I've been reading about Micro Drones claim of 1 hour flight and I have been pouring over some numbers trying to figure out if this is possible with LiPo batteries. My answer is simply no.
I've look at different batteries and different motors. Typically the motors are able to thrust 10g per W. This means that for every gram of thrust needed you are going to consume 0.1Wh (watts per hour). Even this number is slightly optimistic, some motors / props have half of that output others go as “high” as 11-12g per watt.
Let’s use 0.1Wh per gram of thrust.
Now, let’s look at batteries (I’ve compared thunder rc and hk batteries) and the best pack for the punch is about 650 grams for a 8400mah battery (3s). With LiPos you are supposed to drain about 80% which gives about 75Ws for this battery. If you divide the weight of the battery with the Whs you find that you get about 0.11Wh per gram of battery weight.
So, to simplify; just to carry the weight of batteries you will burn up all the charge in one hour. It doesn’t matter HOW many batteries you add. The equation is still the same. However, I have seen that typically LiPo batteries packs more punch the bigger they get, but I could not find any reasonably priced batteries larger than 8400mah.
My dream of building a 1 hour flight octo with 4lb carry capacity is just impossible.
The only possibility I see is to tweak and build a really large copter and gain a few % here and there or come up with another source of energy than LiPos.
Can someone correct my math if it’s off please, or direct me to more efficient motors and batteries?
Check this stress test.. I might try this :)
Hmm, weight is 45g it seems. I ordered one just to verify.
I believe that is the protected version that has circuitry to prevent excessively high discharge or charge rate and overly high or low voltage.
Sorry Roger, I deleted the 23g battery post as the weight was obviously misstated. I believe the unprotected Panasonic NCR 18650 cells are 45g.
No need to solder those Panasonic 3.7v, 3100mah batteries. You can get 6200mah pre soldered 4s2p (8) cell packs for $85.
I may have to get one of these packs and try it out.
My TTO weight 1390g FPV quad will hover at 95w (6.5a at 4s). If I swap out the existing 469g 5000mah 4s lipo for a 360g 4s 6200mah li-ion pack, that 100g drop hover amps to around 6a. I may have to take off the pan/tilt, etc to get more discharge headroom.
The individual cells are rated for a continuous allowable discharge of 3540ma. That should allow for up to a 7a continuous draw at 4s.
Due to the low C rating, maybe it would be better to go with 3s3p or would the amps just go up proportionally?
These Panasonic cells sound incredible! When are you going to do some testing ?
@12amps for just about half the weight of the Turnigy 6amp 3s LiPo I just ordered :)
Let me know how you make out. 12amp at double the density that's available in hobby lipo cells sounds promising!
These batteries seems pretty good.. Not sure you would even have to worry too much about protection circuits.
They just released..
3.4Ah at ~3.6v. 45g. 272wh/kg. Panasonic is not kidding around. They have road road map for Li Si this year. They are at 4Ah, but slightly heavier; so the 3.4Ah still out performs them.
Anyone know of a standard heli design that uses an electric tail rotor motor? To me that seems like that might be a decent way to go.
Is there an easy way to calculate how much tail thrust you need to counteract your reaction torque?
The Maxi Jokers have direct drive tail options:
Anyways; here are the motors / props I'm ordering. Skipping the T-motors due to a lot of bad reviews.
I've also seen some strange looking thrust benches. I'll try to build one which does not use a L to apply force to a scale, and place the motor on a long stick attached to a 4kg weight at the end. Place the weight on my scale and read how much it can lift. If you have to much stuff right behind the prop it will give you incorrect readings (since the force of the prop will push the plate down at the scale and counter the thrust of the prop). Kinda like what happens if you put a big plate underneath a helicopter and try to take off with the plate attached (yep, I saw this on Myhtbusters :) ).
2-6 cell batteries (where it makes sense to use them).
(already have this one)
(Graupner 14x8 e-prop)
I feel I need some more props to test; but these seems to be what people recommend. I did find some 16" graupners but no CCW :/
I'll keep you posted!
That's quite an order. I'd be happy to lend you some of that stuff for testing as I would love to see the results.
I just received the panasonic ncr18650B (3400mah/ 3.6v) and A (3100mah/3.6) cells.
The a cells weigh ~45g giving 248wh/kg.
The b cells weigh ~46g giving 266wh/kg (about 7% more density).
As far as I know the B cells does not have the heat protection layer, so they might take a little more love and care.
A cells I can get around $7 in bulk, B cells over $20; but they are just coming to market.
The cells look legit, but I'm going to do a drain test just to confirm that the chineese didn't just buy some fancy wrapper.
The one hour flight is becoming more and more real :)