# Self Leveling Seesaw. Is It Possible?

1. Apr 25, 2012

### TUVIX

Hi all. A friend and I were discussing whether or not it was possible to construct a mechanism of weights and pulleys etc. or other methods to keep a seesaw level regardless of where the weight was placed on the platform. The end result would be the ability to step onto one side of a level seesaw, and walk to the other end without it moving on its horizontal plane. Here are a few illustrations to help visualize the forces at work:

What does everyone think? Is it possible?

2. Apr 25, 2012

### DrewD

I think that's called a bench

3. Apr 26, 2012

### JHamm

Place a large block of wood underneath each side.

4. Apr 27, 2012

### haruspex

Since the input to the mechanism is the degree of tilt, it cannot be possible to compensate completely. As soon as it had done so, it would detect no tilt and stop compensating.
Another problem is the response delay. The delay in response opens the possibility of finding the mechanism's natural frequency.

5. Apr 27, 2012

### elegysix

Definitely agree with haruspex, it is not possible because the restoring force depends on the displacement. You can make the seesaw tilt very little, but there will still be tilt.

6. Apr 27, 2012

### andrewmh

wont work. not possible

7. Apr 27, 2012

### jetwaterluffy

A Self Leveling Seesaw kind of takes away the point of a see-saw.

8. Apr 27, 2012

### Staff: Mentor

Fix both cables (at "2" and "4") at the ground ;).
But apart from that, you won't be able to get a full compensation without any active mechanism. However, a large mass at "?" could reduce the tilt a lot.

9. Apr 27, 2012

### sophiecentaur

It would be a see-all-the -time?

You could arrange for the pivot to be very high in the air (an inverted T shape, with a long vertical bit and short horizontal bit). The displacement for any imbalance would be very small then as the angle subtended by the cm and the mid point would always be small.
Failing that, you would need a servo system to maintain the see saw horizontal whatever loads were applied.

10. Apr 27, 2012

### jambaugh

Build the seesaw out of neutronium. Then put the hinge on the top so the center of mass of the seesaw plus riders stays effectively right below the pivot point. Since it levels by itself and the mass of the riders is effectively nil they won't budge it (by a measurable amount).

A self stabilizing seesaw is effected by letting the cross beam roll on a large radius cylinder. As it rocks the pivot point moves toward the side which tips lower. Any mechanical pulley system will be equivalent to this. In the limit where it stays exactly level, you've chosen a cylinder of infinite radius, in short you're setting a board on the ground and the kids sit on it. A mechanism with pulleys will do the same in effect becoming tethers in the limit where it works perfectly.

In either extreme, the mechanism which levels will by definition freeze the seesaw... as mentioned making it a bench. One could however create an active mechanism, requiring input of energy, which will stabilize over some time frame but do so slowly enough that the kids could rock. Do it with servos and sensors, or a more complicated mechanical clockwork which needs the empowering mass or spring to be cranked up.

11. Apr 27, 2012

### jambaugh

In short a swing.

12. Apr 27, 2012

### DaveC426913

Make the seesaw of zero length. Thus you can travel from one end to the other while always remaining under/over the pivot point.

13. Apr 27, 2012

### DaveC426913

This thread makes me think we need an silly engineering contest.

A problem is proposed, contestants enter blueprints, sketches. Winner goes to most clever solution.