During factory testing, I would leave the device deployed and step away for a break. When I came back, technicians were standing on it, working on the car. Nobody asked me if it was safe. I suppose it looked solid enough.
What I didn’t see at the time was what it was telling me.
It was a detrainment system for MTR’s Shatin to Central Link (SCL) project in Hong Kong. I was a mechanical engineer at Hyundai Rotem, and I volunteered to take it on. Its job was to get passengers off a stopped train and down to the track safely.
Most detrainment devices are ramps at the end of the car, where the drop to the rail is always about the same. This one had to come out from under a side door, with the ground anywhere from 1,000 to 1,700 mm below. It had to fold into about 800 mm under the floor and open to the full 1.2 m door width. Every step had to carry two adult men. A handrail had to rise on its own to at least 900 mm. Deployment in three steps or fewer.
I decided early that one motor would drive every motion. That turned out to be the hardest part of the project. Steps and handrail had to move as a single-degree-of-freedom mechanism, reach any height in that range, and bring the handrail up tight against the car. I worked it out from the first concept, including the handrail linkage, which I synthesized myself.
The payoff was simplicity. With one motor there was nothing to synchronize, so the whole thing could run on plain electrics. Power in, the motor runs, a switch cuts the power. No control board, no electronics.
Because it was a safety device, it also needed a secondary lock. The supplier’s existing lock didn’t always engage. I took it apart and changed the latch inside so it would engage reliably.
It took several pilot units to get there. When the trains were delivered and the device was demonstrated on site for the first time, the client accepted it with no comments.
I presented the design at the Korean Society for Railway conference. A company president stopped by and said it would be more useful on an ordinary day than in an emergency. Park the car in the yard, open it up, and technicians can get in for cleaning and light maintenance.
That was when I thought back to the factory. In my head it had only ever been an evacuation device.