US Patent 7661655 Dual capstan puller and method

A puller is provided with a number of advantages. Pullers are described that have a high power to weight ratio, and a high power to volume ratio. Examples of pullers and pulling systems include harmonic drive gear reduction elements and configurations that provide high cable friction in a small device volume. Examples of pullers and pulling systems also include constant force pulling which is desirable in particular for small diameter pipe replacement. Using pullers and pulling systems as described, minimally invasive pipe replacement operations are possible. Reversible pullers are also provided that decrease the amount of time needed to burst or split multiple segments of pipe.