A remote-controlled mine clearance vehicle
Taking a dangerous job away from the person doing it
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The mine clearance vehicle prototype on a workbench, showing the red chassis, drive wheels and gears, a small motor, an AA battery pack and the yellow PCB carrying the counter and driver ICs
- Context
- Technology, final examination project
- Year
- 2019
- Role
- PCB design, remote and receiver
- Team size
- 2
- Tools
- Arduino · Infrared transmitter and receiver · 4520 binary counter · L293 motor driver · PCB123 · Fusion 360
- Contribution
- Team of 2, PCB design for the remote and receiver boards
A remote-controlled terrain vehicle carrying a metal detector, built in order to take mine clearance away from a person in a protective suit walking over unstable ordnance. Three custom PCBs, being the remote, the vehicle and the detector.
The problem
Mines left behind in former war zones stay functional for decades, and since it is impossible to keep track of where they were all laid, they continue to put civilians at risk long after a conflict ends. Clearance is usually carried out by a person in a protective suit with a metal detector, which is dangerous due to the mines being unstable, and it is important to note that almost every other repetitive and dangerous task in the western world has already been handed to a machine, so the question was why this one had not been.
What we built
A remote-controlled vehicle driving on DC motors through an L293 motor driver in an H-bridge configuration, with an infrared transmitter and receiver for the control link, and a metal detector using electromagnetic induction on the front. We chose infrared over radio due to the amount of interference in radio control, and we chose remote control over automation since automation would have required sensors and programming that were outside the scope, while steering it ourselves was the more interesting problem anyway. The receiving side runs the incoming pulses through an RC network and a Schmitt trigger in order to clean them up, and then into a 4520 synchronous 4-bit counter, which gives four outputs from a single input and is what allows one infrared channel to drive four separate directions. Three PCBs were laid out in PCB123, and the mechanics were modelled in Fusion and built on a plexiglass plate with two gears and an axle.
What I owned
I was responsible for the PCBs on the remote and on the receiving side, meaning the transmitter board carrying the four switches, the four indicator LEDs and the infrared diode, and the vehicle board carrying the reset network, the counter and the motor driver, while my partner focused on the metal detector. Here the difficult part was the layout rather than the circuit itself, since PCB123 gives you a single copper layer to work with, and this means that every crossing has to be solved either by rerouting the trace or by accepting a physical bridge.
What went wrong and what we would change
A bridge on one board caused a short circuit, the counter's clear input needed to be tied to 5V rather than left floating, and we had to switch to a non-discriminating infrared receiver before the control link worked reliably. Furthermore 3V turned out not to be sufficient for the L293, and the coil, the mechanics and the infrared pair were all identified as things to improve, especially the transmitter and receiver, which would work better at 38 kHz with a proper oscillator. Here the extension we would have liked to build is a weight or a piston that triggers the mine deliberately once it has been detected, since a 4-bit counter gives 15 usable combinations and there was room to send that signal alongside the motor commands.