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1 gram added weight = 1.2 seconds lost flight time

Discussion in 'General Discussion' started by Peter Patricelli, Oct 1, 2013.

  1. Peter Patricelli

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    The point of the exercise is to quantify the effect of additional weight on flight times for the stock Phantom, to determine whether the effect on flight time is linear or more complex, and if linear, to determine a ballpark predictive figure of reduction of flight time versus added weight.

    The craft: a stock Phantom (with square LED electrically unconnected stuck on the door), nothing attached to camera holder slot, stock props (balanced), stock battery (SAME FOR EACH FLIGHT), full charge on the stock charger, stock TX, continuous hover at 3-4 feet in GPS/Atti mode.

    The end points: 1st warning level determined by the beginning of flashing red lights. 2nd point was, after a period when progressively more throttle was needed to keep the craft hovering just off the ground, the sudden, dramatic complete power failure when the craft would drop precipitously. Had it not been only inches off the ground...it would have crashed.

    1st flight, stock, no additional weight. Weight = 0 1st point 10' 30” 2nd point 13 '45”

    2nd flight Hero2 in protective case, bolt, nut W = 185.1 gm 1st 6' 20” 2nd 10' 45”

    3rd flight above plus additional weight W = 364.4 gm 1st 3' 26” 2nd 8' 40”


    [​IMG]

    The first flight, a bare, stock Phantom, is on the ZERO weight line

    The second flight represents a mid-range load on an unmodified craft.

    The third flight represents a near max recommended load for a stock Phantom.

    The relationships appear to be reasonably linear, meaning that generalized observations and predictions are reasonably accurate throughout the loading range at least to near 400 grams. Given that most of the forces (gravity, primarily) are constant, perhaps that should NOT be surprising. As the load increases, the first warning, based on a set level of voltage drop, occurs progressively earlier. For reasons that are less apparent, final complete power failure does not occur at the same rate as the 1st warning point, giving, with heavier loading, a progressively drawn out '”gray zone” when the warning lights are flashing, the craft is wanting to descend and it is taking progressively more throttle to keep it off the ground.

    Whereas in the first and second flights the 2nd endpont, complete power failure, was sudden and precipitous, on the third, most heavily loaded flight, THAT endpoint was not not reached. Instead, the slow, progressive loss of power at full throttle made it eventually impossible to keep the craft off the floor. Had the craft been at altitude, it would have been descending even at full throttle, and probably would soon have lost power precipitously. But in this case, once the craft was on the ground and I could not lift off....I simply shut it down.

    This observation is completely consistent with that of the poster who loaded his craft down with 1.5#. The craft could remain airborne for only 2 minutes. He then unhooked the weight and flew the UN-weighted craft for another 8 minutes.

    So....to tweak the graph, I plotted TIME REDUCTION from unweighted flight time (in seconds) by WEIGHT ADDED (in grams).

    [​IMG]


    The first flight is at the 0 weight, 0 time reduction junction. Displayed this way the data allows me to calculate the figure I hoped for. Assuming a linear or near-linear relationship, from the first addition to a stock, bare craft to the final nut or bolt on a fully tricked out (but otherwise stock) craft, each GRAM of weight is going to cost me 1.2 seconds to first warning light.

    And, while I might KNOW that I have three or four minutes on a fully loaded craft after the first warning lights flash before I lose the ability to hover, the quantity of expensive gear to be lost and the uncertainties involved dictate that I will bring it craft down and back quickly once the warning sequence begins.

    I have just received 2 new sets of props, 9” 2 blades and a set of 3 blades. Since the efficiency of these props will be different, but constant, I expect flight times to change, hopefully for the better. Whether those props efficiency under progressive loading will give the exact same linear slope as the stock props....upholding the 1 gram = 1.2 seconds reduced flight time of the stock props remains to be seen. But I predict it will be close.

    The 1 gram = 1.2 seconds reduced flight time figure for any addition above stock weight is a relentless, cumulative burden. If I want a gimbal and one model is $300 and weighs 200 g (WITHOUT camera) that is necessarily going to reduce each and every flight by 3' 20”. Another popular gimbal weighs 180 g at $100 less, and the most expensive claims to weigh only 180g WITH GoPro 3 attached. Those differences in weight create significant to enormous losses or savings in flight time.....each and every flight.

    The GoPro 2 weighs 100 g, the GoPro 3 only 74 g. That difference alone is almost 31 seconds per flight. The GoPro 3+, just announced this morning, weighs 59 g. All the better bells and whistles aside, that represents 50 seconds longer flight over the GoPro 2. I only have the GoPro 2. Where do I want to put my money for the next addition....and what will be the gains...and the losses.

