https://bbokser.github.io/tags/rexhopper/ Recent content in Rexhopper on Ben Bokser's Blog Hugo -- 0.152.2 en-us Sat, 08 Apr 2023 00:00:00 +0000 https://bbokser.github.io/posts/2023-04-08/ Sat, 08 Apr 2023 00:00:00 +0000 https://bbokser.github.io/posts/2023-04-08/ <p>The new REx Hopper leg parts (which I hinted at in an earlier post) are finally in, and they look great.</p> <p><img loading="lazy" src="https://bbokser.github.io/images/2023-04-08/machined_1.jpg"></p> <p>I was worried they&rsquo;d be expensive, but the total cost for all three components shown here (including shipping from China) was only $312.</p> <p><img loading="lazy" src="https://bbokser.github.io/images/2023-04-08/machined_2.png"></p> <p>As for the other components, they&rsquo;ve been 3D-printed using <a href="https://www.windform.com/top-line/windform-xt-2-0/">Windform XT 2.0</a>, which is supposed to have excellent mechanical properties.</p> <p><img loading="lazy" src="https://bbokser.github.io/images/2023-04-08/3dp.jpg"></p> <p>Anyway, I&rsquo;ve started my new job in Boston, whereas work on the REx Hopper is supposed to continue in Pittsburgh. As such, I&rsquo;ll be directing my design modifications from afar. The project is gradually being transferred into the hands of my former labmates at the REx Lab, who will be running control experiments on the robot.</p> https://bbokser.github.io/posts/2023-02-17/ Fri, 17 Feb 2023 00:00:00 +0000 https://bbokser.github.io/posts/2023-02-17/ <p>The REx Hopper is now capable of balancing! However, it suffers from extreme oscillation at a relatively low frequency (about 8 Hz).</p> <p><div style="position: relative; padding-bottom: 56.25%; height: 0; overflow: hidden;"> <iframe allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share; fullscreen" loading="eager" referrerpolicy="strict-origin-when-cross-origin" src="https://www.youtube.com/embed/9MAG_7aluU8?autoplay=0&amp;controls=1&amp;end=0&amp;loop=0&amp;mute=0&amp;start=0" style="position: absolute; top: 0; left: 0; width: 100%; height: 100%; border:0;" title="YouTube video"></iframe> </div> <!-- raw HTML omitted --><!-- raw HTML omitted --></p> <p><img loading="lazy" src="https://bbokser.github.io/images/2023-02-17/resonance_plot.png"></p> <p>This looks like a controller issue&ndash;perhaps even a simple matter of gain tuning&ndash;until you look closer and slow the footage down. It&rsquo;s a clear case of mechanical resonance&ndash;notice how much the leg flexes back and forth.</p>