Self-Destructing Apple

I was approached by a client in the theater industry who was working on a production of Robin Hood. They required a specialized prop for the famous archery scene: an apple that could sit on an actor's head and "magically" split in half on command when a fake arrow was shot at it. The prop needed to be wireless, visually indistinguishable from a real apple from the audience's perspective, and robust enough to survive falling onto the stage floor night after night. 

With a strict deadline of just two weeks before rehearsals, I treated this as a rapid prototyping sprint. The goal was to create a device that felt less like a DIY science project and more like a finished consumer product. The final result is a self-contained, rechargeable electronic prop that uses solenoid actuation to split apart seamlessly, providing the play with a reliable and repeatable special effect.

Before settling on the final design, I evaluated several actuation methods to find the most reliable solution. I considered using a servo-driven latch, but servos are often too slow and noisy for a magic trick. I also looked into electromagnets to hold the halves together (deactivating them to drop it), but that required constant power which would drain the battery too quickly. Ultimately, I chose a high-force push-solenoid system paired with permanent magnets. The magnets hold the apple together passively, while the solenoids provide a violent, instant burst of force to break the magnetic bond, creating the "pop" needed for the effect. 

To achieve visual realism without the difficulty of painting 3D prints to look like organic fruit, I sourced realistic foam prop apples. I cut one of the apples asymmetrically to hide the seam and hollowed out the interior to accommodate the custom parts. To house the mechanism, I designed a custom internal chassis 3D printed from TPU (Thermoplastic Polyurethane). This was a critical material choice: unlike rigid PLA or PETG, TPU is a flexible, rubber-like plastic. It acts as a shock absorber, protecting the delicate electronics inside from shattering when the apple inevitably falls onto the hard stage floor.

The system is powered by a Lithium-Polymer battery capable of supplying the current needed for the solenoids. To make the prop practical for theater staff, I treated it like a finished consumer product rather than a prototype. I integrated a standard USB-C charging board, allowing the crew to charge it easily between scenes. Additionally, I wired in an unobtrusive switch to completely disconnect the battery during storage, preventing the device from accidentally triggering or draining while sitting backstage. The trigger itself uses an RF remote for instant, reliable wireless communication without the pairing issues of Bluetooth or the need for line-of-sight. 

One of the challenges was ensuring the apple didn't just crack open but actually fell off the actor's head convincingly. Because the device is split asymmetrically to hide the cut, one half contains the heavy battery and solenoids while the other is naturally much lighter. To prevent the light half from "sticking" or failing to fall, I added a weighted insert to its far edge. When the solenoids fire, this extra mass at the perimeter destabilizes the center of gravity and uncouples the magnets, forcing both halves to tumble away from each other violently. This ensures that the apple separates cleanly and dramatically every single time. 

Moving from concept to a field-ready device in under two weeks, this project was a success in rapid product development. The prop performed reliably throughout the entire production run, demonstrating how engineering principles like solenoid actuation and center-of-mass manipulation can effectively solve creative constraints. While designed for Robin Hood, the experience gained in packaging a wireless, rechargeable system into a small, shock-proof organic shape has refined my approach to designing ruggedized consumer electronics.