“Can I Build a Robot Dog?” (Boston Dynamics)

“Spot” by Boston Dynamics is a celebrity. He dances, he opens doors, he inspects construction sites. Natural question: “Can I build one?” Answer: “Yes… but do you like math?”

Building a robot with wheels is easy. Wheels are stable. Building a robot with legs is a war against gravity.

The Math: Inverse Kinematics (IK)

When you walk, you don’t think “Rotate hip 5 degrees, rotate knee 10 degrees.” You think “Place foot there.” For a robot, we have to calculate the angles.

• Forward Kinematics: “If I set the angles to 30, 45, and 10… where is the foot?” (Easy).
• Inverse Kinematics: “I want the foot to be at coordinate (X,Y,Z). What angles do I need?” (Hard).
• The Problem: There are often multiple answers (like bending your knee forward or backward to reach the same spot). The code has to pick the “natural” one.

The Balance: Dynamic Stability

A table has 4 legs. It is statically stable. A walking dog lifts one (or two) legs. It is unstable. It must constantly shift its center of mass.

• The Trot: Lifting diagonal pairs of legs.
• The Creep: Moving one leg at a time while keeping 3 on the ground.

Can a High Schooler Build One?

Yes. Open source projects like OpenDog or Stanford Pupper rely on Raspberry Pis and standard servos. But here is the catch: Wheels are almost always better.

• Wheels are 95% efficient.
• Legs are inefficient (the motors have to fight just to stand up). Unless you are climbing stairs or rocky terrain, legs are “Rule of Cool” engineering. But in robotics, sometimes “Cool” is a valid design requirement.