Design and Comparative Analysis of a Retrofitted Liquid Cooling System for High-Power Actuators

Abstract

This paper presents an in-depth system-level experimental analysis comparing air-cooled and liquid-cooled commercial off-the-shelf (COTS) electric motors. Typically, liquid-cooled electric motors are reserved for large, expensive, high-end applications where the design of the motor's electromagnetic components are closely coupled to its cooling system. By applying liquid cooling to a pre-existing motor design, this work helps bring the performance advantages of liquid cooling to smaller scale and lower cost applications. Prior work in this area gives little insight to designers of such systems. Conversely, this work aims to improve the understanding of liquid-cooled COTS motors by reporting empirically-observed factors of improvement for motor current, torque, output power and system efficiency. These measurements are obtained using a new liquid-cooled motor housing design that improves the ease of maintenance and component reuse compared to existing work. It is confirmed that datasheet motor thermal properties may serve as a reasonable guide for anticipating continuous torque performance, but may over-specify continuous power output. For the motor used in this test, continuous torque output is increased by a factor of 2.58, matching to within 9% of expected datasheet values. Continuous power output is increased by a factor of two with only 2.2% reduced efficiency compared to air-cooling.

Thermal Recovery of Multi-Limbed Robots With Electric Actuators

“…For thermal system identification, the work presented in [7], which is inspired from [6], used second order dynamics to model the thermal parameters of the motor core and the motor case. Utilizing the reported thermal parameters of the motor core from the manufacturer's specification sheet, a step-response test was used to obtain the thermal resistance and capacitance of the motor case.…”

“…When the temperatures of the torso or leg actuators reach unsafe levels, robot operations are postponed until the thermal states of the actuators return within safe limits. Existing techniques to manage the thermal state of a robot fall into three categories: considering heat dissipation in the design [4] [5], the use of novel materials for insulation against external heat [1], and active methods with liquid cooling [2], [6], [7]. However, these approaches are only appropriate during the design and manufacturing phase of the robot as modifying the hardware of existing robots, such as Valkyrie, is difficult.…”

Investigations of a Robotic Test Bed With Viscoelastic Liquid Cooled Actuators

“…Compactness of actuators is also one of the critical design parameters, which encourage us to use elastomers instead of metal springs and mechanical dampers. Our previous work [13] shows a significant improvement in motor current, torque, output power and system efficiency for liquid cooled commercial off-the-shelf (COTS) electric motors and studied several Maxon motors for comparison. As an extension of this previous work, in this new study we studied COTS motors and their thermal behavior models and selected the Maxon EC-max 40 brushless 120 W ( Fig.…”

Optimal Transmission Ratio Selection for Electric Motor Driven Actuators With Known Output Torque and Motion Trajectories

“…As such, although Eq. 17provides a useful reference, the requisite motor current for a given transmission ratio could also be checked against a thermal model of the motor to ensure that both necessary and sufficient conditions are satisfied [21].…”