# What is the relation between the motors in a quadcopter, the propellers, the battery, and flight time?

The quads in question are the Hubsan H107D and H107C.

On a 380 mAh battery, the H107D flew for a little over 4 minutes, while the H107C flew for a little over 10 minutes.  I suppose the difference is due to the FPV camera that is always on on the H107D.  There is a camera in the H107C, but it is on only if there is a microSD card installed (and I do not have one yet).

On a new 500mAh battery, the H107D flew for over 6 minutes, much as I expected given the flight time on the 380 mAh battery.  But the H107C flew for only 8 minutes on a new 500 mAh battery.  I do not understand why.

Is there a good resource that shows the math relating the key properties of the batteries, the motors and propellers in use to the flight time?  (I am no stranger to complex mathematical models; I am just a stranger to this sort of engineering.)

I haven't done enough testing to provide statistically significant results (I have 5 500 mAh batteries, supplied as an upgrade to the 380 mAh battery they come with, so I could spend weeks testing enough to get statistically significant results), but this result has me puzzled.  I know the 500 mAh battery is longer and heavier than the 380 mAh battery (but both fit the Hubsan quads I have), but should that result in such a reduction in flight time?  I thought the bigger battery should result in a longer flight time.  Did I waste my money getting the 'upgraded' batteries?

Thanks

Ted

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Did the flights take place in similar conditions in terms of heat, humidity etc also the flight profiles were they similar. Finally were the batteries fully charged?

Yes, yes, and yes.

The flight conditions and profiles were identical, and I charged the batteries fully.

I repeated the tests today, in identical conditions, with the same results.

A subjective impression (since I do not have any means of weighing these things), is that the H107D is lighter than the H107C, and thus benefits more from the extra power while the extra weight of the bigger Battery stresses the H107C's motors more, making them draw more energy and reducing the amount of time available to fly.  Is there another explanation?  I am guessing the FPV camera is why, even with the benefit of the bigger battery, flight times are 25% shorter for the H107D.  (Is there a way to turn off the FPV camera/video feed, so that the flights can be more comparable?).

In any event, I want to conduct some experiments with copters the size of the Hubsan, and it would be useful to have a mathematical function that relates all these things...

Thanks

Ted

You are right in your latest thinking - weight is a massive influence along with simple stuff like prop balance etc.

The weight of the FPV equipment will have a much larger impact then it's current draw which over a few minutes flight will be tiny compared to the power used to remain airborne.

Thanks Ben

OK, then, I assume that LiPo batteries that provide a lot more energy will also weigh more, and thus, for a given set of motors, may be counter productive.  So what, then, is the trick to get longer flights?  More powerful motors along with the bigger batteries, and lighter bodies (but how does one do that unless on has a very good 3D printer?  Speaking of a good 3D printer, is there one, or a complete kit to make one, that is up to the task of making extremely light and yet extremely durable, bodies and frames this small?

I have all the parts to make another Hubsan H107C, but with the enhanced motors that are available for it.  Would that, with the stronger motors, get a better result from the 500mAh battery?

Following on with what you have said, how does on balance a propeller?  You say that is simple, but I am so new at this, I have no idea how to do that.  What other 'simple' things should I look at, and is there a resource that shows/describes what to do and how?  I only started studying all this about 3 weeks ago (but, I am an old scientist, and so am a quick study).

Also, are there other propellers, such as ones that are slightly larger or smaller, with 3 or 4 blades, and at different angles, that could provide a better result.

What would you expect, in terms of flight length, from something like the Walkera Y6 Scorpion, which has 2 motors and propellers on each of 3 arms?  With the extra motors/propellers, should it be able to carry a larger payload in batteries, and thus obtain a better flight length?  What about the Walkera X8 Spacewalker, which has 8 arms, each with a motor and propeller?  If that could provide a benefit in terms of flight length, what about putting two motors and propellers on each of the Spacewalker's arms, analogous to how Walkera turned a tricopter into a hexacopter?  Just how far could one go?

