JLTRT 37/4 in S7

[Steph Dale]

Pugsley,

If you've got it running on DC, but not with a decoder, might I suggest turning all forms of motor feedback/BEMF off in the decoder. The chances are that the decoder can't adequately distinguish between the feedback signals from all the motors and is getting 'confused'. A pure high-frequency PWM output to the motors would seem most desirable for the multi-motor drive you have.

Good luck, unfortunately you may need it.

Steph

 

[Pugsley]

Thanks Steph. Once I've got the suitable sized rolling road for it, I'll give it a go and see what happens.

Looking around the 'net, there shouldn't be a problem controlling multiple motors under PWM, but I know that doesn't always follow!

 

[Steph Dale]

Thanks Steph. Once I've got the suitable sized rolling road for it, I'll give it a go and see what happens.

Looking around the 'net, there shouldn't be a problem controlling multiple motors under PWM, but I know that doesn't always follow!

Pugs,

The PWM (Pulse Width Modulation) isn't a problem in itself; it's a very conventional method of reducing the speed of a motor when fed by a constant voltage. The pulse width is proportional to the speed of the motor (simplistic view!). The issue is when the BEMF (Back Electro Motive Force or current generated by the motor in response to it being driven) is used as part of the control process ('feedback'). The decoders we use are going to be designed for a maximum of 2 sets of BEMF responses, so getting 3 times that amount is the problem.

In brief (!!) what I think is happening is the decoder interprets the many feedback pulses as being indicative of it driving one (or two) very efficient motors and will reduce the pulse width until it gets a BEMF response it deems nominal. The problem is that your loco is driven by 6 fairly inefficient motors and so isn't getting enough power from the decoder to actually move.

So - break the control alogorithm in the decoder by turning it off and your loco should run. It may be a lttle like a scalded cat when set up like this, so may need some extensive programming to carefully dial in the feedback/motor control values.

I'm still wishing you luck!

Steph

 

[Pugsley]

I can't believe that it's been so long since I updated his thread! If you've been following the project 'over there' you'll know that things have progressed quite well, in so much as I'm now at the weathering stage. It's not without a bit of trepidation, having never done anything quite so large before, but I'm pleased with how things have gone so far.

Although the effect on the roof is deliberately subtle, this pic shows that there is quite a difference from the original finish.


This is how things are looking at the other end:


This is just the initial phase, there's more to go on top of this, but I'll have to wait for a couple of days for it to dry fully before going over it carefully. That is the one disadvantage of the oil paints I'm using - there's no such thing as a quick weathering job!

It's no real problem though, the model is big enough that there are plenty of other areas I can work on whilst it's drying.

 

[iploffy]

Nice one PUGS looking good

 

[dltaylor]

Looks terrific.
Dave.

 

[Ressaldar]

very nice Pugs, keep the pictures coming.

cheers

Mike

 

[Steph Dale]

Pugs,

Looks very well indeed. Have you sorted the running yet?

Steph

 

[richard carr]

Looks lovely, I like the red and white stripes they are really well done. The weathering looks nice too, not overdone. I hate locos that are too dirty.

Richard

 

[Pugsley]

Looks very well indeed. Have you sorted the running yet?

Thanks Steph. Unfortunately I haven't had a chance to test it again yet, but I have remade a few dodgily soldered joints and tweaked the pick-ups, so it should run better than the first attempt.

At the moment, the priority is to get it looking good and the running part will come a bit later.

 

[john lewsey]

Very nice I like it

 

[40126]

Cant believe i missed the painted pics Grrrrrrrrrrrrrrrrr

Looking good

Steve

 

[ZiderHead]

Ive been following this project in your blog on another forum for ... well ... quite a while

Primary and secondary springing, and axle-hung traction motors - truly inspirational stuff and Really Like The Real Thing. Has anyone else even attempted this before in 7mm?

 

[Steph Dale]

Yeah, there are 'traction motor' units available off the shelf from ABC, and I've seen them used a few times. Unfortunately, as Pugs is finding, multiple motors disrupt the drive in DCC decoders. I'm sure it's a solvable problem though...

Steph

 

[ZiderHead]

Ahh yes I remember checking ABC out some time ago, isnt their approach rather different - just a couple of axles powered by large powerful motors rather than every axle with its own small motor?

As for controlling 6 motors I'm not surprised encoders get confused, I think its pretty impressive that they can deal with BEMF from 2 different motors on the same supply.

 

[Steph Dale]

ABC do three options for diesel loco drives;
Conventional motor/gearbox and Delrin chain (when the latter is available)
Traction motors
Built up drive bogies as you describe.

Steph

 

[Pugsley]

Ive been following this project in your blog on another forum for ... well ... quite a while

Primary and secondary springing, and axle-hung traction motors - truly inspirational stuff and Really Like The Real Thing. Has anyone else even attempted this before in 7mm?

Thanks Jon, I don't think anyone else has done anything quite like this, certainly not with primary and secondary coils and six motors. I'm not sure anyone else is quite mad enough to even consider it!

I think DCC can have problems with multiple motors, as Steph mentions, although most of my problems mentioned earlier in the thread were more to do with dodgy soldering and pickups that weren't quite in the right place. The motors are in series on each bogie so, theoretically, the decoder should only see two motors, not six. Of course, this still could be a problem. I doubt I'll be able to turn on the BEMF.

I've spent the last couple of months making it look good, but haven't had a chance to test it. I've now built a display board/test track that I can set the rolling road up on, so next job will be to finish wiring up all the lights and get it running well.