Hornby Class 20 TTS Loco in Consist

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Bigmet
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Re: Hornby Class 20 TTS Loco in Consist

Postby Bigmet » Wed Aug 22, 2018 10:19 am

brammie wrote:... Lima of some age, but excellent runner...

It shows what Lima could have offered the UK customer. They had all the necessary know how in the group to produce the centre motor driving both bogies mechanism layout, of which the class 20 is 'half full'.

It's a very strange set up on the Lima 20 BTW. Reduction is only 4:1, so it would go a scale 400mph if unrestrained. The restraint is provided by the pick ups on the unpowered bogie acting as brakes; these pick ups are metal sheet resting in a U channel on the wheelbacks and are very draggy. So draggy that without traction tyres the powered bogie can barely move the model!

Never having seen Hornby's version of the Lima class 20, I don't know if they have simply replicated the Lima arrangements?

brammie
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Re: Hornby Class 20 TTS Loco in Consist

Postby brammie » Wed Aug 22, 2018 4:06 pm

Re the Hornby Class 20 bogie arrangement; pickups on both bogies, as in:
Attachments
Hornby Class 20 Bogie 2.JPG
Hornby Class 20 Bogie 1.JPG

brammie
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Re: Hornby Class 20 TTS Loco in Consist

Postby brammie » Wed Aug 22, 2018 4:38 pm

.... I've just noticed that on the drive bogie only two wheels have rubber tyres; top right and lower left in the bottom pic.

brammie
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Re: Hornby Class 20 TTS Loco in Consist

Postby brammie » Sat Aug 25, 2018 7:39 pm

It pains me to record that attempts to run one of my Lima Class 20 locos with a standard decoder in conjunction with a Hornby TTS sound decoder has met with failure. I spent a day setting the Lima up with a standard Lenz decoder trying to rig the CVs to speed match the Hornby Class 20 TTS that I had in mind, and finally settled for something workable but not ideal. I then installed the Hornby TTS decoder in the Lima, wired up only to the wheel pickups (black and red) for supply. Whilst the loco was happy to run under the control of the Lenz decoder, it was clear from the ECoS dispay that all was not well. Ordinarilly, each of the (20 plus)TTS sound functions is represented by a symbol on the ECoS controller, but in this case - nothing. I checked out wiring, again, and was left scratching my head, but I am left wondering whether red and black only to the Hornby TTS decoder are sufficient.

brammie
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Re: Hornby Class 20 TTS Loco in Consist

Postby brammie » Sun Aug 26, 2018 10:03 am

Had a flash of inspiration whilst walking my dog this morning. The thought occured to me that I might rig the Lima Class 20 with a Hornby Class 20 TTS decoder again, but this time insert a dropper resistance in series with the motor connections to reduce the motor speed to that of the Hornby Class 20 loco for the same throttle setting. At a guess, I could start with 4ohm, 4watt (max motor current 1 amp) and then replace with higher/lower R value to achieve speed matching of the two locos at cruising speed. If that idea worked, I could then set the two locos up to run in consist, as per the ECoS manual.

brammie
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Re: Hornby Class 20 TTS Loco in Consist

Postby brammie » Thu Aug 30, 2018 6:22 am

Resistors on order, but a four week df! Meanwhile, I am still pondering the theory involved with fitting an in-line resistor to reduce motor voltage. As a young airman I was obliged to learn something about dc motor theory as part of my training, and my thoughts keep returning to the possibilities of the TTS decoder reacting to a level of motor back-emf which differs to that which it might expect to see for a given situation. The inclusion of an in-line dropper resistor is intended to reduce the speed, and by definition will also reduce the back-emf. I think this will be a case of "suck it and see", but meanwhile dark thoughts enter my mind regarding the likely effectiveness.

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Bufferstop
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Re: Hornby Class 20 TTS Loco in Consist

Postby Bufferstop » Thu Aug 30, 2018 9:06 am

I then installed the Hornby TTS decoder in the Lima, wired up only to the wheel pickups (black and red) for supply.

Is this literally what you did, or did you also wire the TTS decoder to the speaker and possibly the directional lighting?
If everything worked with just the TTS decoder, but the speed was mismatched, then I would aim to disconnect the motor from the TTS, ckeck to see if without the motor the sound and other features worked but standing still. Then install a second decoder connected just to pickups and motor. It's a subtle but crucial difference.

[Edit] I just realised I'm assuming the TTS decoder is separate from the speaker, never having seen one.
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brammie
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Re: Hornby Class 20 TTS Loco in Consist

Postby brammie » Thu Aug 30, 2018 11:08 am

Bufferstop wrote:
I then installed the Hornby TTS decoder in the Lima, wired up only to the wheel pickups (black and red) for supply.

Is this literally what you did, or did you also wire the TTS decoder to the speaker and possibly the directional lighting?
If everything worked with just the TTS decoder, but the speed was mismatched, then I would aim to disconnect the motor from the TTS, ckeck to see if without the motor the sound and other features worked but standing still. Then install a second decoder connected just to pickups and motor. It's a subtle but crucial difference.

