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Tennis ball launcher full assembly

Topspin & Backspin Tennis Ball Launcher

BEng Dissertation · Mechanical Engineering

I designed and built a dual-wheel tennis ball launcher capable of producing topspin, backspin, and flat shots — the project’s primary objective. The core spin mechanism exploits the Magnus effect through independent control of two A2212 2200KV BLDC outrunner motors, with a 5 mm wheel-gap compression validated through hand calculations and physical testing at 30–40 mph. The prototype was completed within a £300 budget (~£200 real spend), with all structural components FDM-printed in PETG across approximately 30 hours of printing time.

Beyond the core launcher, I designed and integrated a complete electronics system — independent ESC speed control per wheel, servo-driven ball feeding on a 2-second cycle, and a custom 4:1 3D-printed planetary gearbox pairing a NEMA 17 stepper with a theoretical 1.62 N·m torque output for motorised vertical angle adjustment. The architecture is designed as the foundation for wireless ESP32 Bluetooth control as the next development iteration.

Technical Breakdown

  • Full Assembly Isometric
  • Internal Mechanism Drawing
  • Top Wheel Sub-Assembly
  • 4:1 Gear Reduction Drawing
  • Bottom Wheel Sub-Assembly
  • Ball Feeding Mechanism

Model & Assembly

Designed the complete machine in SolidWorks, producing individual sub-assemblies for the top wheel, bottom wheel, vertical angle stepper system, and planetary gearbox. Each sub-assembly is backed by a full engineering drawing with BOM, tolerances, and material callouts. The 4:1 planetary gearbox — sun, planet, and ring gears all designed from scratch — steps up the NEMA 17 stepper output to a theoretical 1.62 N·m of torque for the vertical tilt axis.

Full Wiring Diagram

Electronics System

The electronics system is built around an Arduino Nano as central controller. Two A2212 BLDC outrunner motors are independently driven by 30A OPTO ESCs, enabling differential speed for topspin, backspin, and flat shots. A servo motor opens and closes the ball-feeding door on a 2-second cycle. An A4988 driver handles the NEMA 17 stepper for vertical angle adjustment. All power is routed from a 12V battery through a 6-way fuse box, with a 12V→5V buck converter supplying logic power. The system lays the foundation for future wireless ESP32 Bluetooth control.

  • Final Prototype
  • Printed Components (Wheel and 4-1 Gearbox)
  • Slicer: Wheel (4h 20m)
  • Slicer: Ball Feeding Mechanism + Frame Sections (6h 21m)
  • Slicer: 9 Part Grid Layout (1d 6h 50m)

3D Print & Final Product

All structural parts were FDM-printed in PETG across approximately 30 hours and 8 print plates using a Bambu Lab printer. Key components include the dual-wheel housings with integrated tread (4h 20m per wheel, 150 g each), the ball feeding mechanism (6h 21m, 252 g), the base plate, and the full planetary gearbox casing. Print orientation and infill were optimised per part for structural strength at key load points. The assembled prototype successfully launches tennis balls with controllable spin at 30–40 mph.