Total Time Spent: 53 Hours

Week 1 (6/10-6/14)

Day 1 (6/10) - 2.5 Hours

Originally me and my friends had grand dreams of a go-kart fleet, but as the process went on they eventually realized it just wouldn't be feasible for them to complete the project this summer. Nevertheless, our planning phase began with us all in a Discord call bouncing ideas around regarding the design constraints and criteria. With my background as a Bad Piggies fanatic, it was immediately clear what theme I wanted to go with.

The idea was simple: What is the bare minimum neccesary to get our wheels to spin? We had to ensure we didn't compromise on safety or practicality, and settled on the 212 CC, 6.5 HP Predator engine from Harbor Freight. It was cheap, reliable, and just fast enough to not risk injury. I concluded the first day with a loose theme in mind and the first item locked in for our BOM.

Day 2 (6/11) - 45 Minutes

For day two, I mainly focused on helping my friends settle on a theme of their own. A couple of them drew inspiration from Mario Kart and Fortnite, with their quad-crasher-banana-machine pictured below. A mechanical disaster if you ask me, but they were confident in their design. Surely that confidence stayed throughout the whole project...

Day 3 (6/14) - 30 Minutes

Day three marked the creation of both the Onshape document I used to create my go-kart, as well a target budget each of us wanted to hit with our karts. Since this is considered an advanced custom project, we ignorantly thought that the $350 grant would be enough to cover nearly all expenses for each project. We later realized this was far from realistic (which considerably contributed to the lack of feasiblity for my friends), but I've commited to covering all expenses beyond the $350 grant.

Week 2 (6/15-6/21)

Day 1 (6/16) - 1.25 Hours

I started the second week off with creating a rough BOM, including links to a possible clutch, pedals kit, spindles kit, steering wheel, and harness. At this point, I wanted to really solidfy the non-janky parts of the kart first, as those were the most important. Buying things as a kit generally proved cheaper, but I moved towards custom designs and individual parts later on since I could confirm the parts would be usable together, and they would be of higher quality. At this point, Amazon was my best friend for finding parts. Here is the status of the BOM after day one of week two:

Day 2 (6/17) - 45 Minutes

Today, I just added the wheels to the BOM. While I'll get into more scrappy ideas I had later, these proved the cheapest option while still being usable. Wheels aren't somewhere you want to skimp out on.

Day 3 (6/18) - 1.5 Hours

While I had an actual steering wheel on the BOM before, I figured it'd be an awesome idea if we started incorporating the scrappiness this early. So the nice, actual steering wheel got replaced with a trash can lid that could probably be found off facebook market place. Going along that theme, I decided that the seat/frame should be a shopping cart. I originally thought a wheelbarrow would be funnier, but it just wouldn't be as feasible due to a lack of weldability and good design references. Another grand idea from your's truly was to have a surfboard be the spoiler. We'll get more into that later... At least I found a high quality 53 tooth split sprocket, hub, and throttle kit for the rear axle.

Day 4 (6/19) - 30 Minutes

The brief time I spent today was finding a good pair of bearings to hold the rear axle. After further research, I also solidified that the rear axle would be 1diameter steel rod with a 1/4 keyway.

Week 3 (6/22-6/28)

Day 1 (6/22) - 1 Hour

With most of the actual parts picked out at this point, week three was spent reevaluating just how janky I was willing to go. First up on the list was a final verdict on the shopping cart versus wheel barrow debate. Needless to say the debate was rather swift, as there were actually zero benefits for using a wheelbarrow. Surprisingly enough, shopping carts were even cheaper on facebook marketplace. So for all these aformentioned reasons, the wheelbarrow was officialy retired.

Day 2 (6/23) - 1.5 Hours

There was great debate among my friends of what I should use for the steering wheel. One even offered up their family heirloom: a gold plated piece of fine china (simiar to the one pictured below).

We thought about encasing it in some sort of resin so that it wouldn't immediately shatter. I argued in favor of the trash can lid due to easier attachment, but we decided it would be best to stick to an actual steering wheel for now. This falls in line with the sentiment we adopted in approaching the Bad Piggies theme: build a normal, functional go-kart to serve as a baseline, and slowly replace parts with scrap you could find in a junkyard. Don't worry, we still went for the shopping cart frame.

