mCPX HP03S upgrade with 8 and 9T pinions - test data
helis:
After recently finding the original brushed main motor was not giving me the power it used to (it was also using much more power from the battery than when new and the flight times were getting shorter and shorter) I decided to take the plunge and upgrade to brushless.
I happened to have a motor which looked very much like an HP03S sitting in an old Walkera 4#3B that had been converted to brushless by ChineseJade but the heli flew so badly I never did anything with it.. until now. Out came the main motor and the search began to find a suitable ESC.
HobbyKing once again supplied me with the answer in the form of the double ESC specifically designed to be a plug and play solution for the brushless mCPX.
Features:
• Both main motor ESC and tail ESC support +- PWM signal
• 10A ESC for main motor, 3A for tail
Specifications:
Type: Dual brushless ESC for micro heli main/tail motor
Operating Voltage: 3.3~4.2V
Main motor ESC current: 10A
Tail motor ESC current: 3A
Dimensions: 26.5x25x8.6mm
Weight: 3.8g
I plugged the ESC signal wire into the socket previously connected to the white, brushed motor wire which goes to the negative terminal of the original motor. Signal wire connects to the positive PWM port on the brushless ESC.
There was a fair amount of work to remove the original motor mount sides and vertical reinforcement. I also had to drill a couple of new screw holes in the frame to move the brushless motor rearwards so that the motor would mesh correctly with the main gear. The original fore/aft holes ended up too large for the screws as I attempted to elongate them to give some fore/aft movement of the motor.
Here are my figures for headspeed, first the original (old and tired ) main motor followed by the new brushless HP03 with a nine and then an eight tooth pinion.
Measured Headspeed (old motor, Xtreme blades):
Start: 4.16V finish: 3.96V
100% throttle / 0deg (50%)pitch : 3900 RPM
100% throttle / 75% pitch: 3330-3450 RPM (approx hover pitch)
100% throttle / 100% pitch: max 2910RPM
Finishing, offload battery voltage for 3330 RPM 75% test: 3.76V (old battery too so may not be delivering best current/voltage under load)
Measured Headspeed (HP03S brushless motor, Xtreme blades, HK double ESC, 9T pinion):
Start:4.13V
100% throttle / 0deg (50%) pitch: 5100 RPM
100% throttle / 75% pitch: 4140 RPM (slightly higher than hover pitch due to faster headspeed)
100% throttle / 100% pitch: 2940 RPM
Measured Headspeed (HP03S brushless motor, Xtreme blades, HK double ESC, 8T pinion):
Start:4.15V
100% throttle / 0deg (50%) pitch: 4920 RPM
100% throttle / 75% pitch: 4020 RPM (slightly higher than hover pitch due to faster headspeed)
100% throttle / 100% pitch: 2800 RPM
Finishing offload voltage for 100% pitch test: 3.84v
Having flown the 8T now I find that the only advantage is a little longer battery life. It still bogs horribly in the flips and doesn't recover headspeed any faster as far as I can tell while flying. So better to go into the maneouvre with more headspeed and live with the bogging. Unless of course an HP05 happened to arrive in the post. Unlikely at the moment.
So the main advantage of the slightly lower headspeed is that the battery lasts a little longer.. currently I'm getting about 5 mins from a 300mAh Turnigy Nanotech. Not as good as I'd hoped from the brushless to be honest. I'm learning that cheap motors are generally much less efficient than the expensive ones! No surprise you get what you pay for. It also suggests that the original brushed motor was actually doing a pretty good job and that the HP03 is just a little too small for 3D on this size of heli.
