For the coupler bar’s design, the specification suggests that we have a degree of flexibility in its dimensions, but I wanted to gauge what restrictions we need to work to so that we are still able to fit the carriages’ couplings and meet the specification’s requirements. Based on the ‘RC05 Drawbar’ drawing, given that only dimension noted as ‘obligatory’ is the 20mm diameter hole for the carriages, are we free to change more or less any of the other dimensions? For example, can we change things such as the coupler bar’s thickness and width?
I have noticed that, in various photos taken at previous challenges, many of the coupler bars are at an angle when they are hooked up to both loco and carriage. My questions are:
1. What is the nominal height of the SMR carriages when statically loaded? Or is there a range of height that the coupler bar can be at when attached to the carriages? If so, what is it?
2. Is there another reason as to why many of coupler bars end up being at an angle? Of course this changes how the coupler bar is loaded, so I need to ensure that it’s strong enough!
The drawing of the coupler bar provided is only an example and, as stated in the technical specification (section 6.2), “The coupler bar design (including length) shall be assessed against the track characteristics, haulage and braking loads as specified in this document, taking into due account the endthrow of the locomotive and all limits of dynamic displacement.” So to answer the first part of the question, teams are free to change the thickness and width of the coupler bar provided the above requirements are met.
Regarding the second part of the question: The Technical Specification states that the locomotive must include on each headstock “A ‘U’ bracket with centreline 10″ above rail head supporting a vertical shaft or pin of ¾″ diameter with suitable retention.” The 10” height is chosen to suit the most typical carriage used at Stapleford but there will be some variation and of course there will also be dynamic movement vertically and laterally between the loco and the carriage during operation. Teams should include allowance for the likely motion in their calculations.