Tennis Ball Feeder

Tennis is about grooving strokes through repetition, and that requires someone to feed balls incessantly. Coaches find it difficult to feed balls while simultaneously watching a student's technique, and varying the feeding pattern frequently is cumbersome. This hampers training effectiveness and is economically inefficient for players.

Players cannot self-train for long hours without a partner or coach, so they spend more on coaching — which is expensive and less effective, since the coach is feeding balls rather than correcting strokes. Training schedules depend on the availability of others, which hinders development.

As a competitive player, Achintya experienced this limitation directly. The need: a machine that automates ball feeding with customisable speed, direction and angle, so players at all skill levels can train solo for hours.

Coaches running group sessions, advanced players grooving specific strokes, and beginner and intermediate players who need consistent, repeatable feeds — on club courts, home courts and anywhere a commercial machine is unaffordable.

Separate questionnaires were written for coaches, advanced players, and beginner/intermediate players. The needs that emerged: variable speed and direction to simulate different deliveries, enough ball capacity for long drills, portability between courts, and a price far below commercial machines.

Existing commercial ball machines were compared for features, price and limitations. They work, but their cost puts solo training out of reach for many players — the gap this project set out to close.

A battery analysis compared options including lithium-polymer cells against requirements of cost, capacity, weight and safety, to power two drive motors and two servos through long training sessions.

A ball-volume analysis looked at high-intensity drills, where a feed rate of one ball every 2–3 seconds is needed. That rate, multiplied across a session, set the hopper capacity target of 200 balls.

A lateral-direction analysis set the aiming range: a minimum of 90° to a minimum of 30° between extremes, giving approximately ±60° of directional coverage. Launch-angle adjustability was specified separately so the machine can simulate different delivery styles — flat drives, topspin and slice.

Candidate materials for the body and wheels were compared in a material scorecard against the qualities the product demanded: strength, weight, machinability, cost and durability outdoors.

The research was distilled into a final specification covering power (40 W), capacity, feed rate, direction and angle ranges, portability, wireless control and cost — the yardstick for ideation and later evaluation.

Five ideation concepts were sketched and dimensioned, exploring different layouts for the hopper, wheel assembly, frame and controls.

The five concepts were evaluated against the specification, and Design 1 was selected as the final product direction.

Height-adjustment options, including an electric linear actuator, were analysed for range, cost, complexity and user convenience.

Direction-adjustment options, including a Whitworth quick-return mechanism, were compared. Servos were the final choice: a higher range, cheap, and very convenient for the user. Two 20 kg servos control direction and launch angle.

The drive was sized by calculation: 80 balls weigh about 47 N; at a common 45° launch angle the force on each motor is about 33 N, giving a moment of roughly 4 Nm on each 12 cm throwing wheel. At 12,000 rpm the wheel rim speed corresponds to a theoretical maximum ball velocity of about 151 km/h, with the kinetic energy supplied split between the two wheels.

Control is by an Arduino Uno with a wireless remote. Two counter-rotating wheels driven by 775 motors launch the ball; the 200-ball hopper sits above the wheel assembly; final weight is 14.3 kg on a wheeled frame.

The frame, mounts and wheel assembly were manufactured using the school's workshop processes, with a full cost breakdown of materials and parts bringing the reported build cost to ₹14,400.

Detailed manufacturing process and cost table to be added from the report.

The machine was field-tested on court with a coach. Reported performance: a maximum speed of 83 mph and directional aiming of approximately ±60 degrees.

Reported challenges include battery life, ball jamming, and noise — all documented as areas for further improvement.

Working through the full design cycle — identifying the problem by talking to players and coaches, writing a specification from research, exploring rough sketches before committing to CAD, and analysing each mechanism on its own merits — taught me that good design is mostly disciplined elimination. The evaluation stage, not the ideation stage, is where the product is really decided.

A commercial ball machine costs many times the ₹14,400 build cost of this one. What does that price gap do to who gets to train? The project is a small study in how the cost of capital equipment shapes access to skill development — and the motor sizing, wheel-speed and launch-angle calculations are applied mechanics throughout.