Day 3 (6/26) - 30 Minutes

In a true stroke of genius, I imagined a world where I could ride around town on literal pots and pans for wheels. Pots and pans for reference:

I've got to say, it didn't get much better than this. Imagine: You can drill straight through the bottom to attach it to the hub. You could cut out wooden circles to fill it to ensure integrity, and just wrap bike tread around them for performance level traction. Yeah, so I ended up back at normal wheels by the end of the day. One day though... One day.

Week 4 (6/29-7/5)

Day 1 (6/29) - 45 Minutes

Week four marks the last week of the planning phase of the project. Today was spent finalizing the wheels we would be using. I debated back and forth between the 10" wheels I had previously found, larger Harbor Freight ones, and more standard go-kart wheels. Larger wheels would let me go further with each revolution, but would require more torque and be more expensive. Standard go-kart wheels were almost immediately ruled out since they were just so expensive, and larger wheels for the same reason.

Day 2 (6/30) - 45 Minutes

Today I determined what the plan for the spoiler would be. Originally I thought it would be funny to have it be a surfboard attached to the frame, but I soon figured out that surfboards were ~8 feet long. Not gonna work. The design I went with (pictured later) will be manufactured out of sheet metal and cut using angle grinders. I took inspiration from the wing on the Porsche 911 GT3 RS, but since it's a non-functional part of the project, how it actually ends up looking isn't a critical concern.

Day 3 (7/1) - 20 Minutes

Throughout this project, I had been watching Facebook Marketplace for anyone selling a shopping cart I could use in my area. I came to the conclusion that at any given point, there were at least a couple within reasonable driving distance, so today I found the closest one at a decent price to put in the BOM. Luckily, whether I end up going with this one or not, I'll always be able to procure a cart despite the nature of Facebook Marketplace's listing model.

Day 4 (7/2) - 15 Minutes

Today's work was brief, just finalizing what steering wheel I'd be going with for this project. It did come with a hub for attachment to the steering column, but I factored in additional sheet metal in case we need to cut out a hub ourselves.

Day 5 (7/3) - 3 Hours

Today was a big one for the BOM; I decided against going with a steering kit and instead designing it myself. It proved more expensive and complicated in the long run, but it'll likely result in a higher quality experience and greatly aided my ability to CAD an accurate model of what the go-kart will actually look like. I also found parts for the rear axle assembly, spindles, and hubs for the rear wheels. The screenshot below also features specific quanitites and sizes of framing materials, but at this phase I only had placeholders and estimates (which were surprisingly close).

Week 5 (7/6-7/12)

Day 1 (7/9) - 1.5 Hours

I started the day off by searching for a 3D model of a shopping cart similar to one I'll be using. I figured I'd save myself days of work trying to model that in Onshape. Here is a link to the GrabCAD I got the file from: https://grabcad.com/library/shopping-cart--2

With a model for the shopping cart as a reference, I got started cadding the frame. I went with 1x 1 mild steel square tubing since it's so easy to weld and is structurally sound. The design I made is likely very overengineered, so if we need to reduce the tubing used there is plenty of places to choose from. Additionally, the exact dimensions of things would change very slightly once we get our hands on the actual cart to take measurements, but I made sure to leave enough margins in the design to accompany many different size carts.

Day 2 (7/10) - 1 Hour

Originally I had the engine mounting tubes centered in the frame, but after importing an engine model I found online I realized that the engine was offset from the mounting holes. I move the tubes over slightly to make up for that discrepancy, and got the engine lined up properly with the frame. Here is a link to the GrabCAD I got the engine from: https://grabcad.com/library/custom-drift-trike-incomplete-1

Day 3 (7/11) - 1 Hour

Today was when I finished up cadding the base frame, with the shopping cart sitting on top nicely as seen below.

Week 6 (7/13-7/19)

Day 1 (7/14) - 2.5 Hours

I spent all of today just researching how a rear axle should be done. Here was where the nitty-gritty of mechanisms I wasn't familiar with began to creep in, so I had to make sure I was well informed before designing. I watched Youtube videos, talked to ChatGPT, read forums, etc. The main components were the axle itself, bearings to attach it to the frame, wheel hubs on either end, a band brake, and the sprocket + sprocket hub that connects it to the engine.

Day 2 (7/15) - 35 Minutes

After my day of research, I confirmed that the parts I selected previously would suffice. The only change I made was switching from a 53 tooth split sprocket to a 54 tooth split sprocket. Honestly this was only done so that both sides would be the same, at no increase to price and minimal losses to top speed.

