PARKJET MOTOR BENCH TESTING

Discussion in 'Electronics' started by e3_Scott, Jul 6, 2013.

  1. If you are waiting on esc and such order a few of the 6X3 TGS props from HK, I think EMP is the same but just labeled different. I have tried a couple other brands and these ones seem to work the best. Make sure to balance them too.
     
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  2. Nakul

    Nakul Ace Pilot

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    i have 3 Emp 6x3 props i ordered from rctimer, i use them every now and then, will try one of those on the paidiss this weekend. Will also take a note on not making the screws too tight. I was thinking the mount that came with paidiss should be better than the ones we get with other motors considering the weight and build of the motor, i have few spare mounts will choose the best one out of them, you are correct about the 5.5 pitch prop, but also i forgot that 2 days prior i was flying up very high altitude and must have got a bit crazy and my range was gone, so my funjet glided and landed on rooftop of an abandoned house, lol, it was just sitting there nicely, i do remember pulling back the elevator stick so it must have just landed on the belly safely and the prop must have had some damage which might result into unbalanced prop ? anyways not trying that one again, i have 2 others to try for now 5.5x4.3 & 4.75 x 4.75 Apc style. But will also take ur advice and fly with 6x3 emp/Tgs first :) I always balance them as per Scott's advice
     
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  3. e3_Scott

    e3_Scott Top Gun

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    Nakul -

    You are entering some uncharted territory for me as I don't have any experience with that motor nor the smaller diameter/higher pitch props you are talking about using. As you change either the prop diameter or pitch, it is going to affect how many amps your motor is going to pull which is the critical number that can cause problems with the motor, ESC and battery.

    For example, even if you go to a shorter prop like a 4.75, but increase the pitch from 3 to 4.75, it could make the motor work harder as the pitch causes more of a "bite" as the prop spins and I assume since it is a shorter prop it might be able to spin faster than a 6" prop.

    I'm not sure if there are any sort of calculators online that can give you a ball park figure of how many amps you will draw. The safest thing to do is get yourself a wattmeter, then you know exactly what your setup is doing before you toss the plane in the air if you are going to experiment with these very power setups.

    The one I currently use from Hobby King is no longer available. I did see this one at Banggood which looks quite similar.

    Good luck:)

    Cheers,

    Scott
     
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  4. Nightswatch

    Nightswatch Top Gun

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    seems right to me what your saying people sacrifice motor life for performance or vice versa

    i found this not sure if it will help never thought altitude and ambiant temp played also a role so in theory which makes sense although you did these tests @ your latitude and long as well as altitude would be meaning less for me at 8000 feet Above sea level as a example .

    Just like when i purge my boiling point is different then in some place down south or when i had to change jets in my carb as per air mixture when i raced in mission raceway then when i raced in Edmonoton speedway park etc

    My guess is start at manufacturers recomended prop and play with it eventually someone will nail it but the problem is again altitude what works good for you may not work good for me
    http://adamone.rchomepage.com/calc_motor.htm
     
    Last edited: Jan 16, 2017
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  5. e3_Scott

    e3_Scott Top Gun

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    Sorry, are you referring to how altitude and ambient air temperature affect gas/nitro motors or electric motors?

    Yes, there will be a drop in flight performance at 5000 ft versus sea level for an electric motor setup, thinner air does not allow the prop to work as efficiently. A person might need to play around with props to achieve the same amount of thrust as a person at sea level keeping in mind the limitations of their motor/ESC and battery.

    Ambient air temperature either too low or too high is always a concern with the setups most folks use in their park jets, too low and the battery performance can greatly suffer. Too high a temperature and heat dissipation in the motor, ESC and battery (as well as the discharge capabilities of the battery) can all be affected.

    I have found from experience a range of 5-25C (41-77 F) is quite reasonable for overall performance, outside that range I try to either use better throttle management or shorten my flight duration to reduce chances of damage to the battery and other components.

    All bench and flight test data that I have contributed to this thread have been assessed at sea level basically. The elevation of where I live in BC is about 13m/43 ft.

    The most recent spreadsheet of test data I have accumulated on some of the more popular park jet motors is attached.

    Cheers,

    Scott
     

    Attached Files:

    Last edited: Jan 16, 2017
  6. Nightswatch

    Nightswatch Top Gun

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    "Yes, a gas engine makes less power when it has to breathe thinner air, but you don't have a gas engine. Electric motors don't care about the altitude. That's not the problem.

