Welcome to PhantomPilots.com

Sign up for a weekly email of the latest drone news & information

either I'm a genius or an idiot...

Discussion in 'Phantom 2 Vision + Help' started by lamiker, May 19, 2015.

  1. lamiker

    Joined:
    Apr 4, 2015
    Messages:
    51
    Likes Received:
    2
    I can't say for sure yet because my stuff to prove it is coming in the mail this week but I'm pretty sure of the following:

    My 2+ will not fly with anything but dji props. Out of the box that is. Got a prop balancer coming and bought a 5\16 drill bit to bore out my amazon fake props but also bought some mid range props and they barely fit too. Never even mind the balancing part

    I'm not exaggerating my phantom stopped being able to hover as soon as i broke my last pair of dji props. If im right there must be many other new pilots like me who calibrate and IMU up the ying yang and their bird still flops around because they bought cheaper props

    I knew I should use dji props but thought it was only to improve performance save wear and tear etc. I humbly reccomend if your bird starts acting strangely consider what props you put on after your last crash
     
  2. J Dot

    Joined:
    Apr 10, 2014
    Messages:
    1,761
    Likes Received:
    900
    Location:
    Sarasota, FL. USA!
    I had same issue,
    Bought a set of aftermarket ( orange props ) eBay, looked great installed them, phantom barely flew, it was all over the place, I gave it juice ( full throttle ) it went up like it was carrying a load? WTH? Changed props back to dji white ones, phantom was back to its snappy self?
    So now I use the Orange ( crap ) props for display ONLY! I only buy DJI props now!

    J Dot
     
  3. lamiker

    Joined:
    Apr 4, 2015
    Messages:
    51
    Likes Received:
    2
    Alright ladies i got my stuff in the mail today!!!

    I wish someone had told me what i ascertained for myself today...

    Namely that there are (roughly) 3 types of props available and understanding their strengths and weaknesses is crucial for all of us.

    1= DJI props - they fit right out of the box and do not need to be bored with a 5/16 drill bit to get them to self tighten. They are made of thicker plastic and since i don't have a prop balancer yet i cannot say for sure but based on how my phantom behaves they seem moderately well balanced (can hover with gps lock) but insanely expensive for a guy like me who busts a few each week

    2= aftermarket props that you buy at places like dronefly and heliopal - they almost fit right out of the box but do need to get bored a little bit with a 5/16 drill bit to get them to self tighten properly. They are made of slightly thinner plastic and since i don't have a prop balancer yet i cannot say for sure but based on how my phantom behaves they seem moderately unbalanced (cannot hover with gps lock but controllable) but still too expensive for a guy like me who busts a few each week

    3= amazon counterfeit props with the 0-xoxo written on the blade - they do not fight right out of the box and require quite a bit of drilling with a 5/16 drill bit just to get them to self tighten properly. They are made of even thinner plastic and since i don't have a prop balancer yet i cannot say for sure but based on how my phantom behaves they seem wickedly unbalanced (cannot hover with gps lock and require a crash landing) but cheap as all hell for a guy like me who busts a few each week

    i thought they were all interchangeable more or less but the only ones that work right out of the box are the dji ones. Once i get my prop balancer i am going to see if i can get my bird to hover with option 2 or 3 because like i said i'm the kinda guy who busts a few each week and so $$$ is the most important consideration

    The REAL reason that i'm writing this is just in case somebody reads this and realizes that there is nothing wrong with THEIR bird often its just the props that make it unstable. Before telling somebody to check their compass and imu after a crash they should be told check your props -did they fit on nice and smooth? Did you balance them? Are they of good quality or do they need some TLC to work right?
     
  4. yorlik

    Joined:
    Feb 9, 2015
    Messages:
    547
    Likes Received:
    91
    What exactly does this mean? I do not understand it at all.

    Either they have the proper thread or not. All props I ever tried turn on about 4 turns and of course stop. What are you drilling?

    I broke all my dji props first few days after getting it trying to learn to CSC on ground. I have since gone thru a couple more ebay 4pair for $2.00 types.

    ALL mine are junk 9443(?) old style dirt cheap and there is no instability at all while flying!
     
