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Towards High Performance Robotic Actuation


Georgiev, Nikola-Zlatkov (2019) Towards High Performance Robotic Actuation. Dissertation (Ph.D.), Caltech. doi:10.7907/W64Q-1R69.


The main objective of this thesis is to enable development of high performance actuation for legged, limbed and mobile robots. Due to the fact that such robots need to support their own weight, their actuators need to be light weight, compact and efficient. Furthermore, a dynamics analysis, shows that the actuators' design may have significant impact on a robot's dynamics sensitivity. These consideration motivate improvements in all actuator design aspects.

First, the application-specific design of outer rotor motors with concentrated windings is considered. It is shown that an intrinsic design trade-off exists between a motor's copper loss, core loss and mass, which allows development of motors with superior performance for a particular application. The three main application categories of interest are: electric vehicles, drones and robotic joints. Due to their outstanding torque density, high pole count outer rotor motors are analysed in terms of their design and optimization for robotic applications. Motor design scaling modes are also described in order to outline the main challenges in the implementation of high torque motors.

Next, the design of gearboxes for robotic actuation is discussed. A novel type of high reduction Bearingless Planetary Gearbox is introduced which allows large range of reduction ratios to be achieved in a compound planetary stage. In this concept, all gear components float in an unconstrained manner as the planet carrier is substituted with a secondary sun gear. The advantages of the Bearingless Planetary Gearbox over current approaches in terms of improved robustness, load distribution, manufacturability, and assembly are outlined.

Finally, analysis, design, and prototyping of rotary planar springs for rotary series elastic actuators is described. A mathematical model, based on curved beam theory, that allows rapid design, analysis, and comparison of rotary springs is developed. Mass reduction techniques based on composite arm structures are introduced and internal arm contact modeling is presented. Motivated by strain energy density analysis, an optimization based spring design approach is developed that allows significant increase in the torque and torque density.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:robotic actuation,limbed robot dynamics sensitivity, permanent magnet motor design, gearbox design, series elastic actuators, rotary spring design
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Mechanical Engineering
Minor Option:Applied And Computational Mathematics
Electrical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Burdick, Joel Wakeman
Thesis Committee:
  • Ames, Aaron D. (chair)
  • Ravichandran, Guruswami
  • Mello, Michael
  • Burdick, Joel Wakeman
Defense Date:15 May 2019
Non-Caltech Author Email:n.z.georgiev (AT)
Record Number:CaltechTHESIS:05222019-132217207
Persistent URL:
Related URLs:
URLURL TypeDescription's contribution adapted for ch. 4, ch. 5, ch. 6 adapted for ch. 5 adapted for ch. 5 adapted for ch. 4
Georgiev, Nikola-Zlatkov0000-0002-7997-5577
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11530
Deposited By: Nikola Georgiev
Deposited On:23 May 2019 20:09
Last Modified:04 Oct 2019 00:25

Thesis Files

PDF - Final Version
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