The Challenger Challenge

[mmagliaro]

See, where I'm going with this is I'm wondering if the grooves could be widened in a lathe.  The cutting is the easy part.
Figuring out how to hold them in a lathe chuck is the tricky part.

[Cajonpassfan]

I dont own any steam but only pulling that car count seems kinda lethargic for a loco that heavy with 6 driven axles.
Heck I have an sw1200 weighing half as much that pulls 50 cars. Do all those idler wheels spin freely?  Im thinking that there is one or more that have excess drag acting like a brake sled. Maybe the electrical pickups can be modified to minimize drag?

Yea, Jeff, that the point, she should pull stumps but doesn't. I checked all the other wheels for drag, nothing out of the ordinary. The pilot and trailing trucks don't lift at all, just go for the ride. Baffling...😬
Stick with your stinky diesels
Otto

[Cajonpassfan]

See, where I'm going with this is I'm wondering if the grooves could be widened in a lathe.  The cutting is the easy part.
Figuring out how to hold them in a lathe chuck is the tricky part.

Way beyond my paygrade, Max...
I tried to work with my newest Challenger tonight. I did widen the gauge a bit, per your suggestion. One of the TT axles was narrow. I also put two 1/4 oz. weights on TOP of the engine just to see what that would do. Substantial improvement in both pickup and traction, I was able to pull an eight car MT "heavyweight" train up the Hill. Not nine, and these cars are quite light, about 1.4 oz/40 grams for an 85' car. I felt good about it until I tried one of my stock BLI F units on the same trainset and it walked away with nine... So it's still a wimp in my book...
Otto

[peteski]

Way beyond my paygrade, Max...
I tried to work with my newest Challenger tonight. I did widen the gauge a bit, per your suggestion. One of the TT axles was narrow. I also put two 1/4 oz. weights on TOP of the engine just to see what that would do. Substantial improvement in both pickup and traction, I was able to pull an eight car MT "heavyweight" train up the Hill. Not nine, and these cars are quite light, about 1.4 oz/40 grams for an 85' car. I felt good about it until I tried one of my stock BLI F units on the same trainset and it walked away with nine... So it's still a wimp in my book...
Otto

Diesel models will always have advantage over steam locos.  Diesels usually have fewer wheels, so the axle load is greater on diesels (thus more adhesion).

Well, the only exception might be Kato FEF3 and GS-4 due to their intentional design of the driver suspension (where the TT-driver supports most of the locos weight). Those things are incredible.  I guess that soon  will will also see how Kato Big Boy is designed and pulls.

[mmagliaro]

Yes, unlike the prototype, a "huge" N Scale steam loco is not proportionally heavier than an F unit for its size.  It's all about weight and wheel contact.  So a big ol' Challenger with 12 driving wheels isn't necessarily going to pull as much as a 4-axle diesel.  EXCEPT, in side that big Challenger body, you should be able to find some space for a lot of extra weight.

Do you happen to have a gram scale or postal scale of some kind?   An old-school 1st-gen Kato F7 weighs about 125g, and one of those will pull 50 cars all on its own with no traction tires.  How much does that Challenger loco weigh?

[Cajonpassfan]

Yes, unlike the prototype, a "huge" N Scale steam loco is not proportionally heavier than an F unit for its size.  It's all about weight and wheel contact.  So a big ol' Challenger with 12 driving wheels isn't necessarily going to pull as much as a 4-axle diesel.  EXCEPT, in side that big Challenger body, you should be able to find some space for a lot of extra weight.

Do you happen to have a gram scale or postal scale of some kind?   An old-school 1st-gen Kato F7 weighs about 125g, and one of those will pull 50 cars all on its own with no traction tires.  How much does that Challenger loco weigh?

All good points Max. And the fact that an F unit, despite its shorter length, has a full width/full height body and a steam engine does not.

Yes, I do have a scale:

The Athearn Challenger weighs in at 6.5 oz/186 grams, the loco alone is 3.9/112 and tender 2.6/74

BLI F7, 2.7/79, BLI F3 2.6/76, KATO (new) 3.8/110

For comparison, the Kato UP 4-8-4 weighs in at 5.1 oz/144 grams, loco alone 3.6/103 and tender only 1.5/41


The Challenger tender is a bit on the heavy side, but that's where most of the electrical pickup is, six axles. The loco only picks up on three in each engine, and two of those have TT's.

