Keeping their eyes on the prize, an ambitious team of Red River College students are building an electric car from scratch to compete in the Shell Eco-Marathon competition in the Electric Prototype Division at the 2018 Americas competition taking place on April, 2018, in Detroit, USA.
“We’re all invested in this,” said Mechanical Engineering student Riley McLeod. “It’s something that we’ve made. It’s our creation.” Read More →
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In a previous post, we talked about how Aerodynamics decide the shape of the car body. Since that shape is essential, the other components are system are designed from there.
Shell has specific rules on the car weight, length, width and height. None of the parts can be on the outside of the car, at all.
(Shell Eco-marathon 2016 Global Rules)
The frame, brakes, electrical, and steering must fit inside the car body (the pod), while allowing space for the driver. Their combined weight must add up to no more than the weight maximum of the rules. This includes a minimum driver weight of 140 kg. Since less weight mean less energy, all teams want their driver very close to that number. It’s another tough challenge, but knowing what percent of the weight the driver will take up allows us to consider the other components weights with respect to it.
The driver also has to be able to see! That’s not so easy to adjust for. Keeping the streamlined shape while adding in the cars various systems makes it a tight fit inside. The driver can’t sit up straight, they must be reclined, conforming to the width and height of the rules.
There’s no door to get in or out. Prototype teams design the pod to split in half along the horizontal. It’s the best method for fabricating and eliminating cracks along the side of the body (which can aversely affect aerodynamics.)
Here’s a visual of how the driver and components are organized in prototype cars:
The first rule about aerodynamics is it’s a sub-field of fluid dynamics.
And we talk about it; a lot.
In the prototype class aerodynamics are the rule. The entire body of the car is made with the aim to decrease air resistance. We want the air to go right over our driver’s head, down the tail of the car and behind it (where our opponents will be)
The outline of the car body is based on a classic ‘tear-drop’ shape; the most aerodynamic shape for anything slower than the speed of sound. We use that shape to tell the air where to go.
The air should flow easily around the car. The upper streams should meet the lower streams at the tail to smoothly glide away.
Here’s the first draft of our Team’s car:
The shape is similar to a passenger airplane, or the perimeter shape of an airplane wing; and a bit like a shark without fins (sharks can keep their fins)
That’s the short and fun explanation of why that body shape is chosen. Next post we’ll be sharing more about the Electric Prototype class and its design constraints. Check back soon and often!