About the Role

Mainspring is seeking an Associate Mechanical Engineer to contribute to mechanical engineering projects for our Linear Generator platform. In this role, you will build practical engineering skills by supporting mechanical design, CAD, drawings, analysis, testing, documentation, troubleshooting, and release activities.

This role is intended for early-career engineers who are developing practical engineering judgment and learning how to apply mechanical engineering fundamentals to real hardware. A strong candidate should be curious, detail-oriented, hands-on, eager to learn, and able to execute well-defined tasks with guidance from more experienced engineers.

Candidates who have already demonstrated independent ownership of defined-scope mechanical engineering work through multiple design, analysis, test, release, or implementation cycles may be better aligned to a Mechanical Engineer role.

Responsibilities

• Support mechanical engineering projects by completing well-defined design, analysis, testing, documentation, and release tasks with guidance.
• Create and update CAD models, assemblies, drawings, test fixtures, documentation, and engineering reports.
• Assist with basic calculations, tolerance reviews, simulations, test setup, test execution, data review, and troubleshooting.
• Learn company processes for design reviews, drawing release, validation, change control, manufacturing support, and field implementation.
• Communicate progress, questions, blockers, and findings clearly while asking for help early when scope, priorities, or technical approach are unclear.
• Build practical engineering judgment through repeated feedback, hands-on work, and exposure to different design, analysis, test, release, and troubleshooting cycles.

Qualifications

• BS or MS in Mechanical Engineering or a similar engineering field, or equivalent practical engineering experience.
• Foundational understanding of mechanical engineering principles, including mechanics, materials, machine design, thermal systems, fluids, manufacturing, or other relevant coursework or experience.
• Experience with CAD tools such as SolidWorks or similar, including part design, assembly design, drawings, or design documentation.
• Ability to execute well-defined engineering tasks carefully, communicate progress, and incorporate feedback from more experienced engineers.
• Interest in hands-on engineering work, including prototyping, testing, troubleshooting, data collection, and design iteration.
• Clear communication skills and a willingness to ask questions, learn company processes, and build practical engineering judgment.

Preferred Qualifications

• Internship, co-op, project team, research, or early-career experience involving mechanical design, prototyping, testing, manufacturing, or hardware development.
• Experience building or testing hardware in a lab, shop, manufacturing, field, or hands-on project environment.
• Exposure to engineering analysis methods such as hand calculations, tolerance stackups, FEA, thermal analysis, fluid analysis, vibration analysis, or data analysis.
• Experience creating drawings, working with GD&T, preparing test plans, documenting results, or supporting engineering release work.
• Exposure to manufacturing processes such as machining, sheet metal, welding, casting, molding, additive manufacturing, or assembly.
• Interest in energy systems, engines, generators, compressors, pumps, thermal systems, fluid systems, structures, electromechanical systems, or industrial equipment.

$100,000 - $113,000 a year

This position is onsite at our Menlo Park HQ. The salary will be adjusted to reflect local market conditions based on employee location as well as the experience of the employee. Along with the base salary, Mainspring offers pre-IPO stock options + benefits.

Before you apply, a quick note on your resume
We care about the substance of your work and want to make sure we learn as much as we can about your design experience. To help us evaluate your experience accurately, please ensure your resume includes:

• What you actually built or worked on - name the real product, subsystem, or hardware (not just "components" or "systems"). "Redesigned the bracket mounting the compressor to reduce vibration failures" tells us far more than "designed mechanical components."
• What you personally did, separate from what your team did. If you contributed to a group project, tell us your specific role and contribution.
• The engineering fundamentals you applied - tie your skills (CAD, FEA, GD&T, thermal/fluid analysis, testing, etc.) to the actual problem you used them on, rather than listing them as standalone skills.
• What happened as a result - did it pass validation/testing, resolve a failure, ship to production, and if so, at what volume or scale (prototype quantity, low-rate production, high-volume manufacturing)? This helps us understand whether your experience is with one-off/prototype hardware or product that shipped at scale.

One more thing: please don't feel obligated to keep your resume to one page. If accurately describing your relevant projects and contributions takes more space, that's completely fine - we'd rather see the detail than have you compress or omit meaningful work to fit a page limit.

Thank You!