The concept of this little buddy has the will to create more playful robots to make my 4 year old boy even more interested in learning electronics and robotics.

Its main feature is the stegosaurus-shaped PCB, which besides being the main part to support all electronics, is a fundamental part of aesthetics.

I intend to show the whole design and construction of this robot for a clearer perception of the context.

The first video shows an overview of concept and design, mechanics, electronics and programming, but I will also describe these steps here with some additional information and details.

Step 1: Design

Sitting at my desk with a stegosaurus toy of my kid in hand for inspiration, I began to draw the parts directly on cardboard.

I ended up with a nice cardboard prototype to test the leg / walking mechanism and get a good overview of the actual size and arrangement of the parts.

Then, knowing the desired dimensions, I began to draw the final model and 2D templates for the mechanical parts.

Step 2: Mechanics

All mechanical parts were made of high impact polystyrene pieces (2 mm thick sheets). This is my favorite material for making custom parts for my robots and I have been using this material for about 8 years.

The method is simple: the templates are glued over the plastic pieces with stick glue. When the glue is well dry, I cut the pieces into the lines with an utility knife. For straight lines, I also use a metal ruler to guide the cuts so that they have a really straight cut.

Some parts need to be further strengthened. In this cases I combine multiple layers to reach the needed strength, and using instant adhesive to join everything.

To give the parts a smooth finish, first I sand them first with # 60 sandpaper to remove excess material and # 500 sandpaper for fine finishing.

The holes are easily made with drill.

The last step is to paint everything. First with the spray primer to see if everything is smooth enough and finally the desired color.

The servo motors for the legs / walking mechanism are all Hitec mini servos. The middle one is an HS-5245MG and the other two (for the front and rear legs) are HS-225MG. I chose them not for any special reason... it was simply because they were the ones I had at home. But they are excellent servo motors with metal gears and have more torque than necessary.

List of materials for mechanics:

high impact polystyrene (2mm thick sheet);
instant adhesive;
gray spray primer;
green spray paint;
Hitec HS-5245MG servo motor (1x);
Hitec HS-225MG servo motor (2x);
M3 nylon standoff 35mm (4x);
bolts and nuts;
sandpaper (# 60 and # 500).

stegobot_templates.pdf
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Step 3: Electronics

The PCB (which I call the STEGOboard) is designed to make it easy to connect the servomotors and NRF24L01 module to an Arduino Nano board. Of course this could have been done with a very small PCB. But, as I said before, the PCB is also a fundamental part of aesthetics.

When I imagined the whole robot in my mind, I had the idea that it should have a large green PCB on its back with that distinctive kite-shaped plates.

The PCB shape file (SVG) was made with Inkscape, and the schematic and arrangement of the electronic parts on the board was made with Fritzing. Fritzing was also used to export Gerber files needed for manufacturing.

The PCB was manufactured by PCBWay.

The PCB has three connectors for servo motors and headers for the Arduino Nano board and the NRF24L01 module. It also has a connector for the power supply. Everything was soldered with lead-free solder.

The power supply is made by two LiPo batteries connected in series, so I have 7.4V. But the servomotors accept a maximum of 6 volts. Therefore, it also has a step-down LM2596 module to provide the correct voltage and not burn the servomotors.

List of materials for electronics:

Arduino Nano R3;
NRF24L01 module;
right angle pin headers;
female headers;
LiPo battery 3.7V 2000 mAh (2x);
lead-free solder wire;
LM2596 step down voltage regulator;
solder flux.

Step 4: Programming

The programming of STEGObot is very simple, as it has only three servo motors, and it was made with the Arduino IDE.

Basically, we have to move the middle servo motor to tilt the front of the body and rotate the front legs' servo (simultaneously, the rear legs rotate in the opposite way). So, it pulls the robot forward.

stego_code.rar
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Step 5: Having Fun

STEGObot can move forward, backward, and make left and right turns. It is remotely controlled with a custom remote that I made to control all my robots.