1. Introduction
A possible shortcoming of many soccer training sessions could relate to goalkeeper and set-piece training. When goalkeeper training takes place, many players may be required to take kicks at goal (which limits their training time), and their incoming shots are in effect predictable (which contrasts with the reality of a soccer game). A machine designed by students from Stellenbosch University that can simulate set-piece training as well as generate random and unpredictable kicks on goal could help teams maximise the training time of out-field players and heighten the effectiveness of goalkeeper training.
Click here to download a summary of the design.
YouTube video ... 01. Tshabalala Ball Shooting Video
YouTube video ... 02. Tshabalala Moving on Track Video
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Competing Students - Ivan Deetlefs; Alex Oelofse; Thabo Mofokeng and Ryan du Plessis.
Email us for more information about these entrants or the Tshabalala Soccer Ball Shooting Machine.
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2. Existing Solutions
Various machines that project soccer balls currently exist. One such machine is named the JUGS, it consists of two wheels that spin at synchronous speeds. This machine also has the ability to curve the ball to the left or the right by having the wheels spin at different angular velocities.
Another similar machine was designed by engineering students in Zurich, they call themselves Team BendIt. Unlike the JUGS machine, their machine has belts instead of wheels propelling the ball. The JUGS machine can only curve the ball in the horizontal plane but Team BendIt’s machine is capable of curving the ball in both the horizontal and vertical planes, this is done by manually rotating the whole drive section of the machine.
Both of these designs are practical for practising set-pieces but are not capable of simulating a pass and shoot scenario since they are stationary devices. These devices can also be used to practise drills such as stopping balls and headers, i.e. a ball is passed to a player in the air and then deflected by the head of a player.
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The JUGS soccer ball machine
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3. Proposed Solution
The proposed solution is that of a machine that can simulate a set-piece kick as well as a pass and shoot scenario. This is proposed to be done by accelerating a machine along a track at speeds similar to that of an actual pass. The dynamic nature of this machine would make it difficult for a goalkeeper to anticipate where a ball is coming from or where the ball would be kicked.
This machine controls itself automatically when used in this mode and ensures that the ball will reach its given target. The machine is used in a stationary operating mode when used to simulate a set-piece kick.
The machine is also able to be taken off the track for this mode of operation and moved around the training ground. Controlling this machine will all be done by user friendly wireless console.
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The Tshabalala Soccer Machine
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Only one person would be needed to control this system with an assistant for safety. Such a machine would greatly contribute to increasing the effectiveness of the training regimes of a soccer team. The proposed designed is named the Tshabalala, a uniquely South African design that intends to transform how soccer teams think of effective training. The Tshabalala makes special use of contactless energy transfer to a moving trolley that houses a rotating turret from which soccer balls are fired. The Tshabalala is designed for the maximum case. The maximum case is defined as the system being the greatest distance from the goal, having the greatest track length and requiring the greatest ball velocities. The proposed track thus lies exactly on the big box line as shown above.
4. Summary of Specifications
The Tshabalala, when moving on the track has three axes of movement which determine the direction in which the ball leaves the turret, one is translational and the other two are rotational. These axes are shown in this figure 8 and the specifications are summarised in the Table of Specifications.
The trolley and ball velocity are dependent on the rotational velocities of the track motor and motors onboard the turret respectively.
Modes of operations
In order to make the Tshabalala more attractive as training equipment for soccer teams, three main operation modes are possible:
1. Manual operation mode: When a user wants to manually select all inputs to the Tshabalala, including the azimuth and elevation angles of the turret. A user thus has full control over the flight path of the ball. This would be used for set-piece training and/or when the trolley is placed off the track.
2. Semi-automatic operation mode: When the turret runs on the track and the user wants to control the Tshabalala manually, but wants each ball fired to hit a specified target, i.e. all inputs are given manually but with the addition of the goal position input on the control console replacing that of manually setting the azimuth and elevation angles.
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Axes of movement
Table of specifications
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3. Fully automatic operation mode: When all inputs are calculated automatically and the Tshabalala operates by executing different shots at random until it is stopped by the user. The turret has to be mounted on the track for this mode of operation.
This allows the Tshabalala to be used for goalkeeper or set-piece training. The difference between manual and automatic operation is whether user inputs are given manually or calculated automatically. Ball velocity is restricted to between 20 and 30 m/s and the spin parameter between 0 and 0.3 for the semi-automatic and automatic operational ranges.
5. Design Breakdown
The design is broken down in to various subsystems and calls for electrical as well as pneumatic components. Wireless Electricity to the turret is provided via SEW MOVITRANS®, which limits the amount of peak power that can be consumed due to restrictions on the number of pickups that can be fitted to the turret trolley. The limited peak power consumption in combination with the high inertia loads of the turret led to the use of pneumatic components with an onboard compressor and accumulator. The compressor accumulator system eliminates the need for high peak power consumption, as the energy needed for the high inertia loads can be stored up in due course in the accumulator.
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Field traversing design subsystems
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5.1 Powering the Track System
The design team examined whether the required power supply task could be solved with MOVITRANS® components and contactless energy or cables. The SEW MOVITRANS® is a method of wireless energy transfer by means of induction, especially for high speed applications. Electrical energy is transferred without contact from a fixed conductor to a mobile consumer. In the design, components on the trolley are supplied with constant power by the MOVITRANS® while the trolley is in motion on the track.
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5.2 Ball loader subsystem
The ball loader subsystem is a pneumatically actuated system, again with some components made translucent to better see the workings of the system.
