Overview and Explanation
So I decided to build a robot. At first I wanted it to be like the ones that compete in the VEX robotics competitions. This allowed me to focus on the robot rather than the problem because the problem was already defined for me. I was given access to a whole sleuth of VEX components. My main reason for making this robot is that I am going to be a teacher in the area of Technology, Engineering, and Design and before doing so, I wanted to learn as much as I could about as many different robotics platforms as possible before I do so. I started by reading the competition instructions for VEX. At first I was following the instructions closely, but after a while, since my main goal was to try and get familiar with VEX EDR and not actually compete, I decided not to follow them as closely. I had decided from the beginning that I wanted to make a three-wheeled robot. My main goal for this was to be different from the robots I had seen in videos of past competitions. Another reason was to try and save weight.
The first thing I did was to draw a few sketches that resembled the ideas in my head. I did this as a brainstorming session while trying to stay within specifications of the VEX competition instructions. I found that my Robot couldn’t be bigger than 18”x18”x18”. If you are reading this and you are planning on making a robot for competition, then I would watch videos from previous competitions for ideas first, mainly because after making my robot and it not working as planned, I changed my idea merely for it to work as intended but not follow the rules of the competition. Having said this, my tutorial will not follow all competition rules. I also drew a sketch of the arm that would carry the VEX "stars", "cubes", and that would pick itself up to perform a "low or high hang". I knew this robot must be stable enough to carry the stars and cubes which is why I made each robot as wide and as long as possible in order to give it a stable base.
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Step 1: Create Sketch
Step 2: Get Specifics
The next thing I did was to decide which idea to go with and clearly generate that idea. I decided to go with my second idea represented by my second sketch. To me this idea seemed the easiest. I knew that I had to have the arm for the claw long enough to overhang the front of the robot in order to be able to grab the stars and cube. I also knew that I would need enough gripping power in order pick up the stars and cubes which weigh 266 grams and 617.4 grams respectively.
Step 3: Measure Twice
Since I now knew which idea I would use I made some initial measurements to see which pieces of VEX angle iron I could use to make the frame and to make sure it fell within the range of specifications. The first thing I measured was the longest piece of angle iron, which measured about 12.5 inches. The next thing I measured were the smaller pieces of angle iron, which measured a little over 8 inches.
Knowing these measurements I knew that I could put two of the smaller pieces together to make a 16 inch piece which would give me 2 more inches before reaching the maximum limit of 18 inches or I could just use 1 longer piece and make it merely 12.5 inches long. I decided to make my robot 12.5 inches wide and 16 inches long with the arm over hanging 2 inches to give my robot a total overall length of 18 inches.
Next I tried to make a list of parts that I would use.
Step 4: Parts List
The materials that I used were:
VEX EDR Cortex Microcontroller box
Various VEX nuts, bolts, and screws.
VEX metal strapping of various lengths
VEX metal angle iron of various lengths and size
VEXnet Joystick controller
(2) Vexnet 2.0 2.4 GHz Bluetooth pairing sticks
(2) VEX motor Modules
(2) VEX 2 wire motors 393
(2) 2 to 3 wire motor controllers
(3) Wheels Gears of various sizes
A USB cable to download the code from the computer
Step 5: Build the Robot Front Frame
First I built the front main frame. This frame would hold the VEX EDR Cortex Micro controller box, the battery, and the front driving wheels with motors. The motors I used for the driving wheels are the smaller 3-wired motors. The battery I used was a 7.2 volt 3000 mAh NiMH.
Step 6: Build the Rear Swivel Piece
Next I built the back swivel piece that would hold the rear wheel and a mount for the arm. I decided to mount the arm here so I could control where it pointed, without having to completely face the robot toward the object I was trying to pick up. Lastly I built the arm and claw.
Step 7: The Wiring
I wired both driving wheels directly to the VEX EDR Cortex Micro controller box. I wired the motors for the claw and claw arm to motor controllers and the motor controllers to the VEX EDR Cortex Micro controller box. Here is a diagram.
Step 8: The Code
I first downloaded the proper software to create the code. I downloaded easyC V5. Next I updated the firmware on the controller and the VEX EDR Cortex Microcontroller box. Then I downloaded the generic code for the VEX EDR Cortex Microcontroller box and synced the VEX EDR Cortex Microcontroller box and the joystick controller. Once I synced them I tried to move the robot. One drive wheel motor turned one way and the other moved a different way. This wouldn’t do, so I had to change the code so that they would move in the same direction when I moved the joystick up and down, but opposite when I moved the joystick left and right. This would allow me to move the robot forward, backward, left, and right. The generic code allowed the claw arm and the claw to move properly so I didn’t have to change this code at all. I had to go through several tutorials on the easyC V5 software in order to figure out how to change the code properly. Above is the code for the driving wheels but since I used the generic code found on the easyC V5 website for the claw and arm, I left it out.
Step 9: Timeframe
This project took me several weeks working on it for several hours each week. The biggest problem I ran into was the swivel piece and the claw arm. The arm would get tangled up on the frame so I had to add a piece of strapping a few inches above the frame so that the arm could rest on it. The swivel piece was a nightmare. I had to change my design several times because of strength issues. It would also get caught up on the frame. I had to attach it to the main frame using an axle so that it could swivel. One axle isn’t very strong. I had to build a frame around the axle to strengthen it up. I also had to add some bolts at certain points to stop the swivel from moving all the way left or right. If it did then the swivel would get stuck on the frame and the robot would stop moving. I had planned on making the robot move autonomously but I used up my allotted time that I had set aside for working on getting my robot to function properly.
Step 10: Reflection
I had a lot of fun working on this project, but better than that I learned a lot about the VEX platform. I feel I could teach someone how to build a robot and code it to perform a task. With that said I completed my goals. I hope this might help you to build your robot. If I could change anything, I would change my robot to my third design. The rear wheel I would change and use an Omni-Directional Wheel. This would allow me the ability to get rid of the swivel piece all together. Unfortunately I didn’t have access to one at this time so I had to use what was around. Thank you for reading and I hope it helped.