This item is intended to be an educational aid to demonstrate the conservation of energy, however it can be expanded beyond that as explained below, working in a way similar in fashion to a newtons cradle, but simpler to produce with a 3D printer.

The track costs ~$0.9 USD to print, with rollers for it costing ~$0.08 a piece assumign the $20/kg cost of filament I had paid to print this.

The SCAD files/code is included with this post, the models were written and commented with variables being used that should allow for easy scaling/tweaking of the files if anyone seeks improvement or wants to fine tune it for their specific needs.

The original idea behind it was to create something akin to the classis physics demonstration of releaseing a pendulum near a person or object, and then demonstrating energy being conserved by having it return to the same location (if friction is ignored) and not hit the person/object.

This proved to be a greater challenge than expected to replicate the effect with fully 3D printed material, as it is difficult to get smooth curves in this manner, making it a challenge to make something roll smoothly without falling off the track.

To address the issues of small bumps in the track bouncing light weight rollers off, a roller specifically for this was designed to rid along a slot in the track and have outer guide wheels to keep it on.

The next challenge, involved the realtively low density of the 3D printable material I have availible. At the moment, I am only able to print in PLA, which results in rollers with low densities even when printed at 100% infill.

Because of this, frictional losses are much more apparent than what would be observable if rollers were able to be made out of denser material that would have more potential energy at their starting heights, where potential energy=mass*g*height.

With a lower initial potential energy, the losses due to friction do not leave the system with enough energy to osicilate for an extended period of time using PLA rollers.

To address that issue and still be able to demonstrate the concept the diameter of the "axle" of the roller was increased to add more mass, and the outer guides of the roller were increased in diameter and thickness to provide more mass to help make friction more negligible.

The second way this was overcome, was by changing this sentence about the intended use of the educational aid, or expand upon it.

If higher mass rollers are avalible, that will yield better results for demonstrating how energy is conserved. However, if that is not an option, if additional rollers are printed, at a cost of $0.08 USD per roller (assuming the $20/kg price of filament I had paid for this material), it can be used in a similar manner to a newtons cradle to demonstrate actions having equal and opposite reactions.

With rollers being released from identical heights of the track at opposing ends, it is possible to observe an identical reaction when opposite forces act upon eachother to ultimately cancel, in a similar fashion, unbalanced forces can also be oberved by altering the release height of each roller, similar to a newtons cradle.