H3X – A Motor with High Power Density

H3X, a motor company started by three University of Madison, Wisconsin graduates, promotes its integrated motor/inverter power plant as “the next step in the evolution of electric propulsion technology.”  With Their HPDM-250’s 13-kilowatt-per-kilogram continuous power ability, it meets ARPA-E’s (Advanced Research Projects Agency–Energy’s) criteria for powering large, 737-type aircraft.

Electronics Weekly reports, “ARPA-E has determined that for a Boeing 737 to complete a typical five hour flight, the propulsion system must be >12 kW/kg continuous.”  H3X adds, “These specifications are estimates based on electromagnetic thermal and structural simulations. Data from dynamometer will be available Q2 2021.”

Their motor is roughly twice as power dense as MagniX motors of similar power, according to H3X.

Weight reduction is an intrinsic part of aircraft design.  In the days of internal combustion engines (still very much with us), conventional wisdom held that reducing power plant weight by one pound could help take two pounds off the airframe.  Even today, ICE engines generally produce only one horsepower for every two pounds of engine weight.  The HPDM-250 produces 7.92 horsepower per pound.  Couple that with modern composite airframes and one can see design possibilities lighting up the skies.

H3X describes its motor drive, a combined motor/controller unit: “The HPDM-250 is an ultra-high power density integrated motor drive for electric aircraft. It combines the electric motor and inverter (+ optional gearbox) into one powerful unit. It is the culmination of H3X innovation in multiple areas including:

“Electromagnetics design optimization

“DMLS (Direct metal laser sintering) 3D printed synergistic cooling jacket

“SLM (Selective laser melting) 3D printed copper stator coils

“Robust fault tolerance

“Thermal resistance reduction

“High frequency SiC (Silicon Carbide) power electronics”

H3X explains their 3D printed stator coils add to the lightness and robustness of the motor.

with >93% IACS (International Annealed Copper Standard) conductivity. “Our AMcoils achieve >70% copper fill factor in the HPDM-250 and offer a 40% improvement over conventional windings in terms of maximum continuous current density.”  They help cool the motor and achieve higher output while being relatively easy to manufacture.

Of course, that’s going to depend, too, on batteries of highly-improved capabilities.  We seem to be able to craft incredibly power-dense motor capabilities only short of dilithium crystals, but lag on energy storage.

Vertical axis is torque in Newton-meters: horizontal axis is RPM x 10 to the fourth power

More detailed specifications show a 250kW (335 hp) peak output for 30 seconds, and 200 kW (268 hp) continuous.  The little motor generates 95 Newton-meters (70 foot-pounds) of continuous torque.  It can manage up to 800 Volt DC with 96.7-percent peak motor efficiency, 99-percent peak inverter efficiency, and a combined peak efficiency of 95.7 percent.  Its 15-kilogram (33-pound) mass fits within a 6.75 liter volume – about three-and-a-half large soda bottles.

The motor’s efficient speed of 20,000 RPM means it needs a propeller speed reduction unit (PSRU).  H3X’s is a 4:1 unit, meaning the prop would still spin at 5,000 RPM at top speed, something that might cause blade tips to approach or exceed supersonic speeds  and generate a terrible racket.  The reduction unit adds only three kilograms (6.6 pound), quite good for a reduction system that can absorb all that power.

H3X founder and CEO Jason Sylvestre explains that without the gearbox, the overall efficiency and power density would be lower.

There’s some question as to whether there is a functional reduction gearbox at this point, since H3X says they “…can design a high torque density planetary gearbox that is integrated into the front end cap of the machine to achieve your desire torque speed requirements.  The example 4:1 planetary is based on a real design that is 3kg and 97% efficient.”

3D printed copper coils increase copper fill, energy density

Keeping it cool helps improve performance and lower weight.  Sylvestre explains, “… We use a single, synergistic cooling jacket to simultaneously cool both the power electronics and motor. This integration reduces system mass and volume. Additive manufactured copper stator coils are used to increase copper fill factor and improve continuous current density capability. This is a new technology that has the potential to revolutionize the motor manufacturing industry as it offers faster development, better performance, and greater design flexibility.”

Primary near-term applications for this motor, said the company, are urban air mobility, EVTOLs, UAVs, “military jets and select regional aircraft markets. Primary long-term applications: large commercial electrified aircraft, such as the Boeing 737.”

Sylvestre projects an interesting future.  “In the next five years, we’re going to see those eVTOLs and small electric aircraft.  But by around 2030, we’ll start to see electrification of large commercial aircraft. That’s really what you want to go after. Aircraft around the size of a Boeing 737, those account for around 50 percent of all the greenhouse gas emissions in the aircraft sector. An aircraft that uses distributed propulsion with multiple 250-kW motors, maybe 16 or so, along each wing. You can imagine the weight of those will add up, and that’s where a motor like ours could make a huge difference.”

The firm intends to start testing by mid-2021 and is seeking letters of interest from potential clients.  We can only hope that companies like H3X and MagniX continue their drive toward lighter, more powerful motors.  The competition will benefit all.‍

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