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Kyosho EP Concept SR Schweizer 300C

The EP Concept flew marginally with the stock K-speed motor, Futaba MC114H speed controller, 1900mAh 7 cell battery, stock EH-15 blades, and stock 16T pinion gear. It barely achieved 3 minutes of out-of-ground effects hover, and felt sluggish, due to marginal power and low rpm (~1300). One solution was to fly it with 8 cell batteries, but that meant faster brush wear and heavier weight. It also meant buying a new charger to handle more than 7 cells...

Another alternative was to use the maintenance-free brushless motor - no more brushes to replace! With 10~15% more efficiency than brushed motors, brushless seemed to be the answer to the EP Concept's sluggishness. After doing some research on the web, especially at Mr. Shimizu's EP RC Models site, I decided to get a B40 size Hacker Brushless Motor. My goal was to get the heli's rpm up to 1400-1500 range with moderate climbing power. The B40-8L (Kv=3750) would have been a good choice with the 7 cell batteries I already had. However, after reading about successes of making the EP Concept fly with standard RC car 6 cell batteries at this website (Japanese only), I became ambitious and decided to get the Hacker B40-10S (Kv=4260). The U.S. Hacker distributor Aero-Model had the 10S but with a gearbox attached for propellers, which I couldn't use. However, they had an open-box demo of the B40-7L (Kv=4286) and Schulze Future 45He brushless controller, both for $260 with full warranty. It was a great deal, so I bought that for my EP Concept.

Home-made Motor Mount vs. Kyosho Motor Mount

Rather than risk making a mistake on Kyosho's stock motor mount (Part EH-99, no longer available), I decided to make my own for the Hacker B40-7L brushless motor. The stock mount is made out of 2mm thick aluminum plate. I used a slightly thinner 0.064" (1.63mm) plate available at hobby shops. I drilled four 2.5mm holes for the tapping screws, three 3.0mm (two to mount the motor, and one for aligning it to the body), and one large hole in the middle for the motor shaft. The 3.0mm motor mounting holes should be oval, to allow gear mesh adjustments. 3/32" and 7/64" drills can substitute for 2.5mm and 3.0mm respectively, but the holes will need to be enlarged slightly.

Enlarged holes on the Heli's Underframe

Materials need to be removed from the heli's underframe so the motor mount bolts don't get in the way. Make sure enough is removed to allow enough clearance for the bolts during gear mesh adjustments. Be careful not to damage the gear inside the underframe, as it's pretty close to the holes.

32 pitch Pinion Gears by Bolink & Robinson Racing

Tower Hobbies sells various 32 pitch, 1/8" (3.17mm) diameter pinion gears that can be used on the EP Concept. The more expensive aluminum Robinson Racing gears are recommended. The cast iron Bolink gears have teeth burrs that generate loud meshing noises. I had to use a small hobby file to deburr each teeth, which took away most of the noise.

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