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2400mAh 6 cell battery underneath the Schweizer 300C
I bought a RC car 6 cell 2400mAh battery pack at Sheldon's Hobbies and decided to use a 15T pinion based on quick calculations. The rpm was higher and the controls responded much better. It hovered out of ground-effect for just past 4 minutes. Next, I tried flying it with a 14T pinion. The rpm slowed, and the heli flew sluggishly similar to 7 cells/stock motor setup. Worse yet, the Schulze controller shut itself off after 2:30 as the motor was drawing too much current. The heli landed hard, but no damage. This meant that with a 14T, the motor was operating out of its efficiency range.
Hacker B40-7L and Schulze Future 45He
Next, I tried the stock Kyosho 16T pinion, and the heli flew very well with better collective response, achieving 5 minutes of hovering outside ground-effect. I tried the 17T pinion next, and its control response was about the same, but again, the Schulze controller shut itself off in about 2 minutes (too much load on the motor). Looks like the 15T and 16T pinions allow the B40-7L motor to operate inside the 0.85-0.90 efficiency range. Had I raised the pitch curve for the 15T (lower rpm), I could have made the EP Concept fly longer, but I was satisfied with the control response and the flight time with the 16T.
Here's a Quick Summary of what I've Done So Far:

MotorSpeed ControllerBatteryPinion GearFlight TimeAverage CurrentAverage Estimated Input Power
Stock K-Speed HeliFutaba MC114H8.4V 1900mAh16T3 minutes
6 seconds		36.8 A283.1 W
Hacker B40-7LSchulze Future 45He7.2V 2400mAh15T4 minutes
8 seconds		34.8 A229.7 W
Hacker B40-7LSchulze Future 45He7.2V 2400mAh16T6 minutes
0 seconds		24.0 A158.4 W
Hacker B40-7LSchulze Future 45He7.2V 3000mAh16T7 minutes
30 seconds		24.0 A158.4 W

Average Current = (Battery Capacity) / 1000 * 60 / (flight time in minutes)
Average Est. Input Power = (Number of cells) * 1.1 * (Average Current)

Pitch Curve: -2° low, 6° hover, 10° high

My EP Concept weighs 1300g (2.87lb., 45.9oz.) and the current configuration has good climbing power.

Ways to Improve Flight Times:
  • More forward flight, less hovering. This takes advantage of translational lift on the rotor disc and reduces input power.
  • Use Schulze's governor mode. Right now, I'm flying the EP Concept in standard mode. The instructions for the Future 45He say the governor mode (speed-controller controls the rpm) should increase flight times.
  • Use more efficient blades to reduce input power. Kyosho's weighted wooden blades (EH-83) or even better, JRC's washout blades are known to give better lift to drag ratios.
  • Use more cells to reduce current consumption. Appropriate motor and pinion will need to be selected. For 7 cells, B40-8L with 16T seems appropriate, seemingly more efficient than B40-7L with 14T or 15T. However, there's a weight penalty for adding more cells.
  • Reduce weight. The EP Concept should fly well with the lighter B40-10S with 6 cells and 16T pinion. For 7 cells, B40-11S or B40-12S could be used. Some metal could be removed from the motor mount. Battery packs can be made lighter by hand-assembly instead of buying pre-made ones.
  • Use 3000mAh NiMH batteres. If the average current is less than 30A, NiMH could be used. However, they don't take abuses as well as NiCd's and take longer time to charge.
  • Doing all of the above, claims of 7~8 minutes or longer flight times with the EP Concept seem achievable.

    • If time and finances allow, I will try these out and let you know the results.

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