If you have taken on the challenge of building a backyard roller coaster, congratulations! However, you’ve probably spent way more time on the track design than the cart. Well the cart is more important to the overall performance and safety of your coaster. Spend some time here; don’t make your mom shut your coaster down.
Backyard coaster cart design comes down to four main components. Understanding the motion of the cart and wheel contact stresses. Next, look at proven cart designs and mimic them. Finally, learn some basic fabrication techniques with common tools.
Understanding Cart Motion
Cart motion can be difficult to understand. For any object in motion there are 6 degrees of freedom. Luckily, a roller coaster eliminates 2 of those (side to side; up and down). These are eliminated because the side and up wheels keep us on the track.
There are 6 Total Degrees of Freedom in a Coaster
- Heave – Up & Down
- Sway – Side to Side
- Surge – Front and Back
- Pitch – Up and Down Hills
- Yaw – Turning left and Right
- Roll – Twisting
This leaves us forward and backward, pitch up and down, roll clockwise / counterclockwise and yaw left and right). This video documents how we plan to handle each one of these.
Understanding Wheel Contact Stress
This is where the rubber meets the road….literally. The interface between track and wheel. I’ve made the following video to answer basic questions of dealing with contact stresses. Short answer, you need larger down wheels.
You may also want to read this article that flushes out track width and tie spacing even more.
Cart Design Case Study – Black Widow
In this video, we will go over the basics how the Black Widow Cart was designed to handle roll, pitch and yaw. This is the most in depth we go with the structures on the cart. Use this to get ideas and not a final design
There is a lot to be said about calculating the stress on the structure. Please remember that this is for educational purposes only. Seek help from a professional engineer where needed.
Fabrication Simplified
Metal working is far more difficult than wood fabrication. As you will see, I don’t have big and fancy equipment to fabricate with so I improvised to make my cart come to life. Below are the basic tools I used to fabricate. Chances are you have these or know someone who does.
- Circular saw with cutoff disc
- Jigsaw with metal cutting blade
- Hand drill and drill bits
- Drill press (not required, but makes things so much easier)
- Welding machine – this is the oddest tool. I bought a flux core welder at Harbor Freight for about $120.
Summary
If you have decided to take on a backyard roller coaster project, you probably already like to tinker and learning these new skills won’t be too much of a stretch. Get out there and build a coaster cart.
