‘Urbee 2’ : Second Evolution of 3D-Printed Car by Jim Kor of Kor Ecologic
Jim Kor of Kor Ecologic is currently working on Urbee 2, the second evolution of his 3D-printed car.
Urbee is a two-passenger hybrid car designed to be incredibly fuel efficient, easy to repair, safe to drive, and inexpensive to own.
There is much about Urbee that is highly innovative. However, the innovation does not lie in expensive ‘start-of-the-art’ technology, the use of expensive materials, or complicated manufacturing processes. Urbee’s innovation is that it uses widely available materials and components in original ways.
Urbee is designed to be environmentally sustainable. This is because it can efficiently store and use exactly the amount of solar and wind energy you can collect on a one-car garage in one day. If you want to go farther in a day, you can use its ethanol powered engine.
The designers of Urbee have attempted to maximize the distance that can be traveled per unit of energy consumed by minimizing seven important properties of the car: weight, coefficient of aerodynamic drag (Cd), rolling resistance (Crr), frontal area, maximum speed, maximum acceleration.
COEFFICIENT OF DRAG
The Coefficient of Drag (called “Cd”) for a vehicle is one of three things that affect how much energy is required to overcome aerodynamic resistance. It is a number that describes the ‘slipperyness’ of a shape as it passes through the air. Urbee is being designed to have a Cd about half that of a traditional sports car.
COEFFICIENT OF ROLLING RESISTANCE
We have attempted to make the coefficient of rolling resistance of Urbee as low possible by using large diameter motorcycle tires inflated to high pressure. As well, the cross sectional profile selected for the tire has a very small contact surface with the road.
The frontal area of a vehicle is approximately equal to its width multiplied by its height. We decided to make the roof of Urbee as low to the ground as the lowest production car ever made, the Ford GT-40, which was 40 inches above the ground. We also tried to minimize the width by placing the two occupants as close as comfortably possible to each other.
MAXIMUM SPEED AND ACCELERATION
By reducing the maximum speed and acceleration of Urbee compared to what many other cars are capable of, we can dramatically reduce the maximum horsepower required to power our car. The smaller motor/engine size in turn decreases the weight of the vehicle and increases the range.
With three wheels and a curb weight of less than 1,200 pounds, it’s more motorcycle than passenger car.
To further remedy the issues caused by modern car-construction techniques, Kor used the design freedom of 3-D printing to combine a typical car’s multitude of parts into simple unibody shapes. For example, when he prints the car’s dashboard, he’ll make it with the ducts already attached without the need for joints and connecting parts. What would be dozens of pieces of plastic and metal end up being one piece of 3-D printed plastic.
“The thesis we’re following is to take small parts from a big car and make them single large pieces,” Kor says. By using one piece instead of many, the car loses weight and gets reduced rolling resistance, and with fewer spaces between parts, the Urbee ends up being exceptionally aerodynamic.” How aerodynamic? The Urbee 2′s teardrop shape gives it just a 0.15 coefficient of drag.
Not all of the Urbee is printed plastic — the engine and base chassis will be metal, naturally. They’re still figuring out exactly who will make the hybrid engine, but the prototype will produce a maximum of 10 horsepower. Most of the driving – from zero to 40 mph – will be done by the 36-volt electric motor. When it gets up to highway speeds, the engine will tap the fuel tank to power a diesel engine.
The design puts a tubular metal cage around the driver, “like a NASCAR roll cage,” Kor claims. And he also mentioned the possibility of printed shock-absorbing parts between the printed exterior and the chassis. Going by Le Mans standards also means turn signals, high-beam headlights, and all the little details that make a production car.
To negotiate the inevitable obstacles presented by a potentially incredulous NHSTA and DOT, the answer is easy. “In many states and many countries, Urbee will be technically registered as a motorcycle,” Kor says. It makes sense. With three wheels and a curb weight of less than 1,200 pounds, it’s more motorcycle than passenger car.
No matter what, the bumpers will be just as strong as their sheet-metal equivalents. “We’re planning on making a matrix that will be stronger than FDM,” says Kor. He admits that yes, “There is a danger in breaking one piece and have to recreate the whole thing.” The safety decisions that’ll determine the car’s construction lie ahead. Kor and his team have been tweaking the safety by using crash simulation software, but the full spectrum of testing will have to wait for an influx of investment cash. “Our goal with the final production Urbee,” Kor says, “is to exceed most, if not all, current automotive safety standards.”
Kor already has 14 orders, mostly from people who worked on the design with him. The original Urbee prototype was estimated to cost around $50,000.