Here is an element that I like to call the Boomerang. It works 95% of the time, it's easy to build and uses 3 knex balls. It's called the Boomerang because once the scale starts to tip over, it will return in the opposite direction.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,
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Place the knex balls exactly in this order.