AUTHOR: Kevin Shin

Outcome

Initial Goal: Research and report the technical implementation steps for Reachy Humanoid

Realized Outcome: Defined tools and steps for implementing safety guardrails at the actuator level to provide 1) Safety fencing/limits, and 2) natural humanoid movements.

Steps to achieve outcome

Outline/Framework/Recipe/Steps

1. Reachy Robot Safety Guardrail/Fencing - using Dynamixel Firmware

   • Safety Guardrails? Why?

     • [x] a. Robots are constantly trying to take over the world and should never be trusted
     • [ ] b. Robots are machines and they break, malfunction, and faithfully execute human mistakes in software

   • Possible solutions for Reachy?

     • [x] Fenced in "Robot Only" zone ← does not meet our vision/goal for Reachy
     • [ ] Implement Electro-Mechanical solution ← Configure actuator/servo firmware to specify minimum and maximum movement range
     • [x] Implement safety zone in the Luos firmware ←Although possible and critical step for Luos modular architecture, we are currently not setup to configure Luos firmware
     • [ ] Implement SW development safety policy for movement and behaviors ← Should be a working document that we continuously update as a part of our Reachy SW framework

     

     

2. Dynamixel Firmware configuration Options

   • Dynamixel Software Development Kit - SDK provides API control functions, but is requires C/C++ or Python language skills and implementing Safety Guardrail and PID configuration can be done using Dynamixel Wizard2.0 - https://emanual.robotis.com/docs/en/software/dynamixel/dynamixel_sdk/overview/
     • Sample Code - https://emanual.robotis.com/docs/en/software/dynamixel/dynamixel_sdk/sample_code/c_read_write_protocol_1_0/
     • Github - https://github.com/ROBOTIS-GIT/DynamixelSDK
   • Dynamixel Wizard 2.0 - an optimized tool for managing Dynamic's from various operating systems. The following features are provided with the Wizard 2.0.
     • Dynamixel firmware update & Diagnosis
     • Dynamixel configuration and test
     • Dynamixel data plotting in read-time
     • Generate & monitor Dynamixel packets

   

3. Recommended Reachy Dynamixel Configurations

   

   • To configure Safety Guardrails/fencing

     • Set limit on the CW & CCW rotation to prevent movement beyond this limit
     • Recommendation - Limit MX servo (shoulder) from moving beyond 45 degrees or less to ensure people/kids around Reachy can not be hit by the arm.

     

   • To configure PID for smoother and accurate movement - Dynamixel MX servos

     • Position P gain (Proportional) - Most commonly used for tuning PID. P determines how aggressive the servo reacts to the command. Think of it was the accelerator in your car. Dynamixel default is 800 which is probably too fast for a humanoid.
     • Position I gain (Integral) - It is the gain that corrects the error over time. When the P overshoots or undershoots, I tries to auto-correct it. I is usually a tiny fraction of the P, and too much will cause oscillation or wobbly effect on the robot's arm.
     • Position D gain (Derivative) - It is used for dampening effect from the P. Think of it as the break in your car. Too much D will cause a drag, but good if the movement is overshooting to target.
     • Recommendation - MX servos (shoulder) will have to biggest effect on the arm movement. As such, P should be lowered to 200 or even 100. If lowering P causes the positional inaccuracy on the hand/claw, we may have to increase the I with the increments of 5 or 10. We may also need to raise the D by 20 incrementally to reduce the oscillation.

Reference material

• Dynamixel firmware update - https://www.youtube.com/watch?v=ixw8P0qHBxM
• Safety Joint example - https://youtu.be/vkigPdN5pMg

                                            ***Hang in there!  Reachy will be here soon!***