RockSat-X
A sounding rocket experiment series of a single degree of freedom test rig supporting the development of a space-ready actuator
In 2018 (L) and 2019 (R) at the Space Systems Laboratory I undertook the hardware development of an actuator-characterization experiment to fly on a RockSat-X sounding rocket opportunity. The research focus was in progressing the development of the DYMAFLEX-series of SSL actuators in their flight-readiness and TRL. The DYMAFLEX actuator being adapted was a combination of an Allied Motion HT2000 brushless DC motor, and CSG-14-100-2A-R Harmonic Drive, with an RLS incremental encoder and Elmo Motion Control Tweeter motor drivers.
The original DYMAFLEX manipulator was a 4DOF test-bed featuring four of these actuators, and saw experimental time on air bearing vehicles and parabolic flights. Performing characterizations of these actuators in an applicable spaceflight environment was the project’s next step, increasing TRL to level 7 and providing a hardware-iteration datapoint.
The next generation of the Dyma robot series is shown in the renter, a 7-DOF satellite-servicing capable manipulator capable of being launched on a rideshare mission. More details are shown below about the future potential applications and progress of Dymaflight.
Experiment Goals in µg
Characterize actuator through various repetitive sweeping motions
Evaluate manipulator performance against both compliant and non-compliant surfaces
Record a secondary set of data with identical commands after a mass ejection
Recover experiment with valuable hardware such as motor, gearbox, and drivers intact
Instrumentation Included
Through the experiment development, the inclusion of two instruments was deemed necessary. First of which was a parallel-beam load cell mounted as a part of the end-effector to measure both accelerative loads and forces from the impedance testing. Second was a high-precision current measurement circuit designed in-house, measuring current delivered to each motor phase.
Design process
The preservation of the mechanical layout of the actuator was preserved as much as possible, carrying over identical interior/fit dimensions for the motor and Harmonic Drive housings, driveshafts, and encoder support structure. However, the original DYMAFLEX manipulator was entirely 3D printed, and the re-usability goal of this experiment combined with the sounding rocket re-entry means everything had to be transferred to aluminum-compatible designs. The actuator housings were re-designed to include both static and dynamic seals, a sealable torque output plate with support for an upgradeable end-effector, and waterproof connectors. The end effector was designed to house the load cell, support a spring-loaded ejectable steel mass, and a hot-wire cutdown system at the tip for the ejection. Electronics boxes were designed to fit the custom boards and were sealed with a large o-ring and sealing D-sub connectors. All parts were designed, manufactured, tuned, assembled, and tested in house.
The first launch in 2019 was a shared payload plate with a tribocharging-focused experiment also being developed within the UMD Aerospace Engineering department. Our single DOF actuator was placed on one half of the payload plate, as shown in the photos in this section.
2019’s launch was solely focused on the actuator characterization and featured two actuators in the event one was unable to generate data. This, unfortunately, did occur and we were still able to gather the data on the 2019 launch!
Results
The experiment flew two times, August 14th 2018 and August 15th 2019. The 2019 flight is considered a success, after a software glitch prevented the experiment from running in 2018. An edited video from the 2019 flight can be seen in the video linked at the top of this page, and a plot of some of the data collected can be seen on this page, plotting both actuator position (blue) and force sensed (red) from the load cell across the actuation motions. Most notable from this plot is a difference between the pre- and post-ejection forces recorded in the latter half of the data. Overall the experiment was considered a success, and the next-generation of DYMAFLEX began its design, standing on the shoulders of its predecessor and evolving to a highly-capable 7DOF manipulator capable of satellite servicing in a small ~1m package able to be launched on an orbital-class rideshare program - DymaFlight.
The design team for this project included:
Dan Gribok - Electronics and software
Nick Limparis - Electronics and software Guru and Hardware Mentor
Nick Bolatto - My 2019 Hardware Buddy
Natalie Condzal - Integration, Hardware, Software
Dr. Akin - PI
Myself - Hardware design, manufacturing, and assembly lead
DYMAFLIGHT
Following the successful 2019 sounding rocket launch, Nicolas Bolatto, Nicholas Limparis, and myself were interested in progressing the Dyma-actuators into the next phase of a larger research project. The renderings on this page are a few that I have completed to include in papers, presentations, and funding proposals!
Dymaflight aims to be a rideshare-scale manipulator arm capable of inspection, repair, and servicing. Dymaflight is intended to be a low-cost manipulator arm, capable of being launched without great concern for capital hardware loss, while still providing adequate force and torque (20 lbs/20 ft-lbs from NASA’s satellite servicing guidelines).
Dymaflight is going to be less than 1 meter in length in the minimum configuration, likely weigh 25 kg, and for the first developed manipulator capable of simulating servicing tasks underwater in our neutral buoyancy research facility. Dymaflight is being designed to accept link extensions in its bicep and forearm links to satisfy requirements for long-reach tasks or simulation of other robots with extended DH parameters.
While I have been focusing more recently on the hardware manufacturing of VERTEX and BioBot, Nicolas has been leading actuator design improvements for the Dymaflex housings. I aim to return to the hardware development process for Dymaflight after the conclusion of my dissertation, ideally bringing my manufacturing experience from VERTEX to the project and make the production of the arm an easier process.
