Motor Chart - Vol vs Surface Area

Motor Chart - Vol vs Surface Area

This is a chart of stator volume vs surface area. The stator volume calculation does not take the bearing space into account. Some motors of the same size have larger bearings than others and this could lead to reduced thermal dissipation or otherwise varied performance. Usually larger bearings are preferred but often make no difference (specifically in the case of 5" prop motors and 9 vs 10mm bearings, even durability)

This chart is best used to compare motor sizes to one another and does not represent any information about any specific motor(s). Generally motors with a greater surface area to volume ratio tend to have improved heat dissipation properties whereas those with a lower ratio tend to have taller magnets, more power and less heat management potential. Kv and expected power output throws a wrench into this as do super wide motors like gimbal motors. Fixed wing/constant on motors are NOT represented here.

General things presented in this chart:

I have personally labeled the prop size zones along with green size transition zones. By doing this, you can almost make out a 'golden proportion' of sorts but nothing has been confirmed. Just a notion and interesting to point out.

The blue line is arbitrarily extrapolated over a series of motor sizes that are characterized by having some degree of improved low RPM flight feel. The true relationship is unlikely to be linear and this line is mostly accurate within the 5" prop range. Motors on or above this line have improved heat dissipation abilities.

The orange line represents motors that have more power, more response, more high throttle control and also have a higher chance of overheating. These motors tend to have taller magnets.

HEAT KILLS MAGNETS AND IS BAD. Motor heat can substantially change the way your craft flies. You may tune it for a cool or med temp motor but when it gets hot, it'll fly much worse.

Larger motors with physical advantages such as larger stator and magnets tend to have better flight feel than small motors with high Kv values even if the two motors produce the same overall power. The smaller motor will usually have better average efficiency.

IMO the magnets are the single most important aspect of motors today. The issue is that we only have so much space to work with. Taller stators allow for taller magnets which is a plus but then driving that stator to the sky high RPM's under load that we do causes them to overheat. Similarly, magnet thicknesses start to have diminishing returns and increase weight a lot past ~1.6mm thick.

I've personally tested just about every motor on this chart. I've even tested 2x motors vs 1 big motor keeping the prop size the same such that the two smaller motors have the same overall weight but improvements in other metrics. The complexity wasn't worth the benefits which there were little to none. Please draw your own conclusions.


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