Reaction Wheel Assembly Motors by ThinGap

Small form-factor and high inertia-to-weight ratio ideal for microsatellites

Today’s Low Earth Orbit (LEO) satellites, including “SmallSat” and “CubeSat” microsatellites require a range of critical functions to serve their mission as cost-effective spacecraft. One of the most important functions is Attitude Control, which enables high accuracy pointing capabilities.

Reaction Wheel Assemblies (RWA) are used for multi-axis Attitude Control. RWAs use multiple motors that each spin at varying speeds creating a change in kinetic energy in the desired axes. RWAs utilize optimized rotating inertia, speed, and torque to accomplish this.
Motors used in RWAs need to have the optimal balance between torque and inertia, with negligible rotational losses and smooth motion performance. Zero cogging is critical to achieving this smooth motion. Additionally, parts must be made with low-outgassing materials, have flight heritage, and be sourced from suppliers that can support space programs’ stringent requirements.

ThinGap has tuned its product offering of “air core” motors to meet the demands of this application. This moving magnet air-core motor lends itself to very low drag at high operating speeds, and a wide speed range with constant torque. ThinGap’s ironless stator puts all the magnetics (the heaviest part of the motor) in the rotor, maximizing the inertia for a given weight and size requirement. The reaction wheel’s necessary flywheel mass can be reduced, and sometimes fully incorporated into the rotor. The resulting package is lighter weight for the same momentum storage capacity.

Smooth operation is achieved through a zero cogging slotless design that maintains sinusoidal torque versus angle curves with total harmonic distortion of less than 0.5%. The precision wound coil results in a phase-to-phase balance within 1%. Hands down, ThinGap has the highest precision RWA motors available, yielding pure torque vector control, with very low losses and zero cogging.

Motor sizes range from 25mm to 250mm in diameter and axial heights as small as 22 mm, with through holes up to 80% of the outside diameter. Since 2015, ThinGap has shipped thousands of Space-grade or MIL-STD rated motor parts for use in commercial satellites, military and commercial aircraft, and flight-grade NASA programs.

ThinGap Motors Used For RWA Applications

ModelODWeightSpeedContinuous Torque


TGR 29-1229 mm0.03 kg6,000 RPM0.012 N-m
TGR 45-2045 mm0.11 kg10,000 RPM0.075 N-m

Coming Q3 2022

TGR 79-2679 mm0.26 kg16,000 RPM0.664 N-m
Existing RWA MotorsTG384276.2 mm0.14 kg28,400 RPM0.190 N-m
TG51XX136.4 mm0.51 kg<10,000 RPM3.57 N-m
TG71XX182.0 mm0.75 kg<10,000 RPM4.83 N-m

To learn more about the TGR Series of motor kits, click here.