Ultimate 3D Printed RC Car + Laser Cut Chassis

Designed by Ethan Liu and Maxwell Hu in Ms. Berbawy's Makerspace 2022-23

Check out a video of our car in action.

Radio controlled cars offer something not enough people have in their lives: the opportunity to re-experience the child-like glee of something that functions like magic. But what's even more interesting is putting the parts together, each gear and axle and wheel working and performing together to move the car. Our project allows for both of these freedoms.

This build performs best on flat surfaces.

Inspired by the works of Rambros' "Easy to Build 3D Printed RC Car - Dragon R1", and modeled after the Lamborghini Aventador.

Check out his awesome project: 3D Printed RC Car Open Source

Our project is also open source. Any modifications are encouraged. 

Equipment:

• 3D printer (ideally PETG for parts and Ninjaflex for wheels)
• Laser Cutter
• SLA Printer + Durable Resin
• Solder Kit

Supplies ($50~$100):

• 10V A2212 BLDC motor
• Electronic Speed Control (ESC)
• 10x Bullet Connectors
• 11.1v LiPo Battery + Connector
• Mini Servo
• Remote Control and Transmitter + Batteries
• Super Glue / Gorilla Glue / Hot Glue
• 2mm Steel Rods
• M3 screws (15+ 8mm, 8+ 12mm, 8+ 20mm)
• Mineral oil
• Velcro

3D Printed Materials

• 4x Rim
• 4x Tire
• 8x Connector Pieces
• 2x Rear Bearing Holder
• 2x Front Bearing Holder
• 2x Bearing to Screw (Steering Connector)
• 2x Screw to Rod Holder (Steering Connector)
• 1x Rod Holder / Servo Connector
• 2x Front Gearbox
• 1x Rear Gearbox (left)
• 1x Rear Gearbox (right)
• 2x Axle
• 1x Big Gear
• 1x Pinion Gear
• 1x Base Pair
• 2x Rod Holders
• 1x Front Bumper
• 1x Windshield Base
• 1x Left Frame
• 1x Left Large Cover
• 1x Left Door
• 1x Left Front Cover
• 1x Right Frame
• 1x Right Large Cover
• 1x Right Door
• 1x Right Front Cover
• 1x Front Top
• 1x Middle Top
• 1x Back Top

Software:

• Prusa Slicer
• Autodesk Fusion 360
• Adobe Illustrator
• SLA Slicer
• Laser Cutter Software

All images above are in order of steps below.

If you want to design the car yourself, the car is mainly divided into two gearboxes (assembly shown later)

