I Built a Robot Dog Using... Rope?

Summary

In this video, the creator showcases the design and development of 'Cara', a highly dynamic robot dog powered by innovative capstand drives. Built using rope-driven joints for precise movement, Cara is designed to be modular, lightweight, and aesthetically pleasing. The video takes viewers through the technical challenges, including motor tuning, inverse kinematics, and stabilizing the robot's walking mechanics. After numerous tests, including overcoming parts failures, Cara is brought to life with advanced programming and hardware solutions. The creator also introduces upcoming upgrades and the promise of an open-source smaller version.

Takeaways

• 😀 Cara is the fourth robot dog created by the builder, and it features unique rope-driven joints powered by capstand drives, making it the most dynamic and well-designed so far.
• 😀 A capstand drive is a rope-driven speed reducer that uses tensioned rope instead of gears, offering zero backlash, low noise, and precision.
• 😀 The builder faced challenges in achieving a perfect 8:1 gear ratio with the capstand drives, but solved it by interpolating data between two test drives to create the ideal one.
• 😀 The robot dog design utilizes Eagle Power 90 KV brushless motors for high torque and responsiveness, paired with low gear ratio capstand drives for precise joint movement.
• 😀 To control the motors, the builder uses Orive S1 FOC controllers that allow for high-precision control of position, velocity, and torque.
• 😀 Cara’s legs are designed with a five-bar linkage for evenly distributing loads, and its joints use a unique approach to enhance precision and dynamic movement.
• 😀 The robot's walking ability is based on a trotting sequence, where diagonal legs move simultaneously during stepping, ensuring stability with at least two legs on the ground.
• 😀 The builder experimented with different step trajectories, such as triangular and rectangular patterns, before opting for a cycloidal step trajectory for smoother and more natural movements.
• 😀 The robot is powered by a 24-volt drill battery and controlled via an RC remote and receiver, with modular design and a focus on aesthetic simplicity and portability.
• 😀 The robot’s structure is designed with detachable parts for easy assembly, repair, and modularity, using strong materials like carbon fiber tubes and TPU for flexibility and strength.
• 😀 The robot’s stability is enhanced with an IMU (inertial measurement unit) that helps maintain balance by adjusting the robot’s tilt on uneven surfaces, achieved through advanced inverse kinematics.

Q & A

What makes Cara's design different from previous robot dogs?

Cara's design stands out because it uses capstand drives, where her joints are powered by rope instead of gears or pulleys. This makes her more dynamic, precise, and responsive than previous builds.

What is a capstand drive, and why was it chosen for Cara?

A capstand drive is a rope-driven speed reducer that uses tensioned rope wrapped around drums instead of gears. It was chosen for Cara because it has zero backlash, low noise, and is cost-effective, making it ideal for precise robotic movements.

How does the use of capstand drives improve the functionality of Cara?

Capstand drives allow Cara's joints to be highly precise, with virtually no backlash, ensuring smooth and accurate movements. This improves the overall dynamic performance of the robot dog.

What challenges did you face with gear ratios during the build of Cara?

The challenge was achieving a perfect 8:1 gear ratio with the capstand drives. The problem was solved by recalculating using the effective diameters of the drums, which accounts for the rope diameter, and then interpolating between different drives.

What is 'quant direct drive' and why is it used in Cara?

'Quant direct drive' refers to using a low gear ratio with a high-torque motor for robot joints. It allows the motor to drive the joints almost directly, leading to high torque and fast, responsive movements.

How did the leg design impact the robot's overall performance?

The five-bar linkage design for the leg was chosen because it evenly distributes load to the actuators, ensuring balanced and efficient movements. This design was a proof of concept, with future revisions planned for more advanced designs.

What is trotting, and how does it help with Cara's walking?

Trotting is a gait where diagonal pairs of legs move together, ensuring stability with at least two legs always on the ground. This allows Cara to maintain balance while walking and provides smooth, coordinated movement.

What was the issue with Cara’s stepping trajectory, and how was it fixed?

Initially, the triangular step trajectory was too jerky at high speeds. The solution was to implement a cycloidal step trajectory, which provides smoother takeoffs and landings, giving a more natural gait.

How did the IMU contribute to Cara's stability?

The IMU (Inertial Measurement Unit) measures Cara's tilt in different axes, helping her adjust her posture to maintain balance. It allows Cara to stay level on sloped surfaces by adjusting her body angle to compensate for the tilt.

What improvements were made after testing Cara, and what challenges remain?

After testing, several parts were redesigned to prevent breakage, the step length was reduced to avoid collapsing, and stability algorithms were implemented. Challenges remain in refining the stability algorithms and ensuring long-term durability.