Linkage Mechanism Design and Simulation

I'm not a fan of pneumatics on FRC robots. The advantage of pneumatics is force and speed. They create two-position linear motion for the robot. They require a lot of additional hardware and add several points of failure to the overall robot. My resistance to pneumatics is an overall cost-benefit analysis. I can't clear the benefit with the costs to overall reliability of the robot.

A Linkage Mechanism can achieve the same motions that pneumatics can. I think one of the reasons that teams keep selecting for pneumatics is because they don't include linkages as an option in their trade studies. And the reason linkage mechanisms are not considered during trade studies is because teams have little to no experience with linkages.

As World Championships for the 2022 season approach, we need to start thinking about project for the Internal Research and Development (IRAD) Season (from Graduation to First Day of School). The IRAD Season is the opportunity to gain experience in systems and mechanisms that we've never done before. 

If you're looking to experiment with linkages during the IRAD Season, start by building the linkage used on the 2022 Everybot (https://www.118everybot.org) to raise and lower the intake mechanism. The great thing with this linkage is that we can see many 2022 robots that use pneumatics for this same motion. 

The next stage to gaining experience with linkage mechanisms starts with the Solarbotics GraviTrack marble run (https://www.solarbotics.com/product/60410). This uses a series of linkages driven by a single motor to move two arms to return the marble to the start of the run. This can be seen in the video of the GraviTrack in motion (https://www.youtube.com/watch?v=_qIAJ4MHyL4).

The GraviTrack was designed using David Rector's Linkage Mechanism Design and Simulation tool (https://blog.rectorsquid.com/linkage-mechanism-designer-and-simulator/). The design of the GraviTrack ball lifter from the simulator is available at https://www.youtube.com/watch?v=CmLF00YgAVY. The simulation allows you to trace the endpoints of the arms to show the curves they trace out. 

David Rector's YouTube channel (https://www.youtube.com/channel/UCj3siyJnn6sfuz9gyUI0irQ) has several other linkage simulations and videos of marble runs he's designed and built. It is worth spending time running through his videos to get a sense of all the designs that can be achieved with the software.

As I've been talking about the GraviTrack with mentors, I remembered years ago an episode of Tested with Adam Savage where he assembles a LEGO kit of Sisyphus pushing the boulder up the hill (https://www.youtube.com/watch?v=U46Yo_6z_F4). 

The kit for this automata has been updated. The original design (https://jkbrickworks.com/sisyphus-kinetic-sculpture/) references a paper from Disney Research about finding ways to design for natural curves for things like leg movements and arm movements. It is the Computational Design of Mechanical Creatures (https://la.disneyresearch.com/publication/computational-design-of-mechanical-characters/). Essentially, Disney developed a software tool where an animator could draw out the curve that they wanted the arm or leg to move through and then the software would figure out the linkages needed to create that motion from simple rotation inputs, like a single motor. A video of the software in use is available at https://m.youtube.com/watch?v=DfznnKUwywQ. 

The work to develop the software is out of the range of most FRC teams. Still it should be possible to use the Linkage Mechanism Design and Simulation tool to build the sorts of motion that teams are getting from their existing pneumatic designs.

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