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- our final motor gearbox with 36.75:1 reduction,
- our original Chebyshev mechanism,
- strengthened legs,
- timing belts with manual tensioners, and
- our v4 v3 counterweight.
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Due to the extremely compact and feature-dense nature of the machine, drawing and analyzing every single piece of the robot in CAD was essential to the success of the project. Every single screw, washer, and belt was modeled and analyzed for interference and motion, allowing us to find and prevent many problems before fabrication.
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It would not suffice to merely decrease the counterweight mass. The current weight is required to maintain balance with the current robot geometry. A lighter mass could be used if the counterweight shaft were longer, increasing the moment arm length about the edge of the support polygon, but this would mean that the counterweight travel time is longer, meaning the legs would have to slow down, and the legs are already fairly slow. The counterweight shaft angle also could not be reduced, as it is already near the minimum angle required to overcome static friction reliably and decreasing the angle would also increase travel time. It might be possible to change the counterweight trajectory, to do something clever with a non-linear counterweight movement. Similar to how a brachistochrone is more efficient than a linear slope, it might be possible to find a curve that reduces our transit time and reduces impact force, but moving the counterweight along a specific curve instead of allowing it to slide along a straight shaft due to gravity is a very messy mechanical problem and we did not have time to address it.
Conclusions
We are quite satisfied with the results of this project. We successfully used the analytical tools learned in this class to inform our design and decision making process and ultimately we achieved our goal of producing a reliable bipedal walking robot using only mechanisms. Our biped walks reliably using a combination of bar linkages, gears and pulleys, and discontinuous sliding mechanisms, and our project would not have been completed successfully had we insisted on using any one of these groups on its own. Of course our machine could be improved, but we are satisfied with what we achieved in the time available.