Introduction: Arachnoid

First, we would like to thank you for your time and consideration. My partner Tio Marello and I, Chase Leach, had a lot of fun working on the project and overcoming the challenges it presented. We are currently students of the Wilkes Barre Area School District S.T.E.M. Academy I am a Junior and Tio is a Sophomore. Our project, the Arachnoid is a quadruped robot which we made using a 3D printer, Bread Board, and a Arduino MEGA 2560 R3 Board. The intended goal for the project was to create a walking quadruped robot. After a lot of work and testing we have successfully created a working quadruped robot. We are excited and grateful for this opportunity to present to you our project, the Arachnoid.

Step 1: Materials

The materials that we used for the quadruped robot included: the 3D printer, support material washer, 3D print trays, 3D print material, wire cutters, a breadboard, battery holders, a computer, AA batteries, electrical tape, scotch tape, MG90S Tower Pro Servo Motors, Crazy Glue, Arduino MEGA 2560 R3 board, jumper wires, the Inventor 2018 software, and the Arduino IDE software. We used the computer to run the software and the 3D printer that we used. We used the Inventor software mainly for designing the parts so it's not necessary for anyone making this at home because all of the part files that we created are provided on this instructable. The Arduino IDE software was used for programming the robot which is also unnecessary for the people making it at home because we've also provided the program that we're using. The 3D printer, support material washer, 3D print material, and 3D print trays were all used for the process of fabricating the parts that the Arachnoid was made of. We used the battery holders, AA batteries, jumper wires, electrical tape, and wire cutters were used together to create the battery pack. The batteries were put into the battery holders and the wire cutters were used to cut the end of the wires of both the battery pack and jumper wires so they could be stripped and twisted together, then taped with electrical tape. The breadboard, jumper wires, battery pack and Ardiuno were used to create a circuit that supplied power to the motors and connected them to the Arduino's control pins. The Crazy Glue was used to attach the servo motors to the parts of the robot. The drill and screws were used for mounting other elements of the robot. The screws should look like the one in the picture provided but the size can be based on judgement. The Scotch Tape and Zip Ties were used mainly for wire management. In the end, we spent a total of $51.88 on the materials that we didn't have around.

Supplies That We Had on Hand

  1. (Amount: 1) 3D Printer
  2. (Amount: 1) Support Material Washer
  3. (Amount: 5) 3D Print Trays
  4. (Amount: 27.39 in^3) 3D Print Material
  5. (Amount: 1) Wire Cutters
  6. (Amount: 1) Drill
  7. (Amount: 24) Screws
  8. (Amount: 1) Breadboard
  9. (Amount: 4) Battery Holders
  10. (Amount: 1) Computer
  11. (Amount: 8) AA Batteries
  12. (Amount: 4) Zip Ties
  13. (Amount: 1) Electrical Tape
  14. (Amount: 1) Scotch Tape

Supplies That We Bought

  1. (Amount: 8) MG90S Tower Pro Servo Motors (Total Cost: $23.99)
  2. (Amount: 2) Crazy Glue (Total Cost: $7.98)
  3. (Amount: 1) Arduino MEGA 2560 R3 Board (Total Cost: $12.95)
  4. (Amount: 38) Jumper Wires (Total Cost: $6.96)

Software Required

  1. Inventor 2018
  2. Arduino Integrated Development Environment

Step 2: Hours Spent on Assembly

We spent quite a few hours on the creation of our quadruped robot, but the most sizable chunk of time that we used was spent on programming the Arachnoid. It took us approximately 68 hours to program the robot, 57 hours printing, 48 hours designing, 40 hours assembling, and 20 hours testing.

Step 3: STEM Applications


The scientific aspect of our project comes into play while creating the circuit that was used to power the servo motors. We applied our understanding of circuits, more specifically the property of parallel circuits. This property is that parallel circuits supply the same voltage to all components within the circuit.


Our use of technology was very important throughout the process of designing, assembling, and programming the Arachnoid. We used the computer aided design software, Inventor to create the entire quadruped robot including: the body, lid, thighs, and calves. All of the parts designed were printed out of a 3D printer. Using the Arduino I.D.E. software, we were able to use the Arduino and servo motors to make the Arachnoid walk.


The engineering aspect of our project is the iterative process used to design the parts made for the quadruped robot. We had to brainstorm ways to attach the motors and house the Arduino and breadboard. The programming aspect of the project also required us to think creatively about possible solutions to problems we came across. In the end the method that we used was effective and helped us to get the robot to move in the ways that we needed it to.


The mathematical aspect of our project is the use of equations to calculate the amount of voltage and current that we needed to power the motor which required the application of Ohm's Law. We also used mathematics to calculate the size of all of the individual parts created for the robot.

Step 4: 2nd Iteration Quadruped Robot Lid

The lid for the Arachnoid was designed with four pegs at the bottom which were sized and placed inside of holes made on the body. These pegs, along with the assistance of Crazy Glue were able to attach the lid to the body of the robot. This part was created to help protect the Ardiuno and give the robot a more finished look. We decided to move forward with the current design but it'd gone through two iterations of design before this one was chosen.

