The $50 robot project is far enough along to post some details on it and to rename it “Bootstrap,” reflecting its purpose to develop in the builder a set of skills that can be used to independently develop and build similar projects.
Over the next few weeks materials will be posted to the Bootstrap page on this site providing all the resources needed to build a Bootstrap robot for around $50.
A few pictures of prototype 3 are posted here, illustrating what will be the base model. Major features are very unlikely to change at this point. Its about 130mm (5″) in diameter. Some of the wiring in the pictures is a bit raggedy because it has been moved across a series of chassis–but all will be cleaned up in future versions.
Bootstrap is powered by an Arduino Nano and the basic sensor suite for obstacle avoidance consists of an HC-SR04 ultrasonic sensor and a bumper connected to two switches. Many more sensors can added to this base configuration. The version illustrated here has a 3D printed chassis and other components. However access to a 3D printer is not required to build the robot. The chassis can be hand cut from plywood or other sheet material and the other components can be purchased or easily fabricated.
A few more details can currently be found on the Bootstrap page–with all the details soon to follow.
I have had to make a series of decisions to keep the project within budget and to maximize the changes of success (and minimize the hassle factor) for the first-time builder. Three examples of these decisions concern voltage, fasteners, and component sources.
The simplest of circuits run at a single voltage. But as projects become more complex one quickly discovers that multiple voltages are required: common microcontrollers want 5 or 3.3 volts, sensors will take one or both of those, and motors can run in a range of voltages. In addition, batteries come in different voltages: Alkaline cells are nominally 1.5v, Nimh rechargables are 1.25v and Lipos are 3.7v. An early decision to simplify all this was to run everything at 5 volts. Bootstrap features a dc to dc boost converter that will bring battery power from about 2.5 volts up to 5 volts to an output of 5v at about 1 amp. This means 3xAA alkaline cells, 3XAA nimh rechargable cells, or single cell Lipo batteries can all be used. The switches, diode and other components are specced operate above an amp. The 5v output feeds an Arduino Nano, the sensors, and a set of N20 gearmotors (via a motor controller). A 3.3v output is available via the Nano, but everything is designed to run at 5v, keeping the circuits simple and parts count down.
Chasing down screws, standoffs, nuts, etc. in different sizes when you only need a few of each is a real pain.
Not to mention the requirement of having the bits available to drill different sized holes when hand fabricating a chassis. Everything on Bootstrap attaches with m2x12mm screws and nuts. Everything.
Every component save one (the fabulous Protostack prototyping board) on Bootstrap can be obtained from multiple suppliers. These are all pretty common parts that can be purchased cheaply. I have developed design files for 3D printing all the parts that can be printed, which saves money. Yet a builder without access to a 3D printer will be able to obtain all the parts from reliable sources.
There are some compromises in these decisions. The 6v rated N20 gear motors are going to run a little more slowly at 5v on Bootstrap. Nimh batteries aren’t going to last that long before they need recharging. I had to play around with counter sinking and double nutting to get the 12mm screw length to work for everything. However I hope these decisions make building Bootstrap less maddening than it otherwise would be.