Woodhead in Blue - A Class 76 Introduction
Written by: Edward Fisk.
Edward Fisk, of Partner Programme developer MeshTools, delves into the re-worked and Pro Range-suited simulation of the Class 76, which is to be included with the upcoming Woodhead Electric Railway in Blue route!
Read about the Class 08 by clicking here.
Read about the Class 506 by clicking here.
And now we get to the main event of Woodhead, the mighty Class 76. The version of Class 76 included this time around is the 76-bX variant, in other words, the locos modified for multiple working and fitted with dual brakes. The Class 76 has certainly been the most time consuming of the locos to script (130 hours + around 20 hours research and prep work) and has been incredibly fun and rewarding to work on. It is also by far the most challenging of the 3 locos to drive. One thing which sets the class 76 apart from the other two engines the Class 76 features a unique advanced mode. In advanced mode it is possible to completely fail the locomotive through poor driving. It also has a couple of control interlocks which are normally disabled in standard mode. But I’m getting a little ahead of myself.
First off, the model the new Class 76 is a rework of the old one, but it has received a substantial overhaul to bring it up to modern standards. The textures are now much higher resolution and detailing of the model increased. In addition, all the relevant modifications needed to convert the original 76 into the multiple working dual braked 76 have been carried out including a heavily modified cab. All model work was carried out by the locos original author, Ricardo Rivera (Reppo) with some additional tweaks by DTG-Ben (and yes, the vacuum brake hoses are now on dummy couplings).
Then it came to scripting the 76, it is fair to say that the Class 76 is a product of a bygone era. Unlike modern electrics where a computer handles most of the driving work, driving the 76 is completely down to the Motorman’s (drivers) skill and there are very few interlocks preventing bad things from happening to the locomotive. This means an awful lot of scripting was required to just replicate the complex control system on the 76 as accurately as possible.
The main driving on the controls are simple enough from an outside perspective (but a lot more goes on under the hood), there are 14 resistance notches, a full field running notch and 4 weak field running notches. There are then 2 different motor combinations which can be used; series (all four motors connected in series), or parallel (2 groups of motors in parallel with 2 motors in each group connected in series). Then it is also possible to weaken the fields of the motors on the lead axles on each bogie (via the weight transfer switch) to reduce the likelihood of the lead axles slipping while accelerating (I think you can start to see where this gets complicated). Weight transfer on the bogies is modelled, this is a fairly unusual trait of the 76’s due to the unique way the bogies are designed; while there is a load on the drawbar (which gets naturally worse during acceleration), weight is transferred off the lead axle and onto the rear axle on each bogie, meaning the lead axles are much more likely to slip. Of course, the locomotive also features my standard adhesion model making driving in adverse weather conditions even more challenging (use of sanders is advised!).
And then we get to the brakes, of which the Class 76 has quite frankly a bewildering number of them! There are 6 braking systems in use on the 76 and they have hopefully been recreated as faithfully as possible. The braking systems on the 76 are as follows: Locomotive straight air brake, Train air brake, Train vacuum brake, rheostatic brake, regenerative brake and finally the parking hand brake. At this point I must give special mention to Jonathan Morton for his assistance in helping me figure out the regenerative brakes.
I won’t go into each of the braking systems in detail as this article would probably be about ten times too long if I did, but probably one of the most interesting to model was probably be the rheostatic brake. For those of you who can remember the original 76 model, you may recall that it didn’t have rheostatic brakes. Indeed, when originally built the 76’s didn’t have them either, they were added post-1955 after a series of accidents. For those who might not know, Rheostatic brakes are what you may otherwise know as dynamic brakes. They work effectively by turning the motors into generators (and the 76 does this is a fairly unique way) and having them load onto a resistor bank causing a braking effect. On the 76 these brakes are effective right down to around 2mph and are very powerful, but naturally can’t be used for very long otherwise the resistor banks would overheat. The problem was, how were these brakes operated?
One of my books mentioned a switch with 4 positions labelled Off, B1, B2 and B3 which varied the excitation of the motor fields, but the problem was, could I heck find this switch. This eventually culminated to a trip to the National Railway Museum technical archives to view the original manuals for the Class 76 (4 enormous bound books with literally every part of the 76 described in extreme detail). But concerningly that didn’t offer much in the way of help as the manuals were 1953 originals (when the 76s didn’t have rheostatic brakes), but it did help with replicating the control system. There was one part which wasn’t mentioned in the manuals, but which on the original model was used as the pantograph selector switch. Then we had a breakthrough, we were able to find a picture of this switch and on it you could just about make out the lettering B1. It turns out the switch appears to have been the rheostatic brake switch, not the pantograph selector switch after all!
I could go on about every little intricacy of the 76 and the interesting times had researching and scripting them, but in the interest of brevity I will cut that bit short (unless you actually want to read about that in which case leave a comment below!). Put simply, the Class 76 is probably the single most complex and complete Electric locomotive in TS currently, and at around 6500 lines of code it probably rivals even some of the most advanced steam engines in terms of complexity! One thing I will mention is that the sounds have been redone completely from scratch, and the loco now has an appropriate single tone horn (well it has got two tones, but both sound at the same time). It may not have perfect sounds but hopefully they are about as good as you can get for something which hasn’t been heard in 37 years.
To cut a long story short, the Class 76 offers a bit of something for everybody. From the outside the locomotive isn’t terribly tricky to use (save for a few small intricacies which may require a brief look at the manual) and I’m confident everybody will be able to get it moving, to stop it and drive it to a reasonable standard.
For those who like a challenge, driving the 76 well, especially in advanced mode, will require some practice to master the locomotive and can be quite a rewarding experience when you learn how. Especially tricky is controlling speed accurately on a downhill gradient, and knowing when to use each of the braking systems available. Then in advanced mode you have the addition of the temperature simulations to think about, draw too much current for too long and you may burn the motors out. Stay in the resistance notches too long and the resistor banks will fail. Both of which lead to a terminal failure of the engine, as such you must learn good driving practices. The key to this is learning what the locomotive is and isn’t capable of, practice driving it, and never be afraid to ask questions if you don’t understand something. Oh, and don’t forget to read the manual!
I hope you have enjoyed these first looks at the Woodhead locos. If you have enjoyed them and want to see more, or have any questions feel free to leave a comment on the Dovetail Forums. Of course, upon the route’s release, any feedback on the locomotives is also greatly appreciated. Mistakes can’t be corrected or improved upon in future if they aren’t known about! ■
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Woodhead in Blue - A Class 76 Introduction