Michael Skupien

Wireless Emergency Stop Switch

As my co-founder and I were developing our self-driving golf cart for our company Varden Labs (more information about the company here), it became clear that when possible, an empty golf cart driving around had a profound impact on those watching. On our first test, within about 10 minutes of the system working, the two of us both jumped out and were running around a grass field jumping in front of our prototype with no way to stop it should something go wrong other than chasing after it (which we knew we were capable of). To continue performing these amazingly visual demonstrations, we decided that we needed a way of safely stopping the vehicle wirelessly.

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Our vehicle used a National Instruments roboRIO board to interface with the vehicle and accept commands from a Linux PC. The roboRIO was designed for use in FIRST Robotics, a competition that both my co-founder and I were very familiar with having participated in it. This board already had a sophisticated watchdog system designed for FIRST that required a specific UDP packet to be fed to it to enable the controllers outputs. Having already reverse engineered this UDP packet so that our Linux PC could supply the packet to the roboRIO, we decided that we could simply use an internet router on the vehicle to create a local network that a wireless board could connect to and send that UDP packet to the computer would would relay it down to the roboRIO.

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I mechanically designed and manufactured a compact unit to house the necessary electronics. Inside was a Particle Core, a wifi connected micro-controller, a repackaged usb external battery pack that could be recharged with a micro usb and powered the unit, a couple LEDs and a microswitch trigger.

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Pressing the trigger down enabled the vehicle and letting go would leave the vehicle enabled for 2 seconds while applying full brake. For dual redundancy, in the event that software on the device failed or the switch failed, the unit could easily be powered off on the bottom of the device which would obviously halt the transmission. Also, the specific packet necessary was a response to a packet originating on the roboRIO and continuously changed making sending the same packet continuously useless. Furthermore, no other device had the capability or knowledge of how to produce the specific packet and instead they simply relayed the messages back and forth.