Why Does the Dyna Robot Lean Its Torso?

Jason Ma gave the Dyna robot a torso that can lean because people use the waist and back for ordinary tasks, and a body that only travels up and down cannot match that motion. A couple of years ago he pulled a muscle while exercising. The next few days after a pulled muscle, or after sleeping in the wrong position, movement locks up and the neck gets very stiff. Daily life uses many muscles and degrees of freedom that stay invisible until one of them fails, and then tasks that usually feel natural turn awkward.

Reaching for a bottle works the same way. The arm does not act alone, and holding the upper body still on purpose feels strange. People move the torso all the time without thinking about it. A robot built to learn from human data needs the same freedom so the model can take in the motion and control the body. Without a lean, the transfer gets weaker, and the robot gets less dexterous and more awkward.

The new robot was ready not long ago, so it has much less data than the stationary arms. The model had not seen the new robot in pre-training, yet a pre-trained model learned the demo tasks very quickly. Pre-training on humans started before the hardware was ready, because the robots were going to be like people. The training side moved ahead while the hardware caught up, and the transfer is there and very helpful.