About the Role
Mainspring is seeking a Senior Mechanical Engineer to own significant mechanical engineering projects, subsystems, or technical workstreams for our Linear Generator platform. In this role, you will develop robust mechanical designs, drive projects through the full design cycle, and work cross-functionally to validate and release hardware into production or field use.

This role is intended for engineers who have already demonstrated independent ownership of meaningful mechanical design work through multiple design, test, release, or implementation cycles. A strong candidate should be able to own a significant subsystem or project area with limited day-to-day guidance, make sound technical tradeoffs, identify risks early, and drive cross-functional execution.

Candidates who are still primarily building independence on bounded tasks or single workstreams may be better aligned to a Mechanical Engineer role, while candidates who regularly improve technical decision quality across multiple projects or teams may be better aligned to a Staff Mechanical Engineer role.

Responsibilities

• Own significant mechanical projects, subsystems, or technical workstreams from requirements and concept development through validation, release, and implementation.
• Develop and release robust mechanical designs for complex parts, assemblies, fixtures, subsystems, or processes, balancing performance, reliability, cost, manufacturability, serviceability, safety, schedule, and system integration.
• Build and drive project plans, requirements, validation strategies, schedules, risk assessments, and release plans within an agreed scope.
• Use engineering analysis, test planning, experimental data, tolerance reviews, simulations, and hands-on troubleshooting to make design decisions and validate performance.
• Identify and mitigate technical, schedule, validation, manufacturing, quality, supplier, and service risks before they become major issues.
• Lead cross-functional technical discussions, design reviews, risk reviews, and project decisions with engineering, manufacturing, quality, reliability, test, supply chain, suppliers, and service stakeholders.

Qualifications

• BS or MS in Mechanical Engineering or a similar engineering field, with demonstrated experience owning mechanical design work beyond task-level execution.
• Repeated experience designing, testing, iterating, and releasing mechanical hardware across multiple design cycles, not only supporting isolated tasks or one phase of development.
• Ability to independently own a significant subsystem, project, or technical workstream with moderate ambiguity, cross-functional dependencies, and meaningful program impact.
• Strong mechanical design fundamentals, including practical experience with complex parts, assemblies, fixtures, mechanisms, structures, thermal systems, fluid systems, electromechanical packaging, or other relevant mechanical systems.
• Demonstrated ability to use analysis, testing, data, and engineering judgment to make design tradeoffs, validate performance, and resolve technical problems.
• Strong communication and project execution skills, including the ability to define scope, manage dependencies, escalate risks with recommendations, and align technical and non-technical stakeholders.

Preferred Qualifications

• Experience taking hardware from early concept through production release, manufacturing implementation, or field support.
• Experience with PLM systems, drawing release, engineering change processes, supplier qualification, production ramp, or field implementation.
• Experience with reliability testing, accelerated life testing, failure analysis, design of experiments, structured root cause analysis, or risk-based validation planning.
• Experience working directly with suppliers, contract manufacturers, production teams, quality teams, or field service organizations to resolve hardware issues.
• Experience designing hardware for energy systems, engines, generators, compressors, pumps, thermal systems, fluid systems, structures, high-cycle fatigue environments, precision alignment systems, or industrial equipment.
• Experience contributing to design reviews, risk reviews, troubleshooting efforts, or technical decisions outside their immediate project area.

$140,000 - $165,000 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!

Does your experience not meet all of our posted requirements? Studies have shown that some people are less likely to apply to positions unless they meet every listed requirement. At Mainspring, we are committed to building a diverse, inclusive, flexible, and collaborative environment, so if you want to help us transition the world to clean and affordable electricity, and don't meet all posted requirements for a particular role, we'd still love to hear from you. Mainspring can sometimes be flexible enough to shift responsibilities for the right person, or otherwise identify open or upcoming roles that may better fit your professional background.