|
wlfk -> 2S option?! (9/23/2007 3:47:29 AM)
|
I've been considering something that may seem a bit radical: using a 2s setup on my T-rex.
II
which fits well under the current canopy and would be about the right weight, unlike any 3s configurations I can make up.
I'm currently using 3s 2100mAh 20C li-pos that weigh 180g for a total of 3x2200x3.6v = 22680mAhV.
2S 2400mAh 30C A123 would weigh about 150g and would have a total of 2x2400x3.3v = 15840 mAhV - 0.7x the energy of my current setup with a 30g weight saving.
30C at 2s and 20C at 3s = the same power output for both systems.
At the moment I'm getting 2400 rpm with a 13t pinion and a 2800kv motor. If I used a 15t pinion and a 3700kv motor, I figure I should get much the same headspeed. Perhaps I should move up to a 4000kV motor to get a bit more headway if needed.
I would need to use a very low dropout BEC - perhaps just 2 diodes to limit the max. voltage (7.2v) to the receiver/servos by about a volt, with a bypass transistor activated when the output voltage went below 5V(min would be 4.8v). I could rig this with something homebuilt. The ESC would need to be 45A and therefore weigh a few grams more than normal.
Does anybody think this would be feasible? I'm guessing the drawback would likely be in the motor - I presume a suitable low voltage high current motor would be heavier than my 400lf?
My main concern is basically to use A123 batteries without losing too much in terms of performance. Given the larger ESC that would be required, I don't expect to make any weight savings, but I don't mind the shorter flight times. I don't have anywhere safe to charge/store Li-Po batteries and this makes me a bit queasy about them.
K
|
|
|
|
