My new MK heavy lift copter project

Discussion in 'Cinestar 8' started by Dave King, Jan 4, 2014.

  1. Dave King

    Dave King Well-Known Member

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    Thanks Chris I see what you are talking about is that number a throttle percentage? Or is it a throttle gas?
     
  2. Chris Fox

    Chris Fox Active Member

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    Hey Dave, just on the phone now, so can't open a gpx file to check, but in the Sticks window it is shown as a percentage on the slider, and I think the number in the data view is the raw stick input, if it is just divide by 250 if that is the case to get the percentage.

    But someone is bound to chime in with right answer any moment now ;)

    Cheers
     
  3. Michael McVay

    Michael McVay Active Member

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    Another perspective is to consider the specs from Tiger on the U5 motor. Using a 6 cell battery, at 65% throttle each motor puts out 3.2 pounds of thrust. That would basically get you to the hovering range if you were about 25 pounds all up weight. At 50% throttle the U5s put out about 2.2 pounds of thrust. You would probably need to be at 75% throttle (or higher) for any climbing - which gets you to 4.2 pounds per motor. I'm sure things like aerodynamics and wind are other items that would need to be added to the equation to be more specific (I'm sure the specs are the best case scenario or ideal conditions), but this might be a way to know if you are in the ballpark on your numbers. Here is the chart from Tiger:

    Also, when using the amp draw from your gpx file as a throttle indicator from the chart below, it would probably put you in the 65-70% average throttle range for your entire flight.

    Going to 16 inch props looks like it would help a little for you.

    U5 Specs.jpg
     
  4. Gary Haynes

    Gary Haynes Administrator
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    Chris is correct. If you view your GPX file in the viewer you can watch the sticks window and there is a numeric readout for the stick as well as the graphic position. Easy to get an approximation from the graphic and then look at the numbers.

    Looking at the GraphView Status Flags window I searched for time when you were not in AH. First 3 seconds, 93-132 seconds were the only times you were in Manual mode. So when you mention flying down the street at 50%, the stick was centered but you were in AH which masks the amount of throttle you are using.

    At 101 seconds the throttle was at a stick value of 73. Full range is 0-254, so center is a direct value of 127 and adding 73 to that you are 200. 200/254=78.7% throttle.

    Your highest throttle position during the 93-132 second period was 97 or 88.1%.

    You might want to try a flight, same setup, totally manual and see the trend in throttle. Rule of thumb seems to be to have a ship that is in the 50-60% range. Past that and it may be that it is overloaded even though your amps/temps are reasonable. And as pointed out by Chris props/hover throttle are affected by temperature (i.e. Density Altitude). Your flight at 35 degrees may have totally different results than an 85+ degree summer day.
     
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  5. Dave King

    Dave King Well-Known Member

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    Thanks Michael this was very helpful. I see the light now. I agree that 16 inch props would help but my copter won't fit in the trunk of my car with 550 mm booms. It barely fits wit the 500's.

    I think what I'm going to do is to wait till I get my actual gimbal and camera functioning and then weigh it compared to the payload that I have simulated. It might actually be less than 10 pounds. I really don't want to switch motors, not becuase of cost but because it seems to be really be a good combination with the flight time. Maybe I can mcGiver it some how by pulling down the back seats.
     
  6. Dave King

    Dave King Well-Known Member

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    Gotcha Gary. Thanks for explaining it makes complete sense.
     
  7. Michael McVay

    Michael McVay Active Member

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    No problem...Take a look at these as alternative motors to carry a heavy rig:

    U7 - 490KV

    They are a bigger motor and will be a little heavier than a U5, but look at the thrust on them:

    Using the same batteries and props you would have 3.5 pounds per motor instead of 2.2 per motor (@ 50% throttle). At 65% you would have 5.3 pounds per motor - giving you over 42 pounds of thrust total. Full throttle is crazy at 9 pounds per motor - but at that rate you are pulling 40 amps per motor as well. You might be able to downsize to 14x8 Graupner props if you had a size limit for your vehicle. The extra pitch makes up for some of the difference in length.

    U7specs.jpg
     
  8. Steve Maller

    Steve Maller UAV Grief Counselor

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    Michael, are you using eCalc to do this? Is there a tutorial on how to use it? I have tried numerous times and I get input errors and it won’t do anything. I’m planning to fly a coax/X8 and I know the results are not reliable that way, but I’d at least like to get a baseline. Thanks!
     
  9. Dave King

    Dave King Well-Known Member

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    HI Michael

    I did compare the motors and I would only switch motors as a last ditch effort because the U7's are not nearly as efficient as the U5's in trust per watt. My biggest problem will be the length of the motor wires with the bigger booms. I don't think they will be long enough. I might need longer pig tails. The U5's are about 32% more efficient (trust/watt) at 50% throttle and 26% more efficient at 65%. That means battery time could go down to 13-14.5 minutes. I'm going to wait and see what my actual payload is going to be and then if I need to switch the booms and the props just do that and keep the back seats open. I also would like to do some testing in warmer weather before doing anything. Most of my work I do I'll be in altitude hold 95% of the time so it might not be a factor. I just want to see how motor current and temps change.
     