  5. J Dot

    Joined:
    Apr 10, 2014
    Messages:
    1,761
    Likes Received:
    900
    Location:
    Sarasota, FL. USA!
    My aftermarket clockwise props fit easily on the motor shafts, but BOTH CCW props would not go onto the motor posts ( they are self tightening, ) but the whole is slightly smaller than stock dji motor shaft, I had to drill the plastic a bit ( right before metal threaded insert ) just a bit, but then they went on smoothly! But they turned out to be crap, slow accent, slow recovery from quick descent, all around poor performance, put stockers back on. ZOOM-ZOOM!

    J Dot
     
  6. cjmwales

    Joined:
    Apr 30, 2015
    Messages:
    157
    Likes Received:
    51
    Location:
    Cardiff, Wales. UK
    I don't understand why anyone would risk non OEM propellors on such an expensive machine!

    They're precisely manufactured with a known RPM/thrust performance curve that's been tuned to suit the powerband of the motors & the output of the ESCs. It's amazing that the phantom manages to get off the ground with those dodgy props. You might be paying a bit extra, but that R&D costs a few quid :)

    Edit: If you're interested in the maths:

    http://www.electricrcaircraftguy.co...-thrust-equation-background.html#.VV46dpNViko
     
    dtitus6297, Tilak and garamouni like this.
  7. robsquad

    Joined:
    Dec 4, 2014
    Messages:
    962
    Likes Received:
    422
    Location:
    Wolverhampton, UK
    what he said
     
    dtitus6297 and IflyinWY like this.
  8. yorlik

    Joined:
    Feb 9, 2015
    Messages:
    547
    Likes Received:
    91
    nonsense!!! totally!!!

    It is NOT fair to relate thrust to our dji drones operation like that!!! WRONG WRONG WRONG!!

    You are comparing apples and oranges!

    This is identical to saying "I will make my car go 72.4mph but I am going to change my engine from the one I normally use rated 215hp to one rated 272hp." Guess what? Your foot will push DIFFERENTLY on the gas peddle AS REQUIRED to make your car go 72.4mph ANYWAY! It is all based on FEEDBACK.

    Yes, your link shows how thrust is related to physical dimensions of the prop. That post is 100% correct in his calcs, building from F=ma up. All is correct.

    BUT you are trying to say that since thrust is different with different airfoils - sure correct - but that has NOTHING to do with our how our dji phantoms ACTUALLY USE THEM!!!

    We have FOUR completely INDEPENDENT controllers called ESC units. That stands for Electrical Speed Controllers. they get a command from the MCU main cpu controller. THAT command is as required to do what the MCU demands!!!!

    So if the props give more or less thrust than your OEM dji props IT DOES NOT MATTER! If the commanded speed for each independent ESC and motor does not give the response the MCU requires, THEN IT WILL SIMPLY CHANGE ITS COMMAND TO MAKE IT SO!

    This means you can even use cheap 9443 props on 3 and 9450 dji prop on the 4rth and it still should operate identical!

    We can list all the aerodynamic equations we want; bottom line is the MCU will give the command required for the required speed to the ESC that makes the thrust required on each independent motor.

    So again, slightly less thrust of either off brand or even on brand dji 9443 vs 9450 props MAKE NO DIFFERENCE. The MCU will simply speed them up or slow them down as required to do what is required.
     
    cjmwales likes this.
  9. cjmwales

    Joined:
    Apr 30, 2015
    Messages:
    157
    Likes Received:
    51
    Location:
    Cardiff, Wales. UK
    So... if the motors are designed to operate within a certain RPM range - down to bearing specifications, balancing etc - and using non OEM props cause these motors to operate beyond design parameters, there's nothing wrong with that? And what about the ESCs running hotter due to increased current draw to support the higher revs?

    I agree that the MCU will compensate for mismatched props, but why would you want to put additional demand on the system for no real benefit? I'm with the fresh prince: If it ain't broke, don't try to fix it; some clever people at DJI have already prototyped all these components to come up with an optimum combination that covers most flight conditions.

    I'm happy to be proved wrong though. it's not my money on the line :D
     
  10. yorlik

    Joined:
    Feb 9, 2015
    Messages:
    547
    Likes Received:
    91
    Hey, don't get me wrong! If either of what you said were true, then I sure would not go there either!

