Bachmann class 20's and Hornby decoder

[Dan Griffin]

Hello all,

 

I have fitted a Hornby TTS sound decoder to one of my dads  Bachmann 8 pin class 20's, and all works well and as it should,

 

he also has a br green Bachmann 20 that has a 21 pin decoder fitted. I have altered the cv to allow them to run together, however, the green one, with its 21 pin chip it a heck of a lot faster than the sound fitted one. running them together at the moment is proving an impossibility.

 

can anyone advise me on what cv's to alter on the 21 pin equipped 20 so that they run in unison?

 

I am using a Dynamis to alter the cv's if that makes a difference. I have no other dcc system to use.

many thanks

 

Dan

[Phil S]

The Hornsby tts chip is 'based' on their basic decoder rather than the sapphire; therefore it has no cv5 (max speed) adjustment ... But the decoder in your other class20 may well do .... So try reducing its maximum speed with cv5 and it will proportionally rescale the lower speeds.

Cv6 may be available to alter the middle speed value if the original linear change is not quite right .....and ultimately, a full featured decoder will allow you to replace the basic CV 2,3,4,5,6 ( start, acceleration,deceleration, maximum and mid speeds) with a whole series of valuè of your own .... Although that sort of setting is best done with a computer screen showing you the curve eg with a Sprog and jmri together.

A cruder method of slowing the faster model might be to add a series resistor in the motor leads.... But it would need to be only a few ohms and possibly 1Watt rating ... Which is not the smallest!

[34theletterbetweenB&D]

Further to what Phil S posted, when reducing the speed of the faster (21 pin decoder equipped) loco it is helpful to take off the couplers on one of them, so that when run close together for speed comparison you are not forever having to uncouple. Test in both directions too if there is any noticeable difference forward/reverse; this said the Bach centre motor mechansm doesn't have this problem in my experience, unless there is a fault like a loose drive coupler. 

 

if it is possible to disable CV's 3 and 4 on both decoders, then do so.

 

The way I would then go about this is to first set CV 2 if available on the 21 pin decoder for the best start match between the locos that can be achieved.

 

Then CV 5 for maximum speed match.

 

Then if CV 6 (or alternatively different curve types) are available,  compare the middle of speed range and if there is a mismatch adjust the speed curve as applicable to get as close as possible.

 

Finally with CV's 3 and 4 enabled, set these to match accelerations.

Edited May 7, 2018 by 34theletterbetweenB&D

[WIMorrison]

I time the locos over a known distance at full speed and then match the fastest loco to make it have the same top speed as the slowest loco.

 

Once I have the top speeds sorted I then use Decoder Pro from JMRI to create a custom curve for each loco using the new top speed - generallyy I just match ends for a straight line and write this back - you will find they are pretty even across the board then.

 

I generally set the top speed to match the prototype and work from there. I have seen me having one loco with 180 as the CV and another with 70 to get the same top speed - it is more of an art than a science, but Decoder Pro is very helpful here - as it a known timing point to measure the speed.