Project Overview
These days there are many examples of Hexapods on the internet, normally built from plastic parts sourced from 3-D printers. This design uses a very different approach, being created in 2-D using PowerPoint, then cut from 3mm hardboard using a fret saw. There are 13 MG90S micro servo motors used in this design, which are driven from a 16 channel PWM driver board, over the I2C bus, to reduce the load on the microcontroller. The coding challenge was quite complex as I incorporated an ultrasonic distance sensor in its rotating head, which makes way for fully autonomous movement. So this design was based on using an Arduino MEGA board for maximum code space. It has button switches to select modes of operation, but it can also be controlled from a mobile phone app using Bluetooth. Click the image to the right to watch a short video of my Hexapod in action -->

All of the parts needed to make this robot, including its stand, were designed in PowerPoint and made from 3mm hardboard. This method is quite accurate and allows you to included in your design a wide variety of graphics, that would otherwise prove to be very difficult in other manufacturing methods like laser cutting and 3-D printing. Many of the parts are made from two pieces glued together back to back, which makes for a very strong 6mm material.

The servo motors and other parts which may need to be removed at a later stage were glued in place using soft melt glue. This can be applied directly from a glue gun, but I prefer a method in which the glue is first extruded into long thin rods in a shallow tray of water, then applied like a welding rod using a temperature controlled soldering iron. The glue can easily be removed at any time by reheating it with an iron and removing it with cotton buds. As servo motors can fail unexpectedly this is a good method to adopt in practise.

The robot is powered from a 7.2v Lithium battery pack, made up from 6 x AA rechargeable batteries. The power plug from this pack plugs directly into the Arduino MEGA power socket, so there is no need for a separate ON/OFF switch. During prolonged software development these batteries can easily be substituted by a 7.5v DC mains adapter.

A lot of current is drawn from the batteries by the servo motors when the robot it driven from rest to its free standing position, and this can cause a dip in the supplied voltage which is sufficient to reset the microcontroller. To prevent this electrolytic capacitors are needed to absorb this current spike. The robot also has an array of multi-coloured RGB LEDs around its body, which all in all makes the robot quite power hungry.

The circuit diagram for the Hexapod is shown here on the left, with the Arduino connected to the thirteen servo motors via a 16 channel PWM pcb. The Bluetooth transceiver requires resistors to perform level shifting for its 3.3v input, and the 16 RGB LEDs are simply connected in series with 5v and GND rails.

I have shown you how to wire up the 3 button board, which mounts the Bluetooth transceiver and status LEDs.

Given the power needed to move the legs of the robot, particularly when standing up, I used 1N4006 diodes as a voltage dropper to feed the 16 channel PWM pcb with 6 volts; the maximum for these servos. Some electrolytic capacitors may be need to sustain the Arduino power, as surges in current for the servos can result in the micro resetting.

Given the number of servos involved, and the need to calibrate their positions and motion, I decided to write a servo control app using Processing for Windows. This then moved onto an app for controlling the robot; as in getting it to stand up, sit down, turn ON/OFF LEDs and behave autonomously, again written in Processing.

Then, once happy with that I finally moved on to developing an app using MIT App Inventor 2, which you can use to develop Android based apps for your mobile phone or tablet device. This free tool, now provided by Google, has both a screen designer and code block editor. As it supports the connection of Bluetooth devices it was ideal for this application, and I found it relatively easy to learn and use.