Best Of The Stephenson Rocket

[mmagliaro]

Yes.... I'm still working on it... ha ha.

This time, some work on the "pony wheel" (the smaller one on the engine), and the tender wheels.
In order to really explore my options for the tender motorization, I realized I should first get wheelsets into the tender so I could really see where the axles land, and how much room I have between a potential drive mechanism inside the tender and some sort of gear mounted on a tender axle.  So I diverted to getting some wheelsets and the necessary contact plates made.

[randgust]

OK, now you have me puzzled.

Nice end-axle pickups, and what looks like a solid metal axle.... so are you picking up power on the tender axles or was that just for decent end-bearings?

Oh, never mind, now I actually read your post....duh. 

[martink]

Have you considered cannibalizing a T gauge powered chassis?  There is now a commercially available 0-6-0 diesel shunter (a British Class 08) that is smaller than your target, and replacing by the axles and/or wheels it could serve as the rear wheels and tender.  Also FWIW, I made a much, much cruder linear-motor powered model of Rocket in 1:350 a little while back.  It slides rather than rolls, so definitely a cheat, but still...
[ Guests cannot view attachments ]

[mmagliaro]

@martink
I went and found the T gauge diesel 0-6-0 you are referring to, I think.  A BR 08, correct?  But I can't find any pictures of what the insides look like.
Yes, I would certainly consider using a commercial chassis that is small enough, although there are a lot of complications because the Rocket tender is not just a simple shell that can be dropped over a mechanism.  It is all open underneath, and it really needs to stay that way to look right.  But if the motor and geartrain could be adapted, I'd be all for it. Got any photos of the "guts"?

[Chris333]

/>
They also make a 0-4-0 

I found a photo of the 3D body, but not the chassis. I found others asking for a photo of the chassis, but no photo.

[dem34]

/>
They also make a 0-4-0 

I found a photo of the 3D body, but not the chassis. I found others asking for a photo of the chassis, but no photo.

Mechanisms have come a long way in the last couple years.

[Point353]

I'm wondering how you will achieve reliable electric pickup from such a lightweight model, with relatively few areas of contact with the rails.  Will you have it pulling a sort train with all its wheels picking up power (similar to what Minitrix did with their Adler set)?

Even though it's (presumably) a DC model, perhaps a small non-polarized capacitor could be fitted - maybe in the smokestack - to help smooth out any intermittent contact issues.

[mmagliaro]

Even though it's (presumably) a DC model, perhaps a small non-polarized capacitor could be fitted - maybe in the smokestack - to help smooth out any intermittent contact issues.

The first issue there is that no other load can be on the same track.  But even allowing for that, it would have to be a pretty big capacitor to be of any use for even a very low-current motor.  Let's consider a 50 mA motor load, which is optimistically low.
Some quick fiddling with the capacitance discharge equation for a 120 ohm load at 6v (60 mA), shows that even a 1000 uF cap would only hold the voltage to about 3v for 0.1 seconds.  Now maybe 0.1 sec is longer than we need.  But even at half that time, 50 mSec, we would only have about 4v on the cap.   And this is for a 1000 uF cap.  There won't be room in the Rocket for a cap that big.

[Chris333]

If you want to try I use these: 5.5V .047F capacitor.

https://www.mouser.ca/new/kemet-electronics/kemet-fm-supercapacitors/

You cannot go over 5.5 volts! 

I use them in a few HOn30 locomotive and they work great. I can pick up a locomotive and set it down off the track and it's still going.

[peteski]

If you want to try I use these: 5.5V .047F capacitor.

https://www.mouser.ca/new/kemet-electronics/kemet-fm-supercapacitors/

You cannot go over 5.5 volts! 

I use them in a few HOn30 locomotive and they work great. I can pick up a locomotive and set it down off the track and it's still going.

Those caps are polarized, and I would say physically too large.  You are successful in powering in powering them under wrong polarity (as in running in reverse)?!?!

[Point353]

The first issue there is that no other load can be on the same track.

What other load might be on the same track (or in the same block)?
Is there any possibility of putting the drive in the tender?

[mmagliaro]

The drive is going in the tender, but there still is nowhere to put a large capacitor.  Even if I gave up the weight slug in the loco boiler, that cavity is only 5mm in diameter and about 10mm long.  And this has to be a bipolar electrolytic (or roll-my-own two electrolytics back to back).  The available space in this project is far smaller than it looks, even though it looks incredibly small already, because the architecture of the Rocket has all open space underneath.  The whole thing, engine+tender is 1.75" long.

One step at a time.  There will be a post soon when I get all the wheels back in it and start working out the geartrain details.

[Chris333]

I was successful in not blowing them up yet. 

I use them in both directions, but never switched direction without it coming to a stop first. I just use them for ultra tiny 4 wheel chassis that run in a display loop.

If Max can get pick-ups on all 8 wheels it will be just like an Atlas diesel pick-up wise.

[mmagliaro]

I was successful in not blowing them up yet. 

I use them in both directions, but never switched direction without it coming to a stop first. I just use them for ultra tiny 4 wheel chassis that run in a display loop.

If Max can get pick-ups on all 8 wheels it will be just like an Atlas diesel pick-up wise.

I did some review reading on these.  I had not played with super caps in many years.  They can be charged in a polarity opposite to their terminals, unlike a conventional electrolytic, but their capacitance will be diminished.  How much, I don't know.
The analogy to the 8 wheel diesel is only partially valid.  A Kato F unit weighs between 80g (new ones) and 125g (old ones).  This thing will only weigh about 25g, I think.

[randgust]

To me it's always a trade-off on the idea of a capacitor vs. the idea of using the same space to add weight, which improves both contact and tractive effort.   As I'm admittedly 80's old-school, you stuff whatever full of lead, tungsten, depleted uranium, whatever to increase weight and deal with both issues as best you can.

So... how big are these ultra-caps, and are they only for a constant-voltage supply like DCC?   I just don't get how they'd work for conventional DC except to make it impossible to shut off the throttle; momentum run amok.  Chris' comment on 'you can take them off the track and they are still running' would appear to verify that.

I have a decent sized fleet of Richmond Controls caboose lighting systems that are all capacitor-based and directional sensitive on DC, they work great and will glow a marker LED 20 minutes after I leave the layout room, so I get the idea here.    But I'd think you'd have to have a DCC receiver in there to really make the keep-alive concept truly valuable for a motor circuit?