Thank you Bufferstop. The TTS speaker is directly connected to the decoder - as delivered. If I understand your post correctly, I did what you suggest - but in the reverse order, ie; installed the Lenz decoder connected to the motor and the pick ups (tested OK), then connected the TTS decoder to the pickups only (no sound).

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Bufferstop
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Re: Hornby Class 20 TTS Loco in Consist

Postby Bufferstop » Thu Aug 30, 2018 12:37 pm

As I said I've not handled a TTS decoder, so that connection was ready attached, and yes you've done what I was aiming for by a different route. What I don't think any of us quite know is the software configuration of a TTS decoder. It's bound to be different to a full fat model. Hornby can't help but meddle trying to shave a few pence off here and there and they'll be in no hurry to tell people what they've done. What's needed is someone who has all the gear to do a complete disassembly of the code. They could then tell you what to do to get a certain result, but it would be illegal for them to publish the code that they've found.
Any one who does it can only draw up a "black box" specification that tells you what outputs for any input. This is the process called "reverse engineering" You build something that behaves exactly the same by writing your own code to do it.
The most notable example of doing this was when Compaq did it for the IBM PC and produced their own "work alike" and released their code to the public. If they hadn't done it IBM would still have a strangle-hold on the PC market.
The situation with DCC is totally different, the DCC spec has been open source from the start it's only what is in the sound decoders that is propitiatory.
Growing old, can't avoid it. Growing up, forget it!
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brammie
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Re: Hornby Class 20 TTS Loco in Consist

Postby brammie » Thu Sep 13, 2018 1:00 pm

Well, having completed their long journey from Hong Kong the resistors have arrived (4ohm 5watt in the packet). Somewhat larger in size than I imagined and room for one only within the body. I soldered one in series with the motor supply and tested ...................... still runs 20% faster than the Hornby for the same throttle setting. Back to the drawing board. Looking for a ten ohm resistor.

brammie
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Re: Hornby Class 20 TTS Loco in Consist

Postby brammie » Mon Sep 24, 2018 5:56 am

A range of small value resistors now on order from a German supplier - good old German cottage industries! Meanwhile, I soldered a second 5ohm resistor in series with the first for a trial run. Speed difference now reduced to 15%, so I will insert a third and trial that. The physical size of the resistors I am using precludes their long term use, so the Germany sourced items will hopefully provide a solution, when they arrive.

brammie
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Re: Hornby Class 20 TTS Loco in Consist

Postby brammie » Mon Sep 24, 2018 6:56 pm

Added a third 5ohm resistor to the Lima Class 20 network today hoping to reduce the motor voltage even further, and reduce the speed to that of the Hornby Class 20. Odd thing, Lima is now 10% faster up to the mid speed point, and from that point the Hornby becomes progressively faster. Bu##er!

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RAFHAAA96
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Re: Hornby Class 20 TTS Loco in Consist

Postby RAFHAAA96 » Tue Sep 25, 2018 12:04 pm

brammie wrote:Added a third 5ohm resistor to the Lima Class 20 network today hoping to reduce the motor voltage even further, and reduce the speed to that of the Hornby Class 20. Odd thing, Lima is now 10% faster up to the mid speed point, and from that point the Hornby becomes progressively faster. Bu##er!


Have you got BEMF turned off where possible.
Rob
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http://www.halton96th.co.uk

brammie
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Re: Hornby Class 20 TTS Loco in Consist

Postby brammie » Tue Sep 25, 2018 4:08 pm

Hi Rob. Not tried that, but it will be next on the list. CV10, default 128, will try setting at various points between 50 and upwards with all resistors removed. Will let you know.

Otherwise. I explained in my last post how the Lima behaved with 15 ohms of resistance added in series with the motor. If the Lima and the Hornby were both represented on a graph, the mid speed point (as described in my post) would be that point at which the two graph lines crossed over. If, by trail and error with varying resistances, I could set that point to the ideal running speed of the Hornby, I think I would have a solution. Running them in consist would then involve some uneveness at lower speeds, but I think it might provide an answer. That is, if your suggestion re back emf does not provide a solution.

Thanks for your help

Mike

brammie
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Re: Hornby Class 20 TTS Loco in Consist

Postby brammie » Wed Oct 03, 2018 6:21 am

With a range of differing value resistors to hand, and having tried a variety of combinations, it would seem that the 15 ohm option is the nearest I can get to "synchronised" control of the Hornby TTS and the Lima Class 20 - albeit that this only achieves speed matching at one point over the speed range. As a last resort I removed all resistors from the Lima and carried out a number of runs with the locos linked up, resetting CV10 on the Lima TTS decoder to several different values from 25 up to 100. I must now conclude that the only possible future for these two Class 20 locos is for them to lead seperate lives on my layout, and hope that one of my Christmas presents is a new Hornby TTS Class 20. Thanks for all your help folks, it was worth a try.


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