The system is actuated by a Festo DSNU-32-320 cylinder, which in combination with various mechanisms loads balls from the ball magazine on to the ball acceleration and spin subsystem. The ball magazine in the current design holds five balls, with one ball ready to shoot. The magazine can however be configured to hold more balls depending on preference. The ball loader also serves to bring the ball up to speed, which decreases the amount of energy needed by the motors in the ball acceleration subsystem to shoot the ball at a maximum require speed of 30 m/s.
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Ball loader subsystem
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5.3 Ball acceleration and spin subsystem
The ball acceleration and spin subsystem is responsible for taking the ball from the speed at which it leaves the ball loader to the desired shot speed, whilst also providing the ball with spin about its own vertical axis. Spin on the ball allows the ball to be curved when fired. The amount of curve that can be achieved is relative to the amount of spin on the ball. For a maximum design speed of 30 m/s of the ball, with a maximum spin of 14rps (840 rpm), the ball should theoretically be able to curve four meters at a shot distance of thirty meters (Soccer ball physics, 1998).
The ball is accelerated by passing between two poly v belts of 80 mm width, which are driven by two SEW DRE80M4/FF motors.
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Ball acceleration and spin subsystem
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5.4 Turret elevation subsystem
The turret elevation subsystem actuates the elevation angle of the turret with respect to the ground. Accuracy of the elevation angle is of high importance, as a small angle error at the turret leads to a large error at the target which can be up to 30 m away.
The system employs a Festo DSMI, with power being transmitted to the hinge shaft of the ball acceleration sub assembly via a synchronous belt and pulley system. The synchronous pulley system prevents any belt slippage allowing for accurate control.
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Turret elevation subsystemopen
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5.5 Turret azimuth angle subsystem
The turret azimuth angle, is measured in relation to the track layout. The turret has an azimuth angle range of -60º to +60º, were an angle of 0º is for the turret facing directly forward. The azimuth angle is actuated by a Festo DSMI.
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Turret azimuth angle subsystem
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5.6 Track subsystem
The purpose of the track is to accelerate the Tshabalala to simulate a realistic pass-and-shoot sequence.
This subsystem is composed of further subsystems namely; the Intermediate track section, Front track section, Rear track section and the Trolley.
The track is designed for maximum ease of installation, all parts are therefore joined using bolted connections to avoid heavy machinery such as cranes and digger loaders damaging the field during installation.
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Track subsystem
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5.7 Drive assembly
The motor and gearbox is a synchronous motor supplied by SEW Eurodrive. This motor was selected to provide the Trolley with an acceleration and velocity of 6 m/s2 and 6.5 m/s respectively. As energy efficiency is a significant consideration in the design, the selected motor is compared to the same size AC motor also supplied by SEW Eurodrive, regardless of the fact that a Servo motor is required for the design. It was found that a larger AC motor is required to provide the same acceleration and velocity when using the same gearbox. The motor was selected using SEW’s Eurodrive DriveGate online.
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Drive assembly
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5.2 Pneumatic system
This figure shows the pneumatic system layout excluding control. Compressed air is provided by an onboard compressor and stored in an accumulator tank, or reservoir, with an attached pressure indicator. The accumulator air is passed through a filter and condensate drain to a pressure regulator.
These components ensure the safety of the entire system. A pressure indicator after the regulator allows the operator to set the regulator to the required pressure. The Festo proportional directional control valves (VPWP) are required for the operation of the DSMIs, and a 5/2 solenoid and spring actuated valve for the double acting cylinder are connected to the regulator.
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Pneumatic system layout
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The line supplying the return stroke of the cylinder is fitted with a throttle valve which reduces the volume flow to the cylinder. Speed of the cylinder is reduced to prevent damage of certain components in the ball loader subsystem. All ports to ambient are fitted with silencers, reducing noise during operation as well as preventing dirt from entering valves via these ports.
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5.3 Trailer system
The trailer system is design to allow for maximum mobility of the Tshabalala turret. The turret and trolley from the tracked system are used exactly as they are, and mounted on a standard ATV (Quad Bike) trailer. The trailer can be towed either by Quad Bike, Golf Kart or gardening utility vehicle. This is a stationery system, with only movement in the elevation and azimuth angles, which can be used for set piece training such as corner kicks.
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Turret mounted on trailer
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SEW Eurodrive Components
AC Motor - DRE80M4/FF
Synchronous servo motor with dual shaft gearbox and resolver - K67CMP80M/BP/KY/RH1M/SBB
Drive inverter for speed control on AC motors (MOVIDRIVE®) - MDX61B0110-503-4-0T
Drive inverter for position control on synchronous servo motor (MOVIDRIVE®) - MDX61B0008-503-4-00
MOVITRANS® TPM12B mobile converter - 030-ENE-SA2-2
MOVITRANS® installation plate - TIS10A025-V00-0
MOVITRANS® THM10E pick up - THM10E015-009-000-1
MOVITRANS® TLS supply cable
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Festo Components
Double-acting cylinder - DSNU-32-320
5/2 solenoid valve (700L/min) Terminal valve
Swivel module with absolute encoder - DSMI-40-270-A-B
PROFIBUS module - CPX-FB13
Position controller - CPX-CMAX-C1-1
Sensor interface - CASM-S-D2-R3
Proportional directional control valve - VPWP-4-L-5-Q8-10-E-F
Flow control valve - GRO-QS-3 (193971)
Pressure gauge - MA-15-10-QS-4
Air filter - LFR-MS-D-7-5M-MILRO
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