Hi, i was wondering what is the difference between an L shaped arm (ex: 2023 jack in the bot) or a normal one jointed linear arm. is there a mechanical disadvantage of the L shaped arm? would the motor need more torque to turn it?
Short answer: not really
Longer answer : The L shaped arm has more material, therefore more mass (assuming similar construction techniques), but this is marginal.
The advantage to the L is most geometric, meaning the tube comes at at more favorable angles when 2910 used it, and may of had some center of mass cinsiderations. I suspect they also needed the L for packaging the reduction as well, (but this is off the top of my head).
A straight arm on 2910’s 2023 bot with the same pivot (assuming packaging works), would have performed similarly. (At least that is what my gut says)
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The other big advantage of the offset pivot (“L-arm”) is that it allows the pivot to be a dead axle. We went to the extreme with a precision machined large-OD axle and thin section bearings in 2023, but you could get the same functionality with a smaller tube and bushings or even MaxSpline or SplineXL. The dead axle provides a lot of additional rigidity to the structure.
More traditional Pink arms are live axle, at least in the sense that the bearings are on the fixed structure and the axle rotates with the arm. This is required because the axle can’t pass through the middle of the arm since that would conflict with the extension motion.
The main downside is the arm is “unbalanced” and will see a bigger radial force when rotating quickly, which affects robot stability a lot more. That can limit how fast the arm can rotate without kicking up the base.
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