To start working on the project we first printed the standard version of the otto ninja. It took two prints, one for the body and one for the wheels. We recommend printing without supports and with default infill.

To build the project we just follow the instructions of the otto project as they are concise and well laid out.

To more power the ESP board and to connect all the components easily we decided to build our own PCB, this was however a lengthier process than originally expected.

Our first plan to power the board was to use a 9V battery and a circuit like this to drop down the voltage to 5V. But testing on a breadboard proved that the amperage was not enough to power the board, much less to power the board and motors as originally planned.

Seeing this, we pivoted to using a portable phone battery, which already has the required voltage and simplifies the wiring. This is the perfboard we made after this change.

After making this prototype the idea was to design a pcb and order it, but after the designs were made, it ended up being way more expensive than we expected. We still used the designs as inspiration for the final versions of the board though.

The gerber files for the pcb can be found here.

In order of achieving the objective of covering the body and the electronics and making the robot resemble the original idea, we designed a simple cover piece with the shape of a dreadnought's main body. This decision posed a problem, as we didn't now how much space we had to save inside of the head for all the electronics we wanted to fit in, so we designed a tight belt to go around the otto's body in order to hold the dreadnought head.

For the design of this two parts the software used were Blender in the start, because is the tool we are more familiar with and it give us the possibility of creating the body in a more artistic way, and then the parts were modified in FreeCad to empty the solid body and make the holes for the camera and battery wire.

To change a file from .Stl to a FreeCad file we used this tutorial: Stl2FreeCad

We also used Freecad to make the blueprints of the parts using the tool TechDraw.

And also to create the assembly, that can be found here.

After finish the new designs for the body we once again printed them with the same parameters.

But this was too long a wait, so we started to play with the slicer settings. After raising the printing temperature and speeding up the motors, we dropped down the printing time, while maintaining a certain level of confidence that it would print correctly.

This step is optional, but to more closely resemble the original inspiration for the project we used an airbrush and a couple miniature painting techniques to give a coat of paint to the boring plastic.

First we decided on a color scheme, and since we had a can of black primer on hand we went with the black templars. Their color scheme is convenient and hides printing imperfections. These were our references.

After priming black, we printed some stencils to add the details of the templar's cross, and painted parts in white and metallic.

With all the painting done we moved to the weathering with a drybrush of metallic paint; and adding the purity seals (the prayer papers waxed and wax stamps that are on the reference pictures).

To make these we used painters tape as weathered paper and red dyed hot glue as the wax.

Still, sometimes the servos would give out and not move enough, so a small change was made to the board to add a condenser, to hopefully fix the drops in voltage that would stall the motors.

This seemed to work, so we moved on from the first prototype board to our final board. This time using a double sided perfboard and a better division of space, we managed to cram the same components into a smaller form factor, allowing us more freedom in the design.

But, this new board was made using the first one as reference and then when we tested it with the body we designed, the cam from the ESP32 was not aligned with the hole because the orientation of the board was upside down. For this reason we decided to make a new one. This third board has a more clean wiring and the space used is reduced again.

The ESP32 used in the project needs a 5V power supply the same as the servos. For this element of the robot at start we used the output from our laptops or a 5V phone charger.

We learned in different blogs and documentations that is better to add a different power supply for the board and other for the servos. The main idea was to use two Lipo batteries but due to budget and that we didn't have a way to connect them, we had to still use a phone powebank, wich has an output of 5V and 2.1 Ah.

Furthermore, the wire we use is an old phone charger wire that is longer than expected and too rigid, so it cause instability to the robot.

This and the size of the battery made us make the decision of keeping the battery outside of the robot and using the length of the cable to increase the range of the robot evangelion style.