Here are instructions for a simple side-loop. This loop works with the fat coaster tubing or the classic tubing. The drop needs to be very long to succeed the loop, making the drop alot shorter isn't an option. Once the ball goes over the loop, the ball spins sideways so it's possible that the ball falls of the track, or you can use a construction that holds the ball into place. It works about 90% of the time and is quite easy to build. you can always watch the video to see it in action.
If there are any problems/ questions feel free to ask me in the comments below.
Thanks for watching/ building,