I guess part of the trick would be that the increased number/power of the motors should be associated with a weight that does not increase as fast as the weight of the motors (and are there more powerful motors that draw less energy while weighing less and providing more thrust?), and that the increase in energy consumed by the extra motors should not increase as fast as the energy stored in the batteries.  Will a 2Ah LiPo battery weight 4 times as much as a 500mAh LiPo battery?  But then, that brings me back to the mathematical relations among all these variables.  I still need a good source on that.

I guess, in terms of what I need, I need not only pointers to information I can use, but also to parts suppliers that can provide what I need in Canada (or that can ship to Canada).

Thanks

Ted

Hi Ted,

Although not much use for the little Hubsans, Xcopter calc will let you "configure a number of multicopters" and see what flight time you might expect to get.

http://www.ecalc.ch/xcoptercalc.php?ecalc&lang=en

The little FPV Hubsan is pretty heavy in relation to the propeller size and is thus pretty inefficient.

Generally, the bigger the propeller swept diameter and the slower it can turn at hover the higher the efficiency.

But that also requires motors that are designed to have their peak efficiency at that RPM and power output.

Generally battery weight makes up most of the weight in a copter designed to fly for extended periods and it is important to balance maximum reasonable prop diameter and motor efficiency at a given weight to achieve an optimally efficient copter at hover.

By far the most important consideration on multicopters is their hover efficiency, they are "normally" flown very close to their hover efficiency.

With the exception being extreme acrobatics or very gusty winds.

One of the problems with the current crop of very small copters is that they tend to use too small a prop diameters and too high a motor speeds for optimal efficiency.

Also, the brushed motors on the Hubsan are way less efficient than brushless ones like say on the Blade 200QX which is a fantastic small quadcopter in spite of still having too small a prop.

Even though peak motor efficiency may be similar, typically brushed motors are only optimally efficient at one speed and fall off rapidly on both sides of that speed whereas brushless maintain much higher overall efficiency at all speeds.

The motor efficiency I speak of here is not a small effect, it can be 2 to 1 or worse.

Big props, efficient slow motors, as little unnecessary weight as possible.

Generally Quadcopters can be more efficient than copters with more motor/prop units because the 4 larger props can actually have greater swept area than more smaller props in a similar area.

Best,

Gary

Hi Gary,

Thanks.

I don't suppose that there is a tutorial on how to use that page you have the link to: especially with regard to where I find the data to enter into it.  I ask half in jest.  I am sure I can figure it out, but I am not sure where I'd find all the data I'd need.

I wasn't aware that the motors in the Hubsan are brushed motors.  Are there brushless motors I could replace them with?  Are there other propellers, perhaps larger ones or ones with more blades, that I could put on my Hubsan's?  They fly very well, and I am learning quickly how to control them; but the learning would go faster if the flights weren't so short.

As for the Blade 200 QX, I read one of the reviewers on amazon remark that he put larger propellers on it and he observed much better results.  He said he used gemfan 5030 5" x 3" propellers.  Is that as good a choice as he reported, or is there a better choice?  I did a search on amazon.ca for those propellers and found only XT-XINTE carbon fiber  paddle Mini 5030  propellers (I have no idea if those are the same thing that he used but by a different brand).

Based on what you said, I'd hazard a guess that propellers that have 3 or 4 blades may provide even more efficiency, perhaps depending on their geometry.  I guess this amounts to asking if a greater number of blades on a propeller can compensate for not having a larger radius?  Would that intuition be close to being right?  But then, where could I find (slightly) larger propellers, perhaps with more blades, that would fit (or that could be made to fit)?

Is there a good source that provides these properties of motors that you describe for motors that are available for small multirotor copters, so that I guy like me has a hope of  finding a good combination of motor, propeller and battery?

