3D-printable Nitro Powered RC-car Design

This 3D design of a nitro-powered RC-car is a project i was interested in to make. The goal of this project was to design a nitro powered RC-car, with printable parts.

This document can be used for a basic understanding on how an RC-car works.

Some parts in this design are recommended to be bought online, those parts are:

1. Engine
2. exhaust
3. Bearings
4. differential
5. fuel tank
6. servo's
7. receiver
8. clutch bell
9. damper

Parts that can be considered to be bought, but also can be made are:

1. "Upper wishbone"
2. throttle arm
3. central transmission, including braking system
4. wheels

Before starting any of the design process, it's useful to know what type of car you are designing. there are a few car types on the market with each having different strengths:

Type; Best Use; Speed; Terrain

1. Buggies; Racing; High; Mixed
2. Trucks; Off-road; Medium; Rough
3. Truggies; Versatile; High; Mixed
4. On-road; Paved; Very High; Roads
5. Monster; Climbing; Medium; Trails

Also the scale of the car matters. A more common scale for an RC-car is more likely to be more like a 1/10th or a 1/12th scale car.

For this design, i went fore the 1/10th scale truggie like car. The reason is because it's more of an allrounder in the different categories and also any part easier to come by

The design of the bottom plate is roughly estimated by de chosen scale of the RC-car. It's design can be the limited factor if you have a desire to make an scale F1 car, but can undergo a lot of changes if the type of car is not of any concern.

The thickness of this bottom-plate is designed to be 5mm. The thickness is because 3D-printed parts are less than aluminum parts. The stiffness can be increased by adding ribbons in the final stages of designing the RC-car. Those ribbons can be added now, but most certainly must be changed when adding the servo's or engine.

A rule of thumb for choosing the right nitro engine is:

Engine Size; Typical Displacement; Common Tank Size; Approximate Runtime

Small engines; 0.12-0.15cc; 75-100ml; 6-10 minutes

Medium engines; 0.18-0.21cc; 125-150ml; 8-12 minutes

Large engines; 0.25-0.30cc; 175-250ml; 10-15 minutes

The small engines is most commonly use in 1/10th RC-car models. For 1/8th RC cars, the medium/large size engines are used for more experience users or racing applications.

In order for the car to move, a drivetrain has to be designed.

The speed of the output shaft of the nitro engine, goes too fast to move the car. To resolve that problem, a clutch bell on the output shaft is connected to a central transmission. The central transmission reduces the speed, but also creates more torque in the process. The central transmission can be a one speed, but also 2-speed gearbox if the output shaft of the engine is large enough for the clutch-bell .

There are different ways to get the power from the engine to the wheels.

1. with belts, more common in an all wheel drive design.
2. Is with so called 'T-bones', also used in this project.

The T-bone, as well as the belt, are connected to a differential. Some sort of planetary gears, used for cornering. When the car is turning, the inner wheel will rotate slower than the outer wheel. If the two wheels rotate at the same speed when cornering, the inner wheel will slip or some onderstreping will occur.

The wheels are connected with a T-bone to move the car forward.

For the suspension, there are some design choices to make. A few of those are:

1. Toe-in/Toe-out
2. Camber
3. Caster
4. Steering
5. Damper
6. the use of the lower- and upper wisbone.
7. The use of the upright, which is connected to the lower- and upper wishbone

Each of these choices have effect on how the car responds. In the design stages, it's important to keep in mind that the setup must be easy to change. Otherwise the printing will never end.

It's important for the lower- and upper wishbones to be the same size. if that's not the case, the wheel will rotate upwards or downward because of the different turning circles.

What the effects from the suspension are, is explained in the added document.

The controls consists of two servo's, connected to a receiver. one servo is used for for the steering, the other is used for the throttle and the brake.

The steering servo pushes/pulls a slider with the steering arms connected to the upright.

When the throttle and brake servo rotates counter clockwise, the throttle will open. The brakelever on the other hand will also rotate, but the face on the brakelever, where a pin is connected to, is eccentric. Therefore, no brake pressure will be applied. When the servo is moving clockwise, there will be brake pressure applied, but no throttle.