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Degrees of Freedom Counter

Run the Degrees of Freedom Counter MicroSim Fullscreen

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Description

Use the counting rule on eight mechanisms, from a door hinge to the reBot-DevArm: read the joints each one contains and work out its degrees of freedom. Used in Chapter 2.

Each mechanism is shown as a picture beside the list of its joints and the counting rule. The arms are drawn by robot-arm-lib.js, the shared drawing library that is copied into each arm MicroSim of this book.

The arm pictures are schematic side views, not to scale. A side view cannot show a joint that turns about a vertical axis (shoulder pan) or about the arm's own length (wrist roll), so count from the joint list and not from the circles in the picture. The joint lists for the SO-ARM101 and the reBot-DevArm B601 follow the chapter.

Lesson Plan

Grade level: Middle school and up (age 12+). Time: 5 to 10 minutes.

  1. Read the joint list. Every mechanism lists the joints it includes. Revolute joints turn and prismatic joints slide.
  2. Apply the counting rule. Count each independent single-axis joint once. Choose the number and press Check. You get one attempt per mechanism.
  3. Read the reason. The feedback gives the count and why.
  4. Compare the two arms. Mechanisms 5 to 8 show each arm twice, once with its arm joints only and once with its gripper.
  5. Review. The last screen lists all eight mechanisms with their degrees of freedom. Mastery is 7 of 8.
  6. Think about it. A datasheet says an arm has 6 DOF. What would you ask before you compare it with another arm?

Specification

The learning objective, evidence of mastery and content for this MicroSim are specified in Chapter 2: Anatomy of a Robot Arm.

References

  1. Degrees of freedom (mechanics) - Wikipedia - Why a free rigid body has six degrees of freedom and how joints remove or add them.