Grip Module

03
Jan

2010

Grip Module, Lesson 4: Corners

Gondolas turn corners by automatically switching from one cable line (blue) to another in intermediary angle stations (orange circles)

Corners are important because all cities have them. If your transit technology cannot turn corners, you cannot exist in cities. It’s just that simple.

As I said before, however, no one has taken the time to explicitly and simply explain how cable deals with them. For those who’ve never encountered Cable Propelled Transit before, you may not even believe CPT can turn corners.

For the sake of ease, I’m just going to talk about Gondola systems. Cable Cars are a whole other issue, one that I will get to in the future. Know, however, that Cable Cars can turn corners with or without detachability.

For Gondola systems to turn corners, however, detachability is an absolute prerequisite. An attached gondola, for all intents and purposes, cannot turn corners because corner-turning is dependent upon detachability (let’s pretend that’s a word, okay?).

If you’ll recall from Grip Module, Lesson 2 detachable grips allow cable gondola systems to stop at intermediary “angle” stations. This same technique is used to allow gondolas to turn corners by locating the opposing terminals of two separate cable lines in the same station. A gondola enters the station, detaches from the first cable line, is decelerated then moved through the station so that it aligns perpendicularly with the second cable line. The gondola is then reaccelerated, attaches to the second cable line and departs the station.

A Gondola Angle Station

This technique allows gondolas the flexibility to realize an almost infinite number of configurations. Furthermore, deceleration at the angle station is not a prerequisite. Gondolas can switch lines in angle stations at operating speed without the need to slow down.

Most (but certainly not all) turning stations are too large right now, admittedly (as the image above implies). The above image, it should be noted, is not merely a turning station, but a turning station coupled with a maintenance bay. It is therefore a very large station. Unfortunately it is the only photo I have of the internal workings of a turning station. One thing the cable industry should pay attention to is slimming the profile of their stations which is entirely possible given the technology.

Proceed to Grip Module, Lesson 5 (coming soon)

Return to Grip Module, Lesson 3: Atttachable Grips



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30
Dec

2009

Grip Module, Lesson 3: Attachable Grips

San Francisco Cable Car

The exception to Detachable Grips are what I like to think of as Attachable Grips. This concept is best exemplified by the familiar San Francisco Cable Cars. I will not go into a long description about the technology. Instead, I’d like to point you to Joe Thompson’s Cable Car Guy website which does an excellent job of explaining the technology.

In summary, the vehicles attach themselves to a below-grade cable by “picking up” or “gripping” the moving cable. This is unlike virtually every other cable technology in the world. In typical detachable systems, vehicles are attached, detachached, slowed and accelerated automatically by off-board mechanisms located within terminals and stations.

Not so in San Francisco.

Gripman

San Francisco cable cars have virtually no automation. Attaching, releasing, braking and accelerating are all done manually by an operator known as a Gripman.

Beyond the desire to maintain a heritage technique, the Gripman is an essential feature of a San Francisco Cable Car given the system’s configuration and relationship to the city’s traffic.

Unlike all other cable transit systems, San Francisco’s cable cars operate within mixed traffic. This co-mingling of transportation technologies, makes automation a virtual impossibility.

The vehicles must be capable of “picking up” or “dropping” the cable at the near-instantaneous discretion of the Gripman.

As such, it’s best to classify the San Francisco cable cars as utilizing Attachable rather than Detachable Grips.

The difference is subtle, but has a significant impact on the systems’ strengths and weaknesses, a matter which I will get to in a later post. For the time being, an easy way to remember the distinction is this:

In Attachable Grip systems, attaching, detaching, acceleration and deceleration are executed on-board the vehicle in a non-automated manner.

In Detachable Grip systems, attaching, detaching, acceleration and deceleration are automated actions executed in stations or terminals off-board the vehicle.

Proceed to Grip Module, 4: Corners.

Return to Grip Module, Lesson 2: Detachable Grips

Creative Commons images David Hudson Floyd and johntrainor.



Want more? Purchase Cable Car Confidential: The Essential Guide to Cable Cars, Urban Gondolas & Cable Propelled Transit and start learning about the world's fastest growing transportation technologies.

20
Dec

2009

Grip Module, Lesson 2: Detachable Grips

Detachable Grip

It’s important to recognize that the term used to describe a Detachable Grip is detachable not attachable. Detachable grips are attached to a cable with heavy, industrial springs providing the pressure necessary to create the grip’s vice-like hold. Until a constant, targeted, external and specially-designed force is applied to pry open the grip, the grip’s hold is (for all intents and purposes) permanent. The above image should give you a better idea of the mechanism.

So who cares, right? Why would anyone want to detach from the cable?

For a cable transit line to have intermediary stations, vehicles must be able to stop at those stations. But to stop a vehicle means the cable must also stop, which in turn means that every other vehicle attached to the cable must stop as well. This was a problem back in 1872 for an Austrian fellow named Orbach and he solved the matter by patenting and inventing what would be the world’s first detachable grip:

Image from Orbach's original patent.

Detachable grips allow a cable vehicle to stop at a station without stopping the flow of the entire line. 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.

Basically, without the detachable grip, intermediary stations and corner-turning would be impossible, at least for aerial supported cable systems. And as urban transit needs many stops and turns many corners, detachable is almost always the way to go.

Proceed to Grip Module, Lesson 3: Attachable Grips

Return to Grip Module, Lesson 1: Introducing Grips

Creative Commons image available here.



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Analysis / Grip Module / Research Issues / Urban Planning & Design
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18
Dec

2009

Grip Module, Lesson 1: Introducing Grips

Gondola Grip

If you’ll recall, cable cars, funiculars, aerial trams and urban gondolas are propelled by means of transit vehicles attaching themselves to a moving cable. Hence the term Cable Propelled Transit. But how does that occur?  With Grips, that’s how.

Grips are just what they sound like. They are like a fist grabbing onto a rope and holding on for dear life. But whereas a rope can slide through a fist given a strong enough tug on the rope, a CPT vehicles’ grip on a cable is fixed in place and cannot shift. (There is one exception to that rule, which we will discuss later on in this module.)

Like that only without the slippage or rope burn.

Like this only without the rope burn.

There are two major types of grips and cable technology can be subdivided into two categories based on those types: Detachable and Attached. Those terms describe whether or not a gondola is capable of detaching itself from the cable or not.

That may scare you initially, but don’t worry, just because a gondola is detachable doesn’t mean it’s dangerous as you’ll see in the next lesson.

Proceed to Lesson 2: Detachable Grips (Part 1)

Creative Commons images by Alan Cordova, and toffehoff



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Analysis / Grip Module
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