    "Yes, the thin air has less density but about the same viscosity, so the Reynolds numbers of your model are lower, even considering the faster airspeed. This means that your model has more drag. This also means that the wings have less maximum lift coefficient, which further increases the stall speed. That is still not the main problem.

    "The main problem is your propeller. The inflow angle, angle of attack, and the required pitch angle of a propeller blade depend on the true air speed. At your altitude, if the setup of motor, prop and battery isn't changed from the low altitude arrangement, the prop is trying to pump thinner air, and has to do it with less angle of attack! The thin air also hurts the prop's efficiency as well.

    "The motor's RPM is determined mostly by voltage, so the prop really doesn't turn much faster in the thinner air, so there's little compensation from that. And since the prop can't pump as large a mass of air, it doesn't put as much load on the motor, so the motor doesn't draw as much current, so the motor doesn't put as many watts into the prop. It's like trying to fly with only part throttle.

    "You need to increase the pitch of the prop to match the reduced air density and the higher true airspeeds you need for flight in that thin air. Increasing voltage (adding a cell) is another approach; it makes the motor and prop turn faster, which does similar things to increasing pitch, but not as effectively. Because of the non-linear relationship between RPM and power absorbed by a prop, you won't be able to increase RPM enough from extra cells to make up for the change in inflow velocity and the lower air density. Yes, you'll get more watts, but at a "pitch speed" that might be still too slow for the airframe's needs. The best approach is to either twist more pitch into the prop you have, or find a prop with more pitch.

    "Although static power and thrust measurements are a relatively poor measure of prop efficiency, you can get away with using a static watts measurement to judge approximately how much of a change you're making in power due to a prop pitch change (at least it's better than trying to use the "TLAR" method!). When the prop you're using approximately matches the static wattage (on the same batteries) of a prop OF THE SAME DIAMETER that works well at lower altitude, you should be in the ballpark.

    "[At 5500 feet MSL,] the air density (at "standard day" conditions) is only about 87% of the density here at our farm. Your Lite Stik will need to fly about 7% faster than mine (lift is linear with air density, but proportional to the square of the airspeed), so you'll need about that much or a bit more prop pitch, a little over 5" of pitch. Add some more pitch (I'd guess maybe around 5.3" to 5.4" pitch [compared to the stock Lite Stik prop of 4.7 inch pitch]) to take care of the Reynolds number and mass flow effects, and you should be in business."
     
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  7. Nakul

    Nakul Ace Pilot

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    Thanks Scott, time to get a wattmeter haha
     
  8. bimoadiprakoso

    bimoadiprakoso Top Gun

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  9. Nakul

    Nakul Ace Pilot

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    I agree with you Bimo, i just now finished my Gripen project and she flies so so good, just wow and looks like a rocket in the sky (with wings) apart from that i have 3 other working models to fly and i am already planning my next model with no space in the house to store haha. Collected so many motors, batteries, chargers,electronics, spares, and its like i keep ordering something or the other every few weeks, haha. i have a desk for parkjet next to my studio music desk, so when i'm not making music i turn to my parkjet desk and do something there, tv and news watching is 0 lol
     
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  10. Maybe you could write, sing and do a video with the parkjets. ;) It better be professional looking too. :) Can you have it done by next week please?
     
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  11. Better be some cute girls in the video too!
     
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  12.  
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  13. Nightswatch

    Nightswatch Top Gun

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    lol nice flying buddy here is my next 6 second ride i will get going once cash starts flowing again like oil n gas . As you can see i have little more expensive hobby besides RC planes :) 63 vette 63  tubbed.jpg bbig HP.jpg
     
  14. My knees are quivering already, better then s*x. :)
     
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  15. Nightswatch

    Nightswatch Top Gun

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    Raw power just think after you read this sentence i already reached 251 mph in 6.05 seconds :)
     
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  16. My partner built a 41 Pro Street Willy's , BBC, Blown, Nitrous injection, they detuned the engine to under 900 or so hp and that was without the nitrous. What a rush to drive that car, 00000000000000000 THROTTLE LAG. :d
     
  17. Nightswatch

    Nightswatch Top Gun

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    nothing like hearing blown alcohol

     
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  18. Now that's flying. :)
     
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  19. Nakul

    Nakul Ace Pilot

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    oh woooowwwwhooooo!!!
     
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  20. Nakul

    Nakul Ace Pilot

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    i could def add my music to my rc videos :D Once i start recording high quality videos :p
     
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