One fascinating aspect of trolleybus design history is that of the current collectors - the trolleybases in particular, and that is the subject of this article. Much overlaps with one of the trolleybus's step parents, the tram.
1880-1 - the beginnings
One, interestingly early reference to the idea of a trolleybus is in the Journal of the Society of Arts vol.XXIX, 1880-1, on page.574, written by Dr William Siemens, "Another arrangement by which an ordinary omnibus might be run upon the street would have a suspender thrown at intervals from one side of the street to the other, and two wires hanging from these suspenders; allowing contact-rollers to run on these two wires, the current could be conveyed to the tram-car, and back again to the dynamo machine at the station, without the necessity of running upon rails at all. "
William Siemens worked in England and had his three Siemens factories here, (he was big enough to go public in 1881). So could the idea for a trolleybus be just as much British as German? The article pre-dates the 1882 Halense experiments of his brother Werner Von Siemens. It certainly would seem that William and Werner were working together on this, as it also says in a reference (Transport World 5/12/53) "...Werner wrote to his brother William in England, asking him to obtain 50 iron telegraph posts of largest size." Sir William's company also supplied the equipment to the "first long electric tramway in the world" in Portrush, Northern Ireland, built between 1881-3 using hydro-electric power and sprung loaded rail collector shoes - so he was certainly involved in electric traction at this time. (Klapper, 1961) His achievements, which included the provision of Britain's first electric street lighting in Surrey, secured him the first presidency of the Institution of Electrical Engineers.
In America, where the electrification of tramways was just beginning, Belgian Charles Van Depoele patented a under-running trolley wheel pressed against an overhead wire in 1882 in Chicago. He used over-running trolleys on trams in four cities but at the 1885 Toronto Exposition and in Montgomery Alabama in 1886 he used booms counter weighted about a centrally roof mounted pivot. He also used 1400 volts at 18 amps.Frank Sprague left the US Navy and then Edison to perfect street transport electrification. "Legend has it that no less than 40 designs of trolley were tried out" (Miller, 1941) before the Richmond, Virginia tram line was built at the end of 1887. 200 similar tram lines followed by 1889. He later claimed to have thought of the idea for a "self-adjusting, upward pressure" trolley while traveling on the "almost asphyxiating" steam powered Metropolitan underground railway in London in 1882, but didn't patent it until 1885. A patent battle with Van Depoele ensued, resulting in Van Depoele winning but allowing mutual use. Sprague was certainly the more scientific of the early pioneers and had far more success, he was using sprung activated booms by 1889. The basic idea for springs had come from one of his draughtsmen, Eugene Plommer in 1886. (Klapper, 1961) His company was bought by Edison-GE which was re-organised and then absorbed Thompson-Houston as well by 1892.
1909 - Britain
In 1909 a deputation from Leeds inspected the trolleybus system at Mulhausen incorporating a single boom (illus. Soper p.416). This was the design of Max Schiemann. They went on to Milan where they inspected the Filovia system "using a pair of trolley poles pressed against the overhead cables to keep the wheels in position", and also inspected the Cedes-Stoll system (see 1912) using a flexible cable and over-running trolley in Vienna (illus. Soper p.417). By contrast the first British trolleybus, an R.E.T. demonstrated at Hendon on 25 September 1909, used both a trolley base and trolley head of great complexity and weight. Said to be based upon the Schiemann system it incorporated a pair of trolley booms turning together upon a sort of turntable base, and linked at the top by another turntable carrying a trolley running under the pair of wires. I cannot see any justification for the complexity, though Soper reports (p.419) "the twin overhead wire system was demonstrated, but in order to avoid all possible danger, a third wire was contemplated. It was claimed that with a triple trolley head the electrification of the framework would be infallible and permanently avoided". For safety reasons, there was accommodation for third wire running at the Hendon trials. Be that as it may, it does draw attention to what must have been a problem with any trolley head combining both positive and negative polarity, namely that of insulation between the two, especially in wet weather. Perhaps because of this all subsequent British equipments using trolley booms had independent positive and negative booms each with its own trolley head. The 1909 RET demonstration trolleybus in fact, had a unique version of the under-running Max Schiemann system - the booms were parallel to the body, with the leading boom 'steering' a circular trolley head casting that pivoted on the casting that joined the two booms. Insulation must have been complex. The trolleybase was a like a standard single deck tramcar base with a forward facing compression spring with an additional second spring superimposed under it to raise the leading boom. The base was thus single pivoted. Edward Munro, the Railless Company Chief Engineer, had had a patent granted, patent. No.764 of 12th January 1909, that comprised a self-aligning sprung base, a single boom and a double under-running trolleyhead, very different to that which famously was shown to the press a year later in MET's Hendon depot. Munro was still designing trolleybases in the 1920's.
1911 - public service
Thus on 20 June 1911 when Leeds and Bradford simultaneously opened Britain's first trolleybus services the vehicles used had 'improved' bases. The trolleys of the Leeds and Bradford cars were of "Railless Electric Traction Co.'s double trolley type, complete with two poles and trolley heads, and capable of allowing the vehicle to run at a distance of not less than 15ft. from the centre of the trolley wires". (LRTJ, 7th July 1911) The trolley base was described as being two ordinary tramcar trolley heads, specially mounted and supplied by Brecknell, Munro and Rogers. Each base pivoted about a single mounting point. However it appears from photographs that the springs did not turn with the base - probably because with the cumbersome springs and mountings employed this would have restricted the movement of the booms to either side. Later Leeds and Bradford (and Rotherham) trolleybuses were fitted with entirely new bases incorporating vertical springs. These would allow the booms to swing sideways until the boom fouled the neighboring base, i.e. nearly a right-angle to the line of travel, and would also be much simpler and lighter.
