# Simple Structural Support for Your Backyard Roller Coaster

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.

## 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.

## Rail Spacing

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

## 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.

(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

Corey Rasmussen

Corey is the Managing Director of the Mentored Engineer and owner of Rasmussen Designs. He received his BSME from Baylor University and holds a professional engineering license in North Carolina and Texas. He has been an engineer since 2002 with extensive experience in engineering design, fabrication and troubleshooting. He specializes in mobile equipment, hydraulic systems and machine design. He has two patents

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