale model is already gaining popularity with drone enthusiasts around the world, with the full-sized manned model expected to take flight in the near future."

 

[jdennings]

Very cool ... Had not seen this kind of innovation for quite a while. That rectangular folding frame design, along with fully protected propellers, makes a lot of sense.
Meanwhile in the world of theory vs practice, disc areas and X8 vs flat 8, something doesn't quite square up: http://www.multirotorforums.com/sho...8-28x9-2-props&p=180021&viewfull=1#post180021

 

[R_Lefebvre]

Just a note here... I went to charge one of the Multistar batteries for the first time, and the charger warned that it was reverse polarity. Checked the plug and... yep, they soldered it backwards. :upset:

While fixing it, I noted that the soldering of the connector isn't great in any case. Kinda skimpy. Best to check them all.

 

[Motopreserve]

Just a note here... I went to charge one of the Multistar batteries for the first time, and the charger warned that it was reverse polarity. Checked the plug and... yep, they soldered it backwards. :upset:

While fixing it, I noted that the soldering of the connector isn't great in any case. Kinda skimpy. Best to check them all.

Thanks for the heads up. I'll be putting some Anderson's on mine so I'll keep an eye on whether they're reversed.

 

[Ronan]

Which soldering tip do you guys prefer to use? I use XT60's and the electronic 'pointy' tip is horrible to heat up the metal. Even on my 100w solder.