Sunday, June 16, 2013

1. Sketching and Idea Generation

For the first week of our EV project, we generate ideas about the rough shape and outline for our go-kart. We read through the websites and the blogs posted by MIT students before, the following are the sketches we did along the way.

From the very beginning, we've decided to use two non-driven wheels in front, one driven wheel at the back. Cause two driven wheels would mean two motors and two controllers. Plus three wheels compose a rather stable structure. When I did this very first sketch, I was thinking more of the aerodynamic shape of a race car or a bullet. So the driver would be kind of lying on his back as he drives the car. This idea was then abandoned during our first discussion cause we feel that the driver would risk a quite high chance of being thrown out when turning, and since the driver is lying down, he cannot really see what's going on in the front, but mostly the sky. 

We then evolved our second idea, in which we lift up the back of the 'seat' so that the driver has a clearer view of what's going on in the front. My teammate Jiawei then proposed that both of the previous ideas make the kart too long, which would inevitably increase the overall weight of the kart. And the gesture of the person still makes it quite possible for the person to be thrown out when turing, cause the driver's center of gravity is quite high.

So we changed the gesture of the driver and decided to make him lean forward, which is kind of like riding a motorcycle. We also tried to ride on the go-karts built by MIT students before and it works like a charm. At first I was thinking more like a motorcycle except the whole body of the kart is lowered down a bit so the center of gravity is low as well. But still, another question would be how to prevent the driver from being thrown out of the kart when turning as we all saw what happened to one of the teams in the Youtube video :p Both my teammate and I liked the kart made by Nick and amwang (I didn't find the kart's name in their blog), which would be kind of secure for the rider to ride on. So we decided to adopt the same gesture. We increased the distance between the two front wheels to increase the stability and also widened the body of the kart a little bit (where the driver sits) so the rear wheel could fit under the kart. We also moved the steering wheel to the very front of the kart so its rotational angle won't be limited when turning. Basically we moved the upper body of their kart backwards to hide the wheel and thus prolonged the part with which the driver would have physical contact. So the driver is still able to lean forward and not reach out of the kart.

Here comes our final sketch for the first week, it looks like those little horses that children would ride on.

We're going with chain drive instead of gear drive so there won't be a part sticking out from one side of the rear wheel thus leaving no space to put the driver's feet. Chain drive is also easier to build, so.... We're probably using the 8 inch wheel provided to us as the rear wheel. As for the design of the steering wheel, we compared the methods of the previous go-karts and finds the chibikart has the best maneuverability, so we are going with that for now. For the curvature part, we are still not sure how to do that. Jiawei pointed out that maybe we could just buy one of those plastic horses for children to ride on, then secure it to the aluminum frame. But will it be kind of heavy? And not very customized for our design. We're also not sure how well plastic and aluminum come together so.... Or maybe stuffed animals? a long pillow? a sofa cushion foam? Or the wood laser-cutting patterns used by the other group before?

The top view and side view are attached below:
*All of the three drawings are in scale. 1'':0.5cm

Top View

Side View 

Note: We haven't decided on the wheel size yet. In the above picture, the rear wheel looks much bigger compared to the two front wheels...which may not be true as we proceed to next week. And we've decided to move the wheel out from the chassis a bit cause it doesn't look very safe intuitively.  We'll look into that later. Btw, we are planning to put all the batteries, controllers etc. on the chassis right in front of the rear wheel. 

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