    Having a solid figure for weight = lost flight time allows me to consider that further dimension in pros and cons for every possible alteration and $ spent.
     
  2. rilot

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    It's not a linear relationship though.
    From your graphs, with 525g added I would expect the light to come on immediately after takeoff.

    How many data points did you take? I can only see 2
     
  3. martcerv

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    From the GoPro website Gopro 3 black +

    Not sure where you got 59g, only the housing is lighter the camera is pretty much the same weight as the hero 3 black.
     
  4. syotr

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    One other thing to consider. If you are adding powered items such as a gimbal, OSD or FPV transmitter, the power required by these items will also reduce flight time.
     
  5. marcus_canada

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    Way too many variables to count flight times down to the second and to issue results based on a per gram basis.

    What flight conditions are you using as reference? Unless you're in a windless environment with constant temperature you simply cannot issue results with this amount of resolution, especially from 2 or 3 flights. Add even a slight wind and the results are muddied, especially if you're in GPS mode. Start flying circuits and the results are pretty much nullified entirely.

    Is precipitous the current forum word-of-the-month?
     
  6. Roadkilt

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    Well, besides the details of camera weight and other variables, the concept is empirical and we observe it on every flight with a load. Thanks for doing the work, if anything it demonstrates how significantly reduced flight times become with even "modest" loads in the 100 gram range. I'm surprised to see so little effort to reduce weight in the quad designs and accessories, more open arms, more carbon, less lengths of wire, less cheap plastic, less solder. When you see the equipment in the space program where every kg costs $10k to lift, you see those weight saving designs. As much as I like the aeroxcraft gimbal it looks like a box of meccano parts with little effort to minimize weight. Next project: external mounted bigger battery increasing flight times versus weight penalty and handling like a pig.
     
  7. martcerv

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    Minimizing weight should be a priority but not at the cost of functionality. Carbon fiber is over used quite a bit and it has a nasty property of not being very good at letting 2.4 or 5.8ghz radio signals to transmit through it.

    There are some carbon mods that are heavier then stock plastic parts such as some landing gear I have seen at 200g in carbon and 40g I think for stock plastic landing gear.

    I see very little point in such mods as plastic has less effect on the radio signals and if the carbon parts are also heavier why would you want to use it.

    Seeing I can fly a 1.3kg setup for 8 minutes and 1.15kg setup for 10 minutes and I cant remember the last time I just hovered around. Then there are more variables to consider for longer flight times then just weight but also the lift your props give. Less lift will use more battery as you get heavier due to needing higher rpm from the motors, getting heavier and not dealing with the lack of lift will also make it fly like a pig while getting much shorter flight times.
     
  8. Peter Patricelli

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    rilot,

    There are three data points, the first being the unweighted, W=0, the second at W=185.1 g, the third at W=364.4 g. Three data points is not exactly a statistical cornucopia. This is a work in progress. But my and others expressed observations are that flight times are really quite consistent and predictable. It would take 5-10 flights at each weight to establish a range of deviaton, standard deviation, etc....IF.....one were trying for scientific credibility. But all that effort would only establish what MY Phantom, MY battery, MY props, etc. would do. It is NOT worth testing 10 phantoms, 10 batteries, etc.. This is a ballpark observation and gives a ballpark figure, but one which seems well within others observations as I have read them. This just puts out a more focused and specific way of thinking about the issue.

    And no, the graph is not exactly linear. No plot ever it. But within what I predict the variation from run to run would be, a linear plot TO THE LAST DATA POINT is well within and probably fits the situation best. I doubt anyone cares if it were established that, between 0 and 100 g the loss is 1.22 seconds/g and between 300 and 400 g it is 1.89 sec....or something like that. I chose 364.4 g for the last plot because the manufacturer recommends NO loading a (stock) Phantom beyond 2 KG. It would not surprise me in the least if the behavior beyond 400 g becomes non-linear. But for me, given how short the flight time is with a stock setup (props), I am not going beyond that (or even close to that) anyway.

    I got two new prop sets last night. With the 9" CF 2 blades a flight at 365.4 gms gave 4' 50" to first warning and 9' 40" to power failure. If and as heavily loaded flight times improve, then it might be interesting to see how it varies out to, say, loads giving 3 minute flights. But again, whether the figure is 1 second or 1.2 second I don't think is going to change my thinking about this issue. The value is in giving the weight/time dimension some reasonable, simple, tangible effect.