I am finding that the batteries and motors I have been provided by vendors have print that is too faded, or in a very tiny font, so my old eyes haven't a hope of being able to read them.  I have a bunch of LiPo batteries, all 3.7 V, ranging from 250 mAh to over 300 mAh, and I can't tell the one from the other, and they are all so similar in size I can't even use that to distinguish them.  And, the vendor gets them in bulk and distributes them in clear plastic, unlabelled, bags!

Thanks

Ted

Hi Ted,

The explanation is that a given motor equipment, a given ESC, a given prop design and all of the combinations thereof result in a global "efficiency" that can vary a lot.

So in your case the extra capacity of a new battery translate into more weight with probably such a bad efficiency that you actually loose flight time (for ex your ESC draw exponentially more amps because of the weight increase; they were probably already optimized for a given weight with the smaller battery)

ecalc  .ch

Also - small batteries like that tend to get weaker after every use. So older batteries don't charge up as much.

I flew bunch of coreless brushed driven toy quadcopter modded into FPV.  My tip for you is that any stock coreless brushed driven quad can only carry 30~35% extra from its stock weight, anything beyond that is reduced in performance.  All you can do right now is to remove anything that is not necessary on H107D/C main frame such screw, support plastics, thick wires and thing that you can remove without compromising the structural integrity of the quad frame and its flying characteristic.  For you reference i got a bunch of cheap mini FPV quad project  i did that perform better than bigger brushless multirotor, flew extremely well under various weather condition and longer runtime after huge reduction of weight.  Check at my project blog for your tips and references: http://www.supermotoxl.com/FPV/UAV-models-builds-and-flight-reviews...

Also i build 3d printed version too smaller than X4 on other section of my blog.  All flew well on 500mah 1s for 12 min.  Remember lightweight is everything.

Thanks

What size battery does not have this problem?  Or does it apply to all LiPo batteries?

I guess, from what has been said so far, I am looking for a flying battery, with some number of light motors that turn relatively slowly and that have over-sized propellers.  Right?  But where do I find such things?

Hi David,

Thanks.

You want to check on the links you provided in that blog, as those for the propellers are broken. But, had you considered something like the Genfam GF 5030 3 blade propeller (or printing your own 3 or 4 blade propeller - something I'd do if I were to seriously investigate 3D printing of multirotor copter parts).

Since you have built 3D printed quads, can you provide links to some of those you made?  I see you have a fondness for WL's V929.  What do you think of WL's more recent offerings, such as the V262 Skylark and V202 Scorpion?  And what about the latest offerings from Walkera?  What would you be able to do with Walkera's Y6 Scorpion or X8 Spacewalker?  Do you think you could obtain a better result with these (with the greater number of rotors) than you did with the V929 (or that you could with the V222)?  Have you tried?

I notice you also didn't say anything about the motors or propellers in that blog. Surely, if one can go the route of making a 3D printed frame/body, one could examine the range of motors, propellers, and batteries that are small enough to make a copter, and even make the propellers with the size and shape your calculations indicate as being optimal; right?

I like the Skylark as the body is made of extremely thin plastic (is there anything lighter than that that can be used for the same purpose) and yet it is almost as durable as the hubsan and MUCH lighter, and I like the notion of having a body to keep things together and protected.  Besides, a flying wire frame is just plain ugly.  ;-)  I find that even though the Skylark is much lighter than the Hubsan, it does not fly significantly longer than the Hubsan on the same battery (though I do not yet have objective measurements on that - it is just a subjective impression for now).

Can one print a body where the frame and body combined weigh less than the Skylark. perhaps making use of bigger batteries feasible: a body and frame whose parts are paper thin, as strong as steel but as light as a feather?  The more I think about 3D printing, the more I like the idea, but I have yet to find a source for either the printer or the materials used for printing in Canada at a price I can afford.  Think about it: if you can print these things, using plastic or nylon, or something else that is both strong and light, then you can experiment with the number of blades, the length and shape of the blades, and the angle they form relative to the axis on which they spin.  And if you're going that route, why not find the best quality, most efficient motor that can be obtained to spin propellers of that size at the right speed?  Alas, I still do not have the basic science reference that tells me how to do that, though I am sure such a reference exists because engineers have had to do this sort of thing at different scales for over a century.

