Powering a 4-8-2 locomotive

Melbournesparks

Melbournesparks

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Technical question time:

I'm planning on building a large 4-8-2 locomotive, using Bachmann 4-6-0 parts. It will be powered by a pair of standard Bachmann motors and gearboxes, driving the outer two driving wheel axles. The two motors will be wired together in parallel, and the axles mechanically linked by the connecting rods.

Does anyone have first hand experience with an arrangement like this, or can anticipate problems? I want to try and avoid any sort of excessive mechanical load on the connecting rods caused by the motors running at different speeds, but I'm hoping with new parts that shouldn't be a problem.

dGnfiMa.jpg
 
Hmmmm..... while I don't have any direct experience, I would not be happy with such a set-up for the very reason you ask - if there is any difference at all in the motor speeds, then I would think you'd risk a lot of strain on the motion rods.
The only commercial loco model I can think of which uses two motors driving wheelsets physically connecting by coupling rods is the LGB Harzbulle (the 2-10-2)........ then again, no-one seems to have trouble with them, so maybe it is OK after all if everything is using high quality motors and well-matched parts.....?

Jon.
 
The two motors on the LGB Harz Bulle are directly connected to each other inside the chassis block using a universal joint.. Same with the Mikardos.
I think you may get binding problems with two motors at the outer extreams.
 
Assuming this will be a fixed chassis - ie. no flex like the LGB Mikado has - then can you fit some conical gears and run a lay-shaft between the two drives?

The Aristo Mikado (later versions at least) used their "prime mover" blocks which drive each axle through a gearbox and link them together with shafts.
 
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The Bachmann drive has a well documented history of splitting gears, and also parts availability comes and goes. You will make the problem worse by forcing them to synchronize and this will put additional stress on the gears.

The Aristo gearboxes are much more robust and modular in nature.

I have 2 "bashed" locos a 4-8-4 Northern, and a 2-10-2 Mountain type made from these gearboxes.

Greg
 
Thanks guys, sounds like rigid mechanical coupling is the way to go.


ntpntpntp said:
Assuming this will be a fixed chassis - ie. no flex like the LGB Mikado has - then can you fit some conical gears and run a lay-shaft between the two drives?

The Aristo Mikado (later versions at least) used their "prime mover" blocks which drive each axle through a gearbox and link them together with shafts.
Click to expand...

There will be a degree of compensating, but it might be possible to couple the two motor shafts via a long shaft between the frames.

Greg Elmassian said:
The Bachmann drive has a well documented history of splitting gears, and also parts availability comes and goes. You will make the problem worse by forcing them to synchronize and this will put additional stress on the gears.

The Aristo gearboxes are much more robust and modular in nature.

I have 2 "bashed" locos a 4-8-4 Northern, and a 2-10-2 Mountain type made from these gearboxes.

Greg
Click to expand...

These are version 5 gearboxes, which I believe are less prone to split gears than the earlier versions. Still, they're not particularly heavy duty. Is there a source for Aristo gearboxes? Unfortunately a lot of large scale parts are hard to get in Australia, especially if cost is a factor.
 
stockers said:
The two motors on the LGB Harz Bulle are directly connected to each other inside the chassis block using a universal joint.. Same with the Mikardos.
I think you may get binding problems with two motors at the outer extreams.
Click to expand...

Thanks Alan - I suspected it had something like that, but wasn't sure till I looked at the service diagrams!

Jon.
 
Until Bachmann replaced the nylon gears with metal ones, the split gears have continued. I think the latest gearbox has a brass gear on the main axle, but now we are getting reports of stripped idler gears... but that may be a situation of overloading.

In any case, I would not use what you have pictured.

