1895

Item 1895

OTHER: Electrical - Motor - Miscellaneous

Electrical Gearing ~ Electrical Speed Reduction and Torque Increase:

Due to an increase in the number of permanent magnets.

Divide 360deg by number of magnets then divide by 3 phases.

This provides the degree of movement per step sequence.

6 cycle step sequences needed to complete 1 revolution of the magnetic field.

A to B / C to B / C to A / B to A / B to C / A to C

Examples:

10 magnet:

360deg / 10 mag = 36deg || 36deg / 3 phase = 12deg
(12deg / step) x 6 steps = 72deg. Sequence
360deg / 72deg = 5 or 5:1 gearing

14magnet:

360deg / 14 mag = 25.71deg || 25.71deg / 3 phase = 8.57deg
(8.57deg / step) x 6 steps = 51.42deg. Sequence
360deg / 51.42deg = 7 or 7:1 gearing

48magnet: (bought F & P)

360deg / 48 mag = 7.5deg || 7.5deg / 3 phase = 2.5deg
(2.5deg / step) x 6 steps = 15deg. Sequence
360deg / 15deg = 24 or 24:1 gearing

48magnet: (F & P x 1.33)

360deg / 64 mag = 5.625deg || 5.625deg / 3 phase = 1.875deg
(1.875deg / step) x 6 steps = 11.25deg. Sequence
360deg / 11.25deg = 32 or 32:1 gearing

Mechanical and Electrical Measures: [Source ~ BPMMD section 1.7]

Electrical position = Number of pole pairs x Mechanical position.

Miscellaneous:

Investigation on Pole-Slot Combinations for Permanent-Magnet Machines with Concentrated Windings
Emetor the online electric motor design software

Wiring Diagram Table ~ Have hard copy.

Efficiency: BLDC motors are often more efficient at converting electricity into mechanical power than brushed DC motors. This improvement is largely due to the absence of electrical and friction losses due to brushes. The enhanced efficiency is greatest in the no-load and low-load region of the motor's performance curve. Under high mechanical loads, BLDC motors and high-quality brushed motors are comparable in efficiency.

A thought: Might this imply that an oversized BLDC motor could be used to produce the same speed and torque, but run closer to its low-load region. The extra weight of this motor may be less then the reduction in the battery weight for the same flight time due to the improved efficiency of the motor. In addition, the larger motor may run cooler and thereby increase its efficiency further; assuming that running cooler is not the reason for the efficiency in the first place.

Reply from PC; I think that the Agni motor is 92 % efficient with 1.8 Kg of controller. For the same power a brushless motor would be 95% efficient with 9 Kg of controller, so I am not really sure if I agree with all of this…

Last Revised: November 8, 2011