WE WROTE A BOOK! It documents all the engineering, design, plans and process! Check out our website http://backyardrollercoasters.org
This POV was used in a Disney Channel episode. Look for episode 5 of "Stuck in the Middle", in April 2016.
Today I finished my 3D backyard roller coaster track. It needs some reinforcing on the slower portions, but I went ahead and did a test with about 44 pounds of payload.
Specifications: 180 foot length, 8 ft total height drop, average drag 4.4%, steepest drop 63 degrees, fastest predicted speed 13.8 MPH, maximum positive g's 2.12g, maximum negative g's -0.64.
Will verify via smartphone accelerometer app.