At first glance, when somebody claims a big leap in the efficiency of an electric motor, it is always suspect as we all know you do not get something for nothing. When I first considered the CR Drone Motor counter rotating prop drone motor and their claims of huge efficiency leaps, I was skeptical at best. We set up the test bed, ran the tests and I realized that I was not looking at an increase in motor efficiency, but rather an increase in process efficiency or usable thrust. Most motors are judged on efficiency on what usable horsepower they put out for the number of watts that they are using. You bolt a motor to a test bench,(infinite mass) place a load on it and verify the wattage used. Unfortunately this does not go far enough in the process. When you load the motor down, the force of the reaction is absorbed by the mount. We are all familiar with the term, for every action there is an opposite and equal reaction. Since the motor has to be mounted in order to pull work out of it, the evaluation stops there. What would happen if you could use the energy being absorbed by the mount fully? Obviously a drone is not infinite mass. It is very light, the motor vibrates and torsions allowing some of the energy to be absorbed by the mount. Theoretically there is a certain amount of energy expended on the mounting from the motor.
This is what happens with the CR Drone Motor counter rotating drone motors. Instead of hooking the motor to a rigid mount so that the thrust of the propeller can be transmitted to the drone, they hook the drone motor to the drone with a rigid rotary power transfer device (PTD) that allows the motor to fully use the energy generated by both the active and reactive force of the motor. The propeller spins in the direction of the motor, while the opposite propeller spins with the motor housing utilizing the reactive force as well. This means that the only loses in the CR motor design, is the losses through the PTD and the fact that the trailing propeller is not running in as clean of air as the front propeller so it does not get the propeller efficiency of the front propeller but does remove the spin vortex that you get off of a single propeller and converts it back to straight air flow significantly increasing air thrust and velocity. Interestingly the same motor that turns at 6000 with a single prop, turns at 10,000 with a double prop with the first one spinning at 5500 and the rear one spinning at 4500.
This is where you run into the huge by product savings of the CR technology. Because the stator is now spinning as well as the rotor, you just turned the stator into an axial compressor and are forcing large amounts of air through the windings. The net cooling effect is so great that in several of the test motors that we were running we were able to pull twice the power out of the motor without over heating the motor. The test motor that we are using is rated at constant 8.5-9 amps at 22.3 volts at 34 Deg.C ambient temperature. The motor would get up to about 120 Deg.C. You can run them up to 140 Deg.C but you are so close to failure temperature that we chose not to push them past 120 Deg.C. We ran several at 140 Deg.C and had them spike in temperature and fail. Using the CR technology we were able to run the same motor at 23 amps at 30 volts at 34 Deg.C ambient and it only went up to 120 Deg.C after running for extended lengths of time. This is pulling 690 watts out of a 200 watt motor on a constant basis. In most cases this doubles the usable payload of the drone.
When looking at the CR Drone Motors, don’t think motor efficiency gain, but instead look at process efficiency gain. Their innovative use of the drone motors can drastically increase range, life, payload and duration of a drone platform, while eliminating almost all reactive forces sustained by the drone structure. This will allow for a much lighter frame required for mounting the motors as you have no reactive torque to deal with. Their process efficiency cuts the power drain drastically for equal thrust or increases the usable thrust drastically for the same power usage, depending on the requirements of the drone mission. The gain in power efficiency goes up with the power requirements of the drone.
The value added for a drone manufacturer is both significant and calculatable, as well as making a significant technology boost to the drones themselves and their customer base.