Highway to Undercity

(Fast, rugged, and 3D Printed RWD RC car with 2x Drone BLDC motors)

Time Spent: ~4 hrs kicked off the build w/ a lot of tea and a LOT more random ideas. brain was kinda everywhere today.

grabbed a notebook and just started dumping whatever ideas came to mind. i knew i wanted 2 axles and rear-wheel-drive. that’s it.
came up w/ this dumb but cool idea — 2x 1000KV drone motors feeding into a single GT2 pulley. totally overkill. totally doing it.
most ppl online use PVC or alu for the frame, but i’m going all in on 3D print. like, every single part. even washers if possible.
thought of a rear pod that swings to fake suspension vibes, while the front just stays stiff w/ steering.
scribbled a BOM for parts: motors, pulleys, MG996R, ESCs, bearings. if it’s in the junk bin, it’s fair game.

set myself a challenge — every single part must fit on a 220x220 bed. no glue. no slicing into 20 parts. no nonsense.

Time Spent: ~5 hrs onshape the GOAT (die fusion360) . built most of the back end.

put 2 A2212 motors mirrored and modeled a GT2 pulley system that feeds torque into a single 5mm axle.
made hex wheel hubs that press-fit onto that same axle — no diff, both wheels spin same speed.
made a custom bracket that holds both motors tight w/ cutouts and belt tension slots.
added ribs n’ walls to the pulley block so it doesn’t flex when the car's ripping around.
everything either snaps in or bolts together. no glue, no epoxy, no drama. full module is swappable like drone arms.

spent too long on belt tension — finally just threw in a top roller and extended the flanges. it’s holding fine now.

Time Spent: ~4 hrs ugh steering. didn’t wanna do this but had to.

made some chunky knuckles w/ pivot arms and mini stub axles for the front wheels.
linked up the MG996R servo to a drag link + tie rod. it’s janky but it works.
kinda followed ackermann steering stuff? not too serious. close enough for dirt.
servo sits in a nice little pocket above the axle — hidden and outta the way.
front axle bolts to the spine w/ 4 screws. fast to swap if anything breaks.

Time Spent: ~5 hrs made the skeleton. simple, strong, modular.

the chassis is just a long rail. every part bolts on like train cars.
added slots for everything: front axle, rear pod pivot, ESCs, battery tray, RX.
made zip tie guides and wire tunnels in the side walls — zero spaghetti cables.
tried to keep everything symmetrical so future changes don’t break stuff.
split the whole spine into 3 printable sections (<200mm). added pegs so it snaps together clean.

every part’s mounted using M3/4 nuts and screws. they’re everywhere. everything locks down tight now.

Time Spent: ~4 hrs started playing around w/ suspension ideas.

rear pod kinda dangles under the car now. looks like a mix of a buggy and a moon rover.

Time Spent: ~4 hrs put everything together in cad. moment of truth.

t725

this thing fits together like LEGO. every part either slots or bolts. super satisfying.

Time Spent: ~4 hrs prep day. time to get slicer-ready.

fixed orientation for every STL so there’s less support and stronger prints.
named files properly — no more final\_final\_real.stl stuff.
double-checked tolerances using the caliper tool in cad. everything should fit.
added pegs + markers to help line things up while assembling.
estimated around 380g PLA/PETG total, 11-12 hrs of print time unless the bed acts up.

also made a proper BOM & wrote down readme.

all cad files are final and exported. STLs are cleaned up and sitting in the print folder. now just waiting for the real-world parts to show up:

as soon as stuff lands, printing begins. fingers crossed it drives like a beast and doesn’t melt the first time i hit throttle.

KX-36