Lessons

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.



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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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20
Nov

2009

Basic Lesson 5: Propulsion

Unlike traditional vehicles, CPT vehicles do not have an onboard engine or motor. Propulsion is provided by an off-board engine that moves a cable.  Vehicles are equipped with a grip used to attach and detach the vehicle to the cable.

The vehicle is therefore propelled by the cable which itself is propelled by engines and bullwheels in a wheelhouse. Remember those old clotheslines with wheels? It sort of works like that.

Like That

Like That

San Francisco Wheelhouse

San Francisco Wheelhouse

Proceed to Novice Lessons 1: Corners

Return to Basic Lessons 4: Propulsion

Creative Commons image by threefingeredlord. San Francisco Wheelhouse image used with permission by sjgardiner.



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17
Nov

2009

Basic Lesson 4: Support

In Cable-Propelled Transit (CPT) support describes the guideway along which a vehicle travels. Support can either be provided from above the vehicle (in the case of Gondolas and Aerial Trams) or below the vehicle (in the case of Funiculars and Cable Cars).

Support can either by provided by rails or cables.  In all but the rarest of examples, support from above is provided by cable and support from below is provided by rails.

Support From Above

Support From Above By Cable

Support From Below

Support From Below By Rail

There is one rare class of Cable Car that is also supported by rails. This rare class uses rails that are actually embedded within the asphalt of roads. Though historically widespread, street-supported Cable Cars are limited only to San Francisco’s historic Cable Cars. Modern Cable Cars tend to be supported on elevated guideways.

Historical Street-Supported Cable Car

Historical Street-Supported Cable Car

Contemporary Cable Cars Typically Use Elevated Guideways

Contemporary Cable Cars Typically Use Elevated Guideways

Proceed to Basic Lesson 5 to learn about Propulsion

Return to Basic Lesson 3 to learn about Aerial Trams & Funiculars

Creative Commons images by bristol’s family, digika, Saopaulo1, and Perugia-City.com



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Basic Lessons
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13
Nov

2009

Basic Lesson 3: Aerial Trams & Funiculars

There are two minor sub-groups of CPT technology:  Aerial Trams and Funiculars.

Aerial Trams are like larger Gondolas.  I’ll discuss this technology in greater detail later.

Generally speaking, however, Aerial Trams are (relative to Gondolas) an out-dated mode of Cable-Propelled Transit.  Compared with Gondola technology, Aerial Trams exhibit longer wait times between vehicles; lower line capacity; an inability to turn corners; and little potential for intermediary stations.

Ironically, Aerial Trams are on average more expensive than Gondola technology despite their numerous short-comings.  They are a high-cost, low-value technology.

Aerial Tram

Aerial Tram

Funiculars, on the other hand, are very similar to Cable Cars except Funiculars are used almost exclusively to ascend steep inclines.  In fact, you’ll often find Funiculars referred to as Inclined Rails.

The incline of the vehicle is equivalent to the incline of the bottom-supporting guideway while standing and seating areas are at a flat incline relative to the horizon.

Traditional trains and rail lines are incapable of ascending greater-than-10-degree inclines which gives Funiculars are decided advantage.

Funicular

Funicular (Inclined Rail)

Again, like in the previous post in the Basic Lessons series, because there has never been a CPT typology, people often incorrectly refer to Funiculars and Aerial Trams as Cable Cars.

Proceed to Basic Lesson 4 to learn about Support

Return to Basic Lesson 2 to learn about Gondolas & Cable Cars

Creative Commons images by Phillie Casablanca and Les Chatfield



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10
Nov

2009

Basic Lesson 2: Gondolas & Cable Cars

There are two major sub-groups of Cable-Propelled Transit (CPT) technology:  Gondolas and Cable Cars.

Gondolas are supported and propelled from above by cables.  Most people are familiar with this technology as used in alpine ski-resorts, however it is finding increased usage in non-alpine urban regions.

Gondola

Gondola

Cable Cars on the other hand, are supported and propelled from below.  Propulsion is provided by a cable whereas support is provided by rails of varying configurations.

Cable Car

Cable Car

Cable Car

Cable Car

It’s important to understand that since there has never existed an exact typology for Cable-Propelled Transit, people tend to use the terms Gondola and Cable Car interchangeably.  Hopefully, The Gondola Project can help solve that problem.

Remember:  Gondolas are from above and Cable Cars are from below.  That’s all you need to know.

Proceed to Basic Lesson 3 to learn about Aerial Trams & Funiculars

Return to Basic Lesson 1 to learn the definition of Cable Propelled Transit

Creative Commons images by borkur.net, Dede90 and Matthew Black



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