Telescopic Limbs
Telescopic limbs
Image from Juan Ochoa and Steve Bowers
The appendages of various vec, cyborg, and robotic entities are capable of marked elongation with respect to their minimum length. Such limbs employ technology originally developed for the extensible legs of aircars.

Generally, the only differences in technology from aircar legs are the periodic spacing along their length of articulated joints, and larger power and data conduits to supply the joints and limb end effectors. Power and data conduits, aside from those that power and control the telescopic action, are inside the hollow core of the limb, and spool out and in in conjunction with changes in limb length. In some designs, electro-lasers or lasers are used to transmit data and power through the hollow limb core without the use of wires or optical filaments. This technique can fail as long limbs flex while slewing, and the lasers lose line-of-sight. This engineering technique is generally not favored for long limb designs.

Limb joints are built to withstand high stresses, so are not capable of the space efficient stowing ability of the rest of the limb. Single, double, and triple axes joints are used--double and triple being the most common. Joints in telescopic limbs have engineering trade offs. The more joints there are, the more flexible the limb, but the larger the fully collapsed size. Properly designed limbs are relatively flexible: joint assemblies that consist of a two-axis joint on the end of a three-axis joint allow the limb to fold back on itself, and have a pointing envelope of nearly two complete hemispheres.

Aircar legs can stow to a centimeter in thickness, a few centimeters in diameter, and extend to ten meters when fully elongate. A telescopic limb of equal diameter and a fully collapsed length of a meter (excluding the length of any possible joints) can extend to ten kilometers. Larger limb diameters allow even greater elongation. Such extreme lengths are only possible in low gee or free fall environments, or up and down under planetary gee loads (active stabilization is required, affected by jets affixed at the joints, and the joint actuators themselves).

Typical telescopic limb maximum lengths are in the range of ten to several hundred meters.
 
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Development Notes
Text by John Edds

Initially published on 30 December 2010.