1912 - Cedes-Stoll
The over-running trolley attached to be bus by flexible cable still had its advocates. It was simpler and much lighter in weight than the cumbersome booms and bases, though still with the inherent disadvantage that overhead junctions were virtually impossible. And it had its own unique advantage that the flexible cable allowed the bus to manouevre in almost any way (provided it remained within reach of the overhead). Vehicles could for example reverse up a side street in order to turn round at any point on the route, thus in some degree overcoming the lack of junctions. Cedes-Stoll in conjunction with Brush demonstrated one of their vehicles at the M.T.A. conference in West Ham in 1912, and their system was adopted by Keighley in 1913, Aberdare in 1914 and also briefly by Hove in the same year. All these systems used a four-wheel over-running trolley. Meanwhile Stockport, in 1913 adopted the Lloyd-Kohler system with wires in vertical configuration and a trolley having two wheels running on the upper wire and a bow contacting the lower wire.
The Trackless Trolley Ltd, claimed "great flexibility" in 1911 adverts for Cedes-Stoll, and an article in 1913 on the Stockport Lloyd-Kohler system states one set of wires was an advantage, with current gear being exchangeable at any convenient meeting place. These were the days, after all, when trolleybuses were seen only as feeders to tramways, not to be used in busy city centres, but serving "growing but scattered populations". (Aberdare Trackless Installation, Light Railway and Tramway Journal, 7th November 1913)
1912-1921 - refinement
Like so much else in this story of design evolution, some ideas were not easily rejected. The advantage of a single pivot, if not a single boom, was championed up until the 30's. Estler Brothers of Victoria Docks in London, tramcar trolley equipment builders, who did have a connection with Brush, designed their superimposed trolleybase in 1912. It's always been stated that it was to avoid infringing Brecknell, Munro and Rogers patents, but the Estler trolleybase had it's own elegance and could turn through 360 degrees; a fact utilised by Keighley Corporation when they finally gave up Cedes-Stoll overhead but still had to turn out of a main road and into a narrow lane to get to the depot. (King, 1964) The Estler patent didn't stop Garretts copying the arrangement which had been modified in 1921 and added a second slip ring to completely insulate the base - it had previously used the main casting for return current. The solution created greater height, which was to become a problem later for double deckers. Garretts, with their well preserved archive, present a fascinating insight into the research and development that was involved in perfecting trolleybases - work that went on after they had sold their last trolleybus. They solved the height problem in at least one instance, (Doncaster 1-4) by splitting the base in two, which might have again created the possibility of entanglement on sharp bends, although the bases were now insulated and so may not have short circuited.
1922 - the answer
So the trolley boom, based upon the original Schiemann under-running system finally triumphed, though with many modifications over the years. The use of vertical springs has already been mentioned. These were of some height so were not used on double-deck vehicles, for which bases with compression springs projecting horizontally in front were used - for trams and trolleybuses alike. Another development borrowed from the tram was the use of a trolley mast, one for each boom, and mounted on the floor of the lower deck or upper deck. These . patent cam. types had the special advantage of transferring the heavy weight of the trolley gear (not to mention shock loading in the case of dewirement) from the comparatively flimsy roof structure of the vehicle. In fact modern trolleybuses all incorporate some form of trolley gantry to transfer the load from the roof itself at least to the side pillars. Some were built into the roof structure, but many were separate, with the advantage of minimising noise transmission. The compression spring (projecting to the front) had the advantage of "going solid" if it should break, so preventing the trolley crashing down on to the roof or to either side perhaps causing injury. But when the trolley deviated to either side the projecting spring fouled the adjoining trolley base preventing deviation to anything like 90°. Compression springs require control to prevent buckling so tend to occupy more space than tension springs The next development was to use tension springs projecting horizontally to the rear, which allowed the trolley to reach more nearly to 90° deviation, whilst improved quality of the springs themselves reduced the risk of breakage.
The ultimate solution - why did nobody think of it before? - was to use inclined springs more or less parallel to the trolley boom (especially so when the booms were low). The overall height of the base was as low as any, and, most important, there were no springs projecting to front or rear so that provided the overhead wires were at normal height, the trolley could deviate to 90° and beyond. In fact a stop was provided near the straight-ahead position so that it could not make a complete circle which would have twisted the cable. This base, which was known as the Brecknell-Willis "Light-weight" also presumably had the
additional advantage of lightness, became from 1933 onwards the standard for all
The Brecknell,Willis 'new' design was brand new in 1933, first appearing, I think, on London United 61 in March of that year. (The last "Diddler" no.60 was also so fitted, but it's not known when this was, or if it was experimentally fitted to gain running experience.) An AEC/English Electric advert of December 1933 even shows No.61 with the 'old' Brecknell,Willis 'low' type and trolleybuses were supplied with this superseded design up until 1935 (on Wolverhampton no.210).
Also in 1935, there was a strange design by GD.Peters (of air brake fame) for an articulated trolley method. Neither Brian Dyes of Ipswich Transport Museum (who rescued the 4 drawings from Tees-side) or I can understand either the point or how it works! By the mid-30's the spirit of invention, at least as far as the fundamental design of trolleybases for trolleybuses was concerned, was no longer necessary. Since then, innovation has been mainly concerned with retrieving errant booms, using hydraulics and with new lightweight materials. The long gestation was over.
Written by Ashley Bruce and John Senior, August-December 1999.Trolleybase blueprints and table