Challenges of Quadruped Four-legged Robotic System

Robotics is an interdisciplinary subject involving science, technology, engineering, math, and art (STEAM). A realistic robot requires precise integration of structure, circuit, software, production to perform specific tasks.

Especially for a quadruped robot, its movements and balance all rely on the instant and discrete foot-ground contacts. The four legs are equivalent to four robotic arms installed inversely and have to collaborate both in spatial and time to make the smooth and stable motion, and avoid a collision. The robot should be free to patrol independently from power/control cables, which puts a higher demand for power, perception, and adaption.

All working robots have experienced a long search with empirical instinct, careful calculation, and thorough experiments, to converge to a practical solution.

The Evolution of Robot Dog

Humans have been fascinated by robot dogs. Robot dogs have frequently coexisted with humans in cartoons, fiction, movies, and TV series such as Metalhead (Black Mirror).

Sony Aibo was the pioneer in bringing the robot dog concept to the consumer market in 1999.

Tekno the Robotic Puppy (also known as Teksta the Robotic Puppy) was a popular electronic robotic toy that launched in late 2000.

There are other robot dogs targeting the massive toy market. Those remote control pet robot puppy dogs actually run on wheels, so that they cannot have realistic dog-like limb movements. Examples include WowWee CHiP and Chippies robot dogs, and Zoomer robot dogs.

There were only a handful of laboratories and companies that can manufacture quadruped walking robots. Boston Dynamics is an outstanding representative of industrial quadruped robots as its demo videos have attracted a great following. In 2021, it was once used as a police dog for NYPD in NYC, but critics likened it to a dystopian surveillance drone.

Robot dogs also have use cases for the military. One example is that Air Force deployed robot dogs from Ghost Robotics and Immersive Wisdom to add an extra level of protection to the base.

Another popular use case of robot dogs is in IoT robotics automation.  For example, when equipped with a lot of sensors, a fleet of robot dogs can patrol and monitor factories for worker safety improvement and assist in disaster recovery by going into dangerous areas first to monitor air quality, and temperature and find victims.

In the academic field, MIT open-sourced its solution for a small quadruped robot in 2019. Its work greatly promoted the research of industrial quadruped robots. However, apart from lowering the barrier of research and development, the various hardware required by the quadruped robot often needs to be specially designed and customized. The supply chain supporting cost is high, the cycle is long, and it is difficult to achieve mass production.

By 2022, many more robot startup companies develop large quadruped robots similar to mini cheetah ad spot mini. They are still at a high price tag that only the rich and big industrial companies can afford.

Because of the lack of mass adoption, robot dog applications are still unclear, and it may take a long time to find the product-user fit and product-market fit.

How Petoi has Solved Some Key Challenges with Bittle

The challenges of designing a consumer-grade palm-sized robot dog and an industrial robot dog are significantly different. It has to achieve all complex functionalities at a sweet price tag and should be easy to use without professional maintenance. Petoi designed their robots with more creativity rather than piling up expensive components:

• Ingenious interlocking frame to reduce the weight and difficulty of assembling, while keeping the robustness to sustain shock and pressure
• Specially tuned consumer-level servos as the joints to simplify the control system and reduce the cost
• Spring-loaded joints to reduce the shock on the gears of the servos
• High-performance battery with convenient installation mechanism for 1-hour playtime and easy swapping
• Efficient simulation and approximation to achieve high dynamic performance with simplified calculation
• Sweet point of power/weight factor to achieve impressive agility (maximum speed at 5 body lengths/second!)
• Bionic design to simulate the behavior of real animals
• Open source code with multiple control interfaces including C++, Python, Scratch, and mobile app
• Comprehensive documentation and tutorial videos
• Compatible with Arduino and Raspberry Pi to embrace the global community of developers