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Pumpkin drop event

TBS Discovery AerialMob Endurance kit.

#1
Hi guys,

Long time Flite Test fan, first time forum poster, so be nice!

Long story short, I will be using a TBS discovery for a Design project I am doing at university, I will be adding extra modules to it to extend its capabilities.

So on that note, before purchasing, I need to know if the extended range kit gives any notable increase in payload capacity over the standard aircraft? Logic would say yes, but I need some figures for calculations, and my funding board!

Thanks in advance!
 

joshuabardwell

Senior Member
Mentor
#2
The short answer is: yes. One way to increase range is to take an existing power system and stick a bigger battery on it. Your TWR goes down and the copter becomes less responsive, but you get a longer flight time. Obviously, in this case, longer flight time does not correspond to increased cargo capacity. You would do better to leave the original battery and use the "extra" weight for your cargo.

The TBS endurance set upgrades you from 4S voltage with 750 kv motors and 9" props to 6S voltage with 400 kv motors and 15" props. This is a total redesign of the power system, for more efficiency. Higher voltage, lower-kv motors, and bigger props are all more efficient than the alternative. There's no question that you will get more cargo capacity with the endurance set than with the standard set.
 
#3
Thanks for the help Josh.

Stability will greatly help this project, so the lack of maneuverability is a bonus in my eyes.
So basically, get the endurance kit, and stick with the 4S battery?
 

joshuabardwell

Senior Member
Mentor
#4
Thanks for the help Josh.

Stability will greatly help this project, so the lack of maneuverability is a bonus in my eyes.
So basically, get the endurance kit, and stick with the 4S battery?
The motors and the battery voltage must be matched. If you get the endurance kit, linked here, you should use it with the 6S batteries it was designed for.

To go a little more into detail, a motor's kv rating is the number of rpm's per volt it will make, at no-load. So a 2000 kv motor supplied with 11.6 volts (nominal 3S voltage) will make 2000 * 11.6 volts = 23,200 rpm. In reality, once you put a prop on the motor, the rpms will drop, and the actual rpm made will depend on many factors. But comparing kv rating is a good way to compare motors. All else being equal, a higher kv rating motor will spin faster than a lower kv rating motor.

What about prop size? In short, a larger prop will require more power to spin at the same rpm as a smaller prop, because it encounters more air that it has to move. A larger prop will produce more thrust than a smaller prop, and more importantly, it will be more efficient. It is more efficient to swing a large prop slowly than it is to swing a small prop quickly. You will get more thrust for less power.

Finally, battery voltage. In short, higher voltage batteries let you select motors than lower voltage batteries.

The key takeaway is that all three components (motor, prop, battery voltage) must be well-matched. There is some variability, but only within a range. You can't take a motor/prop combo designed for 6S and drop them to 4S without taking a performance hit. Better to use a motor/prop combo designed for 4S. There are cases where it makes sense to mis-match your components and accept the performance hit. For example, the motors that I have on my copter now are able to handle 4S voltage with 10" props, but I'm only using 3S packs because I already have a bunch of them. If, later, I go up to 4S, I can expect longer flights, more power, and more efficiency. But if you're starting from scratch, do it right.
 
#5
Ok, well take a look here, this a comparison file I made. The highlighted green components are the ones I would prefer.

I see! I have a good aerodynamic understanding, just my first touch into quadcopters. I would be happy to go for the endurance, just my project supervisor is looking for some facts and figures.

Thanks again josh.
 

joshuabardwell

Senior Member
Mentor
#6
I see you're choosing a Spektrum receiver. Have you already got a transmitter that you own? FrSky is a good alternative to Spektrum, for much less money. But if you already have an investment in Spektrum, it's probably not worth it to switch.
 

x0054

Senior Member
#8
A 6S 4,000mAh battery is a very large battery. If you are looking to have larger payload capacity, I would consider getting a smaller battery. Stick with 6S, as that's what the motors are designed for, but you can drop the Ah rating to shad some wait for those extra goodies you want to carry.

Also, that's a pretty pricy kit, in my opinion, but TBS makes good stuff. You can probably build a similar quad for about 1/2 the price, if that's a concern. But if money is not a problem, TBS is a really nice option.