Gokart Reflection

Posted: 5 August 2013

Lord Charles has ordered us to do a reflection. He has given us some pointers to follow so here we are answering it!

Assessment of your machine’s performance.

Consider the differences between your design calculations and the actual performance.

This is an interesting one. There were many things we had to calculate at the start. Firstly, there was this sprocket to gear to wheel size ratio that is quite complicated. A small sprocket, with a large gear allows the vehicle to achieve a good top speed but poor acceleration. A small sprocket with a small gear allows the vehicle to achieve poor top speed but superb acceleration. Now for the tricky part: the wheel size also matters because everything evens out in the end. A small sprocket with a small gear but huge wheel, will have poor acceleration as the amount of torque required to move the vehicle is crazily high -.- And there are just so many permutations but I’ll just key it in some good and logical ones we thought of.

Sprocket: Small, Gear: Small, Wheel: Small (Gear about same size as wheel)

Fast acceleration, poor top speed.

Sprocket: Small, Gear: Big, Wheel: Big (Gear about same size as wheel)

Poor acceleration, fast top speed.

Sprocket: Small, Gear: Big, Wheel: Impossibly big

Impossibly slow acceleration but (possibly) great top speed? If the motor can even reach that high of a torque to spin it at a high RPM.

Note that all small sprockets in this blog are 12 teeth ones. Team 7 (Ian, Karen, Shun Him) almost wanted to use 10 teeth sprockets. That would have yielded some crazy acceleration there.

So… Evidently, we chose the small sprocket small gear small wheel. And that’s the picture of our wheel.

Allow me to go on a tangent here. Initially, we wanted to build our own differential and do lots of crazy stuff but thankfully Andrew was convinced not to pursue such ambitious dreams haha. We adopted the conventional method of a 4 wheel kart.

How did the machine work?

The handling was awesome, the acceleration was awesome, the turning was awesome. Andrew made a good call of making the CG as low as possible and we came up with the towel seat. We are barely like 2-3 inches off the ground? We had a really poor top speed but we could actually reach our top speed in like 3 seconds? It was really kinda like how we expected it to be from our initial conception of the idea.

Perhaps some things that were bad would be that the wheel worn out so badly on the tarmac.

Describe what real-life factors might have influenced the machine.

uhhh. perhaps the length width ratio of a lambhorgini? We did refer to that but pfft we didn’t follow it as the kart was gonna be long.

Comparison to other machines and designs.

We worked closely with Team 7 and as such, our vehicles were almost the same. Identical controllers, motors, frame size, etc.

Our machine stood out because of the wheels. Team 7 chose the small sprocket big gear big wheel combination and as such had a poor acceleration. We were lucky that the track had relatively short straights and as such, we were able to take the bend fast and go super fast on the straights.

If the straights were longer, team 7 would totally have destroyed us and won the race!

Another machine that really stood out was GoldKarts (Edward, Jin Kai, Olivia). They had only 1 149kv motor but they were going as fast as our 2 149kv motor kart! I guess the single controller could give such a high current that totally offset the 2 motors! Impressive stuff :)

Single best idea would be Team 7 I guess. They were generally really good. Comfortable seat, great wheels, could go over rough terrain. Batt Mobile was generally very rough during the ride as the wheels were small and susceptible to damage quickly as we were so close to the ground! We would have owned indoors but outdoors was bad.

Gauge your own learning

I can’t speak for Andrew, but I’m sure he is super proficient in building a mini go kart.

These are the pointers that Charles gave:

Mechanical power transmission design using CAD software, analyzing mechanical systems for torque, speed, power, etc. with first-order math Understanding, designing, and fabricating low-voltage electrical systems Ability to read product specifications and gauge their usefulness to your design Correlating design calculations and specifications to existing parts in a catalog and making design compromises based on that. We are proficient in all of them.

Many thanks to Jon and Kate, Charles, Justin, Nancy, Farhan, SUTD, and many others for this learning experience. It was great.