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Space Systems Lab
University of Maryland Extravehicular Activity Three-Dimensional Roller Wrench

A prototype extravehicular activity (EVA) wrench shown in Figure 1 has been developed that has the three-dimensional (3-D) roller mechanism shown in Figure 2 in place of the traditional ratchet mechanism.

Figure 1 Extravehicular Activity Three-Dimensional Roller Wrench

The EVA 3-D roller wrench operates using 3-D rollers connected with springs installed between concentric cylindrical races as shown in Figure 2. The pins "disengage" one set of rollers, which allows its "engaged" partner roller to roll up the wedge surface of the hub (shown in Figure 3) when the wrench is turned in one direction. Rotation in the other direction causes the roller to roll down the wedge surface, disengaging the clutch for overrunning. This action allows the wrench to apply torque in one direction and free spin in the other like a traditional ratchet wrench. Moving the pins clockwise so that they engage neither roller will cause the wrench to become a rigid bar, allowing the wrench to apply torque in both directions. Rotating the pins further clockwise will cause them to "disengage" the rollers that were previously engaged, allowing the wrench to apply torque in the opposite direction as before.

Figure 2 3-D Roller Wrench Mechanism

Figure 3 Hub

The following tests of the EVA 3-D Roller Wrench have been run:

KC-135A Reduced Gravity Flying Laboratory Tests

Comparative tests were run with the EVA 3-D roller and existing Shuttle ratchet wrenches during 80 periods of 20 - 25 seconds of weightlessness.

Neutral Buoyancy Laboratory Evaluations

Comparative tests were run with EVA 3-D roller and existing International Space Station ratchet wrenches by suited subjects during Hubble Space Telescope Servicing Mission training runs.

Space Experiment Module Flight on STS-95

The 3-D roller mechanism was flown on Space Shuttle Mission STS-95 in October 1998 to evaluate its performance in an extended period of micro-g.

The EVA 3-D roller wrench is being considered for flight on a future Hubble Space Telescope Servicing Mission and also for International Space Station construction missions.

I have also written papers describing the EVA 3-D roller wrench:

  • Roberts, B., "Development of a 'Ratchetless' Wrench for ExtravehicularActivity," 1999 AIAA Region I Mid-Atlantic Student Conference, 16-17 April 1999 (alsopublished as SSL Document Number 99-005).[ paper (371 K PDF) | presentation ]
  • Roberts, B. J. and D. L. Akin, "Weightless Testing of a 'Ratchetless'Extravehicular ActivityWrench," SAE 1999-01-2036, 29th International Conference on Environmental Systems,12-15 July 1999 (also published as SSL Document Number 99-007).[ paper (566 K PDF) | presentation ]
  • Roberts, B., "Evaluation of a Three-Dimensonal Roller Clutch Reversible Hand Socket Wrenchfor Extravehicular Activity," Master of Science Thesis, Department of Aerospace Engineering,University of Maryland, 9 August 1999 (also published as SSL Document Number 99-012).[ paper (3.5 MB PDF) | presentation ]

The wrench has also received some publicity:


EVA Wrench Home 3-D Sprags and Rollers Commercial 3-D Roller Wrench EVA 3-D Roller Wrench
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