Project Overview
One of my earlier projects was a self-balancing robot, based on an Arduino NANO, which worked really well, but unfortunately you can no longer obtain the wireless transceiver part. So here I’ve re-designed this robot, using an ESP32 microcontroller, and themed it on a Mandalorian helmet. You can control this robot using a Wii Nunchuk controller, using my well established ESP-NOW Wi-Fi link, or you can control it via Bluetooth using a controller like a Magicsee R1.

This robot has new features like RGB LEDs, a speaker for sound and a laser range finder, built into the helmet. As the helmet is detachable, for battery charging, you could also design and make a different upper body of you choice. Click the image to the right to watch a video of my MandalBot in action -->

All of the robot chassis components were produced on my 3-D printer and modelled using the free 3-D design package from RS Components, DesignSpark Mechanical. Small 2x10mm self-tapping screws hold the main parts together quite rigidly. And some parts are glued together, as they would be difficult to 3-D print otherwise. RGB LEDs are mounted inside the helmet, but at a shallow depth, such that they shine through the white PLA material. The laser range finder is mounted at the base of the helmet, with the sensor looking through a small aperture. With additional code this could make the robot autonomous, capable of manoeuvring objects, and navigate round them.

This design mounts the electronic components on a chest plate, so they are easily connected together using wire wrap technology. Whilst this approach requires a small amount of investment up front, it makes the wiring process very straight forward, and has the advantage that the built unit can be tested before final soldering.

One of the great thing about ESP32 microcontrollers is there built in Wi-Fi circuitry, which makes it relatively easy to include ESP-NOW for Wi-Fi communications. As with many of my later projects, the MandalBot can be controlled from a Wii Nunchuk controller, connected to a WEMOS D1 mini transceiver unit. The protocol I have developed not only provides a control channel, it also includes a bi-directional transparent data channel, offering many forms of telemetry, as seen later with the Monitor+ application..

If the robot is powered up, or released from RESET, whilst the right-hand button switch is pressed, then the code adopts Bluetooth as the Wi-Fi protocol. In this case it allows you to connect a Magicsee R1 controller. This might be just what you want, but the downside is that you lose the telemetry feature; and having both ESP-NOW and Bluetooth available consumes a lot of programme memory. Therefore the code has to be compiled using the ‘Huge’ code profile in the IDE. Of course, you could remove one of these options.

The circuit diagram for the robot is shown here on the left, with the ESP32 connected to the two stepper motor drivers, the MPU 6050A 3-axis gyroscope and two button switches. As the RGB LEDs can draw a relatively large current from the 3v3 supply rail, this design uses a 3v3 buck voltage regulator, to step-down the 11.1v battery voltage needed by the NEMA14 stepper motors. A resistive voltage divider feeds the microcontrollers ADC with a sample of the battery voltage, keeping a close eye on battery voltage.

The DRV8825 stepper motor drivers have current sensing, to control the amount of energy being fed into the motors, and the boards have a small potentiometer for adjustment. To aid setting this current limiting up, for each driver board, the robot can be fed power from an external DC power supply via a socket, mounted on the rear of the robot. If the current is too small, the stepper motors will have limited torque; where as if it is too large, the motor will run very hot and could be permanently damaged, relatively quickly.

For projects incorporating a 128x64 OLED display, I developed a monitoring app that could convey the display contents back to a PC, and then onto a large monitor for folk to see. I then realised that this useful feature could also be used on projects not including an OLED display, and from then on this Monitor+ app was developed. Simply put, over Wi-Fi the code in the ESP32 can send the contents of numerous displays, to be shown in the monitor app. This could include text, and also data, to be displayed like the serial monitor as waveforms.

With this system you can now click on the left or right-hand side of the Monitor+ display to tell the code in the microcontroller to present different display content, and with coloured text (in this case blue) you can make numeric fields adjustable with the click of the mouse. In this project I have a display for PID controller coefficients, which you can adjust in real time, whilst the robot is self-balancing. Best of all, you can code and include more displays, and could use this approach in other projects you might develop. It’s quite easy to adapt..