Introduction: 3D Printed Quadruped

About: I am interested into music and robotics.

It is my first project with 3D printing. I wanted to make a cheap Quadruped with all the operations. I found many project on internet regarding the same but they were more expensive. And in none of these project did they teach about how design an quadruped? As I am a budding mechanical engineer these principles are very important. Because anyone can 3D print an already existing model and run the same code. But nothing of value is learned.

I have made this project during my semester brake and will add the improvements over time.

I have uploaded the video. You can download and watch it.

Step 1: Designing of the Chassis

The chassis should be designed as such that the max torque applied on the motors are within the ratings of the motor.

The main parameters to be kept in mind while designing the chassis are:

1. Femur Length

2. Tibia Length

3. Estimated Weight (Keep it on the higher side)

4. Clearances Required

As this is hardware adequate clearances must be taken. I have used Self Tapping screws every where. So my design does have threads in them. And making small threads with 3D printer is not a good idea. You may have to print small parts first so as to check clearances before the final cut. This step is only required when you do not have enough experience like me.

The chassis has been designed on Solid Works 2017-18. The link for the same is:

If you want even greater control on your quadrupeds movement. The gait design should also be taken into the equation. Since it was my first project I realized this a bit later.

Step 2: 3D Printing the Chassis

I 3D printed the chassis in PLA (Poly Lactic Acid). Sand the parts to get adequate clearances. Then assembled all the parts with servos as I have had designed. Please keep in mind that all your servos are of same manufacturer as different manufacturers might have different designs. This happened with me. So check before hand.

Step 3: Circuit for Operation

I am using an Arduino UNO and 16-channel servo controller for my bot. You can find them very easily online. Connect the pins accordingly. You need to write the connection of servo pins is with which pin. Otherwise it will get confusing later on. Bundle the wires together. And we are good to go.

For battery I have provided two LiPo cells (3.7V) with high current discharge. I have connected them in parallel as the max input to servos is 5v.

Step 4: Coding the Quadruped

Though it may seem tough at beginning but it gets easier later. All you have to keep in mind while coding is the gait design. Remember the following:

1. At all times the center of gravity of the quadruped must be within the area formed by your legs.

2. The angles are to be taken from a set reference. This depends on your design and how you want to move your legs.

3. I am using a 180 degree servo not a geared motor so you have check this while you are fixing the servos

Regarding the explanation to the code this link will suffice:

These are my codes

Step 5: Geometric Calculations

The angles are a calculated via trigonometry:

1. You have first find 2D leg length

2. Then check the elevation of you bot

With these two constraints you can easily calculate the angles for your servos.

Write I have written code for moving forward. I will update the code later when I pursue it again.

Step 6: Further Improvement

I will add a bluetooth (BLE) module for the control of the bot from phone.

Thank You for viewing my project, Any doubts are welcome.