Offset Outrunner Harmonic Drive for Compact High-Torque Actuation
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Solution Overview
Problem
Existing harmonic drive assemblies for aircraft and VTOL systems require a compact design that provides high torque while ensuring effective thermal management and angular precision, with a need for a motor-driven system where the motor is embedded within the drive assembly to enhance torque output and reduce thermal load.
Innovation Solution
A compact harmonic drive system with a motor positioned within the flexspline cup, utilizing an outrunner configuration with a large radial air gap and thermally coupled stator windings to achieve high torque and efficient thermal management, and a deployment system to support moment loads perpendicular to the rotation axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a motor is embedded within the harmonic drive assembly, then torque output is enhanced and thermal load is reduced, but the design complexity increases
Solution Approach 1:
The motor is nested within the harmonic drive assembly, specifically with the motor positioned inside the flexspline cup. This nesting arrangement allows the motor to be integrated into the existing harmonic drive structure, enhancing torque output through the outrunner configuration while managing thermal load within the compact space, without requiring a completely new separate mounting system
Solution Approach 2:
The motor and harmonic drive assembly are merged into a single integrated unit. The motor housing is combined with the flexspline cup structure, and the motor shaft is directly coupled to the wave generator. This merging eliminates the need for separate torque transmission mechanisms and reduces the number of external components, thereby enhancing torque while managing the complexity through integration
2Power
If an outrunner configuration with large radial air gap is used, then torque is increased, but the motor volume increases
Solution Approach 1:
The motor uses an outrunner configuration where the rotor rotates outside the stator, creating a large radial air gap that extends in the radial dimension rather than requiring increased axial length. This dimensional change allows the air gap to extend radially outward from the stator teeth to the rotor magnets, maximizing torque leverage while maintaining a compact axial profile that fits within the flexspline cup
3Temperature
If stator windings are thermally coupled to the drive system structure, then thermal management is improved, but the manufacturing complexity increases
Solution Approach 1:
The stator windings are thermally coupled to the drive system structure by integrating the thermal management function into the existing motor housing and flexspline cup structure. The stator housing serves dual purposes as both a structural component and a thermal conduction path, eliminating the need for separate thermal management components and simplifying the overall manufacturing process
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables a compact, high-torque harmonic drive system with improved thermal management and reduced volume, allowing for efficient rotational positioning and load support, enhancing the performance of aircraft and VTOL systems without the need for additional torque transmission mechanisms.
Implementation Method 1
The motor may use an outrunner configuration with an outboard rotor made up of magnets, allowing for a large radial distance to the air gap and resulting in higher torque
Implementation Method 2
The interior stator windings are thermally well coupled to the drive system structure
Data Source
AI summary
A compact harmonic drive system with a motor residing within the flexspline cup. The motor may reside further into the flexspline cup than the wave generator, and the air gap of the motor may be further out radially than the interior of the wave generator bearing. The motor may use an outrunner configuration with an outboard rotor made up of magnets, allowing for a large radial distance to the air gap and resulting in higher torque. The interior stator windings are thermally well coupled to the drive system structure. The harmonic drive may be coupled to a deployment system adapted to support moment loads perpendicular to the rotation axis such that those loads are not supported by the harmonic drive.