2 Speed Manual Transmission

Project Overview

Our team designed and built a two-speed transmission system capable of forward and reverse motion, with a neutral setting that automatically engages a braking mechanism. The system was intended to lift and lower a 2 kg load at controlled speeds while holding the load securely in neutral. We implemented a dog clutch mechanism to shift between gears, bevel gears to change the direction of input power, and a ratchet-and-pawl braking system for stability in neutral.

Design & Components

The transmission was constructed using a combination of laser-cut acrylic, 3D printed PLA components, and standard hardware. We carefully designed custom pulleys, flanges, and the dog clutch to ensure proper alignment and durability. A bill of materials and cost analysis was tracked throughout the project, with a final budget utilization of $109.35 out of $150.

Engineering Analysis

We conducted thorough engineering analyses to ensure the systems reliability:

Shaft Analysis

Calculated internal forces, bending moments, and torsion to evaluate stress distribution. The critical point near Support B was analyzed, yielding a factor of safety of 13.29 against yielding and 9.22 against fatigue failure.

Bearing Analysis

Determined that the ball bearing inside Support F could withstand loads with an estimated life of 5.28 × 10⁸ hours, far exceeding project requirements.

FEA Analysis

Simulated stress on Support B in Fusion 360, confirming that the maximum von Mises stress (2.7 MPa) was well below the yield strength of PLA, with a safety factor of 10.4.

Performance & Testing

The final transmission successfully lifted a 2 kg load at 0.5 ft/s and lowered it at 0.33 ft/s, meeting speed targets. The ratchet-and-pawl brake held the load securely at the neutral position. However, some challenges were identified:

Difficulty shifting from forward to neutral due to friction and tolerance issues in 3D printed parts.
Belt tension in the forward gear required frequent adjustments.

Proposed improvements include refining shaft geometry, improving alignment of the sliding mechanism, and redesigning dog teeth for smoother engagement.

Key Takeaways

This project combined mechanical design, CAD modeling, materials selection, and structural analysis into a fully functional prototype. The process highlighted the importance of precision in fabrication, the role of tolerance in shifting mechanisms, and the value of simulation in validating designs before testing.