Badger99 Posted September 12, 2014 Share Posted September 12, 2014 Some while ago I picked up a R2980 County of Radnor 1908 Olympics set at a very good price in a Hornby sale, but the loco would just not run properly straight out of the box. No low speed control, wouldn't move off unless the throttle was three quarters open, and a low top speed. At the time I thought the motor was faulty and asked hornby for a replacement motor which they supplied (returning the whole box to them from Australia would cost a fortune in postage).Months later I have just got round to fitting the new motor and whilst there was a definite improvement, it was still a poor runner. Remembering a mention of changing CV10 (back emf setting) on the forum, I changed CV10 in railmaster from 128 to 5. Instant success! It now moves off smoothly, has good low speed control, and a good top speed. Was it the new motor or the CV change? A bit of both I think. Thanks to greg99 for his CV10 posting back in 2011. Link to comment Share on other sites More sharing options...
idlemarvel Posted September 12, 2014 Share Posted September 12, 2014 It probably was the back emf setting that sorted it.For others reading this it depends on the decoder you use whether CV10 controls back emf or not. On the Hornby R8249 it is but on e.g. ESU it isn't CV10 it's the first bit of CV49. So be careful before blindly changing CV10. Link to comment Share on other sites More sharing options...
Wobblinwheel Posted October 23, 2014 Share Posted October 23, 2014 Wow, I'd like to know more on this! I just got a brand-new DCC-fitted Hornby "Mallard" that runs "jerky" (for lack of a better word). I've checked and lubricated the drivetrain (even the quarter of the drivers) and have found nothing wrong. Sort of surging, or "camming" as it runs. Could be BEMF? It's default is 128....too high? Link to comment Share on other sites More sharing options...
Fishmanoz Posted October 23, 2014 Share Posted October 23, 2014 First try running it in for an hour or so at medium speed,Cohen see how it goes. Then if still jerky, try BEMF adjustment. This CvVs is supported in your 8249. Link to comment Share on other sites More sharing options...
RDS Posted October 24, 2014 Share Posted October 24, 2014 After reading about back EMF in one of the posts recently, I thought I would look at the description on the R8249 leaflet. It says, CV Name: EMF Feedback Cutout CV 10, default value: 128 Description: Contains a value between 1 and 128 that indicates the speed step above which the back EMF motor control cuts off. Having read the description, I was left doubting that this was the same thing that had seemed so easy to understand in the post. Link to comment Share on other sites More sharing options...
RDS Posted October 24, 2014 Share Posted October 24, 2014 Thinking about this more and the value of 128 as a default means that CV10 is effectively switched off, because the speed step at which EMF motor control cuts off is actually the maximum possible speed step (128). Does that make sense? Link to comment Share on other sites More sharing options...
Fishmanoz Posted October 24, 2014 Share Posted October 24, 2014 RDS, I looked at the 8249 leaflet before I replied (apologies for the typos, Cohen should be then). Put it the other way and you get default for BEMF is ON. BEMF causes the voltage to be increased when the motor is under load to try to maintain the no load speed. This effectively means the motor is operating in a "feedback loop" and, as with all such loops, operation can be jerky if it is not properly "tuned". So reducing CV10 to 1 turns BEMF OFF for all speed steps above 1, which means it is off all the time and cannot make things jerky. The downside is the motor slows under load and you have to turn up the throttle yourself to maintain speed. Link to comment Share on other sites More sharing options...
Wobblinwheel Posted October 25, 2014 Share Posted October 25, 2014 After experimenting with CV10, I have found out that it only works (properly) two ways: ON or OFF! I set my BEMF cut-out at 25 to keep my very-slow speeds constant, and my higher speeds smooth. Looked good on paper....... Unfortunately, under acceleration when speed step passed 25, the loco sped-up abruptly, and on decelleration, it "slammed on brakes" at step 25. I have high settings on CV's 3 and 4 for slow accel and decel, and it looked really bad.......The good news is I've finally gotten my Kadee conversion for the Mallard's tender (What? no NEM pocket???) and after about an hour of fabricating, I can now pull a string (10) of coaches. With BEMF on up to step 80, it runs MUCH smoother with a heavy load behind it! I believe an ESU decoder is on the horizon. Their speed-control is second to none in my book. I want to install sound, but my tender is full of the old casting for the "pancake"? motor. I know they want to cut costs, but this is getting ridiculous........ Link to comment Share on other sites More sharing options...
RDS Posted October 26, 2014 Share Posted October 26, 2014 RDS, I looked at the 8249 leaflet before I replied (apologies for the typos, Cohen should be then). Put it the other way and you get default for BEMF is ON. BEMF causes the voltage to be increased when the motor is under load to try to maintain the no load speed. This effectively means the motor is operating in a "feedback loop" and, as with all such loops, operation can be jerky if it is not properly "tuned". So reducing CV10 to 1 turns BEMF OFF for all speed steps above 1, which means it is off all the time and cannot make things jerky. The downside is the motor slows under load and you have to turn up the throttle yourself to maintain speed. Thanks for that explanation. Link to comment Share on other sites More sharing options...
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