This Robotic Smoke Grenade Is the Coolest Movie Prop Ever

I’ve always had a fascination with prop making. It involves many of the same skills that makers use for normal projects, but the emphasis is on the appearance of functionality rather than actual functionality. Usually that means that prop makers get to cut corners, so long as the final product looks like the real deal. But sometimes the unique requirements of filming introduce added layers of complexity. That was certainly the case with a film that forced Davis DeWitt of Backhaul Studios to get creative when he built this robotic smoke grenade prop.

Let’s set the scene: a bunch of armed men are about to breach a stronghold of similarly armed men. They have the element of surprise, so they start by rolling in a smoke grenade to push their advantage. The director wants to get a nice dolly shot following that grenade as it rolls along the floor spewing smoke. But that requires predictable movement and that’s where this prop comes in.

This prop is brilliant, because it looks like a real smoke grenade and emits “smoke” on-demand. But a clever internal mechanism lets a remote operator control its movement. They can roll it forward or backward at whatever speed they want, and even change speed if the shot calls for it.

That’s possible thanks to internal motors that essentially turn the outer body of the smoke grenade into a big wheel. A Seeed Studio XIAO SAMD21 development board controls those motors through a DRV8833 driver. A connected radio receiver lets the operator control motor speed and direction with a standard transmitter remote, like the kind used for RC cars.

Power comes from a pair of 18650 lithium battery cells, which also act as weights to keep the components inside level as the outer shell rotates around them. The “smoke” comes from a vape cartridge with a tiny blower fan. The operator can switch power to the vape cartridge to turn the smoke on or off.

The physical parts were all carefully modeled in CAD to resemble a real smoke grenade, then 3D-printed. Like any good prop maker, DeWitt put a lot of effort into paint and weathering to make it look like something that has been sitting on an armory shelf for years. Some labels made on a Cricut craft vinyl cutting machine added to that effect.

The result is really impressive and I can only hope that DeWitt shows us how it looks in the movie once filming is done.