Day 3 (7/17) - 2 Hours

With the rear axle planning complete, it was time to start cadding. And wouldn't you know, it's my favorite part of this whole project: trying to CAD parts off of vendor reference images! Today specifically, I started working on the sprocket and hub CAD. This was made much easier thanks to the Sprocket featurescript I have grown accustomed to for FRC.

Day 4 (7/18) - 50 Minutes

Today I finished the CAD for the sprocket (red) and the hub (blue):

I also modeled the bearing blocks off of (you guessed it) Amazon product images. Luckily they provided many of the needed dimensions, so it wasn't so bad.

Day 5 (7/19) - 3 Hours

Today I worked on the centrifugal clutch, chain, tires, and tire hub CAD. Once all these parts were done I was able to put it all together in the assembly:

I went with #35 chain because I was already very familiar with it.

Week 7 (7/20-7/26)

Day 1 (7/21) - 4 Hours

Now's where things start to get complicated. I had never designed anything close to steering from scratch, so I followed a similar method to the rear axle and just spent the first day researching about how the tie rods, spindles, steering column, etc. all interact.

Day 2 (7/24) - 8 Hours

Just when I thought I had a good grasp on how I would go about designing the steering for my go-kart, ChatGPT brought up an interesting gimmick I had never heard of. It's called Ackermann Geometry. Basically, it states that the spindle arms should be pointing directly towards the center of the rear axle. If that is done correctly, when you turn, the inside wheel will be at a sharper angle than the outside one. Originally I thought you would want them to be parallel, but this actually makes sense, because the inside wheel has a smaller circle it has to trace to complete the turn. The unfortunate part, is that the spindles I selected have arms at a fixed angle, meaning that I couldn't adjust them as needed. To improvise, I decided I could create little brackets which attach to the spindle arm, connecting the tie rods and the spindle at just the right point to simulate the spindle arms being pointed inward.

Day 3 (7/25) - 3.25 Hours

Today was when I started to CAD the steering. Once again, I used Amazon reference images to design the spindles, tie rods, steering column bearing, and steering wheel.

Day 4 (7/26) - 3.5 Hours

Finished up the steering CAD today. Figuring out the location of the steering wheel was difficult, but I believe I found a decent place which still has working steering geometry. The little plate at the end of the steering column will have to be made myself, but I've made worse with less tools before for FRC.

Week 8 (7/27-7/30)

Day 1 (7/27) - 2.5 Hours

We're in the final stretch now. Today I finished up the pedals and spoiler, and with that this was the last day I actually spent cadding. I also added the little human model and made sure that a reasonably sized person could fit without getting smushed. It's definitely a tight fit, but you can't ask for much when your chassis is a shopping cart. The only things I left out were the throttle and brake cables, as well as the brake drum itself. I've made sure that there is ample space on the rear axle no matter where I want to mount it, and cadding the cables would just be unnecessary. One thing to note is that a slot can be cut out in the front of the cart so that the pedals can be pushed further, and depending on where you make that slot you can set the mechanical stop for the pedals.

Day 2 (7/28) - 1.5 Hours

With the CAD complete, today I just focused on calculating exactly how much metal I need and finding where I would source it. I settled on a place local to the Raleigh area, Metal Supermarkets. With these specifics in place, I finally have a complete BOM and accurate price estimate.

Day 3 (7/30) - 2 Hours

Today was mostly spent organizing all of my files, journal entries, and work for submission. As a bit of budget analysis: what started as an optimistic $350 project quickly grew to nearly a thousand dollars. However, with $350 of that still being covered through this incredible program, I will be fortunte enough to just barely fund the rest of this project myself. Keep in mind however, this is with ample spare materials. Things will go wrong, and things will have to be refabricated. That's the point of this whole project, and I've budgeted that in. In hindsight, I had to make quite a few sacrifices to the theme of Bad Piggies to ensure that this thing stays practical and safe. But the advantage of this, is that once I have a working go-kart I can slowly start integrating that jankiness back in instead of doing it all at the start and hoping it works. It allows for continual iteration and... improvements. Just you wait, pots and pans are coming 😼. Once again, thank you so much to the folks at Hackclub for making this possible, and I'll see you on the highway 🚗💨.