Mechanical Engineer

C5R builds research facilities for frontier models: physical environments where models can design experiments, operate instruments, learn from results, and be evaluated on real scientific work.

We build facilities end to end, bringing together the physical site,instruments, robotics, software, and operations. By working closely withmodel developers, we continuously produce the data and physical feedback their models need for pretraining, lab-in-the-loop post-training, an devaluation.

We are hiring a mechanical engineer to design, build, and iterate on the physical systems that make an automated research facility work.

Our facilities are built from smart benches, robot arms, mobile carriages,custom fixtures, and reverse-engineered scientific instruments — all ofwhich have to work reliably, repeatably, and around the clock. You will ownthe mechanical design that holds it together, and you will be on the floorwhen it doesn’t.

You will work across the mechanical stack: CAD, fixture and tooling design,structures, enclosures, thermal, tolerance stack-ups, and fabrication.

Examples of work might include:

• Designing a gripper fingertip or plate fixture that survives ten thousand pick cycles without drifting out of calibration tolerance.
• Building the mechanical interface between a robot arm and a scientific instrument that was never meant to be automated.
• Designing enclosures, mounts, and cable management for benches packed with arms, cameras, power distribution, and networking.
• Running tolerance and structural analysis on a bench frame, then machining or printing the part yourself the same week to prove it out.
• Collaborating with controls and ML engineers to understand why a robot failed, then concretely improving the fixture, mount, or mechanism to fix it.

• Strong practical mechanical engineering experience. You should have built and debugged real hardware, not only models.
• CAD fluency (Onshape, Solidworks, or equivalent) with real design intent — parts that get made, not parts that look good in a render.
• Hands‑on fabrication experience: 3D printing, machining, laser cutting, sheet metal, or other rapid prototyping workflows.
• Good fundamentals in tolerancing, materials, fastening, and mechanism design.
• Comfort at the boundary with other disciplines — you should be able to read a schematic, reason about a motor’s torque curve, and talk to a controls engineer without a translator.

• Precision motion, kinematic mounts, or repeatable fixturing.
• DFM/DFA and experience taking a design from one-off to a small production run.
• Electromechanical packaging: connectors, cable routing, thermal management, interlocks.
• Experience with lab automation or scientific equipment.

We are open to full‑time roles and temporary stints of at least 3 months. Compensation depends on experience and structure. This role is on sitein San Francisco only.