As the use of LiPo batteries in the 1/12th scale class has been gaining ground and sanctioning bodies and manufacturers have begun standardizing cell formats, BMI Racing have finally developed a new version of the DB12RR for this class. The LiPo edition features a lower chassis that has been optimized to locate and retain a 4000mah 3.7v LiPo pack. The chassis has had the slot dimensions adjusted to match the pack as well as pocketing of the chassis to lower the pack for optimum center of gravity.
Even you use 3.5R in order to have speed gained, the efficiency will be low as it isn't the purpose of those high speed motor designed for....any valid reason to use 3.7V
From westerner's forums, people usually run 1S lipo with higher turn motors (like 10.5 or 13.5). The main reason is because for lower turn motors, it requires a LOT of power from the battery. In single cell lipo, it may not be able to provide that power... causing the battery to fail.
Here is my understanding:
eg: 4.5R motor usually needs 450watts
Power = Voltage x Current ... so in this case Current = 450W / 3.7V = 121A
In order to provide ~ 120A, the lipo needs to be at least 5000mah@25C.
Westerners are trying out 1S + 10.5R. The speed is similar to 4Nimh + 13.5R
With 1S lipo, the car is lighter and less wear on the tires.
hardmankam 發表於 2009-6-25 23:40
Lipo itself is very light. I think the different between 1S and 2S isn't significant. But the speed will be highly affected. In addition, ESC may need something to do to cope with the lowered voltage. Still don't understand the advantage of using 1S......
The problem of 2S is not the weight, but the size of lipo. If they can make 2S smaller with a high C and high mah, then it is much more flexible than 1S.
If my calculation is correct;
assume your 4.5T motor has 9000Kv, with 4.8V you'll get 43200RPM,
with factory recommanded rollout, max speed equates to 79.05Km/h
if using 3.5T, 10500Kv at 3.7V, you'll get 38850RPM
with factory rollout, max speed around 65.35Km
May need to sacrifice heat and accelaration when re-gearing to the same speed