Qianjun Xia
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RoboVoxel

Inferring soft-body physics from videos

Under ReviewPyTorchVideo TransformerVAEEvolution GymPhysics Simulation
RoboVoxel
Where
Columbia University · Creative Machines Lab
Advisors
Jiong Lin, Prof. Hod Lipson
My role
Dataset generation, model design, training and evaluation

A rigid robot arrives with a CAD model: clean masses, known inertias, documented joint limits. A soft body arrives with none of that. Its material properties vary across space, it deforms far past the linear regime, and its actuators may be buried where no camera can see them.

RoboVoxel asks whether a short video is enough to guess the rest.

Given a few seconds of a deformable body moving, can we recover the material field and actuator placement well enough to reproduce that motion in simulation?

Method

The trick is to stop treating this as parameter fitting and treat it as translation. The input is a grayscale video. The output is a single parameter image, where each pixel is a voxel and each colour channel carries one physical quantity — stiffness, mass, damping, actuator direction.

That image is exactly what the simulator eats. If the simulator’s rollout matches the original video, the inferred parameters mean something.

From grey motion, to coloured physics, and back to motion.

The pipeline has three parts:

  1. A synthetic dataset. A modified 2D spring-mass environment, built on Evolution Gym, generates matched pairs for many random beams, blobs and soft robots: a grayscale motion sequence, and the colour parameter image that produced it.

  2. A frozen decoder. A convolutional autoencoder is trained on parameter images alone, then frozen. It becomes a renderer: low-dimensional latent in, full-resolution parameter field out.

  3. A video transformer. A TimeSformer-style model reads the grayscale frames and emits a latent vector for that frozen decoder. Training supervises the predicted parameter image directly.

To hand a prediction back to the simulator, the continuous output is clustered into a discrete set of material and actuator types, then simulated.

Results

Simulated beam rolloutSimulated blob rolloutSimulated soft robot rollout
Rollouts driven by inferred parameters — a beam, a blob, and a soft robot.

My contribution

Dataset generation and the simulator modifications, the model design for both the parameter-image decoder and the video transformer, and the training and evaluation that connects them.