Rail Tie Fabrication

The rail tie to rail joint (RTJ) is the most critical area of the coaster. With this we will be paying special attention to all aspects of it. From selecting material to staining, we will do everything possible to make sure it is as strong as it can be.

https://youtu.be/YlvEEsvvAy8

Attaching the Rails to the Rail Ties

As we just saw, one critical joint is the rail to tie joint (RTJ). Since we are going to do this many many times, we need to be sure that we are doing this one right. Each joint needs 2 screws per side. They must be pre-drilled, countersunk and use the right length screws for maximum load bearing.

https://youtu.be/N3SjzdIt0yQ

Joining Track Sections

Joining track sections is difficult because we need to bond on the inside surface of the pipe rather than the outside. With 1.5″ PVC pipe, this is even more difficult because the ID is 1.61″ and there is no standard size tubing or pipe that can fit in here. The best option is to get a 1.25″ Schedule 80 PVC pipe and turn the OD down to 1.60″. This will get rather pricey unless you have your own lathe.

As a result, we will take 1.25″ sch 40 PVC pipe and make it a smaller diameter by cutting out a strip of it along the length so that it can squeeze into the rail pipe. It will then be secured with glue and screws.

After this pipe didn’t hold with glue alone, I skipped gluing all together. I added 4 screws on each joint, (2 on each side of joint) to secure the track pieces. I also switched to the #10 2.5″ long screws but plan to replace them with something shorter in the near future.

I speculate that the reason PVC pipe joins with glue so well is that normally there is no slit in either piece. In normal functions, the glue needs to resist a pure twisting or a pulling force. With the slit, the joiner doesn’t work together so a twisting motion does not evenly load the glue and shears off. This will be a subject of more investigation in the future.

****Update****

Upon disassembling the Black Widow, I discovered that the joints take a longer time to cure. I now recommend using glue and screwing for a strong, long lasting joint. (01/12/23)

https://youtu.be/pLx3GSut_cc

No one wants their roller coaster to fly apart as you’re riding it! We need to understand our loads so that we can prevent failure. Using our general calculations, we are able to know what they are. We will want to select track radii and height for turns and hills with limits in mind so that we don’t destroy the coaster.

In order to make a structurally strong backyard roller coaster, we must identify the loads applied, and critical joints, and know how the wheels contact the track. Finally we need to select the track spacing and how far rails need to be apart.

Identifying Critical Joints

In this video, I demonstrate the maximum G forces that I will subject The Black Widow to 3g down, 0.7g lateral and 1g up. Your normal weight, like on a scale is 1g down or 1 times the force of gravity. If I weigh 200 lb, a 3g situation would make me weigh 3 times my normal weight and put 600 lb on the track. If not factored in correctly, this could cause the destruction of your coaster!

The rail connection to the Tie (RTJ) is the most critical joint so we will dive deep into that.

https://youtu.be/Is7Bk_kLIOU

Understand Wheel Contact Stresses

How that Effects Tie Spacing and Track Width

While this topic is probably more suitable for the cart section, we need to understand how the wheels interface with the track. The diameter, wheel spacing, and number of wheels will determine key things about our roller coaster. Mainly the rail tie spacing and and the allowable weight limit. Overall efficiency is at play as well.

Normally I would like to calculate all this, but it will be nearly impossible due to the hollowness of the tube and rolling resistance.

https://youtu.be/DjStLl_uOWA

Rail Spacing

The Black Widow uses a 20″ center to center spacing between the rails. Find out why.

https://youtu.be/lt9kQY9Xrzo

Rail Tie Spacing for the Black Widow

Depending on your G force, you will need to change the tie spacing. Higher G forces require more support (you know, because there is more force). These calculations are a simple way to calculate how far apart your rail ties need to be.

https://youtu.be/mfJmR3S2vZw

G Force	Tie Spacing
Less than 1.9 G	20 in
1.9 G to 2.0 G	16 in
2.0 G to 2.2 G	10 in
Over 2.2 G	6.5 in

(More research to come on this topic.) For those that want more information on this topic. Watch this video on the subject of Hertzian Stress

https://youtu.be/pmim38c2QrA

Designing a roller coaster can be a tedious challenge. Where do you begin? So many decisions to make is daunting to anyone. We’ll, how do you eat an elephant? One bite at a time.

In order to design a good roller coaster, you must consider the proven track designs and select one. Also, consider the terrain available to make your layout unique. Finally, use design the layout so that it will give you the forces you want.

Common Track Types

If you look at modern roller coasters, it seems that each ride manufacturer has their own unique track design. Each has benefits and drawbacks for a backyard roller coaster.

This video explores some of the popular ones and I select one for my roller coaster.

https://youtu.be/TGr9EygUxGk

Terrain – Make the Best Use of What You Have

Every yard is different so get creative on how to use it. Is there an existing structure that can be incorporated? Is there a small pond or pool? Trees you can miss or fly through? Think about such things as you start developing your track plan.

https://youtu.be/3qq81nKyHpY

Designing Your Track Layout

Laying out your course can be a daunting task. This spreadsheet will aid you in your design by removing most of the math needed for a successful coaster. The spreadsheet will allow you to calculate the velocity, energy and G forces at any point. I selected only the critical points, but you can add points every foot or meter if you’d like!

The main unknown here is your coaster’s efficiency. The Black Widow had a 6% coefficient of drag, but I only knew that after it was built. Unfortunately, I planned for 5% so the cart doesn’t make it all the way back to the station. I recommend that using multiple coefficients of drag for your design to ensure a complete loop.

Plan on a worst case 6.5% efficiency so that the cart makes it all the way back around. Then use a 4.2% to see if the ride becomes too violent for your taste. End up somewhere in the middle (5% to 6%) for what your actual coaster may do.

Download the Track Layout Planner Here

The video will explain how to use the spreadsheet. (Side note: remember that a straight line has an infinite radius and not ‘0’)

https://player.vimeo.com/video/460277813?h=47ec437a8e