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As part of the fulfillment of requirements for the Mechatronics class and as MA1 students in electromechanical engineering of the Bruface program, we were tasked with creating a working mechatronic system that incorporates what we learned in theory during lectures, mainly mechanical and electronic design as well as programming. The project was a group assignment and we were a total of four students working on it. We were given access to resources from the Fablab (e.g Laser cutter, 3D printers, and various other tools) and a global budget of 200 euros.
The goal of our project is to sort lego blocks based on their color and put them in designated boxes using a gripper system. The lego blocks are fed to the sorting mechanism using a mini conveyor belt equipped with a color sensor that gives the signal to the sorting mechanism to put the block in the adequate box. The system can be divided into three main parts: lego feeding system (conveyor belt), system that drives the vertical and horizontal motion for sorting (cart moving on frame), and the gripper.

The belt is made out of two sets of side supports that would hold both rollers at the extremities. Additionally, the rollers would hold the tensioned belt and drive its movements. The material chosen for the supports was 6mm thick plywood and the material for the rollers was PLA (Polylactic acid) that is used for 3D printing.

The side supports on the motor’s side are as follows: side support for the motor is cut on 6mm plywood and linked with the support that has screws for the motor which is cut on 3mm plywood.

For the rest, the supports have normal 8mm holes to incorporate the bearings and we cut 5 of them on 6mm plywood plus one additional one on 3mm thickness.

Additionaly, we added a frame made with a proximity sensor support, a color sensor support, and a hollow frame so we won’t get detection errors from the proximity sensor. The frame on the belt serves to detect the block and stopping the belt so that the color sensor that is positioned on the roof of the frame senses the color of the lego. Then, the lego moves to the initial position so it gets sorted as is shown on the video.

To link the supports together, a piece of 6mm plywood with four contact points was added and would also act as a tension tuner tuner for the belt. Finding a mechanism to correctly tension the belt without redoing the entire design was a very challenging task and the result isn’t the most efficient. For future reference, we would advise the reader to first think about a good tensioning system for the belt and then design the entire conveyor belt system around it. That being said, even though the tension tuner isn’t optimal, it does the job since the loads are not that big.

For the electrical circuit an example is given above. It shows how the motor driver has to be connected with the DC motor and the Arduino. Note that for the belt only one DC motor is needed. The blue component is the color sensor that has to be fed with 5 V and two pins have to go to the analog ports of the Arduino. The two cables of the color sensor that are connected to the digital pins of the Arduino are not mandatory for a good functioning of the sensor.

Components needed:

- 6mm plywood
- 3mm plywood
- 3 608-2RSH bearings
- 4 x M3 16mm screws
- 8 x M3 25mm screws
- 2 x M3 10mm screws
- 14 x M3 nuts
- 8 x M3 washers
- Laser cutter & 3D printer
- JGA25-370 DC motor 120 RPM (or similar)
- 50mm x 694.25mm x 1.5mm rubber belt
- Thread (to join extremeties of belt)
- 8mm diameter metal shaft
- 1 x E18-D80NK proximity sensor
- 1 x TCS34725 color sensor
- 1 Motor driver L298N

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