Team project: a small tracked robot that drives into a mock-up of a collapsed building (basement level, concrete, lots of rebar and debris) and reports gas (CO, CH4), temperature and battery, plus low-res video so the operator can drive. Range from the operator is up to about 60 m through two or three floors’ worth of concrete.
We’ve argued for a week about Wi-Fi vs LoRa vs 4G vs 433 MHz modules and nobody has data. We’d also like the telemetry on a Hermetry dashboard for the judges, which is the easy part.
What would people pick, and what are the trade-offs we’re missing?
LoRa for sure, it goes for kilometres
LoRa won’t carry video at all, the data rates are tiny.
Video needs Wi-Fi-class bandwidth, and 2.4 GHz through that much concrete dies fast.
Not an engineer, but our hotel hosted a rescue robotics demo last spring and I spent the day asking their team exactly this. What they did, and why:
Video and driving went over a tether: a thin cable on a reel on the robot paying out as it drives. They said every radio they tried for video failed in their rubble tests, and a cable also means the robot never loses control when it turns a corner.
Telemetry and an emergency stop went over a separate sub-GHz radio (868 MHz in Europe) at a low data rate, so if the tether snapped the operator could still stop it and still see gas readings.
When they had to go wireless for video they dropped small relay nodes behind the robot as it went in, each one in sight of the last.
4G was useless underground for them. The base station laptop was the only thing that talked to the internet.
For your dashboard: the laptop forwards the telemetry over MQTT, the robot never talks to the cloud itself. If you do use LoRaWAN rather than point-to-point LoRa, Hermetry’s network server follows the gateway’s frequency plan, so EU868 gear in Ireland.
Went with 100 m of Cat6 on a reel for video and driving, and 868 MHz point-to-point LoRa for telemetry and the e-stop. The base laptop forwards to Hermetry. Pulled the tether out in a test on purpose and the e-stop still worked over LoRa. Judges liked the gas chart.
If the laptop forwards for the robot, make the laptop a gateway device and report the robot as its child, then the robot has its own device page and alarms.
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