As per video the seesaw will be mounted on this kind of rotating wheel/ disc.
https://youtu.be/SikOJblbhV0The disc will rotate back and forth.
Now see the sketch.
The counterweight will be some heavy than the ball.
The tube of counterweight will be like "U" shape.
Now see the design of tube of ball .
There are sliding point on the both side of tube .
The design of long tube will be work in this way that the ball will fall down after getting a certain angle.
The device will be mounted in middle of disc.
Measurements.
The length of long tube is =50 cm.
The length of tube of counterweight is ,
The curved arms =20 cm.
The straight arm=10cm.
The counterweight will be also a ball.
Mechanism:
When ball will fall down then it will hit the bottom of tube an due to it's kinetic energy the device will rotate and the ball will get back it's initial position or even more height than the dropping point.
The curved shape of tube of counterweight will work in this way that the movement of counterweig ht ball will work to provide the momentum.
The same mechanics will work again when ball will again fall down.
The disc will rotate clockwise and anticlockwise.
I would like to insist on the rotating mechanism of disc as it is very important in it as there is no pivot point in it.
I have tested it and it will work.
If you could design the disc using with ball bearing then it will work beyond our expectation.
At first you please test it without design the tubes with a long tube and drop a ball from some height.
The ball will get back it's initial height.
I want that you please use spring based lock or brake system to prevent the device from further movement.
Though we can use secondary lever system instead of spring but at first test it with spring.
All things are same except there is a disc which will oscillate due to impact energy of ball.