Welcome to the second version of the DIY SMARS Robot! In this tutorial, I’ll guide you through producing this enhanced robot with new features like an OLED display, RGB LEDs, and a buzzer for melodies. Follow along as we design the circuit, assemble the PCB, and 3D print the mechanical parts. Let's bring this robot to life with motion control, Bluetooth connectivity, and customizable eye expressions.

Begin by designing the circuit schematic in Altium Designer. The heart of the design is the Atmega328p microcontroller in its SMD VQFN version, chosen for its compact size. Integrate the following components into the schematic:

With the schematic completed, transition to designing the PCB layout. Ensure the PCB dimensions match an Arduino UNO board for compatibility with the robot chassis. Here are key placements:

Solder Paste Application
With your PCB and stencil ready, the next step is to apply the solder paste. Begin by securely positioning the PCB using some old PCBs or a jig to keep it steady. Align the stencil over the top side component pads accurately. Drop the solder paste onto the stencil and gently spread it across the pads using a squeegee or a similar tool. Ensure the paste is evenly applied to all the pads to guarantee a clean and efficient soldering process.

Component Placement
Once the solder paste is applied, start placing the SMD components onto the PCB. Use tweezers to carefully position each component on its corresponding pad, following your design layout. Pay attention to the orientation of components like the LEDs and the ICs to avoid placement errors.

Soldering
After all components are in place, use a hot plate or reflow oven to solder them onto the PCB. If using a hot plate, gently place the PCB on the preheated surface and monitor the soldering process. The solder paste will melt and form solid solder joints. If using a reflow oven, follow the recommended reflow profile for your solder paste.

Inspect the solder joints under a microscope to ensure they are properly formed and there are no solder bridges or cold joints. Clean the board with a flux remover solvent to eliminate any residual flux, resulting in a clean and professional finish.

Solder the through-hole connectors for the OLED display, ultrasonic sensor, and motor outputs. Attach the HC-05 Bluetooth module and the 9V battery connector to the PCB. Ensure all connections are secure and test each component for functionality.

Mechanical Parts And OLED Display Assembly

Mechanical Parts Assembly

Begin by 3D printing the mechanical parts of the robot using the STL files available on Thingiverse. Once printed, assemble the robot chains. You can use 1.6mm brass wire or 1.75mm 3D printer filament for the joints. Insert the wire or filament through the links to create flexible chains. Secure the joints with super glue if needed. You'll need 16 pieces per chain, making a total of 32 pieces for both chains.

Next, attach the wheels to the DC motors. Start with the slave wheels, applying some force to fit them in place. Then connect the master wheels to the small DC motors. Secure the DC motors and the 9V battery in their respective holding board parts. Finally, attach the chains to join each slave wheel to its master wheel, completing the mechanical assembly of the robot.

OLED Display Housing Assembly

For the OLED display, design and 3D print a housing. Insert 2mm threaded inserts into the housing to provide secure mounting points. Place the OLED display into the housing and secure it with screws. To enhance the display clarity, consider adding a resin cover to the housing. Screw the housing cover in place to complete the assembly.

Now, you have both the mechanical parts and the OLED display housing ready for integration with the PCB.

To control your SMARS Robot, you will need a custom Android app. Using MIT App Inventor, develop an app that includes:

Set up the app to transmit serial characters over Bluetooth for each button press. Here’s a brief overview of the steps:

Develop an Arduino code to interpret the serial characters sent from the app. This code should:

Upload the code to the Atmega328p microcontroller using the Arduino IDE. Before uploading, un-bridge the Bluetooth RX line. After uploading, place back the jumper to re-establish the Bluetooth connection.

Now, you’re ready to test your Android app with the assembled SMARS Robot.

Connect the circuit board to the 9V battery and insert it into the robot chassis. Connect the motors and OLED display to their respective connectors. Upload the Arduino code, ensuring to un-bridge the Bluetooth RX line during programming. Test the robot using the custom Android app developed in MIT App Inventor, verifying all functionalities including motion control, LED color changes, and eye expressions.

Congratulations! You have successfully built the second version of the DIY SMARS Robot. Enjoy exploring its new features and feel free to share your own modifications and improvements. Keep creating and happy making!