    Martcerv,
    You are correct. I got the announcement in an email this morning and saw "20%" reduction in weight" in two places and assumed it was in camera weight, not CASE weight.

    For the other criticisms that are coming in as I type....read the post completely. In the title I actually tried to specify STOCK PHANTOM...but there was not enough typing space. The one commonality is that we ALL start with a stock Phantom, stock prop, etc.., and start modifying from there. A hover-only flight 3-4 feet off the ground is as reproducible as I can come up with. Does anyone think more complex maneuvering is going to seriously lengthen flight time? For the record, I was at 400 feet elevation and 55 degrees and within my garage, relatively windless. Again about as reproducible as I can get. I never claimed the figure covered ALL Phantoms, all batteries, all set ups, etc.. I also never claimed the figure was scientifically carved in stone. See above. But it IS a figure that at least has SOME basis in actual observation behind it...for lack of ANY OTHER published figure that actually tries to give a ballpark prediction of what each and every gram addition to your aircraft will do to flight time. As a newbie looking at all the variations within the options for upgrading, etc....I have already made $ mistakes.....which I would not have made had I SOMETHING to guide my thinking on this.

    I did a 364.4 g flight with 9" CF props this AM....4' 50" to first warning, 9' 40" to power failure. Different props will generate different graphs....but the SLOPE, gram = seconds lost flight may or may not be different. We won't know until someone actually does it and reports it....will we.

    Work in progress. Ballpark. Calls attention to and gives a starting point for beginners thinking about options.

    If someone wants to knock themselves out to prove that the figure is actually, precisely 1.17369 seconds....I will be delighted.

    Peter Patricelli
     
  9. FrankB

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    Well, first- thank you for taking the time to do this; very useful and informative!

    What this all tells me is that with all the variables involved, it is much better to get some little transmitter that tells you exactly what the battery voltage on the Phantom is, and sounds a warning when it gets low.

    I gather that the new Phantom Vision will have that.
     
  10. stargazer75

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    I disagree. In order to determine how weight affects flight time he needs to control as much of the other variables as possible. It sounds like he's done that. I think he needs a lot more data points to give us more meaningful data. It sounds like hes aware of that and is doing that. If you'd like to see how wind, or temperature, etc. affects flight time, that would be great work to do, but would be different experiments. Obviously being limited to one phantom, one battery etc, isn't good from a scientific standpoint, but the data would still be useful. If others are interested they could repeat his experiments with their phantoms and the data would be even more meaningful.
     
  11. BruceTS

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    Other factors not accounted for, motor consistency, battery quality, the nut behind the stick flying the quad.....etc.

    Sorry I personally think it's a waste of time trying to quantify any number related to weight vs flight time. You could take 5 Phantom owners and do the exact same test, your results will differ greatly. The moment you start changes, all those numbers get skewed. the type of props, motor, balancing and care, then there's the lipo batteries, as time passes they diminish in strength, how much determines on how they were cared for.

    The reason for the current light system, makes it simple to determine when to end your flight, that is enough for the average person to understand. Just go out, fly and enjoy your new hobby, run a timer, keep track a record of you flights, this gives you a good indication when you need to trash your battery.

    As for my flights, they can range from 5 to 12 minutes, it all depends on how aggressive I am.
     
  12. Gizmo3000

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    I'd say that's a pretty good ballpark figure.
    my gimbal, GoPro and FPV weigh in at around 300g or so, that would come to a loss of around 6 minutes, and I get anywhere between 5 and 6 minutes of flying time.

    So while yes, there are indeed a lot of additional variables to consider - flying style, wind conditions and additional power drain, that's probably a solid figure to throw out at newbies who are getting into it and wondering why they're getting such short flight times.
     
  13. rfernandez

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    I think that all these quantum mathematics is all fine for and dandy for dead weight, But what no one has taken into account is, if a gimbal is installed how much milliamps the brushless motors consume placing additional load on the battery.
     
  14. OI Photography

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    I haven't tested a Zenmuse, but with my Arris2000 added in the current draw only seemed to increase by about .3A, so it's not a significant amount at all. With that and all the other electronics combined, including vTx (and no motors), the draw stayed below 2A total. Running the motors can draw over 20A easily, so it's still a fraction of that.
     
  15. ElGuano

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    Since this was posted last year, 1sec/gram remains a good "rule of thumb" when adding weight to a Phantom, within standard payload limits.

    Typical accessory power (gimbal, VTX, OSD, LEDs) is minuscule compared to weight, cumulatively the power drain from that 300g of additional components may add up to 30 seconds less of a standard 10-minute flight setup (while the extra weight accounts for a ~5-minute drop).