1. Rear Gearbox (acceleration)
2. Essentially, this is just a box with enough room to hold a large bearing. Additionally, the components are split in half, with 3M screw holes on the sides to connect the parts, and allow access to the gearbox. 
3. Gearbox: 30mm x 30mm x 30mm 
4. The large gear fits snugly into the cylindrical hole, and there is space for a pinion gear to rotate (attached to BLDC motor axle), as well as two axles to protrude.
5. Large gear diameter: 30mm
6. Pinion gear diameter: 11.67mm
7. BLDC motor axle diameter: 3.3mm
8. Axles diameter: 8mm 
9. There are additionally 4 holes each on the top and bottom spaced in a square, 20 mm apart. This is so the connectors will fit to it.
10. Front Gearbox (steering) - Print 2x
11. The space is more hollow than the rear gearbox, this time square shaped. There are no gears for the front, but instead, there is a mini servo that connects to the wheel bearing holders that allow it to rotate. A small screw is attached to the servo, and the hole fits into a 3D printed piece that connects to the rod.
12. Rod diameter: 2mm
13. The other small pieces just act as holders for the rod and attach to the sides of the bearing holder with space for a 3M screw.
14. Bearing to Gearbox Connectors / Supports - Print 8x
15. These are the almost triangular pieces with two long arms that stretch out to help support the gearboxes. They connect directly from the top and bottom of the gearbox’s holes (should be 4 on top/bottom), and they all connect to its own bearing holder. Each should have 3 holes at 3.05mm.
16. Approximately 43mm long, 37.5mm for each arm, 27mm wide
17. Bearing Holders - Print 2x of each kind
18. This is a cylinder that fits around a regular ball bearing. There are holes on top and bottom that allow for screws to fit and attach to the connectors. There are four of these for the rear gearbox. 
19. The front gearbox has the same bearing holders but with an additional 3rd hole on the side so that the 2mm steel rod “arm” can steer it. It attaches via a 3M screw.
20. Height: 30mm
21. Thickness: 3mm
22. Wheels - Print 4x
23. Rim: The rim needs to be solid enough to hold the weight of the car. There are three major parts of the rim. The inner circle that holds the axle, the outer circle, and supports that connect the center to the outer circle. We used a triangle pattern that repeated around the origin for the supports. Not much is required for a rim to be stable. Five triangles are enough.
24. Inner circle diameter: 16mm 
25. Outer circle diameter: 60mm
26. Tire: This needs to wrap around the rim. For this to be an effective tire, you need a good tread pattern. There are many types of tread patterns that are available: triangles, rectangles, or whatever V shape that you want to include. You can model your tire around your car's tire, or you could base it off a random online model. Ultimately, this doesn't affect the speed of the car too much.
27. Diameter: 60mm
28. Rod Holder - Print 2x
29. This is essentially a rectangular prism with multiple 2.5 mm holes equally spaced apart. It has these so you can choose which 2 mm rod to fit into it, and they will be hidden from external view by the front covers.

Note: all screw holes are 3.05 mm

Excluding the Rod Holder, every part only needs to be printed once.

1. Rod Holder - Print 2x
2. This is a rectangular prism with multiple 2.5 mm holes equally spaced apart. It has these so you can choose which 2 mm rod to fit into it, and they will be hidden from external view by the front covers.
3. Front Bumper
4. This piece comprises of three separate parts, all attached together with two cylinders. Each separate piece has a hole pair that can fit the 2 mm rods. It is designed to emulate the air holes that are found on most cars.
5. Windshield Base
6. This is a curved, long, and flat piece with two large holes that fit with the base pair, that later connect up to the frame and left/right fronts. There are also two 3.05 mm holes for the screws to attach to the two rod holders.
7. Base Pair
8. This provides support for the windshield base, and there are 3 M screw holes at the bottom that will attach to the chassis.
9. Right/Left Frame
10. This is the long piece with a slight chamfer on it, and it may need a large printer. It has a large hole at the bottom that fits into the cylinder of the base pair. Additionally, there are 3 M screw holes equally spaced apart so that the top can be attached to it.
11. Right/Left Large Cover
12. Each of these was created by using lines that model similarly to the Lamborghini, and are extruded out to separate lengths (up to 6 mm). The external shape is covering up everything except for the wheel, and it should be able to fit around. The bottom has multiple holes on it to account for any variance you might have in your own project.
13. Right/Left Front
14. These parts have 3.05 mm screw holes at the base of it that attaches to the right/left frames. These pieces cover the top of the front wheels and will eventually connect to the front bumper and front top. The design is also very similar to the large cover with multiple angles and chamfers.
15. Right/Left Door
16. This door is a separate piece, and will be attached with two separate 2mm screws with holes in the side of the door. It is very similar to the large cover, with different extrusions. There are multiple chamfers that provide detail, and there is even a door handle.
17. Front / Middle / Back Top
18. All of these parts have the same dimensions. They all are flat pieces, with the sides being large enough to have 3.05 mm hole spaces without cracking. They all have depth and multiple angles with chamfers and different details that emulate the Lamborghini. The front has two headlights and the back has more variety of depth.

Caution: Before you print out any of the materials, do a test print to check the screw holes. Make sure the screw fits tightly and doesn't slip out easily.

Slicing and Printing out all the parts

Gears: SLA Print in Durable Resin.

