I'm reasonably certain this makes me a bad person, but, oh, to hell HFS with it.
This design presumes a power-producing structure on the Z0 to connect to the left-hand gear assembly on Z-1. Mine's a perpetual motion machine, but lots of windmills would work too. The point is, the more power the better- It's not unreasonable to assume that the more surplus power you have, the faster any components on the "end" of a chain will spin.
Z-1
╔═════╗
║Xó+++┼ <- lever linked to the adjacent gear
║¢☼==☼║ <- hatch over the ramp to Z-2
╚═════╝
^ ^ and out here (through a channel in the floor)
∟ Power goes in here
Z-2
██╔═╦╦╦╗
╔═╝╫╠╩╬╣ <- surrounding walls made of copper blocks
║▲+╫║☼╠╣ <- magnetite gear assembly over copper block floor
╚═╗╫╠╦╬╣
██╚═╩╩╩╝
Z-3
╔═╦╦╦═╗
║ó╠╩╣+║ <- noble-summoning lever, copper block wall (directly under gear assembly on z-2) insulated by rock walls
║╥▒╫▒ó║ <- lever linked to copper grate (initially lowered)
║╥▒§▒ó║ <- lever linked to copper chain
║╥▒┼▒ó║ <- lever linked to door
║+┼^┼ó║ <- cage trap, lever linked to doors
╚══┼══╝
Operator comes in, noble is summoned, operator pulls lowermost lever to seal both nobles and self inside their respective chambers, then pulls the next lever up to open the execution chamber. Dorf brings goblin and then GTFOs, chamber is sealed again. Dorf pulls lever to raise grate and complete circuit. Bzzt. If goblin survives, door is opened and chain released so goblin blunders into cage trap.
Okay I admit this was a dry run for the massive generator I'm incorporating into my railgun. But why not have a little fun with the gobbos while I'm at it?