A Robot Car With a Catapult

This project features a car model based on the F-150 with a catapult launcher attached. It is equipped with an Arduino Uno and several motor controllers, making it easy to build or troubleshoot. To build this project you can use any model ,but personally I would recommend one that has fewer curves more straight corners , as this makes the finger joints easier to build.

The reason I chose the F-150 as my model is because it has fewer curved joints.This makes it easier to design the finger joints to connect the parts and also is beneficial if you are going to use a laser cutter.Since most laser cutters cut in 2D, the front ,back, top, bottom and sides will be cut separately.

1.Arduino Uno

2.sensor shield

3.Usb cable( to upload code)

4.Wheels(Qty : 4)

5.Motor Controller

6.Motor( Qty : 2)

7.Bluetooth Module ( communication )

8.Micro servo ( Qty 1 )

9.6 AA battery pack

10.Drill Gun

11.sensor( Titri HC- SR04 ultrasonic sensor)

1. Fusion 360 ( needed to build the cars body)
2. 3D printing( to print the catapult and other necessary supplies)
3. laser cutting( to cut the car's body)
4. Arduino ide( to Upload and edit code)

The catapult mechanism should be simple and easy to make. I have attached a file below to 3D print the catapult. Feel free to make any adjustments to it, I recommend making the top bar slightly thicker so its more stronger or you could cover it with foam to prevent it from cracking or breaking.

Since you would be using a yellow motor to build up elastic potential energy . When the ultrasonic sensor detects movement within 10cm, the yellow motor starts spinning forward, this builds up an elastic energy and the servo below holds the catapult in position until the yellow motor stops spinning, once it stops ,the servo releases the arm and the projectile is launched.

To make your car body, take any clear picture , that has straight and clean edges.The reason i used the F150 was because it has more straight edges compared to other car models.This makes it easier to laser cut and make the finger joints.

To import your image

1 Open fusion

2 Go to insert > Canvas > import from my computer.

3 Upload your image and place it on the frontal plane.

Sketching the car

1. Use a line or arc to trace the car's body.
2. Include details like windows or doors depending on your preference.

Extrude

1 After finishing your sketch extrude your sketch to the desired width

2 I recommend extruding the thickness of the sketch to 3mm, since most plywood are 3mm.

Making the inside hollow

After extruding , you would have noticed the inside of the car is not hollow.

1. To make the inside hollow, go back to your original sketch
2. Use offset to create a 3mm inner shape inside the sketch.
3. Extrude that inner sketch to the opposite side to cut out the center and make it hollow.

Finger joints

Since the body of the car will be cut separately, ( front, back, top, bottom, sides) you will need finger joints.

1 Create a rectangle notch at the edges where they interlock with each other.

2 Make the width of the rectangle depending on the material you will be using. eg if you are using 3mm plywood, make the width of the rectangle 3mm.

3 Make sure to change the width depending on the thickness of material.

The code I have for this car will be able to allow you to drive it and control the catapult, since the catapult is fully automated when the sensor detect movement no input is required.

When movement is detected by the ultrasonic sensor within 10cm, the yellow motor starts to spin and builds up elastic potential energy, while this is happening , servo holds the catapult in place. Once the yellow motor finishes spinning, the servo releases the arm, which launches the projectile.

No manual input is required to trigger the launching mechanism, it activates when the sensor detects movement within its Range have included the code below, so feel free to adjust it to your liking.

One of the challenges i faced was making the wheel cutouts symmetrical, to fix this i went back to the original sketch and created a new circle bigger than the radius of the wheel.I centered the circle in the middle to maintain symmetry and then i extruded to the other side, making both sides equally symmetrical.This made sure both sides were equal and the wheels could fit properly.