A mechanical jumper developed by UC Santa Barbara engineering professor Elliot Hawkes
and collaborators is capable of achieving the tallest height — roughly 100 feet—
of any jumper to date, engineered or biological.
The feat represents a fresh approach to the design of jumping devices and advances the
understanding of jumping as a form of locomotion.
For centuries, scientists have explored the limits of biological jump height and for decades,
engineers have designed jumping machines that often mimicked or took inspiration from biological
jumpers.
Despite these efforts, general analyses are missing that compare the energetics of biological
and engineered jumpers across scale.
Hawkes says that there hadn’t really been a study that compares and contrasts the two
and how their limits are different — whether engineered jumpers are really limited to the
same laws that biological jumpers are.
Their research is published in the journal Nature.
Biological systems have long served as the first and best models for locomotion, and
that has been especially true for jumping, defined by the researchers as a “movement
created by forces applied to the ground by the jumper, while maintaining a constant mass.”
Many engineered jumpers have focused on duplicating the designs provided by evolution, and to
great effect.
But the elements that create a jump in a biological system can be limiting for engineered systems.
Biological systems can only jump with as much energy as they can produce in a single stroke
of their muscle.
Thus, the system is limited in the amount of energy it can give to pushing the body
off the ground, and the jumper can jump only so high.
But what if there was a way to increase the amount of energy available?
For engineered jumpers there is: They are able to use motors that ratchet or rotate
to take many strokes, multiplying the amount of energy they can store in their spring.
The researchers termed this ability “work multiplication,” which can be found in engineered
jumpers of all shapes and sizes.
This difference between energy production in biological versus engineered jumpers means
that the two should have very different designs to maximize jump height.
The researcher says tht animals should have a small spring — only enough to store the
relatively small amount of energy produced by their single muscle stroke — and a large
muscle mass.
In contrast, engineered jumpers should have as large a spring as possible and a tiny motor.
The researchers took these insights and designed a jumper quite unlike biological jumpers — the
size of its spring relative to its motor is nearly 100x greater than that found in animals.
Further, they devised a new spring, seeking to maximize its energy storage per unit mass.
In their hybrid tension-compression spring, carbon-fiber compression bows are squashed
while rubber bands are stretched by the pulling of a line wrapped around a motor-driven spindle.
The team found that linking the outward-bending edges of the bows across the middle with rubber
in tension also improved the spring’s strength.
The jumper is also designed to be lightweight, with a minimalistic latching mechanism to
release the energy for the jump, and aerodynamic, with the legs folding in to minimize air drag
during flight.
Altogether, these design features allow it to speed up from 0 to 60 mph in 9 meters per
second — an acceleration force of 315g — and reach the roughly 100-foot height in the researchers’
demonstrations.
For motor-driven jumpers, this is “near the feasible limit of jump height with currently
available materials,” according to the study.
This design and the ability to exceed the limits set by biological designs sets the
stage for the reimagining of jumping as an efficient form of machine locomotion.
Jumping robots could get places where only flying robots currently reach.
The benefits would be more pronounced off Earth as well: Jumping robots can travel across
the moon or planets efficiently, without dealing with obstacles on the surface, while also
accessing features and perspectives that can’t be reached by terrain-based robots.