The collapse of the Crandall Canyon Mine in Utah last August killed six miners, then three rescue workers. The intense pressure on the coal pillars supporting the mine caused them to burst, sending coal and rock flying with explosive force.
After rescuers sent drop cameras down bore holes, they wanted a better view of the mine shaft. Inuktun Services Ltd. in Nanaimo, B.C., was contacted to build a robot that could descend more than a mile through 9-inch-diameter holes and crawl 300 feet.
Mechanical engineer Jeff Stanway and team designed a 19.5- by 8-inch chassis based on the Versatrax 150 crawler from Inuktun. They mounted an articulated arm with pan-and-tilt Spectrum 90 camera out the rear to maintain a low profile. A Crystal Cam camera at the front monitored descent and landing. A 14.5-inch tether-control arm at the rear held the cable out of the way when the 70-pound robot reversed.
“Our control system for these components goes 1,500 feet, so we partnered with Ken Peligrin of PipeEye International in Las Vegas,” says Stanway. Besides field experts, Peligrin supplied a 6,000-foot, fiber-optic tether with telemetry canister. Stanway connected it to 300 feet of soft tether attached to the robot.
On the first day, the clutch on the winch failed, and the robot free-fell until the camera jammed in the bore hole. Stanway repaired the soft tether and winch that night.
The robot was 10 feet from the bottom on the second day when shifting ground changed the channel to an impassible oval. “Rescuers had sent a drop camera down the hole, so this information was a bonus,” says Stanway.
Lowered into a different hole on the third day, the robot landed in front of a small mud pyramid. Two feet of coal, blown from the walls by the pressure of the mine collapsing, littered the floor. “The robot’s 4-inch-high tracks weren’t enough to navigate over the debris,” says Stanway. “Then mud fell on the lens, and even with groundwater flowing past, we couldn’t wash it off.” This information also was important.
On the fourth day, the bore hole collapsed, burying the robot. “The experience was sobering. Anything put into that mountain, it took,” says Stanway.
