Flight time/Batteries

Discussion in 'Cinestar 8' started by Charlie Cushing, Aug 30, 2014.

  1. Charlie Cushing

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    Is there a good way to calculate flight times with the new bigger batteries that are coming out?

    I'm flying a Cinestar 8HL with a MOVI 5 and a Canon T3i or Canon 5D for payload.

    I'm currently using 6S 10,000mAh and getting around 10 minutes. I was told if I went to a 16,000 mAh I would only get about 1 minute longer because of the addition of weight. I just saw a 22,000 mAh battery. What type of flight time could I get from that? It weighs 5.4lbs.

    16,000mAh doesn't seem to be worth the extra weight for only one additional minute of flight time, how much more would a 22,000 give me? Thanks!
     
  2. Steve Overstreet

    Steve Overstreet New Member

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    Obviously I have a completely different rig and there is no real way to compare any rig even if they have the same specs but... I have been flying my Octo with a brushless gimble and a Canon camera and a zoom lense and external battery (don't ask why, it's complicated) for an all up weight of around 24lbs. That includes 2 6S 10,000 mah Pulse batteries and getting around 13 or 14 minutes depending on flight aggressiveness. I almost always have 22%left in the batteries when I am done. If I fly an extra battery (so 30,000 mah) I can get up to 16 or 17 minutes of flight. ( I have always run dual batteries for the simple reason of spreading the amp load when flying and found that it places less stress on each battery.

    IMHO, that all being said i would recommend trying to run dual batteries first to give yourself a good idea of flight time and it may be possible to get a little more time with only one larger battery because of the weight savings but it won't be much.
     
  3. Stefan Weissenberg

    Stefan Weissenberg New Member

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    Charlie there is a suitable way to calculate exactly how much flight time you should get, but it is somewhat complicated. Your current copter is spending 10,000 mAh (or 10 Amp.hours) in 10 minutes, meaning an average current draw of 60 Amps at the base weight. When you up the weight, you would need to find out how much current (or power) your copter needs to stay airborne at the increased weight. This will depend on the specific characteristics of your motors and propellers.

    Once you know the current draw of the motors at the higher weights, it is relatively easy to back-calculate the average flight time from the current draw and the battery capacity. FlightTime = Capacity/Current.

    I can provide this calculation for you if you fill out the following data:
    Motor:
    Propeller:
    Weight of Cinestar with your Payload (no batteries):
    Weight of 10,000mAh battery:
    Weight of 16,000mAh battery:
    Weight of 22,000mAh battery: 5.4 lbs
     
  4. Gary Haynes

    Gary Haynes Administrator
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    Charlie have you tried www.ecalc.ch? They have the tools you need to do all sorts of what if calculations.
     
  5. Albert Chang

    Albert Chang Member

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    guys,
    i been flying with a octo for about 3 months and i built it from scratch. I am also obsessed with hang time v.s. battery capacity.
    but after weeks of trying different things (pay loads and battery size, capacities) here is what i have gathered...
    base line: 8 prop 8 axis 17"
    8 motors: 4114/320KV Brushless Motor
    M5 + 70D (16-35L)
    shock damper plate
    fly controller : DJI A2
    6s 5200mAh x 2
    with above setup, we can get up to 7-8 mins of fly time and the rig is set to sit 3rd 5200mAh battery and fly time can be extended to 10-12min.

    not a great deal of hang time, and i kept on trying different things:
    different motor... different battery (up to 3 x 10,000 mAh)... reduce payload...
    ending up nothing is improving
    the increasing of battery capacity is good, but the weight really drag it down...

    after consult with some professional, the solution is to change the original 17" prop to a wopping 20" and further to a 22"
    with this change, 1 major modification is required.
    the prop can not be on the same plane level, meaning i have to either 1) elevate prop 1,3,5,7 or 2) reverse prop 1,3,5,7
    so i choose the reverse prop 1,3,5,7.
    now the setup ending up to be 2,4,6,8 is station at the normal position, and prop 1,3,5,7 is on the reverse side, so the prop don't get in each other's way...

    there are some "overlapping", but after some calculation, the increased lift over power the overlapping drag.

    now the hang time with original 5200 mAh x 2 (10400 mAh) increase from 7-8mins to 10-12+ (we didn't test all the way, safety first ending voltage 22.4v) and with 3 x 5200mAh (15600 mAh) we can get up to 16-18+mins (again ending voltage 22.4v)

    i am only speaking with my own experience, and it may or may not apply...
    but it makes perfect sense...
    if your motor is capable to handle bigger prop, it's the most easiest way to increase hang time with the same battery power.
    the additional lift from the prop will allow motor to spin at less RPM but achieve same amount of lift, therefore to save battery.

    the rule of thumb is i can continue to add more battery to the point of weight v.s. hang time (lift) ratio is just right...
    1 x 5200mAh = 6-7 mins (base line)
    2 x 5200mAh = 12-13 mins (base line x 2)
    3 x 5200mAh = 17-18 mins (base line x 3)
    in theory i can add the 4th battery to test if it gives me additional 6 mins...
    if so, that's what i can do to increase hang time...
    but if not (4 x 5200mAh = ~19min), that indicate it has hit the threshold and i should not do that...

    again, some personal experiences... hope it helps...
     

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