Automated Illusion Cabinet
Creating a convincing illusion is often as much about engineering as it is about what the audience sees.
For this project, EMP Designs was asked to retrofit an existing large display cabinet with a fully automated motion-control system. The objective was to create a sequence in which an object could seemingly appear inside the cabinet without the audience seeing how it got there.
The cabinet itself already existed, so our challenge was to design and integrate the mechanisms, electronics and control system around the existing structure while keeping everything hidden from view.
Creating the Illusion
From the audience's perspective, the sequence is deliberately
simple.
The front doors open to reveal an empty cabinet. They close again and, a short time later, reopen to reveal an apple inside.
Behind the scenes, however, considerably more is happening.
Concealed doors at the rear of the cabinet open before a motorised mechanism moves an apple into position. The rear doors then close again before the main doors reopen.
A second position can present an apple with a bite taken from it, allowing the system to create a further stage of the illusion.
The rear doors are carefully incorporated into the cabinet so that, when closed, they simply appear to be part of the back of the structure.
Bespoke Automated Motion Control
EMP designed and manufactured the control system responsible for coordinating the complete sequence.
The installation incorporates:
Four electric actuators controlling the cabinet doors and mechanisms
Two stepper-driven linear mechanisms for positioning the objects
A dual stepper motor controller
Relay-controlled actuator outputs
Position and homing sensors
Magnetic sensors to confirm door positions
A dedicated safety circuit
Emergency-stop capability
External connections for additional emergency-stop devices
Remote triggering and system-status communication
Nine relay channels were ultimately incorporated into the system, with eight controlling the direction of the four actuators and an additional relay forming part of the safety-control architecture.
Knowing Where Everything Is
With several moving mechanisms operating inside the same cabinet, sequencing was particularly important.
Magnetic sensors confirm that the concealed rear doors are fully open before either of the object mechanisms is allowed to move. This prevents a mechanism attempting to travel while a door is still in its path.
The motorised slides also incorporate homing sensors.
When the system is powered up, the control software establishes the position of the mechanisms by carrying out a homing sequence. This means the installation can recover its known positions even if it has been switched off with one of the mechanisms partway through its travel.
Designed for a Public Attraction
As the installation forms part of a visitor attraction, the control architecture also incorporates a dedicated safety circuit and emergency-stop system.
Provision was included for additional external emergency-stop devices to be connected to the system, allowing the final installation to be integrated with the operator's wider safety requirements.
The operator can therefore stop the mechanism independently of the normal show-control sequence if required.
Integration with Show Control
The cabinet isn't operated as a standalone exhibit.
Like a number of automated systems EMP Designs has developed for visitor attractions, the controller communicates with the attraction's central technical system using UDP network messages.
The external show-control system can send a command to start the sequence, while the EMP controller can return information about the current operating state.
This allows the mechanical effects to be synchronised with the wider experience rather than relying on an operator manually triggering individual movements.
Designing Around the Installation
One of the less obvious challenges appeared when the final installation requirements became clear.
The control enclosure was positioned on the opposite side of a wall from the cabinet. To allow the equipment to be installed, every cable therefore needed an inline connector so that the wiring could be passed through the wall before being reconnected.
It is a good example of why practical installation considerations can be just as important as the electronics and software when developing bespoke systems for attractions and exhibitions.
When Engineering Becomes Part of the Illusion
Technically, none of the individual movements is particularly unusual. The challenge is in coordinating them so precisely that the audience never notices the engineering taking place behind the scenes.
Doors must reach their correct positions before other mechanisms can move, objects must arrive exactly where expected, and every movement has to take place in the correct order.
The result is an effect that appears remarkably simple from the audience's point of view:
An empty cabinet closes.
A few moments later it opens.
And something has apparently appeared from nowhere.
That's exactly how good show-control engineering should work — the technology disappears, leaving only the effect.
