Day 26: (Mon Nov 25) Video Review

Notes for 2019-11-25. See also the Fall 2019 Calendar.

Agenda

1. Assignments

   • Due Tue Dec 3: Google Slides for final review presentation (5 minutes).

   • Due Fri Dec 6: Final Project Report

2. In-class

   • Video review of museum demos.

     • https://drive.google.com/drive/folders/1AedktR9_XkyIYFL6eLCvzZF9kpgj_kA5

     • morning: Plinko, Sleepy Whale Rescue, Pelican, Dining Dinosaur

     • midday: Marble Maze Melody, Tilting Spiral, Rockem-Sockem, Whack-a-Worm

   • Small-group exercise: lab and fab heuristics. In small groups, brainstorm a list of lessons learned regarding practical details of design and debugging. The results are below.

   • Collection of unused materials.

Lessons Learned

The following are lessons learned the hard way, a collection of debugging and design heuristics for building machines. These have been edited for clarity and organized topically.

• Iterative Design Process

  1. Test, test, test.

  2. Test to failure.

  3. Test under real conditions.

  4. Don’t get too attached to your prototype.

  5. Recut, recut, recut.

  6. Learn when to pivot to a different goal.

  7. Consider the user point of view.

  8. Plan for the unexpected use.

  9. Test subsystems in isolation.

  10. Scaffolding is necessary; you’ll need to rough out some things while developing others.

  11. Everything takes four times longer than expected.

  12. Coordinating collaborative CAD takes planning.

  13. Update your CAD as-built; it makes revision less painful.

  14. Go bigger, have physical presence.

  15. Finish the hardware early. Leave time for software revision.

  16. Read the documentation. Know the features of the software and components.

  17. When debugging, periodically recheck from the beginning of causal chains.

• Actuation

  1. Avoid two servos driving the same axis in parallel.

  2. Avoid gluing to servo horns.

  3. Set your servo horn spline position deliberately during assembly.

  4. Shafts amplify torque and shear forces.

  5. Always screw your servo horns to the servo shaft.

  6. Test and know your motor speeds and torques; estimate loads carefully.

  7. Decouple your servos from mechanical loads and dynamic forces.

• Fabrication

  1. Use the right kind of glue.

  2. Hot glue has its limits.

  3. Avoid glue at shaft joints.

  4. Glue can travel, drip, and seep.

  5. Fishing monofilament is weak, use braided cord.

  6. Avoid flimsy material.

  7. Preserve fastener access; add tool clearance holes if needed.

• Electronics and Software

  1. Always check the power; it’s the source of many problems.

  2. Multiple large servos can draw more than our 2 Amp supplies.

  3. Arduino external power should be 7-12V.

  4. Observe correct polarity: power, sensors, servos, etc.

  5. Don’t let out the magic smoke.

  6. Keep your circuits physically accessible.

  7. Solder and heatshrink, not tape.

  8. Strain-relief your wires.

  9. Label your wires.

  10. Hide your wiring.

  11. Plan your wiring.

  12. Bundle your wires.

  13. Count your I/O and plan your pin usage.

  14. Sensors can self-trigger when the machine moves; check for internal cross-talk.

  15. Ambient sound might be louder than expected; our speakers are fairly quiet.

  16. Arduino loops run arbitrarily fast; use delay() and millis().