Greg
 
I would be vey tempted to use one of the JH Motors, they are very grunty and pack plenty of power. You appear to be competant in terms of what you are planning, so a setup using just one of these with a Gearbox Drive should not be too much of an issue. Power tranposed by Flexible Coupling Rods as per the real thing.

http://www.mscmodels.co.uk/motor-gearboxes/

I can confirm that they are reliable gutsy Motors having used them in 0 Gauge for years. Just for G select the biggest that they have in terms of loading.
JonD
 
dunnyrail said:
I would be vey tempted to use one of the JH Motors, they are very grunty and pack plenty of power. You appear to be competant in terms of what you are planning, so a setup using just one of these with a Gearbox Drive should not be too much of an issue. Power tranposed by Flexible Coupling Rods as per the real thing.

http://www.mscmodels.co.uk/motor-gearboxes/

I can confirm that they are reliable gutsy Motors having used them in 0 Gauge for years. Just for G select the biggest that they have in terms of loading.
JonD
Click to expand...

Those are very nice, and would certainly do the job! Unfortunately the cost is a bit outside the budget, though it's always an option for future projects.

Given the doubts about the Bachmann gearboxes (especially for heavy loads) I ended up building a new one.

FRGwWEA.jpg


It uses a VCR motor, and gears from a photocopier and VCR. Still nylon, but much heavier than the bachmann gears, and I even have spares. This could always be replaced by an MSC models gearbox later, but it should do the job. Thanks everyone for your input on the gearboxes, it's certainly much easier to make design changes at this stage of the project than later on.
 
I've heard a lot of tosh about Bachmann gearboxes (although the Connie problems were largely genuine) but I think most of the problems arise from heavy use of the throttle, and lots of rough stop / starts.

A single Bachmann Annie (not Big Hauler) motor / gearbox should be adequate for a 4-8-2. The big difficulty with scratchbuilt chassis is the lack of flexibility in the axle boxes, which can lead to a reduction of adhesion on uneven sections of track. The reality is that a scratchbuilt 4-8-2 may not be able to haul as much as a factory built 4-6-2, and that we're worrying over nothing.

I scratchbuilt a 2-6-2 with a very expensive gearbox and a Buhler 7-pole motor (one of the best G1 gearboxes available in the UK) but the Achilles' heel is the lack of adhesion due to the rigidity of the chassis.
 
So you made it to well??

Needs to be a ham-fisted job like I would do then!
 
Greg Elmassian said:
Many bachmann locos have split gears (spin on the shaft) out of the box, noticed first time running by very unhappy owners.

Plastic used is crappy quality, and it shrinks over time and creates a crack. Well documented.

Not tosh.

Greg
Click to expand...
That may have been the case with the some of the earlier Big Haulers, but the Anniversary version doesn't suffer in the same way - not sure where, in the 4-6-0 lineage they changed, but the recent locos are OK.
 
Rhinochugger said:
I've heard a lot of tosh about Bachmann gearboxes (although the Connie problems were largely genuine) but I think most of the problems arise from heavy use of the throttle, and lots of rough stop / starts.

A single Bachmann Annie (not Big Hauler) motor / gearbox should be adequate for a 4-8-2. The big difficulty with scratchbuilt chassis is the lack of flexibility in the axle boxes, which can lead to a reduction of adhesion on uneven sections of track. The reality is that a scratchbuilt 4-8-2 may not be able to haul as much as a factory built 4-6-2, and that we're worrying over nothing.

I scratchbuilt a 2-6-2 with a very expensive gearbox and a Buhler 7-pole motor (one of the best G1 gearboxes available in the UK) but the Achilles' heel is the lack of adhesion due to the rigidity of the chassis.
Click to expand...

A fully rigid frames is definitely unworkable for the standard of track I'm planning to run on. Watch this space, I'm working on it. :)

Rhinochugger said:
That may have been the case with the some of the earlier Big Haulers, but the Anniversary version doesn't suffer in the same way - not sure where, in the 4-6-0 lineage they changed, but the recent locos are OK.
Click to expand...

Anecdotal evidence would seem to support that, there's been at least five versions of the big hauler gearbox with far less failures reported for the anniversary version. I still wasn't brave enough to rely on one for this application though, they will be held as spares in case of failure.
 
Melbournesparks said:
A fully rigid frames is definitely unworkable for the standard of track I'm planning to run on. Watch this space, I'm working on it. :)
Click to expand...

Yes, it's a question of introducing enough vertical slop, and sideplay in the axle mountings.

I'll be watching progress with keen interest :nerd::nerd::nerd:
 
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