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# Beer-Pong Catapult

Catapult robot that is built to be able to play beerpong, able to reach up to one meter.

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Catapult robot that is built to be able to play beerpong, able to reach up to one meter and rotate from 0 to 180 degrees with the option to expand. a little bit more, as input for the program developed in Arduino the position of the red cup in the X axis and Y axis is used.

The movement is controlled by a DC motor (H bridge is required), while the launch position is limited by a 600-pulse encoder. The rotational movement of the base is based on a servomotor underneath supported by four crazy wheels. All calculations are done inside the ardruino one board, both motor control and encoder pulse counting.

Project developed for a subject at the university of Chile

The project is about building a robot capable of playing beer-pong, for which it has been decided to implement a catapult that is capable of launching a pingpong ball into a cup located one metre away. For which two sub-systems have been implemented, the first one is the launching system which has the mission to launch the ball, while the second one has the mission to rotate the base so that it is able to launch from [0-180] degrees.

For the first sub-system, launching, we start with the parabolic launch equation, in order to know the launching speed required to reach a certain distance (no friction was considered).

In this case we have the following equations for the motion on the x-axis and on the y-axis, for which we can take off the time and leave everything around the velocity variable. The resulting equation is as follows.

• d total distance
• theta launch angle
• H height of the launch.
• h height of the cup.
• w RPM that we need in the moment of the launch

Then to get the ball up to speed a launch system was created consisting of a 0.2[m] arm attached to a toothed pulley with a diameter of 0.12[m] this pulley is attached to a smaller pulley of 0.012[m], so it is a reduction of 1:10 rpm. This is because the engine speeds were very high.

For the second subsystem we used a much simpler function implemented in Arduino (atan) which allows to identify the angle from the initial coordinates, and then deliver this angle to the servomotor.

The launch point of the system was limited by two variables, the first being the velocity and the second being the launch position which was set to a maximum of 90 degrees or the vertical axis. Initially we tried to implement a PID control for the launch speed, however by not making a correct selection of the initial motor there were problems for the control, this added to the fact that the time in which the motor would rotate was really short before the position variable was breached, the Arduino was not able to maintain optimal control, giving very long term results which was useless for this application.

So it was limited to choosing the position control with the help of the encoder in order to slow down the motor and allow the ball to shoot out.

The encoder allows counting the relative position around an initial point, thanks to a sensor and measuring how much this changes. In this way we can know the position and thus control the moment of launch (being able to calculate an approximate angle), the encoder in this case was 600 pulses so that when we wanted to brake the arm to a position of 90 degrees we had to have an approximate of 4 complete turns giving an approximate pulse of 2400 pulses more than there was in the beginin.

In the same way, a time range could be used to count how much progress was made and thus obtain the RPM, using the following equation.

We also enter the instructions to reload the launch by inverting the IN1 and IN2 inputs of the H-pin.

To go from distance to RPM and then to the PWM value to be delivered to the DC motor, the Arduino map() function was used. However, these results were not as expected, given that the acceleration curve of the motor was not considered, which did not allow the desired RPM to be reached, so a direct transformation from distance to PWM values had to be used. The values that were used for the PWM to behave in a stable way had to be high. Distance was between 30-117 [cm]PWM should be between [190-255], in order to reach a higher distance.

The results seen for a 24V power supply can be seen below

### Codigo_Funcional.ino

ino - 8.50 kB - 12/22/2022 at 03:59

### Lower arm v1 v1 v6.f3d

fusion - 46.71 kB - 12/21/2022 at 19:54

### Shoes v2.f3d

fusion - 53.16 kB - 12/21/2022 at 19:54

### Upper arm v1 v1 v3.f3d

fusion - 40.42 kB - 12/21/2022 at 19:54

### Large wheel side v2.f3d

fusion - 49.99 kB - 12/21/2022 at 19:54

• 1 × PLA filament roll
• 1 × Rotary encoder Encoder Incremental 600 Pulsos LPD3806-600BM 5-24V DC
• 1 × DC motor 775 https://somanytech.com/what-is-775-motor/
• 1 × Steel axis (AISI SAE 4140) 8 mm in diameter and 88 mm long
• 1 × GT2 Pulley 20 Teeth 8mm Bore
• ### Beer-Pong

An initial prototype of the project began, where the main components of the actuator and the preliminary design to be used were established. This can be seen in the following image:

For this prototype, it was considered to use a brushless engine and the implementation of rotary encoder was not envisaged.
After this, and working for the presentation of advance, it was that a more definitive design of the prototype was made, where you can see that there is a breakthrough in both design and the problem of its operation:

Here you can see that you consider a space to place the brushless engine added to a surface where the ball will be placed to launch. The full approach of rotation of the platform was not yet developed, but if it was planned to implement it.
For the final model of our project, a rethinking of the components to use was performed, within this you have the change of the engine to use from a brushless engine to an dc engine, this due to tests performed and the behavior of the manipulator in them. In addition to this, a rotary encoder, capable of turning the axis turn into a signal, this would allow us to know the point where we want to stop the engine and return to its initial position. In addition to this, the structure continued to be improved; adapters for both encoding and dc engine were designed. The last thing that was worked was on the lower turning platform, this would allow to move at work angles and expand the launch spectrum.

• 1
Step one

First it is necessary to print and purchase all the components shown and begged above

• 2
Step two

Already having this, the manipulator assembly is done, using the bolts and structures previously printed. For this, the images shown above are used which show where each bolt and nut are placed.

• 3
Step three

The connections necessary for the operation of the robot are also made, and this is done on the basis of the arduin plate, protoboard, H bridge and batteries.

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