For your reference, I have a math and science background, and have mostly worked in computer programming.  What I am after is a really tiny multirotor (that is extremely stable when flying, which my reading indicates is improved by having more rotors - but I guess that needs extra long arms and larger propellers), to which I can attach multiple sensors to measure different aspects of the natural environment, and which I can use to develop and test swarming flight, specifically with a view toward detecting objects moving toward it, so the copter can take evasive action and avoid a collision.  I'd hazard a guess that a collision between a drone and a bird, or other aircraft, would not do either any good, and so are best avoided (something I'd like to write code to automate - unless that has already been done and deployed in open source software).  Obviously, for such experimentation, the copters I use must be as inexpensive as possible, and yet carry at least multiple proximity sensors.  Unless the US military is funding you, you really do not want to do such experimentation using the commercial kits as they're much too expensive.  If I will crash, I'd rather it be a copter that cost less than \$100 to build than a copter made from a 3DR kit costing five to ten times as much.  But this experimentation really needs something that will remain in the air at least for the better part of an hour, if not longer.  But, I do not yet know if that is possible.

Of course, it will take me a really long time to reach such an ultimate objective (I take the attitude that if it were easy, everyone would be doing it and it thus generally wouldn't be worth doing).  For now, I will be following your example, and making my own clone, as it were, of a Hubsan from the spare parts one can get for it.  Mine, though, will have the upgraded motors one can get for it and will not have the camera.  But, I will do that AFTER I learn how to properly handle a soldering iron (I just bought one, and I think my next tool will be a dremel, followed by a 3D printer that I can rely on to produce quality parts, if such things become available in Canada at a price a working man can afford).  And, I will be watching your blog. among other resources, for further information as you make that available.

Thanks again

Ted

3x blade GF5030 added to much stress for my stock motor on stock V929 coreless motor.  I'm not good at math but i've experienced using various type of prop blades and pitching factor on various motor types to match its endurance since i come from background of 3D plane flying that emphasize matching the right blade for 3D flight.  I use this for V929 and 262 variant multirotor:  http://www.hobbyking.com/hobbyking/store/__28464__GWEP5443_Orange_R...

This prop have slender and flexy tips allow it to cut through wind easily, narrow profile balde to allow increase RPM spin and reduce drag which increase motor efficiency and maneuverability.  Stock prop looks like huge wings which is why most stock owner have problem flying abrupt in the wind and float away by the winds.

The reason for V929 is because it could bind with long range capable Turnigy 9X radio for precision handling and higher radio frequency wattage, V929 board also offer simple 3 axis gyro  for "loose" maneuvering than rigid 6 axis so i could swiftly fly in the wind without the flight control board taking full control over my flight.

I don't have much experience with Scorpion but i'll stay away from Walkera's electronics since our club have piles of them back stores...that include their 350 size.

The reason why i didn't 3D print propellers for small quads because its too small and brittle, the rough 3D printing surface will causes too much friction and drag. 3D printing ABS/PLA ink material also brittle. 3D printing not always a permanent solution for building a proper airframe.  Raw stuff like blocks of foam, carbon rods or sheet of plastics can be a best DIY solution if you are handy with it.  Despite having a 3D printer i still make parts from carved foam and bunch of hot glue. 3D printing parts sometimes can be inefficiently heavy in mass compare to DIY material.

Btw here my 3d printing channel for your reference: http://www.thingiverse.com/3dxl/designs

When building or choosing a quad, just keep "KISS" Keep it Simple Setup. Too much sensors, gyros and complicated FC board just added weight, complexity, maintenance, performance and ruin the joy of flying. The pilot will determine the success of every flight not the hardware itself. By keeping your quad KISS you can start explore from there and grow step by step to advance multirotor flight regardless what size.

I have bunch of autonomous FC boards but my simple cheap quad manage to get the job done manually while my  buddies on DJI phantom 2 struggles hard. :D

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