[Brogan M Pratt] and his students do a lot of 3D printing, and as such found themselves producing a lot of plastic waste. Seeing an opportunity, they built a bike-powered plastic shredder that turns a little human exercise into the power needed to transform waste plastic into small bits. Shredding plastic is a necessary first step for any sort of processing, so getting this part working reliably is as important as it is educational.

Being in the Netherlands, using a bike makes perfect sense. But it turns out there’s a lot more to making a human-powered plastic shredder than simply bolting a sprocket to a shredder, looping the bike chain over it, then climbing on and working up a sweat.

In between the bike and the shredder is a large gear reduction, a fifteen kilogram flywheel, and a heavy-duty frame to anchor everything in the face of so much mass and torque. Add some covers and safety guards and the result is a stationary bike with a hopper for waste, a bin for output, and enough rotational torque and inertia to chew through stubborn bits without stalling.

Now that the shredder works, what’s the plan for all the little plastic shreds? The goal is to turn it back into usable filament which is obviously very useful, but we’ve also seen that compression molding plastic waste can work pretty well, too.

Being an educator, [Brogan] makes it clear that a bike-powered shredder, while pretty cool, is not the only missing link in sustainability. There is currently no easy way to recycle plastic at scale. But the shredder is a critical part of demonstrating the whole process in a hands-on way, and learning why recycling plastic at scale is a genuinely difficult job.