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| Re: Addenda - Re: Pantograph for Trackless Trolley vs. Light Rail or MU (486940) | |||
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Re: Addenda - Re: Pantograph for Trackless Trolley vs. Light Rail or MU |
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Posted by Robert King on Thu Sep 6 22:43:29 2007, in response to Re: Addenda - Re: Pantograph for Trackless Trolley vs. Light Rail or MU, posted by WillD on Thu Sep 6 14:40:51 2007. The poles on a trolley bus are different than the ones used on streetcars in several ways.Trolley bus poles are insulated, and have a thick copper wire inside each pole instead of the pole itself forming the conductor the way streetcar poles do. If you look closely, you can see wire pop out from the bottom part of the trolley coach pole and make a little arc up to the brass shoe that holds the carbon insert. Also, the shoes on trolley coach poles swivel in two planes so that it'll follow the wire straight, regardless of the angle of the pole with respect to the wire. This lets the bus steer around without twisting the shoe against the wire, causing it to pop off. Streetcar shoes don't swivel around. The twisting against the wire's actually used to an advantage on streetcars. At turnouts, the frogs are positioned in the wire after the streetcar's started to turn away from the straight through direction. That causes the shoe to twist agains the wire, and when the twisting shoe passes through the frog, it pushes the pole through the frog in the correct direction so that it followes the right wire - the one above the track the streetcar's just turned on to - if everything works right. Since trolley coach poles don't work that way, passive streetcar style frogs can't be used, and the trolley coach overhead has to have powered switches that actually throw to the selected direction at trolley coach turnouts, to guide the poles through the turnout to the correct pair of wires. Trolley coach poles are also much longer than streetcar poles, to provide enough reach so that they'll be able to get up high enough to make contact with the wires even when the bus is steered a good distance away from the wires. Streetcar poles aren't long enough to reach the wire all the way across from the next lane over while making a turn at the same time. What all this means is that you could spread the wires out to eight feet apart, four times normal. In fact, I've seen video of this happening in Hamilton by accident at a large bus station with two parallel sets of wires for adjacent lanes. The positive pole followed one lane's positive wire and the ground pole followed the other lane's ground wire so the bus kept running fine even though the poles were bent out wildly. It only came apart when the two lanes merged back into one at the end of the bus station, and the poles got knocked off the wires when one got knocked off by the overhead switch, which was going to be mis-set for one of the poles no matter what since it could only be set for one lane at a time - not both. The one free pole started swinging and knocked the other one off it's wire. However, from the video, it severely impacted the manoeverability of the trolley coach to the point where it had to be driven very slowly, the poles were near the limits of their movability and the ability of the springs to pull them up against the wires with enough tension to stay on. There's also the issue of having clearance up in the air to string two pairs of wire with eight feet of space between each pair when you take into account other utility wiring up there, tree branches etc. etc.. When you get into tradeoffs like this, with the operating difficulty and reduced flexibility, you're better off stringing a separate set of trolley coach wires beside the streetcar wire, far enough away so that the streetcar pantographs won't be able to reach over and contact the trolley coach wires. -Robert King |
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