X9 Manipulator (Quad Pincer G1)
This was the first generation quad pincer manipulator. See (FIXME) for the full lineage.
| Mission Tool Summary | |
|---|---|
| Vehicle | X9, ROV Cephalopod |
| Power | M200 brushless motor, lead screw |
| Contributors | Tyler Stagge |
| Predecessors | None |
| Successors | X10 PM, X11 PM, X12 AM/PM |
| Success? | Yes, but with flaws |
The PM was designed to complete a wide range of the tasks in the 2016-2017 competition, manipulating mostly PVC pipe and couplings in the nominal 1" to 1 1/2" size range. It was also _hoped _that it would be suitable to grab 3/8" rebar.
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The PM was designed to be reliable, easy to operate, and multipurpose in the interest of reducing the total number of required tools. These requirements result in a design with only one degree of freedom, but thanks to its unique “quad pincer” design can manipulate a wide variety of objects and pipes in multiple orientations.
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The PM is driven by a Blue Robotics M200 brushless motor using a 1/4" Acme rod. Most of its parts are 3D printed in PLA, though the linkages are laser-cut white acrylic and the back plate is aluminum 7075-T6. The pivoting joints use shoulder bolts and nylon washers. The end effectors are replaceable, which allowed rapid refinement over five iterations. They are dipped in a rubberized coating called Plasti Dip® to increase their coefficient of friction.
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Finally, the Manipulator mounts to the ROV with a custom quick-release aluminum 6061-T6 bracket enabling compact storage and quick setup.
Tyler had the idea for the quad pincer rather early in the season, and had the first prototype working before the rules were even released. That allowed for a lot of iteration, with 5 total end effector designs being printed and tested as we honed in on what the PM would be used for. In response to our pool testing, the vertical "teeth" on the upper end effectors were added to help turn the "locking mechanism" as part of the Entertainment task.
We also gave up on trying to use it to manipulate the 3/8" rebar, in part because the features for it were prohibitively hard to line up, and in part because we didn't have a camera view adequate to place the rebar where it needed to go (the manipulator itself blocked the view, inspiring the use of secondary cameras on X10 and X12 to give an additional side view of future PMs).
While the quad pincer went on to be a mainstay of ROV tool design, this first implementation had a fundamental flaw: the lead screw (acme rod). Lead screws should never be used without limit switches; this tool used no such sensors. As such, at the extremes of travel, the motor tightened the screw. Since brushless motors don't have stellar stall torque, this meant that the PM was constantly jamming itself in the open or closed position. It was still usable enough, but this design should never be repeated. Unfortunately, since we were still hesitant to try pneumatics (it hadn't been done since ROV Model N (X5)), we tried a lead screw-driven manipulator again on X10.
The Plasti-Dip didn't work very well.
- A judge in our technical presentation called the quick-release mechanism "dank".
- After competition, the manipulator was practically destroyed when Sam Deghuee left X9 in his car for a week in the summer. All the 3D printed parts warped to all hell.
- The manipulator was also very effective on beer bottles.
manipulator, pm, acme rod, lead screw, m200, quick release, end effector, claw, quad pincer, plasti-dip
This page was written by Tyler Stagge.