For the past few weeks I’ve been playing around with making a small robot that I could drive around over wifi using an onboard camera.
This is all part of the bigger plan mentioned here about making some kind of game involving one (or more) robots that can be driven by humans vs several autonomous robots in the same level.
The Chassis
The chassis was designed in fusion 360:
The chassis has four mount points on top that an m2.5 threaded insert can be inserted into.
It is designed to use two N20 motors – with each motor driving the two wheels on a side.
All bearings can be press fit by hand
The bearings used are SS623-2RS available from Radionics.
The link to the fusion 360 model is available here
I think this chassis will be useful for lots of different mini robot applications. The design is set up so the width of the chassis etc can be changed by just modifying some parameters. The idea is that this will also be used for the autonomous robots – they just won’t have a raspberry pi etc. The mounting points on the chassis make it convenient to mount PCBs to.
Motor Driver / Boost PCB
I wanted to be able to run the robot off of a single cell lipo so 3.7V nominal. The N20 motors run fine on this voltage but the pi requires a boost converter to provide the 5V it needs. So there isn’t much on the board just a lipo charge circuit so I can charge the battery via micro USB, a boost converter, and a motor driver circuit and that is basically it.
This board sits on the chassis here. The idea is that the raspi zero just sits on top.
And underneath it has three jst connectors, one for each motor and one for the battery:
The Kicad project files are available here
I made one tiny mistake with the boost converter inductor, I accidentally made it 0402 and picked one with a too small current rating and the some magic smoke was unfortunately released. It turns out they don’t make 0402 inductors that can handle the currents I need here so there is an 0602 one on order that I’ll attempt to bodge on.
There is a bit of work to do with figuring out the battery mounting. The general idea is that the battery sits under the robot. There is just about enough space to squeeze it in there . Hopefully the next update will have a robot driving around !