    1) Are you suggesting that the cheap clone props are sooooooo different in airfoil design that they will run at speeds OUTSIDE the ESC design limits? I truly doubt that. Look at them. Try to calculate the thrust they will provide compared to the dji ones per the calculations you find on the internet. I really think you will be hard pressed to find any significant thrust difference. Physics is physics; very similarly copied shape will give very similar thrust. Slightly different, sure, but SIGNIFICANTLY different? Highly unlikely. Even dji has responded in print that their 9443 props are just as acceptable to our P2V+ as the supplied higher thrust 9450 ones.

    2) This is not how servo motors work. CURRENT equals load and VOLTS equals speed (with a few differences on volts - if you REALLY care, V=Kb*N+IR). What makes a motor hot? CURRENT. period. I^2R. so if the current is higher, yep, you got it right, the motor will heat up more. But wait one..... what is current? I= T/Kt.... the current is 100% related to THRUST. If your phantom does exactly the same moves with the cheap props as the expensive props, IT WILL DO THE SAME WORK; Hence, it will pull EXACTLY the same current, irregardless of speed. Speed does not enter the equation at all. So the HEAT in the motor will be IDENTICAL. So it is totally wrong to assume the heat in the motor will be more with the cheap props.

    3) There is NO additional DEMAND on the system to use different props. The MCU will continue to provide minute adjustment demands to each ESC as required no matter what props are used. No difference there. But why say "no real benefit?" I pick up pennys off the street when I see them. I retired early. I see plenty of benefit at least to ME to save a few bucks along the way if there is no down side as in this case. Granted, you CAN get less balanced props with the cheap ones, but it does not cost me money to balance them better if required. I see need to balance as the ONLY down side of cheap props.
     
    #10 yorlik, May 21, 2015
    Last edited: May 21, 2015
  11. IflyinWY

    Joined:
    Sep 12, 2014
    Messages:
    3,470
    Likes Received:
    939
    Location:
    Where the deer and the antelope play
    I just performed a very crude experiment using my FC40 in atti mode at about 5,000 ft MSL @ 64 Fahrenheit. I put a 1600 gram weight on a scale and attached a wire around the arm.

    I took a perfectly good 9450 prop and was able to lift 327 grams.
    I cut the tips off another 9450 prop, bringing the diameter down to 6.25", to exaggerate the reduction in performance, and was able to lift 57 grams.

    My point is, given a lifting capacity well below normal, the Phantom will compensate for the reduced lift on one, (or more motors with crap props), by reducing the output on the other motors. The result will be a slower rate of climb and reduced overall performance.

    All it would take would be 1 low performance prop to severely handicap the Phantom. The other 3 motors would have reduced output just to keep up with the low performer.

    I too wonder if I am a genius or an idiot... :p
     
    Tilak, yorlik, cjmwales and 1 other person like this.
  12. yorlik

    Joined:
    Feb 9, 2015
    Messages:
    547
    Likes Received:
    91
    (edited to add thrust calculator too)

    Great test Ifly! very informative! I would call it genius!

    Can you do it again with cheap prop vs dji prop? We have apples and oranges again cuz you did not use a SLIGHTLY different prop - you cut off a majority of its lift capability cutting it from 9.5" dia to 6.25" dia. Not a fair comparison, although the results are great to see!

    It is cool to see that with a prop surely outside the design criteria of the p2v+ still performed so well.

    From designing and building my own 10' diameter windmill and connecting to the electric grid 35 years ago, I remembered that thrust and stuff went up by the CUBE or more of diameter of the blades. So I just checked and found:

    These equations were known as the Abbott equations.
    Power (WATTS)=P(in.) X D(in.)^4 X RPM^3 X 5.33 X 10^-15
    Thrust (oz.)=P(in.) X D(in.)^3 X RPM^2 X 10^-10

    So assuming the 9.5" dia blades produced X# thrust, then the 6.25" one only could produce 6.25^3 / 9.5^3 = 28% of the thrust! Not fair to compare THAT to a cheap prop that may be 9.4^3 /9.5^3 = 97% still!

