Each reel in the robot series is about 40 seconds: a question, a robot doing something, four options, no answer. It would be quicker to animate the robot by hand. None of them are.
The robots are simulated
The robots run in MuJoCo, an open physics simulator, using open models:
- MuJoCo Menagerie for the arms, the drone and the robot dog: the UR5e, Franka Panda, Kinova Gen3, Skydio X2 and Unitree Go2.
- Unitree's own G1 model and its pre-trained walking policy for the humanoid. The policy runs 50 times a second, exactly as it would on the robot. Nothing is keyframed.
So when the humanoid is shoved and takes a recovery step, that step is the policy's decision. When the drone leans into a turn, a controller is working out four motor thrusts 500 times a second.
The numbers come from the log
Each simulation writes down what happened at every step: positions, speeds, forces, joint angles. The picture is then drawn by replaying that log. The speed readout, the force arrow and the tilt angle in a reel are all values from the run you are watching.
This is also why a solution page can say where the simulation disagrees with the formula. In the drone braking question, the formula gives 5.1 m and the simulated drone needs 6.3 m. That gap is real physics, and there is a separate note on it.
The rules every question follows
- Open on a question. The first line is the puzzle, not an introduction.
- Live numbers in every scene. If the robot is doing something, a measured value is on screen.
- Never show the answer. Not in the reel, and not in any number the answer could be read off from.
- End on four options. One is right. The other three are each a specific mistake that someone would really make.
The fourth rule is where most of the work goes. A wrong option that nobody would pick teaches nothing. On every solution page there is a table of what went wrong for each one: a forgotten square root, a unit slip, the answer to a slightly different question.
What a reel cannot do
Forty seconds is enough to ask a good question and not enough to answer it. That is what this site is for. Every reel gets a page with the solution in steps, the reason each wrong option is tempting, and the follow-ups an interviewer would ask next.
Start with question 1, and guess before you look.