This is the problem with this field, there are a LOT of people giving out bad advice. You have to learn to sort the wheat from the chaff.
What I've learned in the past 3 years is this: If somebody gives you an answer that is really simple, and easy to understand, and makes sense, then it's probably wrong.
If somebody gives you an answer that is difficult to understand, has references to a white paper or textbook, and requires you to break out a calculator, then they probably know what they're talking about.
Or to put it another way, answers that are black and white are usually wrong. (ie: "Best efficiency is at 2:1 thrust/weight ratio"). If the answer is "It depends", then that answer is usually right. Very little in this field is simple, and the answer is usually nuanced.
Rob, I think I'm learning that more and more haha. I've been finding a lot of different explanations to the same question, so there's a lot of gray area like you say. I trust your experience though!
Haha this made me laugh. Thanks, Mathieu!
Generally speaking hexes will be less efficient than quads. This is because quads can fit larger size propellers for any given frame size, and that is where you get efficiency (propeller area per mass).
Just draw some stick figure machines. Draw a quad with 10" props almost touching. Connect the motors with sticks. The total length of those sticks will roughly represent your frame weight.
Now draw a hex with 10" props almost touching. Connect the motors with sticks. The total stick length is relative to what the frame weight will be.
Now for both cases, divide your disk area, but your stick length. You'll see that the quad is higher.
I noticed this too.
In my defence, I only got involved because Bradley was posting here! :)
And... your avatar is freakin me out man!
This is a good exchange, lulz. I want to see the crash reel. Order lots of spare props and arms. They'll come in handy!
Wow! I have learned a lot from this discussion. I thank everyone for their contributions.
I am new to the field and bought too much of a machine and I am not getting the flight time I wanted (at least 20 min). I bought a 3DR X8 and is only giving me around 7 min. with a 6000mAh battery. I am thinking I should remove some motors and see how it does with only 4.
you can calculate, pretty acurately by using, https://www.google.com/search?q=static+thrust+calculator&ie=utf....
you know your prop data, weight, incoming voltage, and your motor resistance. Take your quad weight, divide by 4, this is the theroritcal thrust per prop, play with the calculator to find the right rpm to match the thrust to the required prop hover thrust. This will also give you your watts required. Now take your watts and find the motor inefficiency, IR^2 losses, watts/batt voltage= amps, plug in your amps and multy by the motor resistance^2, now add these watts to your useful power watts. Now that you have (total hover watts)/(battery watts/hour). Batteries are rated in useful amp*hrs. So a 5000 mAh battery will discharge that many amps effectively over an hour. So you should have some fraction like .25 hours, convert to minutes by multiplying by 60. For a safety factor of 5% loss is pretty liberal as it accounts for increased output in winds 5 to 10 mph.
It's all pretty simple math, just a lot of steps to get useful number. I've made excel file, to take out the dumb steps, but once you understand that, you can figure out different multirotor configurations without much problem, and if you are using APC props you can use their data tables to figure out a lot more.
I used my data to calculate 28 minute flight time on my quad, which actual flight came down to 25 minutes, because I set my quad to rtl at 10% battery level
Also you can use the additional payload weight and batteries to calculate new durations, Like doubling up batteries 5000 mAh gave me an estimated 43 estimated flight, which is 53% increase, which is definitely reasonable, but I why loose the extra 10 minutes for convince?
Is anyone aware of the ratio of the power consumed by a drone while ascending, descending and flighting forward?