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?
Thanks,
Roger Larsen
Replies
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 :)
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).
ECU:
http://www.hobbyking.com/hobbyking/store/__17135__Turnigy_TY_P1_25A...
Watt meter:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=...
(already have this one)
http://www.smartdrones.de/collections/propellers/products/multicopt...
(15")
http://www.goodluckbuy.com/1555-15x55-carbon-fiber-propeller-prop-c...
(15")
http://www.rctimer.com/index.php?gOo=goods_details.dwt&goodsid=...=
(16")
http://mikrokopter.altigator.com/graupner-eprop-14x8-propeller-p-40...
(Graupner 14x8 e-prop)
http://www.smartdrones.de/collections/motors/products/brushless-mot...
(550kv)
http://www.smartdrones.de/collections/motors/products/sb-m550k-upgr...
(550kv)
http://www.smartdrones.de/collections/motors/products/high-performi...
(650kv)
http://www.himodel.com/electric/DUALSKY_XM5010TE-9_390KV_Outrunner_...
(390kv)
http://www.himodel.com/electric/HL_W48-30_420KV_Outrunner_Brushless...
(420kv)
http://www.himodel.com/electric/HL_W42-25_390KV_Outrunner_Brushless...
(390kv)
http://www.himodel.com/electric/HL_W48-22_390KV_Outrunner_Brushless...
(390kv)
http://www.hobbyking.com/hobbyking/store/__17923__NX_4006_530kv_Bru...
(530kv)
http://www.rctimer.com/index.php?gOo=goods_details.dwt&goodsid=575
(360kv)
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!
Roger.
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?
I don't understand ppl claiming "It is clear that a great many people are spending billions of dollars on the electrical energy storage density thing. Something useful is bound to come out of it."
The fact the somebody is spending more and more money on a technology, usually means it has reached steady limit, nothing quarantees breakthrough. For example, we are spending most money on taxes and banks. They have consultants, research departments. Yet, there is nothing ultra spectacular achieved by new taxes nor banking in the past century beyond idea of bourse money rental, money transfer etc.
Amount of money spent on energy density in batteries would rather mean it is easier to get funding for this sector beause it is easiest to draw imaginative stories around it. What you will get in shops in ten years from now, is leaving research labs right now. And what do you have in the labs? Energy densities raising by 50%, at best.
My idea is build a small 3 phase generator powered by small nitro .049 engine. If this works then the next phase will be to machine a small turbine that will spin from the heat of a butane flame, the motor will spin a simple over-run clutch that will be connected to the shaft of my spare 1200kv motor. :) from there we can build a LiPo charger that will charge each cell individually. I've got the motor sitting around.. I just don't have a small over-run clutch.
I found the perfect source for the clutch!
http://www.tinyclutch.com/d-series-roller-clutches
What does the group think? I can build oversize landing gear and mount the generator there.
I'll only mount the turbine on the quad. I'll test with the nitro motor outside on a workbench.
I wonder if we can build a small generator that runs on butane ? I picture a microturbine spinning a small 11.1 volt 33 watt generator. The generator will be used to charge the primary LiPo power source during flight. This will be needed so we can have power on demand. The small generator will extend the flight.
Not quite what you want but there is a discussion here about slope soaring a helicopter. That would get you your 1hr flight
http://rc.runryder.com/helicopter/t12043p1/
Ferdinand,
Was the NX-4006 530kv the most efficient of the 3 HK has? A lot of people rave about the 4008's. What size prop would you use with this motor for normal fun flying (but with still slightly long flight time)?
Hello guys,
I am the one with the 65min quadcopter flight. Great to see, that there are a lot of people heading for the same goal (long/longer flight-times)
Just let me add some comments ...
First of all, the most important thing is to be light weight, and with conventional frame design a quad can be build most lightweight, this is just becaus of the armlengh needed, which increases for a Hex or an octo. My frame had 110gr if I remember that correctly.
From the motors perspective I also tried the rc-timer 360KV and the T-Motors. The rc-timer one are good, but the problem with mine was that the drillings to mount the props where not perfectly where they should be, so with that it is hard to mount the props. The rc-timer CF 15,5" props are also a bit ...., you need a lot of work the get the somehow ballenced, the drillings are also off-center.
Regarding the props, the Graupner were a bit of an accident to me, since I was at that time not able to order 14 or 15" props somewhere, so I took the Graupners, but whatever other props I tried so far, (14x4 Foxtech, 15,5x5 rc-timer) the Graupners are not so bad. The efficiency is really competitive, and, just my opinion, you can hear that, when a prop is spinning if it runs efficient or not. Another advantage of the Graupner is, that you can really "fly" (not only hover) with them.
Another story are the T-Motors 650KV. These ones I tested, since they have a nice prop-mount, but on my test-stand, which is just an arm with the Motor and the Prop, they run not that efficient as the Hobbyking 530kv. The Hobbyking ones are a mess to mount the props, but you can run all different load tests, and they do not get even warm (which is a good indicator). The T-motors do, even just running at a lower Power-level. Here I did not find out what was the reason, this might have also been due to some problem/incompatibility with the ESCs. If somebody gets (good) results with the T-motors, please keep me posted.
Regarding the batteries, the maxamps.com are really the best, but also only if you go for more than 30min flying time. (1-2C discharge rate) If you drain more, you can only use less kapa. A good alternative are the zippy flightmax 8000er cells. The maxamps.com you can keep for record flights.
best regards
Ferdinand
Thanks for all the valuable input. Based upon my research and your input I will set up a test to stop guessing and ensure I can get the most trust per W. Stability and what not will be not measured yet.
This is my test set up so far;
ECU
http://www.hobbyking.com/hobbyking/store/__2163__TURNIGY_Plush_25am...
MOTOR
http://www.rctigermotor.com/show.php?contentid=142
PROPS
A bunch of variations from 12 to 15" in size
Graupner E-prop
ACP SF
LIPOS
http://www.maxamps.com/Lipo-11000-74-Pack.htm
- 2,3 and 4s
The idea is to test the trust with different combinations of volts / amps / props.
I also have some ideas to improve airflow / turbulence around the prop to see if that does anything.
Dimpled props apparently doesn't do anything; so I will not try that.
Before I order all of this, let me know if there are other configurations (motors / props) you would like for me to test. Just keep in mind is that my goals are a stable platform, with large carrying capacity and range. My goal is not to get a super fast and agile platform. I will build the copter using CF parts myself instead of ordering ridiculously priced kits.
Thanks,
Roger Larsen
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