Smaller Pieces (<30mm x 30mm x 30mm): Slice in PETG with a raft beneath in superfine (to avoid breaking during print and for extra quality) - These will mainly be the components to help the front gearbox (steering)

Larger Pieces: Slice in PETG/PLA as normal.

Tires (not rim): Print in Ninjaflex (to replicate rubber) or PETG if unavailable.

A note on 3D print supports: All of the pieces should not need build supports. The gearbox casing should be printed as an arc, or you can choose to use supports by placing support blockers where the screw holes are. (see image above)

The axles, which are long, should preferably be printed by themselves, as there is a slight possibility they may fall and interrupt all other parts.

First, the ESC, BLDC motor, and LiPo battery will all have to be connected through bullet connectors (if not already).

Using a soldering station, attach bullet connectors to each of the wires, making sure each is securely attached. Always wait for the metal to cool before touching. Consider using "helping hands" in order to hold the parts. Bullet connectors tend to fall off while being soldered, so do be cautious during the process.

Note: Pull slightly on the wire after soldering. It's stable if it doesn't come off. 

Remember to attach heat shrink tubing to avoid circuit shorting or any other problems.

Note: Make sure to take your time. Lots of motor failures will be caused due to messing up this process. If the wire is too thin, too much copper is exposed, or unintended wires to connect, then the motor will not work properly.

Once all the bullet connectors have been attached, connect each wire with the corresponding part. 

Here's a helpful guide by LahisTech that'll teach you the basics.

ESC to battery:

The black part of the ESC (negative) connects to the black part of the LiPo, and vice versa with the red (positive) leads. 

ESC to Remote transmitter:

This part should not require any bullet connectors. Take the smallest wires and attach it to your remote transmitter (the small device that pairs with your remote control). You may need to read your remote control’s instruction manual.

ESC to BLDC motor:

This is the section with 3 separate wires. You may be able to switch the red and black wires depending on the direction you want your motor to spin. The pairing is fairly easy — just match each one with the color.

Remote transmitter to Servo:

Align the servo wire with the transmitter. Make sure the order of the wires is correct (which is keeping in mind the black, red, and white/yellow wires) or it will cause problems.

Our chassis was cut out using a laser cutter. Although it's optional, it's both faster and cleaner than manually cutting it out. Manually cutting it out can be done with a jig saw.

Note: Image is not to scale and requires a 5.5” x 13” piece of wood minimum. Make sure the screw holes will loosely fit a 3M screw. Otherwise, manually use a drill to create the holes.

The Adobe Illustrator file is attached here.

Now comes the most fun part! 

