Max15 Series Brushless Motors vs Astro Flight Brush Motors

Notes

These diagrams currently reflect our Max15-13Y and Max15-13D motors which are no longer available. The new MaxNEO motors are even more efficient.

Brushless motors simulated with 0.014 ohm controller plus 0.001 ohm wiring to motor.

All brush motors simulated with 0.003 ohm controller plus 0.001 ohm wiring to motor.

Astro motor simulations were calibrated to the graphs in the Astro Flight, Inc. Electric Motor Handbook to the best of our ability. This involved deriving the rotor winding inductance by trial and error until the graphs were closely matched with respect to RPM vs. Current and Voltage. Other motor constants were used as they appear in the book.

The battery pack is simulated with 0.005 ohms per cell plus 0.001 ohm wire plus 0.001 ohm connectors, and 1.25V no-load voltage per cell.

These simulations do NOT take into account any effect of heat.

The gear ratios of the brushless motors are given to illustrate the approximate gear ratio required to closely correspond to the brush motor gearing for the same input voltage and current as the brush motor. They do not necessarily represent recommended gearing for any particular application.

If you want a wide range of performance to allow for 45A takeoff and maneuvers, and you push your plane hard so you average flight time is only expected to be about 6 minutes, this corresponds to about 20A average. The D motor (geared 3:1 and with an 11x8 APC, for example) is a good application for this. It provides about 11% more liveliness in maneuvers.

If the average flight time is 12 minutes, representing about 10A average current, the Y motor is a good choice for its high efficiency in that region. It will deliver respectable top-end performance, as good as the Astro 15 up to 25A. In an all-up-last-down contest, where you might be stretching it to 20 minutes, an average current of 5A allows the MaxCim Y motor to provide 37% more duration.

For 18 cell operation it seems the Astro 25 is more likely to provide reasonable lifespan than the Astro 15, so the 25 is used for this 18 cell comparison.

Here we see the MaxCim Y motor providing an edge at the top end, and a nice margin at the low end as well. The interesting thing is that the MaxCim motor and controller together weigh about 10.5 oz, while the geared Astro 25 with 1.5 oz controller weighs 13.3+1.5=14.8oz.

The above graph illustrates the reason why the FAI series of motors is not suitable for sport flying. They only work well at the very high currents they were designed for. The contrast with the MaxCim D motor is startling, if you consider an application where you want to have 45A maneuvers and takeoff, yet cruise around and throttle back to 10A for a 10 minute flight. The FAI25 is just not suitable for this wide range of operation.

This graph illustrates the wide available power band of the MaxCim brushless motor. In this case the Y motor is compared with the AFI 40 at 18 cells and continues to illustrate the efficiency gain available from brushless. In this case the AFI 40G with #205 or #207 controller weighs 16.5 oz. The Max15-13Y with MaxGR gearbox and Maxµ35-21 controller weighs only 13.5 oz. The Max15-13Y is quite capable of providing even more power in 21 cell applications.