Knowing nothing about go-karts, Aisha (my partner!) and I set off brainstorming possible go-kart designs. We spent hours trawling through blogs of past students, stalking each kart as it was designed. The Singaporean students had the best documentation (because it was a requirement to do blog posts? 2.007 as a class requires that we have a paper notebook, so I’m going to post pictures from my nb).
The design constraints on our car was budget ($500), a max velocity of 20 mph, and our kart had to fit through the door (38″). We got 3 A123 batteries as well as 3 80×20 bars and 2 sheets of aluminum plating (.25″ and .125″).
The notes following will be a random jumble of thoughts / justification for what we’re doing.
Some go-kart features and decisions:
1) 3 Wheels instead of 4; Back Wheel = Driving wheel
We decided that we didn’t want to use 4 wheels because if we had 4 wheels, we’d either have to have two motors driving both back wheels or use a differential with a live axis. We decided that buying (or building) a differential would be unduly complicated for the benefits we’d gain from 4 wheels (stability). Also, 3 wheels are lighter (and cheaper)
One issue with 3 wheels is stability, as having 4 wheels is more stable. We’re going to have to get around that by having a wider wheel base. To increase stability, the COG should be low and near the side-by-side wheels (http://www.rqriley.com/3-wheel.htm). To prevent rollover (from that site), we should have a margin of safety determined by L/H where L is the half-tread and H is the cg height. We’d like to decrease H (CG height) and increase L (half-tread. So, we designed our kart to have the max front width possible to maximize stability.
Wide Wheel base
– more stability when turning
– not as likely to flip horizontally
– con: hard to do
Toe-in – but harder to turn and you lose power – um, no. It would kill our straight turns. I think we’re stable enough as is.
3) Turning/Steering: One important objective we wanted was to turn and steer well. The race will be a grand prix – this means lots of turns. We thought that we would need to drive fast, but more importantly, we needed to be able to turn quickly and with stability. We considered a few things:
Toe-out – makes turning better
– but less stable and you lose power
More Ackerman – makes turning better
– but makes things less stable?
Putting person in front
– CG is near the front – understeering worsens and it is not as stable while braking; but we’ll find the optimal position. We can make the seat adjustable and leave it until last.
4) Pictures of our design sketches:
We decided to design a Phoenix-Kart – that way we have a reason when our motor burns out and our kart catches on fire (jk, we’ll do good motor controller calculations, we swear). I thought pandakart was cute, and we wanted to put our weight in the front. Wings are a good place to put our feet. Also, the steering wheel will be a phoenix.
Aisha’s (she’s great at drawing)
Mine (from my nb):