About this project

I’ve always loved remote-controlled things — they’ve always intrigued me, especially how they work internally. I still remember my first RC car when I was 12: a small Monster Truck operating at 27 MHz that I absolutely loved… until I took it apart to see how it worked and accidentally broke it 🤦.

Fast forward 20 years (one 👷🏼‍♂️ engineering diploma and 👦🏻👶🏻 a couple of kids later), I wanted to share my passion for electronics and computers with my children. Since I recently got a 3D printer, I decided to start a small DIY 3D-printed RC car project with my 6-year-old. It’s not really about building the car itself — it’s about nurturing his curiosity and exploring how things work, together.

Project current Status

01 - Minimal Enjoyable Toy

To get a basic, functional RC car, we’ll need just a few core components:

• A structure
• Power
• Wheels
• 2 motors (one for drive, one for steering)
• A brain to control the car
• A receiver
• A transmitter for the Remote

In detail

Starting a project like this completely from scratch would be tough — especially when trying to keep a 6-year-old interested 😄. So, I looked around for similar projects to use as a foundation. Call it cheating if you want, but let’s not reinvent the wheel 😉.

After a few hours of YouTube research, I found a video that matched exactly what I had in mind. https://www.youtube.com/watch?v=AEbeUMzCr-k That gave us a great starting point to refine our own version. Let’s go through the main parts:

🛠️ Car body

The chassis will be designed in Fusion 360 and printed using my Bambu Lab A1 Mini — a small but surprisingly capable printer.

🪫 Power

A set of Li-ion batteries should provide enough juice to keep the car running for a while. Combined with a Battery Management System (BMS) and a step-up converter, it should form a reliable power source for this small RC build.

🛞 Wheels

I’m no expert in RC wheels, but 65mm seems to be a standard size for similar builds — so I’ll go with that for now.

⚙️ Motors

The plan is to use a brushless motor for thrust and an MG90S servo motor for steering — a simple and well-tested combo.

🧠 Brain + receiver

For the controller, I’ll be using an ESP32 Wi-Fi board. It can be powered by Li-ion batteries and offers built-in Wi-Fi, making it perfect for both control and future expandability.

📡 Transmitter

Any Wi-Fi-capable device can theoretically act as the remote. The initial idea is to send UDP packets from a phone or laptop to control the car.

02 - Shopping list !

Here's the basic shopping list I purchased. Its not a complete one as I had other things laying around

Image	Type	Model	Link	Price
	12mm Wheel Hex Coupler	Short Style-4mm	https://fr.aliexpress.com/item/1005006042552610.html	3,39€
	4 Rim Tyre 12mm hex	6178 black (Not for drift)	https://fr.aliexpress.com/item/1005007129333294.html	8,08€
	Flange Ball Bearings	F604ZZ	https://fr.aliexpress.com/item/1005001473790914.html	4,79€
	Rear axel shaft	150mm x 4mm	https://fr.aliexpress.com/item/1005006293171727.html	0,97€
	Brushless Motor with 30A Brushless ESC	KV2200 30A	https://fr.aliexpress.com/item/1005008190900818.html	9,49€
	ESP32	CP2102 NodeMCU-32S	https://fr.aliexpress.com/item/1005009683698872.html	4,59€
	Servo Motors	MG90S Metal Gear Digital 9g Servo	https://fr.aliexpress.com/item/4001193413905.html	4,89€ (4 pcs)
	Bolts and Nuts	1260pcs Metric Bolt Assortment - M2 M3 M4, 21 Sizes 4MM To 30MM 12.9 Alloy Steel Bolts And Nuts Kit	https://fr.aliexpress.com/item/1005009858588611.html	17.19€

03 - Start Modeling using fusion 360

These parts are more than enough to begin modeling the RC car, starting with the rear drivetrain. Since importing real-world objects into Fusion 360 isn’t currently possible, each hardware component must be modeled manually or sourced from existing 3D models online. In many cases, detailed specifications—including dimensions—are available, which makes it possible to start modeling even before the components arrive. For more complex elements, such as the brushless motor, I was able to find a ready-made 3D model, which saved significant time in the initial design phase.

• brushless-motor-bldc_2212-6t-2200kv-1
• Wheel.iges
• Shaft.iges
• HexCoupler.iges

04 - Gear Modeling by a N00b

Gears turned out to be more complex than I expected. Once I started researching, I realized they can even influence the overall size of the drivetrain. Let’s break it down:

Motor rpm (Revolution per minute)

$$\mathrm{rpm}=\mathrm{KV(rpm/v)}\times \mathrm{Voltage(v)}$$

In my case KV = 2200 rpm/v, if used with a 3S li-ion at 11.1v, it gives 24,420 rpm

Wheel circumference

$$\mathrm{Circumference}=\mathrm{\pi }\times \mathrm{diameter(mm)}$$

In my case = 3.14 * 65mm = 204.2 mm

Wheel rpm

$$\mathrm{rpm}=\frac{\mathrm{speed\; (m/s)}\times \mathrm{60}}{\mathrm{Wheel\; Circumference(m)}}$$

Gear ratio x:x (motor/wheel or commonly used spur_teeth/pinion_teeth)

$$\mathrm{ratio}=\frac{\mathrm{motor\; rpm}}{\mathrm{wheel\; rpm}}$$

• When ratio > 1 => reduction (more torque at wheel, lower top speed).
• Ratio < 1=overdrive (wheel faster than motor — not common with small pinion < spur setups).

On fusion 360, there is a Free add-in in Autodesk called GF Gear Generator. You just fill in the parameters and Voilà! Here's the parameter I've used:

• Module: 0.8
• Pressure Angle: 14.5 deg
• Motor teeth: 25
• Shaft teeth: 40

⚠️ I am a complete noob in gear dimensioning, My gear ratio should be around 1.6, but I might be completly off, I am learning by doing and testing.

In real gear design, it’s not enough for the teeth to mesh correctly—the gear also needs a reliable way to attach to the shaft. This usually requires a mechanical fastening system such as a screw tightened onto a flat side of the shaft, or an embedded brass insert or captive nut inside the gear body. These features prevent slipping under load and ensure the gear rotates firmly with the shaft, especially when dealing with high-speed brushless motors.

I chose a screw-and-embedded-nut system to secure the gear onto the axle. The embedded nut prevents the 3D-printed plastic from deforming when the screw is tightened, ensuring a strong and reliable grip on the shaft. A small slit is included in the gear so the nut can slide into place. The screw is inserted from the pinion side and tightened just deep enough to avoid interfering with the meshing gear—so yes, screw depth matters.

05 - Test fit (and found my first issue)

After lightly sanding the axle with sandpaper while it was spinning in a drill, everything fit perfectly. The gears meshed smoothly with the right amount of clearance, and the wheels rotated freely. However, I realized I had overlooked something during the modeling stage: the rear axle could slide left and right 🤦. I came up with two possible solutions:

• The complex option: redesign everything using double-helical gears, which naturally prevent lateral movement. But that would mean redoing the gear models, and I’m concerned about introducing stress points on the teeth where the screw attaches.
• The easy option: add two small 3D-printed clips on the axle, each with a small indentation so they only press against the rotating part of the bearing.

The clip

I've designed it so I screw in a bolt but it seemed to be tight enought like this. I'll see how it goes without, I can always add it later

• Linkedin
• contact (@) hartakji.com
• Grenoble, France