Strongest robots relative to size

The strongest robots relative to their size are MicroTugs – tiny experimental robots developed by Elliot Hawkes and David Christensen (both USA) at Stanford University in 2015. There are two different classes of MicroTug, "climbing" and "ground". The "ground" model weighs 12 g (0.42 oz) and can drag a weight of 22.5 kg (49 lb 9.6 oz) across a smooth horizontal surface (1,875 times its own mass). The "climbing" model weighs 9 g (0.31 oz) and can carry a weight of 1.1 kg (2 lb 6.8 oz) up a smooth vertical surface (122 times its own mass).

MicroTugs work using a technique called "anisotropic adhesion", which is the same effect that allows geckos to climb walls and windows. Each robot moves around on small pads covered in flexible fibres. These fibres get pulled flat as lateral force is applied to them, increasing the surface area in contact with the surface and therefore the strength of their adhesion. This adhesion is only strong in one direction, however, meaning that very little force (applied in the opposite direction) is required to unstick the pad when the robot needs to reposition it.

If a person had the same ratio of pulling power to weight, they'd be able to drag a blue whale around or climb up a cliff face while carrying an elephant.