Legend of Endurance
When planning the build of the AerialPixels FX8 Pro Elite X8 I wanted to do something epic and amazing. The performance had to not only be spectacular, it needed to be drastically different than what we’ve built in the past. I contacted Patrick from KDE Direct and after a long conversation I decided that I wanted to build the X8 to have what other large birds lack…flight time. Since most heavy lifters struggle to hit even the 20 minute mark, I really wanted to tap into unchartered territory. The goal…. A heavy lifter that can fly an hour!
Unboxing the 7208 motors is shocking experience. At nearly 80mm in diameter, there are only a handful of airframes these will even fit. While it may seem like its all brawn, the efficiency of this motor is its shining claim to fame. Ultra low KV winds and high pole counts make torque to swing up to 26 – 29 inch props. They do this while consuming less than half the power of smaller motors that have to spin faster to produce the same lift with shorter props. Capable of running on 6s, 8s or even 12s lipo, the efficiency and payload range is staggering. Also included in the box are 3 prop adapters. Left and right hand threaded are both in there as well as the typical flat washer to cover direct bolt props. Connectors, instructions and a bag of premium hardware is also included. Lets open one up and dig into the how the magic is made.
Two stage endbell retention system
Flip the motor over and you will see the large billet collar with two set screws. The set screws sit on two flat spots that span only a specific area of the shaft. Even if the large bolt were to be removed, the set screws and collar would still keep you in the air. Together with the bolt, nothing is more secure. I needed to apply heat from a soldering iron to get the large bolt in the center to loosen from the Red Loctite used during assembly. I loosened the two setscrews, removed the collar and brass shim, and pulled the motor apart.
Inside the outrunner endbell are 28 of the highest quality N45UH Neodynium rare earth magnets. Each magnet is permanently fit into a machined channel and epoxied in place and a retaining ring finishes off the installation. Rated for 356 degrees F, these motors can run at temps that would turn the competition to molten scrap.
The steel laminations that make the up the stacks that hold the copper windings are a place where efficiency is gained or lost. KDE uses only the best .2mm high silicon steel. The copper used to wind the stator is ultra pure and rated to a staggering 464 degrees F. Once the windings are wrapped, the stator teeth are wound with Kevlar to keep the windings from ever being able to make contact with the magnets. KDE coats the stator with epoxy, then vacuum pulls the windings to ensure they never move. This greatly enhances reliability. Down the center of the stator are three monster ABEC 7 ball bearings. Ultra close tolerances and construction mean these bearings should outlast the life of your multirotor. To keep the stator from ever coming loose from the mount, the stator is keyed, epoxied and then locked in place with an industrial snap ring.
To put the pedal to the metal KDE includes 30” of 14 guage high temp multi-strand power cables with presoldered 4mm bullets. In the box are the mating female bullets and shrink.
Efficiency vs power
Every motor is rated to produce a certain amount of lift with a specific prop while operating on a certain voltage. To simplify things a bit and level the playing field we can compare motors by looking at how many grams of thrust it can produce while consuming 1 watt of power. The more grams of lift per watt, the more efficient the motor. To put things into perspective, most motors used on heavy lift machines produce about 5-12 grams of thrust per watt on 6S lipos when used at 50% throttle. The 7208 motors produce over 20 grams per watt which means they use roughly half the power. In fact, when used with 6S lipos at the ideal 50% throttle range, these motors don’t even break into the double digits for current draw. Imagine the lift you generate with a 29 inch prop while only consuming 3-4 amps! At 75% throttle amp draw is a miniscule 7amps. By comparison, the to get the same amount of thrust from a smaller motor with an 18” prop would require as much as 3x the amp consumption. The possibilities are staggering and it gets even better. Need more lift? By running these on 12S instead you double the thrust to nearly 7.5 pounds per motor while still maintaining record efficiency.
The final word
Currently the KDE Direct 7208XF-110 is the most efficient motor we’ve ever tested. Its diverse voltage range makes it extremely adaptable to payload requirements and combined with various length props, it can be used with payloads as heavy as a Red Epic or as lightweight as a mirrorless compact. It should be noted that these motors are designed to be used with KDE speed controls for best performance and the latest firmware has been optimized to take advantage of the 7208XF design. With absolutely astonishing flight times now possible, KDE gives you the power, efficiency and commercial reliability to take your business to new heights. Highly recommended.