1. First off, we'll start with the back motor at the back of the car by attaching the connectors to the bottom part of the chassis. Screw four 12 mm screws into the bottom of the chassis.
2. We attached images for reference, and following them will make it much easier. Make sure the screws do not easily fall straight through the holes, and make sure they are 3M.
3. Now attach the pinion gear to your motor. The BLDC motor spins at an extremely high torque and speed, so it is imperative that you attach the SLA gear to the motor correctly.
4. Using superglue (avoid any form of hot glue) and clamps, attach it to the steel rod of the BLDC and firmly press the pinion gear into it. You might want to hammer it in gently if it doesn't go in. Using the clamps, set the pieces together so that it stays firm. DO NOT USE THE GEARS for at least 5 hours (recommend waiting at least 1 day) before using the car. This will disrupt the drying process.
5. Additional note: if you mess up, then you can take the gear back off (even if the superglue solidifed) by using wire cutters and squashing the SLA. You can also use superglue dissolvers.
6. Next, start attaching the ball bearings to the connectors. It requires a bit of force. Watch out to not to break it.
7. You should use WD-40 to lubricate and remove the grease that comes with the bearings. You can put these things into warm water and slide it in. Make sure to dry it to prevent rust.
8. Loosely screw in the bearing holders to the bottom chassis connector with two 8 mm screws.
9. Attach the axle to the giant SLA printed ring gear (the largest one) and use two 12 mm screws to keep them inside. Place the big gear into the bottom rear chassis while fitting the axle into the gears. It's recommended but not required to lubricate with silicone or mineral oil.
10. We strongly suggest that you don't use PLA gears unless you have multiple which you can replace easily. Experimentation proves that they'll shred into pieces in seconds.
11. Afterward, cover up the rear bottom chassis with top chassis using 20 mm screw and 8 mm screw. Then add the top connectors to each with four 8 mm screws.
12. Repeat steps 3-6 with the front servo chassis (except for step 4), and instead of using the big gear, attach the small pieces to the 2 mm rods and use 8 mm screws and corresponding nuts. This should allow the parts to move the bearing holders in a way that lets the car steer.
13. Note: You may need to use big wire cutters in order to cut the 2 mm rods. They definitely require some effort and physical strength to do it. If the rod snaps, it might fly apart, so wear safety goggles.
14. The two gearboxes are extremely similar. The only difference should be the servo.
15. Attach the wheels to the axles, and add the tires to the wheels. If there's too much space between the axle and the wheel, use superglue to keep them in place. If your tires fall off, you can use hot glue or super glue to reattach them.
16. Connect the circuits following our images. You may also want to add some Velcro to keep your LiPo battery in place. Make sure to be careful when using it. Do not let your LiPo battery get damaged.
17. The wires will definitely get clunky because they stick out. Don't worry — there are methods to prevent this. Keeping the wires tight with rubber bands or Velcro straps, you can keep them organized.

After you finish getting the car to work, the next step is to assemble the body. Refer to the image if confused. 

1. Begin by screwing the base pair and large right/left plates to the chassis. These should attach firmly and set up the frame of the car.
2. Attach the rod holders onto the bottom of the windshield base with 3M screws (max length 10 mm).
3. Proceed to slide the windshield base on top of the base pair. This should connect the two together and stabilize it.
4. Next, attach the right/left frame to the top, just above the windshield base. The top of the right/left covers should have cylindrical holes on them that will fit directly into the frame.
5. Using a screw, attach the left/right front side covers to the left/right frames. Each should correspond to its own side.
6. With the 2 mm rods, slide them into the holes of the right/left doors and hot glue them inside. Then, slide the rods into the large left/right covers.
7. With six 2 mm rods, slide each one into the hole of the front bumper. The other ends should go into any hole of the rod holders. Then, attach one rod through the left/right side covers.
8. The image above shows the inside of the car. The front, middle, and back top covers were purposefully left off. 
9. Finally, use four 3M screws per top cover for the front, middle, and back.

The ending result now looks like a car! Everyone is encouraged to make their own modifications - enhancing the look, speed, or adding something completely new. This is your car now!

Congratulations, now you’re done! Go ahead and race!

Using a LiPo battery of your choice, and making sure the voltage does not dip below 3.7V, tie down the LiPo with the Velcro. Alternatively, you can use tape or whatever suits your car. You can even 3D print the holder if you're motivated!

Here's an awesome guide to LiPo batteries by Roger's Hobby Center.

Keep in mind: Any 3D printed parts will break at some point. Just know that if it breaks, it may come in handy to keep a few spare parts. While it is an advantage to print parts and easily replace them, you may want to experiment with the myriad of filaments, settings, and colors available to you.

Remember, this is your car now. You get to decide what you want to do now.

Update 1: Our axles broke after a decent amount of use. We printed replacements in Onyx on a Markforged Mark Two. Onyx is nylon with chopped carbon fiber, so much stronger than PETG or PLA. Here's a PDF of all the settings.

Update 2: The SLA Print Interior wore out after going full throttle on the motor. The BLDC axle spun too fast for the pinion gear to rotate the wheels to compensate, so the friction ended up destroying the grip. Hence, the pinion gear became loose, and would not spin the pinion any longer.

We had to make the SLA gear hole tighter by 0.2 mm and used a hammer to get it in.