MODULE M7 · 15.0 HOURS

Firmware Development and Control

0% complete

Prototype safety boundary

Low-voltage educational prototype, not a certified machine safety system
Do not use stop circuits created by learners as safety functions or emergency stops
Perform normal stops by software torque release; after planned stops, physically disconnect the 3 insulated power adapters and verify the de-energized state by measurement before maintenance or access
Do not place hands in the operating range while power is applied; test from no-load in a fixture
Wear impact-resistant work goggles during cutting, drilling, and tendon tension testing
In case of abnormal heat, odor, or smoke, do not approach; cut the power supply to the 3 adapters via a pre-designated building panel breaker outside the hazard zone or a certified upstream master disconnect and evacuate. If no upstream disconnect is available outside the hazard zone, do not energize the system. Torque release is not a substitute for power disconnection
Before introducing to environments with human access, a dual-channel, manual reset, EDM, feedback-capable dual contactor must be separately designed and verified under the review of a qualified safety expert

LEARNING OBJECTIVES

Module objectives

Understand DYNAMIXEL smart actuator communication and control framework.
Implement actuator and FSR sensor signal acquisition using OpenCR control board.
Design real-time robot control state machine and closed-loop feedback loop.
Program safe power management and torque release sequences.

Firmware Architecture and DYNAMIXEL Control

The robotic hand firmware acquires sensor data and processes actuator commands within a high-speed loop. The OpenCR 1.0 controller is based on a 216MHz ARM Cortex-M7 processor [S13] and processes DYNAMIXEL protocol 2.0 without a separate bridge [S11], minimizing latency. Each actuator supports current, velocity, and position modes, and the robotic hand uses a current-control-based torque grip strategy.

FSR Force Feedback System

The FSR 402 sensor has a resistance characteristic inversely proportional to the force applied [S12]. A voltage divider circuit is configured with a 10kΩ resistor on the 3.3V sensor rail using OpenCR’s 12-bit ADC [S13]. The divided voltage is normalized via ADC value = (V_in * R_fsr) / (R_fsr + R_ref), and this value is linked with the tendon tension of the fingers and used as grip force feedback.

Safe Control Routine

System stop is divided into two stages for safety. In the software stage, actuator torque is released (Torque Off) to immediately remove physical driving force. Before maintenance, you must physically disconnect the 3 independent power adapters and verify that all branches are less than 1V using multimeter DC mode.

WORKED EXAMPLES

Worked examples

1. Setting actuator goal position/current: An example of using DYNAMIXEL SDK to set current limit (Goal Current) for XM430 actuator and updating finger joint final position via a PID loop based on sensor values.
2. FSR voltage data filtering: Code implementation for applying a Moving Average Filter to remove noise from raw data collected from ADC and normalizing the range with upper (20N) and lower (0.2N) limits [S12].

LAB PROTOCOL

Robotic Hand Integrated Control and Precision Grip Practice

1
Verify that the voltage of each independent branch is less than 1V using multimeter DC mode before starting assembly.
2
Solder FSR voltage divider circuit to OpenCR's 3.3V sensor rail and connect to ADC port.
3
Scan IDs of 11 actuators using DYNAMIXEL SDK and set initial positions.
4
Test finger joint drive commands in no-load state and adjust tendon elongation and tension.
5
Visualize FSR sensor data via serial monitor and tune grip force response.

Safety check

Never use 5V or 12V actuator power as supply for FSR sensor circuit.
Never approach the operating range of fingers while system is energized; use fixtures.
Never connect positive (+) terminals of power branch adapters to each other.
Before maintenance/assembly access, physically disconnect the 3 power adapters and verify that it is less than 1V in all branches by measurement.

Lab deliverables

Firmware source code including real-time sensor data feedback
Data sheet for normalization and calibration of voltage divider data
Actuator feedback loop normal operation logs

ASSIGNMENT

Grip State Machine Design and Implementation

Deliverables

Grip and release state machine diagramCode implementing current-based torque controlFinal performance evaluation report

Rubric

Is the current limit range (0-2.3A) according to sensor values stably controlled?
Does the physical tension dissipate immediately upon the torque release command?
Is a safe hardware disconnection procedure explicitly stated in the code?

FIELD CHECK

Completion criteria

Multimeter verification completed that independent power supply and fuse protection for each branch are configured according to BOM specifications
Confirmed precision force signal acquisition and filtering of 5 FSR sensors via OpenCR ADC
Successfully performed the software torque release routine and post-physical power disconnection measurement procedure
The grasping state machine processes actuator and sensor data as intended, and the final report is submitted

MODULE SOURCES

Module sources

OpenCR 1.0emanual.robotis.com · technical_documentation
XM430-W350 e-Manualemanual.robotis.com · datasheet
FSR Model 402interlinkelectronics.com · datasheet