Paul Williams Posted July 8, 2009 Share Posted July 8, 2009 We spoke of this a few days ago and Tim suggested running from one large capacity battery, I can see your point Tim and I was going down that line when I did some testing. The planes flying weight is around 9lb, so I was trying for 1000 watts, If I run a 6s 2800mh 20c battery it should allow me to pull 56 amps but is that divided between the motors? I have two motors that I think are suitable, in tests they pull 38amps each on at 20 volts but together will they pull 76 amps? That being the case it will exceed the C rate of the battery.I can feel a headache coming on !! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted July 8, 2009 Share Posted July 8, 2009 Unfortunately yes they will. If they pull 38A each at 20V thats circa 760 watts, so in tandem your looking at 1520 Watts....probably too much for your needs. To get a combo of 1kw then each needs only 25A ( 25 X 20 =500 Watts ). Even this is oc course 50A in total, and way too much for a 2800 mahr battery. I would suggest nothing less than about 4000m/ahr TBH. Think of the duration as well as the strain on the battery. Either prop down, reduce the cell count, or change the motors for lower Kv ones. Edited By Timbo - Moderator on 08/07/2009 15:49:33 Quote Link to comment Share on other sites More sharing options...
Bruce Richards Posted July 8, 2009 Share Posted July 8, 2009 Yes you have to add the current draw from both motors. However to get 1000w on 6s you only need to be pulling about 45A total or about 23A per motor. I suggest you use an appropriate prop size to ensure the motors only pull a current in the 20-25A range. Also I would never recommend using a battery up to its full capability. If you were to pull 56A from this battery it is unlikely to last very long or to provide very long flight times. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted July 8, 2009 Share Posted July 8, 2009 Hi Paul If each motor is pulling 38 amps at 20 volts then it is using (38x20) 760 watts so that would be 1520 watts in total. Answer? Either A bigger battery (3700mAh 20c) if your really want 1480 watts of power. Or Reduce the prop size and/or pitch to limit the current to 25 amps on each motor (50 amps/1000 watts total) and a 6s 2800mAh 20c battery should be ok however at this power level you will only get 3 minutes duration. I hope this helps. Edited By Simon Chaddock on 08/07/2009 16:05:37 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted July 8, 2009 Share Posted July 8, 2009 A bit of cross posting but at least we all said the same thing! Quote Link to comment Share on other sites More sharing options...
Paul Williams Posted July 8, 2009 Author Share Posted July 8, 2009 cheers guys, 3 minutes flight time is not acceptable I will rethink. Some thing I found interesting is the pull I tried the setup with a 3 cell ( I cant believe they reconmend this) I managed 260 watts with the size of prop that suits the plane. testing the static thrust it managed 3lb.(950kv motor)Just out of interest I then tested the thrust with 6 cell 760 watts it pulled 4.6lb ? When you consider the wattaged I would have thought 760w would pull stacks more. I always use to measure setups using Thrust but for ease went to watts save bolting motor onto test rig but I wonder now which would be more acurate? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted July 8, 2009 Share Posted July 8, 2009 Watts. Thrust will differ of course with pitch /diameter of prop, and in the air V static. EG: you could fit a larger diameter prop with less pitch and the watts could stay the same but thrust will increase. Quote Link to comment Share on other sites More sharing options...
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