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RepRaTS 3D Printable E-Scooter

An electric scooter that can be made entirely from printed parts and off the shelf components without any power tools!

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RepRaTS (Replicable Rapid prototyper Transportation Systems), inspired by the RepRap project, aims to build fully user-upgradable and user-repairable transportation with FDM 3d printing. Modular plastic beams are the core of a RepRaTS vehicle, which allow virtually unlimited adjustability and provide a huge amount of mounting options. RepRaTS require no power tools to build and assemble other than your 3D printer. The first RepRaTS scooter was designed and built entirely in a small NYC apartment. Testing is currently ongoing on this prototype.

The Challenge

FDM 3D printing is one of the most affordable and accessible ways to start working with rapid prototyping and 3d design/modeling.  FDM printers can create a huge number of parts with great utility.  FDM printers require little dust collection or ventilation, so they can be used in residential settings, unlike many manufacturing methods.

While the price and quality of printers on the market is steadily improving, there are a number of challenges presented when trying to produce large and/or load bearing parts with FDM printers.  As printers stack layer upon layer of molten plastic, the strength of the adhesion between these layers is usually a weak link in a printed part.  This means that printed parts are strongest in compression, but in shear or tension can be severed along a part’s layer lines.  Furthermore, overhangs can be difficult to print, requiring supports which can be difficult to remove and negatively affect print quality.  Finally, the maximum build volume of a printer (with the exception of “infinite-z”  printers, which present their own unique challenges) caps the largest size a printed part can be.  All of these challenges make it difficult to use FDM to create large load bearing structures.

My Approach

Using electric transportation as a benchmark, the RepRaTS project seeks to expand the types of objects that can be considered “printable”.  Tensioned threaded rods connecting a series of printed plastic spacers create the structure of the RepRaTS scooter prototype.  This accomplishes two things: first, the tension in the threaded rods gives the scooter its strength and rigidity, and second, the rods force the printed parts into compression to compensate for weakness between layer lines.

The spacers used in the RepRaTS scooter have mounting holes that are printed perpendicularly to the body of the spacer and glued in after printing.  This allows high tension fastening both longitudinally along the beams and laterally across them.  As a result, it is relatively easy to mount components to the printed frame in any direction or orientation.  This is demonstrated by the scooter prototype, which has to accommodate many parts with arbitrary sizes and mounting patterns/orientations.  The battery, motor controller, throttle, brake, hub motors, and handlebar all need to be mounted to the plastic frame and accommodate large loads often in multiple directions.

The prototype uses very large (13” tire) hub motors to demonstrate an upper limit of the design. If a scooter can be designed to use such large and powerful (1000W) motors, then a designer can comfortably build a smaller vehicle.

The goal of the RepRaTS prototype is to serve as a demonstration of what types of structures can be produced with FDM rather than as an end goal.  Using the same technique, one can make other vehicles, furniture, storage, or many other modular load bearing structures.

I am continuing to design and iterate on the RepRaTS scooter and have a number of improvements in the pipeline, namely splash and impact resistant housing for the battery and electronics, a stiffer and stronger headset connection, end caps for the threaded rods, and an integrated lighting system.

McMaster-Carr parts in the OnShape assembly must be used in accordance with their terms and conditions, available here: https://www.mcmaster.com/termsandconditions/

Quick demonstration video:

  • 1
    WARNING!!!!! PROJECT IS IN PROGRESS!!!!! SCOOTER IS NOT YET SAFE TO USE!!!

    There are a number of issues with the current iteration of the RepRaTS scooter.  The current battery mounting is totally unacceptable and extremely unsafe.  I have intentionally excluded it from the OnShape assembly as I am currently redesigning appropriate mounting.  Do not under any circumstances attempt to replicate the battery mounting as demonstrated on the prototype.  There are a number of exposed threaded rods which present a huge hazard, especially on a motorized vehicle.  I am in the process of designing caps and guards for them, which will be posted when available.  Additionally, the headset connection needs to be redesigned to be more rigid.  

  • 2
    Accessing CAD files and printing/assembly instructions

    All of the cad files for the scooter are available in the linked OnShape assembly.  All of the prints were printed in PETG with a 0.8mm nozzle at 0.4mm layer height with a 30% grid infill.  No parts require supports.  If you need supports, check your print orientation.  The parts labelled "plug" are meant to be glued in place.  To do this, first align the plug and spacer against a reasonably flat surface, and then glue with a wicking superglue.  I like to use Loctite 408 because it dries clear, but any superglue should work fine.

    https://cad.onshape.com/documents/bc1719bcd096ae7eea007e23/w/cd7e065a0b15fdf55abf1143/e/ca32f6b46d1a366db804db70

  • 3
    Proper Bolt Tension

    The key to this build is using tension in the threaded rods to give the beams strength and to keep the printed parts in compression.  The printed parts should not deform up to the max recommended torque for 3/8" low strength threaded rod, so do not be afraid to tighten aggressively.  Make sure to evenly and slowly build up to the max torque to avoid warping the beams as you are tightening.  If you find warping the frame to be an issue, simply back the nut out until the warping goes away and try again to tighten evenly.

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