A fixed grip is one that permanently connects a CPT vehicle to the cable. Because of this direct connection, stopping or slowing a fixed grip vehicle involves stopping or slowing the entire system.
Aerial trams and pulsed gondolas both utilize fixed grip technologies. For an aerial tram, cabins are located at opposing ends of the cable so that vehicles dock at the end stations at the same time. Pulsed gondolas operate in much the same way, but often with more groups (or pulses) which must slow or stop en route while others are in a station. A funicular is essentially a bottom supported aerial tram, where each vehicle shuffles back and forth simultaneously along tracks.
Generally fixed grip systems can achieve greater speeds but have other limitations such as longer wait times and reduced capacities, as compared to detachable grip systems. While it is possible to have mid stations with a non-detachable cable system, this is only feasible (or at least most efficient) if the mid station is located in the exact center of the line.
Originally all systems were fixed grip systems so all cabins were permanently attached to the cable — when one vehicle had to stop, the entire system came to a hault. Then in 1872 an Austrian fellow named Orbach and he solved the matter by patenting and inventing what would be the world’s first detachable grip:
A detachable grip is one that can separate itself from the cable. The detachability allows a cabin to slow or stop within a station, without disrupting the flow of the entire system.
Upon approaching a stop, a mechanism located at the station opens the grip and the vehicle is slowed by another mechanism. Passengers get on and off, the vehicle is re-accelerated to line speed, and while departing the grip is re-engaged. This process is incredibly fluid, seamless and is virtually invisible to riders.
Since the design of the grip allows it to only open under a constant, targeted, external and specially-designed force, a cabin with a detachable grip would never simply fall of the cable. This force can and is only applied within a station.
Examples of aerial trams that utilize this technology are the moncable detachable gondola (MDG), bicable detachable gondola (BDG), and the 3S, which is essentially a tricable detachable gondola. The additional cable in the second two systems are support cables, which affect speed, capacity, and stability.
An important feature of the detachable grip is how it allows for midstation and corners.