Lunar Crane Design

When NASA Langley Research Center hired Honeybee RoboticsSpacecraft Mechanisms Corp. to develop a totally mechanical tool changer, therequirements were anything but simple. For starters, the tool changer was to bedesigned for the end of what Langley's Lunar Surface Manipulation System (LSMS)team describes as a robot that could unload landers. After the landers areunloaded, the tool changer must also be able to mate with tools to performvarious science experiments.

In essence, this robot could be likened to a crane but with moredexterity. And on top of all the other requirements, this dexterous crane hadto be able to work remotely so that it could be used on an unmanned missionwithout human interaction.

Design Scope

To start, NASA gave Honeybee a project envelope - afootprint to stay within - that included all the requirements for load ratingsand misalignment allowances.

Lee Carlson, a systems engineer who was part of the Honeybeeteam, describes the project from a design perspective: "The crane might besitting on the lander deck or on the lunar surface and then be driven quite adistance away from the tool to be mated to. This required designing for largemisalignment allowances - and that was our first design challenge. We had todesign the device so that the end of the crane and target tool could bemisaligned by as much as a couple inches in any direction with up to 20 degreesangular misalignment when attempting a mate."

Other requirements included having the tool changer be capable of carrying about 1,000 lb. And since thiswas a lunar project, it has to be tolerant to moon dust. These two designcriteria required special seals to protect large roller bearings.

The original assignment calledfor "dumb" tools requiring no power. The crane would do all the work. Toolswould range from a forklift attachment, a shovel or scoop for acquiring surfacesamples or digging, or even a bucket for lifting human passengers.

The Scope Expands

Then NASA decided it wanted the capability of attachingan electronic or electromechanical tool to the end of the crane. Now the toolchanger would also have to provide an electrical connection. Solving thisproblem fell to Carlson.

"The contract was expanded to add an electrical connector to theexisting mechanical connector, which meant that we had to have a power sourceon the crane itself. However, space to accommodate an electrical connector hadnot been accounted for because it was not a part of the original contract andthe budget did not allow for starting from scratch.

Carlson had to work within theconstraints of the current design because NASA did not want a redesign of thewhole tool changer. They just wanted to add an electrical connector to itwithout increasing the current envelope. With only about 2.50 x 4 inch of freespace to incorporate the male side of the new autonomous connector (theconnector has to mate itself to a female connector mounted on the tool), thetask before Carlson was not an easy one.

To compensate for the newrequirement, Honeybee designed both the male and female sides of the connector.The female side had to be inexpensive and easy to create because each toolwould have to have its own female connector versus a single male connectorattached to the crane.

The male connector has all themoving parts. It is cylindrical and populated with 11 1/16-inch diameteraluminum pins plated with gold over nickel configured in a standard MIL/Specpattern. The connector rides on compact slides - miniature guides made by NBCorp. The top faces of the two glides face each other and Honeybee's componentsreside in between the two glides supporting the connector. This configurationreduces the moment loads on the slides.

"We use a total of six slideswithin the space - three on each side," says Carlson. "The slides ride on eachother in the manner of drawer slides stacked to extend the distance they canopen a drawer. Our configuration achieves an extension of the movement equal,approximately, to the length of three slides. So instead of a half-inch stroke,we could get an inch-and-a-half stroke within a very, very small footprint. Lowmass, low load and very low profile were all required for this application."

Larry Hansen is general sales manager- director at NB Corp. of America

For more information, go to www.nbcorporation.com.