An automatic trapdoor apparatus for double-blind ankle sprain research

João Manuel Rodrigues




Mechanical construction

The pedestal is a wood box, consisting of a rigid wooden frame [insert figure]
with two rectangular trapdoors covering most of the top surface.
The trapdoors are attached by horizontal hinges to a central beam on the box.
Electromagnetic locks mounted on the outside beams of the box hold the trapdoors
in the closed horizontal position.
When power to one of the electromagnets is cut, the corresponding trapdoor is unlocked,
falling immediately under gravity.

Electronic circuit

The electronic circuit can be divided in 4 subsystems:
  1. Control
  2. Power
  3. Operator interface
  4. Actuation
  5. Sensing


The actuator elements are a pair of electromagnetic locks normally used for
fail-safe doors in buildings.
The locks used were Newmark-MCX300M, available from Farnell.
They have a 300 kgf holding force and
operate at 12V or 24V DC, 6W.
This model includes a magnetic bond sensor that can be used to detect
the open or closed status of the lock.

Power to the locks is controlled by two solid-state relays