Spiderbot: An Open-Source Energy-Efficient Hexapod with Passive Gravity Compensation

Ritwik Sharma · Vimarsh Shah · Saransh Agrawal

The spring-assisted hexapod robot on grass.

Open-source hexapod platform

Spring-assisted 2-DOF legs for energy-efficient locomotion.

This platform uses a passive spring-assisted four-bar leg mechanism to support body weight mechanically, reducing standing power while keeping the robot low-cost, manufacturable, and suitable for reinforcement-learning locomotion research.

The robot is validated in simulation and hardware on flat ground, rough terrain, slopes, and payload-carrying trials, with training and deployment code built on mjlab.

Highlights

Designed for accessible, energy-aware legged robotics research.

2-DOF spring legs Four-bar linkage with passive spring support reduces continuous stance torque.
Low-cost build 3D-printed structure and off-the-shelf components target a sub-$400 platform.
RL sim-to-real Policies trained in mjlab transfer to hardware despite closed-loop kinematics.
Payload capable Validated with a maximum payload of 3.75 kg, about 1.25x the robot's weight.

Mechanism

Passive support without giving up terrain locomotion.

The leg design trades the conventional third actuated degree of freedom for a spring-loaded parallel linkage. The mechanism is represented in MuJoCo using equality constraints and tendon springs, while the learned policy controls the two actuated joints on each leg.

Locomotion

Simulation and hardware trials across terrain conditions.

Flat Terrain · Sim

Flat Terrain · Hardware

Rough Terrain · Sim

Rough Terrain · Hardware

Slope · Sim

Slope · Hardware

Interactive Demo

Browser-based MuJoCo viewer.

This mjswan demo loads the Spiderbot MuJoCo model and a flat-ground locomotion policy directly in the browser for lightweight interactive teleoperation.

Interactive Demo

Open full viewer

Payload

Passive compensation under additional load.

Payload trials evaluate whether the spring-assisted leg design maintains its energy efficiency advantage when the platform carries additional mass.

Maximum payload trial 3.75 kg · 1.25x robot weight

Citation

BibTeX

@misc{sharma2026spiderbotopensourceenergyefficienthexapod,
  title = {Spiderbot: An Open-Source Energy-Efficient Hexapod
           with Passive Gravity Compensation},
  author = {Ritwik Sharma and Vimarsh Shah and Saransh Agrawal},
  year = {2026},
  eprint = {2609.26989},
  archivePrefix = {arXiv},
  primaryClass = {cs.RO},
  url = {https://arxiv.org/abs/2609.26989}
}