RMweb Gold traction Posted October 7, 2015 RMweb Gold Share Posted October 7, 2015 Hi, The Bachmann decoder which is a re-branded Soundtraxx type doesn't have a MID or TOP speed limit CV, that is there is no CV 5 or 6. Instead they provide a speed table with default types that you can select. Which ones would be most suitable to use for something like a 4F or Class 153 or Class 24, basically diesels or steam and from there I can sort of narrow down to a more specific speed curve. Be it the Logarithmic or Exponential. The instruction sheet states:- Speed curves The decoder offers a selection of alternative speed curves to tailor the performance of the locomotive. Logarithmic curves give faster acceleration at low speeds changing to slower acceleration at high speeds, exponential curves give slower acceleration at low speed with faster acceleration at higher speeds as shown in the Figure 1. In addition, there is the option of a user defined curve. 36-558.pdf I have attached the pdf instruction sheet so you can see the speed curve graph which may help a little. Thanks Ian Link to post Share on other sites More sharing options...
RMweb Gold Oldddudders Posted October 7, 2015 RMweb Gold Share Posted October 7, 2015 I'm not a great fan of speed curves, particularly for steam engines, where the performance will vary wildly according to load, while most light engines are quite sprightly. The 153 is a different matter, getting off the line quite smartly in my limited experience. Logarithmic sounds better there. I assume you find the default linear acceleration unsatisfactory? I really think the answer to your question involves a bit of suck it and see per model, having regard also to the differences among motors & gearing in each model. Link to post Share on other sites More sharing options...
RMweb Gold traction Posted October 7, 2015 Author RMweb Gold Share Posted October 7, 2015 Thanks Ian, It's more to do with limiting the top speed, as the layout I've built is for children to play with at exhibitions so wanted to limit top speed. As there isn't a top speed CV on this decoder, I had hoped that just using one of the predefined curves would suit, as it would save me from making a speed curve up from scratch. To narrow it down was hoping that a consensus would say logarithmic for the non steam and exponential for steam, from there onwards I could try the different curves to find something OK, even if I almost copied one of the curves but lowered the last few values to limit the speed that way. Cheers Ian Link to post Share on other sites More sharing options...
Crosland Posted October 7, 2015 Share Posted October 7, 2015 If you use JMRI you can set the first and last speed step (i.e. starting and maximum speed) and then "join the dots" to fill in the other steps with a single click with your chosen curve. Andrew Link to post Share on other sites More sharing options...
Adrian Wintle Posted October 7, 2015 Share Posted October 7, 2015 The other thing you can play with is forward/reverse trim for the speed table, which should adjust the top speed (in forward and reverse respectively) while maintaining the shape of the speed curve. Adrian Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted October 7, 2015 Share Posted October 7, 2015 The other thing you can play with is forward/reverse trim for the speed table, which should adjust the top speed (in forward and reverse respectively) while maintaining the shape of the speed curve. Strikes me as potentially a very simple method, Just set the trim values really small (10, 20) until you get a top speed you want, and that's it. It'll be quick and easy to return to normal speed operation too, if the children find the low maximum speed just too low to be interesting. Link to post Share on other sites More sharing options...
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