Shock absorbers using springs can sometimes create problems in robot design. I have had robotic cars where the springs popped loose, the spring restraint system failed, or electric shorting was at risk.

Magnets offer several interesting alternatives. Opposing magnetic poles are familiar to everyone. The opposition gets stronger as magnets are brought closer together. One magnet opposing below and one above can be adusted to give varying strengths of resistance.

Another surprising arrangement gives far different results. Magnets with N and S facing each other generally attract. If positioned slightly to the side and restrained from rotating or contacting they first attract and then repel each other as in this photo.
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Positioned above like this there is a weak attraction that when the magnet gets in this position slams into a firm "rubbery" wall. It requires some considerable force to move it further down. Magnets placed on both sides create an even stronger effect. The next photo shows the magnetic field over two base magnets and one moveable so you can understand the effect.
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The light line shows the NS center of the fields. You can see how the South poles of the fixed magnets come up to meet the South of the moveable magnet.

The following three pictures show potential applications of this technology. Though the pictures show mounts for movement on both ends, real applications will have one end fixed.



I have found these designs very useful. Adjust separations to comply with your own needs.