Build Your Own Bender: Step 1, Controlling a robotic arm with Qt Quick Jon Trulson & Dustin Kassman Presented by • Jon Trulson, Senior Development Engineer – Specializes in Linux/Unix & embedded systems • Dustin Kassman, Program Manager – Herds cats (i.e. programmers) • Key players – Nick Iwuc – Vlad Moolle, Ivan Sobol – Roland Krause Agenda • • • • Overview of the project About the AX-12A Smart Arm Architecture and Components A closer look – Server – Client – User Interface • Demonstration • What comes next The Bender Project • Design & build a library & infrastructure that enables the control of a Smart Arm across a network • Components – AX-12A Smart Arm – Controller with server – Remote client AX-12A Smart Robotic Arm • 5-axis robotic arm – ~20” reach, 3 lb lift • Seven AX-12A digital servos • Aluminum construction • $850 for base arm, power supply, wiring harness, & USB2Dynamixel dongle – Upgrades: Servos, grippers, pressure & ultrasonic – Pro-series models • CrustCrawler Robotics (www.crustcrawler.com) Architecture Client/Server Components Low-level Arm Control Library • AXServo class – Responsible for communication with the arm’s serial network • Sends commands/reports status – Deals with communication errors – Handles dual-servo joints • sendCommand()– lowest level command mechanism • The workhorses - readByte(), writeByte(), readWord(), writeWord() More Low-level Arm Control Library • Common registers – goalPosition, Moving, Speed • Servo health – temperature, errors • Torque – applying force and maintaining the goal position • Telemetry registers - currentSpeed, currentPosition Command Server Component • Handles communication with a local or remote client – Only allows one network client at a time • Simple line-based text protocol – telemetry joint=<jointname> position speed load temperature torque moving error – move joint=<jointname> position=<0-1023> [wait] – torque joint=<jointname> enabled=(true|false) – ping joint=<jointname> – Pause for=<milliseconds> • Also supports entering commands using telnet, netcat, etc Qt Quick Development Client Manual/Script Client Demo Lessons Learned • Expect communication errors • ID servos before assembling arm • Configure servos with proper speed & torque – Some settings require power-cycling servos • Watch for conditions that can damage servos • Make sure servos will respond to all commands – CTRL_StatusReturnLevel == 2 • Don’t try to make a servo exceed the physical limits imposed by the arm Next Steps • AXServo – Add support for joints with >2 servos – Read/write multiple (contiguous) registers – Support MX and Pro servos • Command server – Protocol commands to support describing an arm’s configuration (number of servos, arm length, etc) – Make it easier to move joints simultaneously from a script • User client – Finish manual control version – Develop a full visual control version Contact us • Dustin Kassman ([email protected]) • Jon Trulson ([email protected])