Otto K.

[mmagliaro]

Well, even though 112 isn't terrible, I still say it needs to be a good bit more if you want it to climb hills with a long (i.e. say 30 car) train.    That 112 is spread out over a lot of wheels, and it doesn't have the natty sprung equalized system that the Kato FEF has.
Is there enough room under the boiler shell to put  metal plates all the way down the middle on top of the circuit board, with gaps where the motor and flywheels are?  It would have to be tungsten and it could have a strip of Kapton tape on it so it won't short anything out.  You could experiment with different thicknesses of styrene to figure out what thickness will fit, and then we can go hunt for tungsten pieces that size.

You put 14g on there and it helped, so I'm thinking if you could somewhere in the neighborhood of 25g on it, you'd reach your goal.
Try putting another 1/4 oz on top of the boiler over the FRONT engine truck, in addition to the 1/2 oz you had on the back.

[peteski]

You could experiment with different thicknesses of styrene to figure out what thickness will fit, and then we can go hunt for tungsten pieces that size.

Here is a method I use to quickly gauge the amount of clearance under a shell: https://www.therailwire.net/forum/index.php?topic=55419.msg761385#msg761385

[ns737]

could the motor not have good torque?

[Cajonpassfan]

could the motor not have good torque?

Well, a good question. So far, not an issue, just slips. But when close to maxed out with a load it's capable of handling, the loco does slow down on 18" curves and slightly steeper sections. I'll play with additional external weights, per Max, to see whether that's a concern.
Thanks, Otto

[mmagliaro]

On the motor, yes, let's all remember that the problem here isn't that the loco "stops" on hills or with a lot of cars.
It slips.  So at present, this is purely a traction problem.  Once we get it to stop slipping, if it actually slows down objectionably, then we have a new problem: not enough torque from the motor.  But so far, it's never pulled enough cars to see that.

[sp org div]

If that weight test is favorable…
Maybe already in your head but tungsten putty works out to be similar density to lead
Particularly if space is limited as an alternate you can fit it in the nooks / crannies

[Cajonpassfan]

Max, as usual, you're right on. Time will tell, but I do sense that torque may become an issue with more weight. But first, I need to find a place to put it...

Jeff, I haven't yet tried additional external weight to test it, been busy. We had another op session today and even managed to run one of the Challengers with its full Pony Express train, but only westbound, downhill So for now, it's a one-way Pony...

As to adding weight to "nooks and crannies", there aren't too many of them, see diagram. Even the domes have weights in them, and a good chunk of the mech is taken up by the motor and flywheels. I'd be really interested to see where people add weight to these pups, so far no response to that question I asked earlier.

Otto

[peteski]

The metal weights used in modern locos are not lead - they are made of lighter then lead zinc-based (white metal) alloy.  My point is that if you were to replace the factory installed weights with lead or tungsten putty, you should be able to increase the  loco's weight without finding any empty spaces to add weight. But if the only place this can be done is in the domes, then it is probably not worth the effort.

[mmagliaro]

What are 25 and 26 in the diagram?  Are those the weights that go up in the domes?  If so, how big are they and how much do they weigh?  If they are just typical "white metal", they look big enough that replacing them with tungsten would be worth it.

I was more thinking about any air gap between the top of the circuit board and the inside of the boiler shell. 
And what about right on top of the motor?  Is there an air space there?  Thin tungsten plates can really add up if you can stack
them in there.  It also looks like you could stick some groups of tungsten cubes on top of the circuit board in the spaces between
the motor and the flywheels, and a long strip of little ones along each side right next to the motor.

While it hurts to give up the density of tungsten, sometimes a thin lead sheet is just easier to fit in there.  If you could put in
a long narrow lead sheet (like 1/32" thick) formed up against the inside of the boiler, running all the way from front to back,
that could add a good bit of weight, and it would just come right off with the shell.  Look for cavities where uniformly-shaped
weights can go - those are best suited to tungsten plates and cubes.  Then go for things like inside of the boiler with thin
lead sheet.