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EHCE Dual Hydraulic Control Test Stand P

NASA | Space Shuttle EHCE Prototype

Electro-Hydraulic Concept Evaluation (EHCE) - Electric APU NASA Prototype

(Shown: Hydraulic Cart with Pumps, Motors, and Load)

NASA wanted hydrazine, a dangerous and explosive chemical used to generate hydraulic power for steering the rocket nozzles, off the Space Shuttle.  But was it feasible?

The official assignment was for myself and one mechanical engineer to build a simple all-electric dual hydraulic control (DHC) version of the Auxiliary Power Unit (APU).  The unofficial assignment was to knock the socks off NASA and win the follow-on.


This downscaled prototype was required to operate two high energy BPM motors and two variable wobbler angle pumps so that NASA could spend the next three years learning.  They wanted to experiment with different control algorithms in a live hydraulic system.

NASA planned to experiment with this for 3 years.  After delivery, they knew everything they needed to know in three months.

Under-promise, WAY Over-deliver!

EHCE Dual Hydraulic Control Test Stand P

The $120K NASA Statement of Work (SOW) specified two commercial hydraulic pumps and two commercial electric motors to drive hydraulic fluid through a single manifold and load system.  This would allow NASA engineers to simulate how this might work on a future Space Shuttle upgrade to replace explosive hydrazine fuel currently used Their expectations could be met by installing a series of potentiometers on the hydraulic cart to allow them to manually adjust the wobbler angle of each of the two pumps and each of the two electric motors.

They hydraulic system performed exactly as expected.  But I didn't want to hand NASA a manual system when I had all of the skills to give them a fully automated one - and on budget!


So I began building a system that would wow our customer, Brad Irlbeck, Chief Upgrades Officer for the Space Shuttle.


  • Use NI Data Acquisition (DAQ) hardware and LabVIEW software to fully instrument the system

  • Apply dynamic analog control signals to the pumps and motors

  • Create a series of PID algorithms for the multiple pumps and motors to allow NASA to immediately understand how different failure modes could be addressed by such a system (loss of a single pump or motor or loss of a complete channel)

  • Throw in some extras to showcase our safety culture, and something extra specifically to make our NASA engineers smile!


(To be clear on MY role, another engineer designed built the entire hydraulic cart, and I designed and built the entire DAQ, command, control, electronics, safety, and multiple nested PID control algorithms.)

Systems Monitoring & Control Screen

EHCE Dual Hydraulic Control Test Stand P

Create Dynamic Displays for Electro/Mechanical/Hydraulic Systems

On this screen I applied dynamic LabVIEW indicators for speeds, pressures, temperature, flows, ball valve positions, and error indicators, all overlaid in context on a hydraulic schematic of the system.  This was "next generation stuff" back then, even though now it's quite common.  


This allowed NASA engineers to see the results of various nested PID configurations in action in a single view.

Nested PID Loops on Redundant Systems

My core goal to overdeliver on this project was giving NASA engineers the ability to dynamically experiment with different proportional, integral, and differential settings when working with redundant systems.  The idea was to learn as much about the problems they would face on full-scale systems at a fraction of the cost.  All NASA really expected was potentiometer pots.


What I gave them was every conceivable option for running two Brushless Permanent Magnet Motors (BPMs) and two Variable Displacement (Wobbler) Pumps in different configurations.  

Fault Management & Display

NASA hadn't levied any requirements on safety systems.  But with my experience on Shuttle, I knew it would be wanted and appreciated.

What NASA received included:​

  • On-screen fault displays for motors, pumps, and ball-valve position states 

  • Automated reactions to failures during testing

  • Protection from starting in unsafe states

Monitoring System Efficiency

On the Space Shuttle, you have limited power resources, so understanding efficiency is critical.  Each potential operation mode generates different efficiencies, along with risks, ability for redundancy, and ability to generate raw power.

By installing wattmeters for both channels, paired with my onscreen algorithms selection, NASA could see exactly how different operational modes would impact power requirements.

Prototype Control Algorithms Provided

Operating four competing devices with PID is no simple task.  Redundancy, efficiency, and responsiveness were all trading factors in this system design.​


I created algorithms to create these and other combinations of scenarios:​

  • Each Motor/Pump combination to operate as an independent system, with one dormant unless the other fails (most efficient)

  • Both Motors controlled as one, and both Pumps controlled as one, creating one BIG system (least efficient)

  • Pump wobbler angle as high-speed inner PID, Motor speed as low-speed outer PID

Manual Option - On-Screen Controls

Of course, you ALWAYS give the customer exactly what they asked for!  NASA had specified that it wanted a method for controlling the two motors, two pumps, and the load directly.  We added those directly to the main screen.

This increased operational safety by moving the controls away from the dynamically changing hydraulic systems.  More importantly, the automated functions I provided did the job so well, NASA never needed the basic controls they asked for.

Learning Interactions In Context

All required traditional pressure and flow instruments were mounted to the hydraulic cart.  But by creating an integrated view, NASA could learn more, and do it faster.

In operation, NASA could see exactly how primary systems would increase/decrease motor RPMs, how that interacted with pump wobbler changes, and how each of those interacted with secondary systems - VISUALLY.  They could quickly get a feel for what worked best using different algorithms.

Extra WOW Factor #1

The SOW required a checkout routine that exercised the system at zero pressure.  I noticed that the motors hummed at different frequencies as the speeds changed.


A little engineering ingenuity and music theory, and I had the motors playing "GAF^FC", the notes played by NASA to the visiting aliens in the movie "Close Encounters of the Third Kind". 


NASA's Brad Irlbeck, "What was that? Do that AGAIN!!!"

Extra WOW Factor #2

After instrumenting system, building the dashboards and controls, and adding safety features well beyond NASA's expectations, what could make it more memorable?  

Audible warning messages.  Voice recordings for stand startup, checkout, and failure announcements in the voice of James Earl Jones (ask me how... it was a big hit!  ;-)

I'll never forget our Engineering Manager calling the customer, saying "Listen to this," having me force error announcements, and "that's YOUR test stand!"

Gallery

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