QUOTE (Brendan11 @ 18 Nov 2008, 18:39) <{POST_SNAPBACK}>..I've got a few older locos which I rarely run out as there a bit too jerky at lower/slow speeds, any advice on helping these run better by tinkering with cv values?..
You can use what you have learned on the 08 to adjust CV2 (start voltage) so that the loco motor only just turns on speed step 1, and then try values in CVs 3 and 4 to produce smoother acceleration and braking. Depending on the performance characteristic of the loco it may also be worth adjusting maximum and mid speed, CVs 5 and 6, to deliver the performance that best suits you. As posted earlier, all these CV values may be reset to factory defaults at any time, so don't be concerned about making performance worse, you can go 'back to square one' very easily.
There is however a significant caveat to this, and that relates to the performance of these older locos on DC, before decoders are fitted. DCC does not improve a graunchy old mechanism that cannot maintain a smooth crawl, or will only start if it gets enough current for a scale 30mph. A good decoder can compensate for, and thus mask, some of these deficiencies; but the running performance will not be as good as with the same decoder in a sweet running mechanism. I assume the Hornby 08 is the new scale model; if you have not done so, check it out on DC without a decoder fitted. It is a decent mechanism and powered by an ordinary DC resistance controller will move reliably at a slow walking pace, and will start and stop very smoothly and realistically. From that mechanical performance a DCC decoder can extract extremely realistic motion. You should not expect the equivalent performance from an older model with a worn open frame motor, and relatively low reduction ratio single stage gearing, that only starts on DC with a big jolt, and will not smoothly maintain a slow speed.
You can use what you have learned on the 08 to adjust CV2 (start voltage) so that the loco motor only just turns on speed step 1, and then try values in CVs 3 and 4 to produce smoother acceleration and braking. Depending on the performance characteristic of the loco it may also be worth adjusting maximum and mid speed, CVs 5 and 6, to deliver the performance that best suits you. As posted earlier, all these CV values may be reset to factory defaults at any time, so don't be concerned about making performance worse, you can go 'back to square one' very easily.
There is however a significant caveat to this, and that relates to the performance of these older locos on DC, before decoders are fitted. DCC does not improve a graunchy old mechanism that cannot maintain a smooth crawl, or will only start if it gets enough current for a scale 30mph. A good decoder can compensate for, and thus mask, some of these deficiencies; but the running performance will not be as good as with the same decoder in a sweet running mechanism. I assume the Hornby 08 is the new scale model; if you have not done so, check it out on DC without a decoder fitted. It is a decent mechanism and powered by an ordinary DC resistance controller will move reliably at a slow walking pace, and will start and stop very smoothly and realistically. From that mechanical performance a DCC decoder can extract extremely realistic motion. You should not expect the equivalent performance from an older model with a worn open frame motor, and relatively low reduction ratio single stage gearing, that only starts on DC with a big jolt, and will not smoothly maintain a slow speed.