    To try to verify the Abbott equations, I found some online prop calculators... one:
    http://members.jcom.home.ne.jp/4223215501/staticthrust.htm
    seems to suggest only 18% thrust left with the 6.25 dia. I used my best guesses of values: 9.5" dia, 9500rpm, .7" pitch, 12v total voltage. seems to match up with our hover in place current draws. then I just changed 9.5 to 6.25 to see reduction in thrust....

    And the cheap airfoil may not have same exact twist for the pitch and reduce thrust too, but that term is only linear so it would not make much difference.

    I was not considering the cheap props to be so radically different than the dji ones when I concluded they wouldn't make a hill of beans difference in anything. Obviously radically different ones force the p2v+ to reduce performance of the other props to match this lesser one since it is outside the design capability, just as cjmwales alluded.

    I still think their only downside for the savings is potential balance and cheapness in materials that may cause them to physically break. The cheap ones I have bought on ebay have exhibited neither of those issues so far for me.
     
    #12 yorlik, May 22, 2015
    Last edited: May 22, 2015
  13. IflyinWY

    Joined:
    Sep 12, 2014
    Messages:
    3,470
    Likes Received:
    939
    Location:
    Where the deer and the antelope play
    You're making my head spin again yorlik... :confused:
    I got the part about doing it with whole crap props. I don't have any 9450 knock-offs.

    I did find a set of 9443s, DJI and 9443 XOXO props, so I believe this will be the comparison to consider.
    Last nights battery was pretty low, like I said, a crude test.
    This one should be more accurate.

    5,000 ft MSL, 63 degrees Fahrenheit, ThunderPower 2700 mAh 25C, 12.6 v @ start, 12.3v at end.
    The number shown is grams of lift.

    DJI 9443 with a busted tip (see pic) = 450 DJI = :D
    XOXO 9443 new, never used = 380
    XOXO = KRAP :mad:

    While I was at it I put on a good condition 8050 prop and got 370 grams of lift.
    I also put on my DJI 9450 props and got this:
    New condition = 540
    Nicked a little from one tip over, very minor = 530



    DJI 9443 busted TIP.jpg
     
  14. yorlik

    Joined:
    Feb 9, 2015
    Messages:
    547
    Likes Received:
    91
    Ifly, you have proved the math is close! Great job! Thank you for doing the tests!

    So what do we now know? You proved the cheap props loose some 380/450= 15 percent thrust. Apples to apples. Great!

    So question is: Is $1 ea vs $5 each savings worth this 15% less thrust?

    I think a similar but different example may answer that best. How about this?

    the cheap props may provide 15% less maximum thrust than the dji ones. Say I have a corvette with a 450#-ft max motor. By using cheap gas instead of premium, I only get 380#-ft max thrust. Is it worth the savings? When I want to floor it and lay rubber with 450hp, it is way cool. When I floor it and only get 380hp, I STILL lay more rubber than I can handle! So did I do bad using cheap fuel? I get same rush from either.

    Said another way, how often do we go full 100% thrust or HP? Seems most of my flying time is trying to be 'nice' to my battery and pv2+, so I seldom 'floor it.' If I did, I would get 450# thrust and rise 15% faster than if I had saved all that money and used the cheaper 380# thrust props. Would I even notice? I doubt it.

    So even though 'better props' give 15% more thrust, and longer 9450 props give even more thrust, I suggest it does not really effect our day to day performance.
     
    IflyinWY likes this.
  15. IflyinWY

    Joined:
    Sep 12, 2014
    Messages:
    3,470
    Likes Received:
    939
    Location:
    Where the deer and the antelope play
    Ah, right you are, but, in everyday flying, your motors have to work that much harder to produce a given amount of lift. So, now where are the numbers?

    I do agree that some group of designers and engineers have come up with better numbers than me for matching props with motors. My issue is that they did it at or near Sea Level, not flying around 1 to 1.5 miles up.

    Anyway, we (or at least I) know a bit more today than yesterday... :D
     
  16. kirk2579

    Joined:
    Jan 13, 2015
    Messages:
    1,350
    Likes Received:
    264
    Location:
    Girard. ohio
    interesting thread, I found out early on the knockoffs needed balanced and it was easier to buy dji .

