Ripley: The Evolution of a PiBot – Part 1

I’ve often wanted to get into robotics but I’ve never had the money or the time but, with the advent of smaller, cheaper computers, maybe it’s time do finally do so. My first foray into this world is building an internet-enabled robot called Ripley (yes, I’m a fan of the ‘Alien’ films). Ripley will be built from a radio-controlled car as the base and a Raspberry Pi 3B. The Pi’s OS is currently Ubuntu Server 16.04 and the software will be written in C, with possibly some machine code thrown in for low-level device management.

I will document everything, hardware, code, results etc, on here for anyone to refer to if they want to do a similar project, as I am a great believer in Open Source and sharing.

Please note: I have no pre-built plans, no pre-written software, just a box of parts, a remote-controlled car chassis, a Pi 3B and thirty years of IT experience. It should be fun.

So, without further ado, we shall start.

Ok, to start, this is what I’ll be using as the mobile base of Ripley:

20170201_120143

This is the chassis of a radio-controlled car kit that I purchased and built in 2008 for the sum of £300. It came with an acrylic body in the shape of a BMW Mini, since removed and not needed. The pairs of vertical posts at either end of the vehicle are ideal to serve to mount the various sensors and cameras that will give Ripley her sense of the world.

Note: The following notes are just thoughts and ideas for the moment as I think about what needs to be done. Schematics and firm plans will follow on from these.

To be kept: Front (steering) and rear (drive motor control) servos, drive motor, battery (Tornado Overlander Nimh 3300mAh, 7.2v)

To be discarded: Radio Control unit, speed control pot (to be replaced), antenna, acrylic body.

Power for the Pi will come from the battery via an L7805 voltage regulator. I haven’t yet been able to find the power requirements for the servos (both ACOMS AS-16’s) so it may be that I will have to build in a second power unit to supply those (and other onboard hardware) if the Pi’s GPIO output power is too low (which I suspect it may be). Fortunately, the Pi can supply PWM from any of the standard GPIO pins so, power requirements aside, controlling both servos shouldn’t be a problem.

Proximity sensing will be provided by ultrasonic distance/motion sensors, a camera can be mounted to provide remote views and internet access can be provided by a 4G enabled mobile (keeps the costs down because I have one spare).

Further info will be uploaded shortly.

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