- Mon May 01, 2017 1:13 pm
#398053
Hi all,
Looking for advice regarding picking a motor for an E-Help powered harness for a hang glider. From what I know so-far the formula for RPM is motor kv * motor voltage * losses .8 = RPM. Early E-Help systems use small propellers at very high RPM. More recent higher performing systems are using bigger propellers with geared reduction 1:285. All these designs seem to be using the Rotomax15cc 15kv motor at around 52 volts, which would yield 150 * 52 * .8 = 6240 RPM. After this motor RPM is geared down 6240 / 2.85 = 2190 RPM.
I would like to spec a motor that has high torque at 2000 – 3000 RPM whereby I do not need to add mechanical gear reduction to the design. E-Power Hobby has an 80kv motor that would produce 80kv * 52v * .8 = 3,328 RPM, which puts me within the direct drive range. This motor can actually take 70v, but I would have to add gear reduction. Plus I have had an electric airplane manufacturer mention that they can only operate their motors at 45%. If I run the E-Hobby motor at 52 volts then I am dropping the current by 20% and if I do not operate at full power, just enough power to achieve around 2300 RPM then I generally will not be running the motor at full capacity.
E-Power has a 50kv motor at twice the price and power (45hp). They publish the usage of this motor to be for para gliders. 50Kv * 70v * .8 = 2800 RPM. This may be a good motor to use direct drive if I could get one made at 18000Wt.
I do not know how to factor in propeller load as applied to RPM and motor load.
Any advice is appreciated.
Thanks Tom
Looking for advice regarding picking a motor for an E-Help powered harness for a hang glider. From what I know so-far the formula for RPM is motor kv * motor voltage * losses .8 = RPM. Early E-Help systems use small propellers at very high RPM. More recent higher performing systems are using bigger propellers with geared reduction 1:285. All these designs seem to be using the Rotomax15cc 15kv motor at around 52 volts, which would yield 150 * 52 * .8 = 6240 RPM. After this motor RPM is geared down 6240 / 2.85 = 2190 RPM.
I would like to spec a motor that has high torque at 2000 – 3000 RPM whereby I do not need to add mechanical gear reduction to the design. E-Power Hobby has an 80kv motor that would produce 80kv * 52v * .8 = 3,328 RPM, which puts me within the direct drive range. This motor can actually take 70v, but I would have to add gear reduction. Plus I have had an electric airplane manufacturer mention that they can only operate their motors at 45%. If I run the E-Hobby motor at 52 volts then I am dropping the current by 20% and if I do not operate at full power, just enough power to achieve around 2300 RPM then I generally will not be running the motor at full capacity.
E-Power has a 50kv motor at twice the price and power (45hp). They publish the usage of this motor to be for para gliders. 50Kv * 70v * .8 = 2800 RPM. This may be a good motor to use direct drive if I could get one made at 18000Wt.
I do not know how to factor in propeller load as applied to RPM and motor load.
Any advice is appreciated.
Thanks Tom