Как Сделать Робособаку на BLDC моторах | Часть №2

Summary of YouTube Video:

Key Concepts:

• Robo-dog design and construction
• Quasi-direct drive (Quasi-DD)
• Actuator design (BLDC motor + gearbox)
• Leg kinematics (3 degrees of freedom)
• Torque transmission methods (SHP, belt, lever)
• 3D printing for robotics
• STM32 microcontroller
• SPI communication with encoders
• Force/torque control
• Wave gear reducer (WGR)
• Planetary gear reducer

1. Introduction and Motivation:

• The video builds upon a previous video where powerful servo drives were created using brushless DC (BLDC) motors and 3D-printed gearboxes.
• The goal is to design and build a quadruped robot (robo-dog) from scratch as a robotics exercise.
• The video aims to provide a detailed, step-by-step guide for viewers to replicate the project.

2. Robo-Dog Kinematics and Actuation:

• Most modern robo-dogs have a simple kinematic structure: a base with four legs, each with three degrees of freedom (DOF). Two DOF are in one plane, and one is rotational.
• Each leg uses three motor-gearbox units (actuators) to control the joints.
• Direct drive (motor without gearbox) lacks the necessary torque. High gear ratios result in slow, jerky movements.
• A "quasi-direct drive" (Quasi-DD) approach is used: powerful motors with relatively low gear ratios (around 1:12).
• Quasi-DD allows for force/torque control through motor back EMF and current sensing, enabling compliant behavior and shock absorption.
• The video references a previous project where actuators were built using drone BLDC motors and wave gear reducers (WGR).
• The gear ratio of the WGR is increased to 12:1 for this project.

3. 3D Printing and Materials:

• All parts are 3D printed using PLA and PETG filaments from Bestfilament.
• Structural parts are printed with 25% infill, while others use 10% infill.
• STL files for the 3D models will be made available after the robot is complete.

4. Leg Design and Knee Joint:

• The knee joint is typically unactuated, with the actuation mechanism moved to the hip for weight reduction and faster leg movement.
• Three methods for transmitting torque to the knee are discussed:
  • Ball screw: Used in Spot, involves a ball screw driving a nut connected to a rod that moves the lower leg.
  • Timing belt: Used in Mini Cheetah.
  • Lever: A simple and reliable method using a linkage.
• The lever method is chosen for its simplicity and reliability.
• The actuator is modified by removing the top part of the gearbox and replacing the output shaft with a lever arm.
• A bearing is integrated into the leg structure to support the lever arm.
• The leg is designed with minimal parts, but some parts are split for printing due to size limitations.
• 4mm stainless steel rods are used for joints, with aluminum tubes for reinforcement.

5. Linkage and Joint Construction:

• The upper leg (femur) is split into two parts for printing and joined with an overlapping section reinforced with an aluminum tube.
• Bearings are installed in the knee joint for connecting the femur and tibia.
• Calibrated 6mm stainless steel shafts are used for the knee joint to minimize play.
• A cover is added to the linkage.
• Aluminum tube is used for the linkage, with threaded inserts and ball joints.
• The initial linkage design had excessive play due to loose threads, so the threads were re-tapped using a die.

6. Actuator Integration and Modular Design:

• The second and third actuators are modular and identical, designed for easy connection.
• A flange and lock system are used to connect the actuators.
• Pins are used to transfer load between the actuators.
• The flange is attached to the leg and the actuator.
• The actuator is connected to the leg using the flange and lock system.

7. Testing and Performance:

• A test stand is built using aluminum profiles to evaluate the leg's performance.
• Electronics are mounted on a plywood board for testing.
• An older driver version is used for initial testing due to the new driver not being ready.
• The video suggests using clones of odrive or waiting for the creator's custom driver.
• The Arduino is replaced with an STM32 microcontroller, and AS5600 encoders are replaced with MT6701 encoders for increased speed.
• The MT6701 encoder is connected via SPI interface.
• The test results are better than expected.
• The leg can lift its own weight and additional weight.
• The leg can lift approximately 6 kg, corresponding to a torque of 12 Nm at 8A current.
• The increased performance is attributed to the STM32 and MT6701 encoder.
• The robot dog is planned to weigh around 15 kg.

8. Reducer Design Iteration:

• A second gearbox design with a gear ratio of 14.4:1 (potentially up to 16:1) is created.
• The second design is a traditional planetary gearbox.
• The planetary gearbox is slightly larger than the wave gear reducer but is modular and interchangeable.
• The planetary gearbox performs similarly to the wave gear reducer.

9. Conclusion:

• The video demonstrates the design and construction of a single leg for a robo-dog.
• The leg is capable of lifting significant weight and potentially jumping.
• The project is ongoing, with future videos planned to cover the robot's body and other aspects.
• Viewers are encouraged to subscribe, comment, and support the channel.

Key Quotes:

• "Назовём это квази квази прямой привод и пойдём дальше" - Referring to the modified quasi-direct drive system.
• "у меня тормозов нет я могу сложность проектов увеличивать до предела вопрос заходит ли это вам" - Highlighting the potential for more complex projects based on audience interest.

Technical Terms:

• BLDC motor: Brushless DC motor, an electronically commutated DC motor.
• Quasi-direct drive (Quasi-DD): A motor system with a low gear ratio, allowing for both torque and responsiveness.
• Wave gear reducer (WGR): A compact gearbox using a flexible spline to achieve high gear ratios.
• Degrees of freedom (DOF): The number of independent movements a joint or system can perform.
• STM32: A family of 32-bit microcontrollers based on the ARM Cortex-M core.
• SPI: Serial Peripheral Interface, a synchronous serial communication interface.
• Encoder: A sensor that measures the angular position or velocity of a rotating shaft.
• PLA/PETG: Common 3D printing materials.

Logical Connections:

• The video builds upon the previous video by applying the previously developed servo drives to a new project.
• The design choices are justified based on the requirements of the robo-dog application.
• The testing results are used to validate the design and identify areas for improvement.

Synthesis/Conclusion:

The video provides a detailed look into the design and construction of a robo-dog leg, focusing on the actuator design, kinematics, and testing. The use of quasi-direct drive, 3D printing, and modular design principles are highlighted. The project demonstrates the feasibility of building a powerful and functional robo-dog leg using readily available components and techniques. The successful testing results indicate that the leg is capable of lifting significant weight and potentially enabling jumping, paving the way for further development of the complete robot.