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Joint Limit Chooser

Run the Joint Limit Chooser MicroSim Fullscreen

You can include this MicroSim on your website using the following iframe:

<iframe src="https://dmccreary.github.io/robot-arm/sims/joint-limit-chooser/main.html"
        height="638px" width="100%" scrolling="no"></iframe>

Description

Move a torque limit against the torque a task needs and watch a joint hold with margin, hold with little margin, or stall. Then recommend a torque limit for five joint tasks with the rule of thumb: the smallest limit that is at least 1.5 times the need. Used in Chapter 5.

The gauge runs from 0 to 100 percent of the joint's maximum torque. It marks the torque the task needs, the point 1.5 times higher, and the limit you set. Below the need the joint stalls. Between the need and 1.5 times the need it holds with little margin. Above that it holds with margin, and a still higher limit only raises the push and the heat if something goes wrong.

The 1.5 margin is a teaching rule of thumb, not a standard, and the tasks and percentages are illustrative. The idea of a lower limit for the gripper follows LeRobot's SO-101 configuration, which limits the gripper to 50 percent.

Lesson Plan

Grade level: Middle school and up (age 12+). Time: 10 to 15 minutes.

  1. Predict first. The task needs 30 percent and the limit is 50 percent. Before you move a slider, say what will happen at 25 percent.
  2. Explore. Lower the limit below the need and watch the joint stall. Raise it to 100 percent. The joint does the same job, but the bar under the gauge grows.
  3. Five tasks. Each task gives the torque it needs and three limits. Choose the one you recommend and press Check. You get one try for each task, and 4 of 5 is mastery.
  4. Read the feedback. After each answer the sim shows how many times the need each option is.
  5. Think about it. Set the need to 80 percent. No limit gives a margin of 1.5. What does that tell you about the actuator?

Specification

The learning objective, evidence of mastery and content for this MicroSim are specified in Chapter 5: Actuators and Sensors.