Step 5: 2nd Iteration Quadruped Robot Body

This part was created to house the four motors used to move the thigh parts, the Arduino, and the breadboard. The compartments on the sides of the body were made larger than the motors that we are currently using for the project which was done with the spacer part in mind. This design ultimately allowed for adequate heat dispersion and made it possible to attach the motors using screws without causing possible damage to the body which would take much longer to reprint. The holes in the front and the lack of a wall in back of the body was purposefully done so that wires could be run into the Arduino and breadboard. The space in the middle of the body was designed for the Arduino, breadboard, and batteries to be housed in. There are also four holes designed into the bottom of the part meant specifically for the wires of the servo motors to run through and into the back of the robot. This part is one of the most important as it serves as base for which every other part was designed. We went through two iterations before we decided on the one displayed.

Step 6: 2nd Iteration Servo Motor Spacer

The servo motor spacer was designed specifically for the compartments on the sides of the body of the Arachnoid. These spacers were designed with the idea in mind that any drilling into the side of the body could potentially be dangerous and cause us to waste material and time on reprinting the larger part. That's why we instead went with the spacer which not only solved this issue but also allowed us to create a larger space for the motors that helps to prevent overheating. The spacer went through two iterations. The original idea included: two thin walls on either side that connected to a second spacer. This idea was scrapped because we though it'd be easier to drill each side separately so if one became damaged, the other one wouldn't need to also be thrown away. We printed 8 of these pieces which was enough to glue to the top and bottom of the motor compartment on the body. We then used a drill that was centered on the long side of the piece to create a pilot hole which was then used for a screw on either side of the motor for mounting.

Step 7: 2nd Iteration Quadruped Robot Leg Thigh Portion

This part is the thigh or the upper half of the robot's leg. It was designed with a hole on the inside of the part that was made specifically for the armature that came with the motor which was modified for our robot. We also added a slot on the bottom of the part which was made for the motor the would be used to move the lower half of the leg. This part handles a majority of the major movement of the leg. The current iteration of this part that we're using is the second as the first had a chunkier design that we decided was unnecessary.

Step 8: 5th Iteration of Quadruped Robot Knee Joint

The knee joint was one of the more tricky parts to design. It took several calculations and tests but the current design shown works quite nicely. This part was designed to go around the motor in order to efficiently transfer the movement of the motor to movement on the calf or lower leg. It took five iterations of design and redesign to create but the specific shape that was created around the holes maximized the possible degrees of movement while not forfeiting the strength that we required from it. We also attached the motors using more armatures that fit into the holes on the sides and fit perfectly onto the motor allowing us to use screws to keep it in place. The pilot hole on the bottom of the piece made it possible to avoid drilling and possible damage.

Step 9: 3rd Iteration Quadruped Robot Leg Calf

The second half of the robot's leg was created in such a way that no matter how the robot sets down it's foot, it'd always maintain the same amount of traction. This is thanks to the semicircular design of the foot and the foam pad which we cut and glued to the bottom. It ultimately serves it's purpose well which is allowing the robot to touch the ground and walk. We went through three iterations with this design which mainly involved changes in length and foot design.

Step 10: Downloads for the Parts Inventor Files

These files are from Inventor. They are specifically part files for all of the finished parts that we designed for this project.

Step 11: Assembly

The video that we have provided explains how we assembled the Arachnoid, but one point that wasn't mentioned in it is that you will have to remove the plastic bracket from both sides of the motor by cutting it off and sanding where it used to be. The other photos provided are taken from during the assembly.

Step 12: Programming

The arduiono programming language is based off of the C programming language. Inside the Arduino code editior, it gives us two functions.

  • void setup(): All the code inside this function runs once at the beginning
  • void loop(): The code inside the function loops without end.

Check below by clicking on the orange link to see more information on code!

This is the code for walking.

Servo FrontRightThigh;
Servo FrontRightKnee;
Servo BackRightThigh;
Servo BackRightKnee;
Servo FrontLeftThigh;
Servo FrontLeftKnee;
Servo BackLeftThigh;
Servo BackLeftKnee;
voidwriteLegs(int FRT, int BRT, int FLT, int BLT,
int FRK, int BRK, int FLK, int BLK ){
ServoManager Manager;
view rawQuad.ino hosted with ❤ by GitHub

Step 13: Testing

The videos that we added here are of us testing out the Arachnoid. The points where you see it walking are a bit short but we believe it should give you an idea of how the walking of the quadruped robot was done. Towards the end of our project we did get it to walk but pretty slowly so our goal was accomplished. The videos before that are of us testing out the motors that we attached for the upper part of the leg.

Step 14: During the Process of Designing and Printing

The videos that we added here are mainly progress checks throughout the process of designing and print the parts that we made.

Step 15: Possible Improvements

We took time to think about how we would move forward with the Arachnoid if we had more time with it and we came up with some ideas. We would look for a better way to power the Arachnoid including: finding a better, lighter battery pack that could be recharged. We would also look for a better way to attach the servo motors to the upper half of the leg we designed by redesigning the part that we created. Another consideration we made is attaching a camera to the robot so it could be used to enter areas otherwise unreachable by people. All of these considerations had gone through our minds while we were designing and assembling the robot but we were unable to pursue them because of time constraints.

Step 16: Final Design

In the end, we are quite happy with the way our final design turned out and hope you feel the same way. Thank you for your time and consideration.