Final Project. Building a Sorter Robot

Task: Building a Sorter Robot

Flynn Darko

Lecturer: Dr. Ayorkor Korsah


Final Robotics Project


Introduction & Objective

The objective of this project was to build and program a robot that would sort a number of maize grains painted in different colors. When the color of the painted grain is detected, the sorter robot places it in the assigned container placed in front of it. The robot is supposed to do this until all the grains are sorted into the respective containers.


Design Concept


My first conception of the how the structure of the sorter robot should be was first influenced by a model I saw online which looked like the one shown in figure 1.   I therefore went ahead to build the model using the building instructions that came with it. However, I had stated in my proposal that I was going to make use of colored maize grains. But looking at the model I had decided on, the grains could not be transported along the inclined structure that this model provided. The model could work well for colored balls which would fall along the inclined Lego brick. Though presented as my first milestone, I decided to work a new model which would be more efficient in transporting the grains during the sorting process. Using a conveyor belt was my next design concept.

figure 1: First sorter robot model

figure 1: First sorter robot model

As shown in figure 2, I saw another model which I knew would be the best robot structure model to use. Having no building instructions, I had to build it myself using the various parts from the NXT Mindstorm Lego kit. This took a great deal of the time I had to finish the whole project.


New Picture (1)

figure 2

New Picture (2)

figure 2

Program Algorithm

During the building process of the sorter robot, I had the following algorithm concept in mind which I wanted to implement

  1. Detect and display grain color on NXT screen
  2. Upon detection, stop upper conveyor belt and turn lower conveyor belt (upper conveyor and lower conveyor shown as Uconv and  Lconv in figure 3) to the respective bin collector
  3. Start upper conveyor again till the grain drops in the collector.
  4. Reset lower conveyor to original position
  5. Repeat steps I to IV until all the grains placed on the sorter robot are sorter into their respective bins

The next progress was the implementation stage.

New Picture (3)

figure 3


The above figures (figures 2 and 3) show the model of the robot I built. I used a color sensor to help detect the color of the Lego brick color (the colored maize grains were not being detected well by the color sensor so I used Lego bricks instead).  In order to get a conveyor belt I attached a motor to a wheel which had a conveyor belt wrapped around it. This is shown in figure 4.

New Picture (4)

figure 4



As already mentioned, getting the structure of the sorter robot right was the one major challenge I faced. Though I had the program algorithm written down, I could not implement it without building the sorter robot. I was therefore able to implement the program for the sorting process very late to the due date for demonstration. During demonstration, I still had some modifications to make to the rotation of the lower conveyor (Lconv) so that it moved towards the right bin throughout the sorting process.


This final project proved to be very challenging since I had to build the robot from scratch without any building instructions. However, I found it very fulfilling when I was finally able to get it done an implement my program.

Relevance to Problem Solving in Ghana

In Ghana we could have robots that can sort waste to hasten the process of recycling. For example in homes, such robots can be programmed to sort waste materials into labeled bins which would make the reuse of waste possible and much easier.


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