Introduction to Robotics
Guess first
Can a 2-link arm reach its own base?
Most students get this wrong: where can a two-link arm actually reach?
Quick check · tap an answer to continue
Lesson notes
Key points
- A planar arm with links of 50 cm and 30 cm sweeps a ring, not a full disc, so points closer than 20 cm are unreachable.
- The outer radius is L1 plus L2 and the inner radius is the difference, so only equal links let the tip touch the base.
Takeaway: Unequal links leave a hole in the middle of the workspace.
Quick check: Links 50 cm and 30 cm, rotary joints: can the tip reach a point 10 cm from the base?
- Yes, anywhere inside 80 cm
- Yes, by folding the elbow
- No, minimum reach is 20 cm
A 2-link planar workspace is a ring from |L1−L2| to L1+L2.
Reachable workspace|L1 − L2| ≤ r ≤ L1 + L2
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