  10. Michael McVay

    Michael McVay Active Member

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    @Steve: No, I am just using these spec charts that are on Tiger's website - www.rctigermotor.com

    Each motor has one - although they do not always provide the same battery and prop detail. Then its just a matter of finding the battery and prop info you are after and converting the grams of thrust to pounds.

    I have not determined if the loss of efficiency that people discuss about the coax set up results in loss of thrust, loss of flight time or a combination of both. Either way, once you determine about what your all up weight is you can compare motors, batteries and prop data to pick the best combo to get your lift at 50% throttle.
     
  11. Michael McVay

    Michael McVay Active Member

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    @Dave: I think they are closer to the same efficiency than you think. While they may be quite a bit different at those throttle percentage you have to remember that the thrust they provide at those percentages are also very different. I would look at comparing equivalent amounts of thrust for analyzing efficiency. For example (with 6 cell battery and 15x5 props):

    U5 provides 1490 @ 8.42 g/w (this is 65% throttle)
    U7 provides 1600 @ 7.69 g/w (this is 50% throttle)

    U5 provides 2480 @ 6.60 g/w (this is 100% throttle)
    U7 provides 2400 @ 6.15 g/w (this is 65% throttle)

    25 pounds is basically 1400 grams per motor (x8). Maybe you won't end up that heavy but I would look for a motor, battery and prop combo that gets you that amount of thrust near half throttle.

    I personally like the idea of having power in reserve - especially towards the end of the flight when battery voltages are lower and will be pushing your throttle percentage higher for the same thrust.

    Good luck - anxious to hear how your new Scarlet flies for you. I think we use of Cinestars in similar ways and do a lot of the same type of work.
     
  12. Dave King

    Dave King Well-Known Member

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  13. Steve Maller

    Steve Maller UAV Grief Counselor

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    My gut tells me you're better off with fewer dampeners and a stiffer plate. The problem with 8 dampeners is that you actually want a little bit of flex, but no vibration. 8 of them is going to pretty much lock the gimbal in place. I'd go with 4 and a mix of blue and black, or maybe all black bands. And a thicker plate to reduce the sag.
     
  14. Dave King

    Dave King Well-Known Member

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    Hi Michael

    I see what you are saying. Based on my current draw right now its looking like I need 1600-1700 grams of thrust per motor to hover around 50% throttle. Going with 16 inch props with the U5 motors will give me about 65 percent throttle. In talking with Bill Collydas whos building me the new gimbal its looking like the payload is going to be at least 10 pounds as the gimbal is looking like its going to be 5 pounds. I'm not sure what the red will weigh with the body, lens, and SSID module and battery.
     
  15. Dave King

    Dave King Well-Known Member

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    HI Steve

    I am tending to agree with you. I don't know of a thicker plate but I guess you could always double up the CS plate.
     
  16. Howard Dapp

    Howard Dapp Active Member

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    Michael, we'll be building an upgraded rig soon, very similar to Dave's, could you punch in the Avroto 3520 specs running on a rig with an AUW of 27lbs (12.2kg). I'm very curious about these motors. These motors are supposedly ideal for the heavier copters 26-30lbs

    Avroto 3520:

    Weight approximately 190 grams not including wires.
    Weight with wires 228.4 grams
    Includes accessories to fit 3 hole Carbon Fiber props
    Includes 6mm diameter 4 bolt standard prop adapter
    External Dimensions 42.5mm D x 43mm L
    Stator Dimensions 35mm D x 20mm L
    Stator material .2mm NdFeB sheet
    Internal Shaft diameter 5mm.
    No-load speed: 400 rpm / V
    Ri (Internal Resistance) 58 mΩ
    Io (no load current) 0.3A
    Voltage for Io measurement 10V
    Current capacity 39A/180s
    Max continuos Watts: 1150
    Lipo cell 5s-6s
    Wire length 700mm
    14magnets 12 stator arms 12N 14P
     
  17. Dave King

    Dave King Well-Known Member

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    Michael if I switched motors to the U7 what do you think about running a Canon 7D setup on it? I"m not going to be using the red all the time, if I just got to do a quick job shooting stills it will be with the Canon 7D and old 3 axis gimbal. I was thinking that using the U5's with 16 inch props would be the best combination for both setups. Do you think the U7's would be too large for the 7D setup?
     
  18. Howard Dapp

    Howard Dapp Active Member

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    Looking at the specs it looks like the U7 420kv is very similar to the avroto 3520 400kv
     
  19. Michael McVay

    Michael McVay Active Member

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    @Dave: I think you would be fine. You are just going to be running at a lower throttle percentage to hover because you will not need the RPMs to keep flying like you would with a payload that was 5-7 pounds heavier. If you thought you were at too low of a throttle percentage (in general I think most people agree that faster spinning props provide a more "responsive or agile" feeling to the way the heli reacts to stick inputs) all you would need to do is switch down to 14 inch props on the lighter camera flights. Smaller props would need to spin faster to give you the thrust you need and could probably get you back up in the 40+ throttle percentage for hovering a light camera gimbal.
     
  20. Dave King

    Dave King Well-Known Member

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    Looking at the U7 specs there's a 800 gram thrust difference between 50 and 65%. That seems like that would be a very touch throttle.
     

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