Introduction to Robotics
Guess first
Can a robot arm reach every point inside its reach?
Most students get this wrong about robot arms
Quick check · tap an answer to continue
Lesson notes
Key points
- A two-link arm with unequal links cannot reach points too close to its base, leaving a hollow hole in its reachable workspace.
- The reachable region is a ring between radius L1 plus L2 and the absolute difference of L1 and L2; equal links close the hole.
Takeaway: A 2-link arm reaches only between |L1 − L2| and L1 + L2.
Quick check: A planar 2-link arm has links of 1.0 m and 0.4 m. Can it touch a point 0.3 m from its base?
- Yes, it's within 1.4 m
- Yes, by folding the elbow
- No, it's inside the hole
Reachable workspace is a ring: |L1 − L2| ≤ r ≤ L1 + L2.
Reachable workspaceAnnulus
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