Jenga Robot: SamIlia


The build of the actual Jenga robot could only start when the example robot was completed. The example robot was an obligation for all the students. By building it, the students would get familiar with the different uses of motors. The use of three sort of motors were imposed by the professors. Once the correct use of the motors in the three fields of study were proven, by finishing the example robot, the students were able to construct a robot for the project.

 

The mechanical part was creating a design on the computer with the program called Inventor, which allows designing on the computer. This program was taught in a course in the first bachelor year. The next step was creating a body for the robot. Designing an effective shape for the body had to involve calculations. Those calculations prevented the robot to collapse and the belts to slip over the gears. The forces on the gears had to be calculated in order to increase the work of the motor. For instance, when a big gear is put on the motor and the second gear on the axis is a smaller one, the axis will rotate faster than if it was putted directly on the motor. As a result, if a motor is not powerful enough, a gearbox increases the efficiency of the motor. In the design every hole in the wood had to be precise. The reason for this precaution is that the bearing holders and screws will not fall off the robot

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After considering different designs for the robot; the final design is as follows. In order to move the arm of the robot, motors are required. The choice of DC-motors instead of stepper-motors was made. In fact, two motors are needed in order to move the arm of the robot. The purpose of this choice is to reduce the weight on the arms and prevent a resistance for the arm when it is moving. As a result, there is a loss of mechanical power by putting the motors on the base of the robot.

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By seeing the results of the calculations; it was clear that the DC-motor would be more effective. DC-motors can produce a lot of power, are easily to control, have a high value of holding torque and do not need a lot of current . The only disadvantage of the DC-motor is accuracy. A stepper-motor is more accurate because it works with steps. The faster the steps are followed after each other, the faster the axis on the motor rotates. On the contrary, a DC-motor is not accurate enough because how faster it turns how less accurate the motor is.

To improve the effectiveness of the DC-motors, calculations were made and the best way to improve was implementing a gearbox. Gears with transmissions, which consist of a reduction, of 1 on 16 for the bottom part of the arm and 1 on 19 for the upper part of the arm. The meaning of those reductions for this robot can be shown with an example. For instance, with those reductions this robot can carry a can of Coca-Cola. Achieving this transmission was possible with the use of timing belts. Timing belts are belts which move around two or more gears. When one of the gears rotates, all the gears will start to move. The purpose of the gear is creating more power than the motor already delivers and vice versa. Another goal is to reduce the pressure from the gears and spreading the pressure on over the belt. As a result, the lifespan of the gears is longer than with a worm gear or grinding gears. To conclude, the gears were fabricated by the use of the 3D printers in the lab. 3D-printers take more time to create a gear than the lasercutter, but the gears are also more solid.

The base of the Jenga robot is restricted to area with the dimensions: 25cm x 30 cm. In the instructions given by the lecturers of the course, it was clearly noted that each robot should have maximum one linear motion. One linear motion stands for a linear movement in the direction of one of the axis (x, y or z). The robot that is explained in this lab report moves forward and backwards along the base. For stability reasons, the robot is put on a plate which moves along 2 bars, one of them is threaded. The movement of the robot along those bars is possible with the use of another DC-motor. By putting a gear on the motor and another gear on the threaded bar. The plate with the robot will move like a screw along a threaded bar. Using this method allows the robot to remove a wooden block from the tower, by moving backwards, when the block is grabbed by the hand of the robot.

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The hand of the robot is placed at the end of the arm of the robot. I this part, the employment of two servomotors is more appropriate. The reason for that conclusion is simple. Servomotors have a sphere of activity between 0° and 180°. Another advantage of the servo motor is that it possesses a little DC-motor, which is easy to control. One of the servomotors serves as the wrist of the arm, with a sphere of activity of 180° this motors fits. The second servo is used to open and close the hand, which will grab the wooden block from the tower.

 

Beside the mechanical aspect, there is also an electronic and an IT aspect, which goes along with each other. The first step was drawing an electronic wiring of multiple components on Altium, Altium is a program which allows the user to design such schematics. Once the schematic is made, it should be tested on a breadboard. A breadboard is a board with holes for electronic components. Once the electronic circuit is tested on the breadboard and works, a PCB must be made. The problem with the breadboard are the wires. The wires are easily disconnected. Making a PCB is not difficult. First step is checking if the schematic is correct. Afterwards, the wires must be drawn, which are copper tracks, once they are developed. Once the wiring is done, the circuit has to be printed on a plastic paper.

 

The next step is the lightening with UV light. The result of this method is that the circuit is printed on the copper of the PCB. In order to develop the PCB or remove the copper, that only the electronic circuit is left behind. This is possible, because of the chemical reaction of NaOH (sodium hydroxide) with Cu (cupper).

When the circuit is left behind on the PCB, washing it with aceton is required. This requirement is vital. The reason for this requirement is that the copper tracks that are left behind should stay and that is the reason why aceton should be poured on the PCB.