    I did do the opposite of the 9450 on the P2v1 I have,

    I like to fly in evening and in neighborhood but the noise is really irritating to some.

    I had a set of props from a P1.1.1 8' self lock style. I use them now when flying at home to keep the hornet nest buzz to a low roar.

    The phantom flies fine for what I do and I don't notice any real difference other than it was quieter!!

    I usually only run the battery to 10 minutes or so I don't know if that affects operational time etc.
     
    IflyinWY likes this.
  17. IflyinWY

    Joined:
    Sep 12, 2014
    Messages:
    3,470
    Likes Received:
    939
    Location:
    Where the deer and the antelope play
    Alrighty then, now we're getting somewhere.
    Kirk, you are the first person I know of to go backwards on the props. Do I understand you correctly? You put 8050 props on a bird wanting 9450 props, and it works just fine, and makes less noise.

    I'm going to have to do some more testing, with my camera rolling.
    Thanks for chiming in... :D:D:D
     
  18. yorlik

    Joined:
    Feb 9, 2015
    Messages:
    547
    Likes Received:
    91
    Hey wait! Use cheapskates went backwards too! Not as far, but the cheap props on ebay are shorter, less thrust 9443's! Can't say it is any quieter though. Neat idea on 8050's!

    This has been a real learning experience for me too! I assumed from everyone's comments that our p2v3 motors all ran 9-10,000rpm! I think it turns out they don't even get much above 7500rpm! Standby for next post with actual speeds and thrusts we use daily!
     
  19. kirk2579

    Joined:
    Jan 13, 2015
    Messages:
    1,350
    Likes Received:
    264
    Location:
    Girard. ohio

    P2 V1 with a cgo-1 camera under it. took off the 9443 and used the phantom 1.1.1 8" props.

    I have been flying with them all weekend at home.

    My next door neighbor still has a phantom1.1.1 and when he flew his a couple weeks ago I was amazed how much less buzzing. So I put the same 8" props on my P2v1 (non vision) and been using them since around home.

    they are cheap too!
     
  20. yorlik

    Joined:
    Feb 9, 2015
    Messages:
    547
    Likes Received:
    91
    Facts:

    - P2V3 weighs 1242grams=44oz: so to hover each motor must provide 11oz thrust.
    - 9450 props produce 100g more than 9443 per ratings, for 660grams=23oz
    - so if 9450 can produce 2x weight, they provide 1G (32ft/sec^2) vertical acceleration to max speed rating of 6m/sec (20ft/sec)

    Using an online prop thrust calculator, we can predict what speed is required to make our p2v+ hover and what speed is required to produce max thrust, and what current & power is required for each - ultimately to compare power/battery-life/current for different props.

    Using http://members.jcom.home.ne.jp/4223215501/staticthrust.htm

    I put in 9450 prop specs for max thrust (A):
    upload_2015-5-25_9-21-21.png


    I then put in my cheap eBay 9443 prop specs AT THE SAME SPEED (B):
    upload_2015-5-25_9-22-22.png

    I then said, well what speed is required to produce the SAME max thrust (C):
    upload_2015-5-25_9-22-56.png

    Then I said, well what happens during hover with 9450 props (D):
    upload_2015-5-25_9-23-25.png

    Now to put the current and power requirements for each in a chart:

    upload_2015-5-25_9-20-23.png


    And then potential conclusions based on all this:

    1) I learned a lot about props and thrust! I have no clue what significance Pitch speed is, but it appears important to hobby airplane prop designers.

    2) I believe P2V+ v3 has about 7500rpm max motor speed - that is why cheap props produce less thrust, even though they should be capable of producing more if allowed to go faster. I think the left stick at max up position runs motors at this max 7500rpm.

    2) I believe this proves what I have said previously: cheapo props that produce less thrust do not use significantly more power or require more current; they just produce a tad less maximum thrust is all. I am hard pressed in GPS or ATTI mode to be able to tell there is 19oz max thrust vs 23oz with the 9450 dji OEM props.

    3) In fact, it appears the lower thrust props would indeed be quieter and perhaps give slightly more fly time due to the less work they are doing at lower power and current.
     

    Attached Files:

    volito likes this.