<story><title>Low Cost Robot Arm</title><url>https://github.com/AlexanderKoch-Koch/low_cost_robot</url></story><parent_chain><item><author>xg15</author><text>&amp;gt; &lt;i&gt;The hard part is repeatability. You need tight tolerances and each joint in the arm adds inaccuracy the further you get from the base. If the base has 1mm of wiggle, the 20cm arm has 4mm wiggle at the end, and the arm beyond it has even more.&lt;/i&gt;&lt;p&gt;Could this be solved by software instead of expensive hardware?&lt;p&gt;Some idea I had a while ago was to build an arm out of cheap, &amp;quot;wobbly&amp;quot; components for the large-scale movements, but then add some stages at the end that have a small movement range, but can be controlled very precisely.&lt;p&gt;Finally, add a way to track the deviation of the tool&amp;#x27;s actual position from the desired position very precisely, maybe with a tool-mounted camera.&lt;p&gt;Then you could have a feedback loop in software which tracks the tool&amp;#x27;s deviation from the desired position and uses the &amp;quot;corrective&amp;quot; stages at the end to counteract it.&lt;p&gt;I&amp;#x27;m not sure if this would work, however.&lt;p&gt;(There is also the question how long the &amp;quot;counteracting&amp;quot; would take. It&amp;#x27;s one thing to &amp;quot;eventually&amp;quot; arrive at the desired position at the end of the path - e.g. for pick-and-place - and another to stay below some maximum deviation for the entire path, e.g. for etching or welding.)</text></item><item><author>mtreis86</author><text>I started working on a similarly sized arm. I&amp;#x27;ve got a use-case, long time friends with a glass blower. I was thinking of using it to make faceted glass pendants. They&amp;#x27;ve got a faceting machine but it is manually operated.&lt;p&gt;The hard part is repeatability. You need tight tolerances and each joint in the arm adds inaccuracy the further you get from the base. If the base has 1mm of wiggle, the 20cm arm has 4mm wiggle at the end, and the arm beyond it has even more.&lt;p&gt;You also, for faceting purposes, need much finer resolution than an ungeared servo will have. Gearing it is tricky because you want backlash to keep the join tight, but not so much that it has high friction when moving. You don&amp;#x27;t really want to use a worm gear because they&amp;#x27;re both slow and overly rigid. So a cycloidal gear is the best bet for the gears in the arm. You also need real servos with some amount of feedback because grabbing at glass is sketchy at best.&lt;p&gt;I was estimating 1-2k build cost, bulk of that is in the gearboxes.</text></item></parent_chain><comment><author>brozaman</author><text>I&amp;#x27;m a software engineer myself so I don&amp;#x27;t know a lot about this, but there are a few patterns that are not far off of what you&amp;#x27;re describing. For instance:&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Input_shaping&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Input_shaping&lt;/a&gt;
&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Proportional%E2%80%93integral%E2%80%93derivative_controller&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Proportional%E2%80%93integral%...&lt;/a&gt;</text></comment>
<story><title>Low Cost Robot Arm</title><url>https://github.com/AlexanderKoch-Koch/low_cost_robot</url></story><parent_chain><item><author>xg15</author><text>&amp;gt; &lt;i&gt;The hard part is repeatability. You need tight tolerances and each joint in the arm adds inaccuracy the further you get from the base. If the base has 1mm of wiggle, the 20cm arm has 4mm wiggle at the end, and the arm beyond it has even more.&lt;/i&gt;&lt;p&gt;Could this be solved by software instead of expensive hardware?&lt;p&gt;Some idea I had a while ago was to build an arm out of cheap, &amp;quot;wobbly&amp;quot; components for the large-scale movements, but then add some stages at the end that have a small movement range, but can be controlled very precisely.&lt;p&gt;Finally, add a way to track the deviation of the tool&amp;#x27;s actual position from the desired position very precisely, maybe with a tool-mounted camera.&lt;p&gt;Then you could have a feedback loop in software which tracks the tool&amp;#x27;s deviation from the desired position and uses the &amp;quot;corrective&amp;quot; stages at the end to counteract it.&lt;p&gt;I&amp;#x27;m not sure if this would work, however.&lt;p&gt;(There is also the question how long the &amp;quot;counteracting&amp;quot; would take. It&amp;#x27;s one thing to &amp;quot;eventually&amp;quot; arrive at the desired position at the end of the path - e.g. for pick-and-place - and another to stay below some maximum deviation for the entire path, e.g. for etching or welding.)</text></item><item><author>mtreis86</author><text>I started working on a similarly sized arm. I&amp;#x27;ve got a use-case, long time friends with a glass blower. I was thinking of using it to make faceted glass pendants. They&amp;#x27;ve got a faceting machine but it is manually operated.&lt;p&gt;The hard part is repeatability. You need tight tolerances and each joint in the arm adds inaccuracy the further you get from the base. If the base has 1mm of wiggle, the 20cm arm has 4mm wiggle at the end, and the arm beyond it has even more.&lt;p&gt;You also, for faceting purposes, need much finer resolution than an ungeared servo will have. Gearing it is tricky because you want backlash to keep the join tight, but not so much that it has high friction when moving. You don&amp;#x27;t really want to use a worm gear because they&amp;#x27;re both slow and overly rigid. So a cycloidal gear is the best bet for the gears in the arm. You also need real servos with some amount of feedback because grabbing at glass is sketchy at best.&lt;p&gt;I was estimating 1-2k build cost, bulk of that is in the gearboxes.</text></item></parent_chain><comment><author>tomp</author><text>&amp;gt; Could this be solved by software instead of expensive hardware?&lt;p&gt;Yes.&lt;p&gt;Imagine a human putting a screw in a hole. You don&amp;#x27;t follow the &amp;quot;optimal&amp;quot; trajectory, you adapt it on the fly, even do several quick trials to do it.&lt;p&gt;Humans do it with a combination of vision, touch and planning.&lt;p&gt;Each of these is currently still a &lt;i&gt;huge&lt;/i&gt; problem for AI, nowhere &lt;i&gt;near&lt;/i&gt; human level.</text></comment>