3D-Printed Toy Linear Actuator

I have a small, off-the-shelf geared toy motor and I want to turn its continuous rotation into a clean back-and-forth slide that travels roughly 2 cm to 3.5 cm in about two seconds per cycle. Precision is not critical; this is strictly for a playful proof-of-concept, so a bit of slop is perfectly fine.

What I need from you is a complete, print-ready design for the motion‐conversion mechanism. You’re free to choose the approach—rack-and-pinion, lead screw, eccentric cam, or anything else that can be printed on an FDM printer and driven by the motor without excessive wear. The final assembly should:

• Fit a typical hobby-grade geared toy motor (shaft Ø3 mm, can diameter 20–25 mm).
• Deliver the stated 2 – 3.5 cm stroke with a full back-and-forth cycle time near two seconds.
• Be printable on a standard 0.4 mm-nozzle FDM machine with PLA or PETG, no exotic supports required.
• Assemble with common fasteners (M3 screws, press-fit pins, or similar).

Please provide:

1. CAD source files (Fusion 360, SolidWorks, or STEP) and sliced, ready-to-print STLs.
2. A short assembly guide and a parts list.
3. Any simple calculations or notes that show how the chosen mechanism meets the stroke and timing targets.

If you have previous work designing small 3D-printed mechanisms, feel free to link it; otherwise, just explain briefly how you’ll tackle the problem. I’m keen to move quickly, so let me know your estimated turnaround once you review the specs.