Gearboxes that will drive back

[Guest jim s-w]

Hi ozzy

 

You see, that starts to make a lot more sense to me than all this theoretical stuff

 

Thanks

 

Jim

[James]

Jim, I have to agree with that!

 

With our very small models it is all too easy to apply to much of theoretical engineering to them. For example we should, in P4, build locos with very tight tolerances but one of the smoothest locos I've seen in P4 was a compensated 0-6-0 on a demo stand at Scalefour North which had been run and run and was very sloppy, but it ran beautifully. I olny discovered this when I asked about its drive train!

[bertiedog]

I am not advising anybody to build one scale or standard, but I do support standards that work,,P4 does, and i built models to P4 within weeks of it's start in the 60's, but If I do HO then I use NMRA standards, but both will have decent mechanisms, not the awful things passed of as transmissions in most commercial models, they work, but the acceptance by the customer as "good" is relative and un quantifiable. Some buyers will accept a poor mechanism as good, you cannot persuade them otherwise, as they have few chances to see the way better locos run.

 

In 55 years of modelling I reckon I have seen good running, both enthusiast built like Guy Williams and Mike Sharman,, and professional scale like Beeson, and commercial items from Basset Lowke and Bond's.for museum use.

 

My own standards for running are high, silence, no judder, grind or strain to the mechanism, and dead smooth operation. I have rarely seen any commercial loco from Tri-ang, Hornby, or Kader, that runs right in all respects, good, but no prizes as best. You cannot expect toys to run like hand made models, but you can try your best to keep striving for better. .

 

Longlevity, Tri-ang beat the rest hands down, we did extensive endurance runs with 3F mechanisms, running thousands of real miles in shop display, but they were noisy and would not run slowly. Other makes fail on wear, noise, judder and gear grind noise under load, none of which should be there if the designer and engineers did the job right........But I have been assured by people that Tri-ang "were excellent", and that current Bachmann can't be improved on......they must be easily satisfied or never seen real models running.

 

Compared to other gearboxes the ABC are very well made,accurate and efficient, what more can you ask for?...apart from a 4mm copy?

 

Stephen.

[bertiedog]

On a particular loco running well, like the quote "sloppy" loco that ran well, it is pure chance that it did, all the tolerances worked in it's favour, pure serendipity, but you cannot design mechanisms on that basis, hoping that it will settle down in some way on it's own.....they do however, just like "bad" cars that run well, or expensive cars that are dogs....life is unpredictable.

 

I have seen many newcomers to railway modelling that get it right first time, super running, and some have a full grasp of why, some do it by chance, but in the thousands of models I have serviced or built sound engineering is the basis of good running....most of the time, .....on average..... or whatever reasonable qualification so as not to make a pedantically fixed statement..

 

I was asked why I had not commented on the degree you could see the difference between the types, I had just spent 25 minutes typing a full explanation, and trying to put easy to follow explanations of the differences. it was neither "technical" or a "simple explanation", but it did cover the differences very fully.

 

Stephen..

 

. ,.

[Buckjumper]

I fail to see how though? I mean we are not short of power for what we do, Yes it's obviously better but is the advantage a theoretical one rather than one that had any real term benefit?

 

Don't get me wrong, it's an interesting topic in it's own right

 

Cheers

 

Jim

 

Edit: I started this post before Ozzyo's reply, then was called up to supposedly sleeping children. C'est la vie. I've left my reply in place as it deals with smaller prototypes rather than the big 4-6-0s Oz is building.

 

Not theoretical - entirely practical.

 

It's simple really; etched brass kits are very light, and need lots of weight added for adhesion if they're going to pull a rake of heavy coaches or wagons. So, for example, tanks, particularly front coupled ones, (0-4-4Ts and 0-4-2Ts) need particular care with the placement of added weight, especially in an all-sprung or compensated setup, or they'll never pull the skin off a rice pudding (same can be said for 2-4-0s or 4-4-0s; in fact four-coupled locos are generally a PITA). Boilers and tanks are carefully packed with lead with some in the bunker (have a look at real weight diagrams to see just how much was carried by trailing wheels - a surprising amount), whereas the firebox (a space which would be ideal for added weight in most circumstances) is taken up with the motor, and, if you're lucky, a flywheel - but I've encoundered many prototypes where a flywheel simply won't fit in the available space. So, with space at a premium and an efficient, free-running ABC unit in place I can forget about the lack of a flywheel, dispense with the large high amp '0' gauge decoders needed for worm/wheel drives, and instead safely fit the smaller (2-3 times smaller) 00/HO decoders such as the Lenz Gold. The combination of the natural inertia and the benefits of the DCC chip gives unparalleled performance, and where I'm building a DC loco and there's no room for a flywheel the natural inertia of an ABC unit is a godsend, especially for slow-speed shunting engines.

 

I've been building 7mm locos for a good number of yeas now, all of my early ones were with worm/wheel drives, but once I began to use ABC I was astonished at the difference and I wouldn't go back now, and know many 7mm modellers who feel the same. From a commercial perspective, comparing the costs of time taken to set up and bed in a worm/wheel drive properly (and the occasional hassle) versus the price of the plug & play ABC unit is a no-brainer, so I no longer build for myself or to commission with anything else.

[Guest jim s-w]

 

My own standards for running are high, silence, no judder, grind or strain to the mechanism, and dead smooth operation. I have rarely seen any commercial loco from Tri-ang, Hornby, or Kader, that runs right in all respects, good, but no prizes as best. You cannot expect toys to run like hand made models, but you can try your best to keep striving for better. .

 

 

Hi Stephen

 

You clearly approach your models in terms of pieces of engineering in their own right. Better for you means better engineering, less noise, strain and more smoothness. Compared to you what I do is more dumb and based more on a visual and artistic point of view. That's the beauty of a hobby like this and yet if you see my stuff you may scoff at how it's built, equally I may tale the view that a super smooth tank engine doesnt look realistic in it's movement because it's too perfect.

 

Horses for courses

 

Cheers

 

Jim

[ozzyo]

If we could get skew cut spur gears in these sizes this would cut the noise down even more, but at what cost?

OzzyO.

 

 

Hello all,

 

as I said in this post, if we could get skew cut spur gear in these sizes it would cut down gear noise, the reason is that the gears are sliding into mesh rather than arriving into mesh with the full gear tooth.

 

Some of the noise that I am getting will be from the roller bearings, due to me locking the shafts to the inside bearing ring and now allowing NO play between the two. I have always been of the persuasion that if the bearing (roller) is running loose on the shaft (or in the housing) it's not doing it's job.

 

Going back to the whine of the RG4s etc. most of it would be caused by the first set of gears, and not the spur gears.

 

But can we please get back to the O/P is there a gearbox that will drive back in 4mm available?

 

 

OzzyO.

[dajt]

I have a number of these ABC gearboxes. Brian offers a number of variations and different motors. My dock tank has one with a 16/24 Machima I have another with a 18/33 Cannon. They are very efficient. In my Beaconsfield 4-4-0 the normal models would not fit as the final gear was to large to hide under the cab floor. No problem Brian made up a special. I have found no problem with noise. The only thing I have found is using a cassette system the motorgearbox is so free that the loco can roll down a slope so you have to watch out that you don't tilt a casette (and keep the ends blocked). The other issue is the price. Compared to the cost of 0 gauge kits wheeels etc the price is not excessive and is similar to other motor gearboxes such as the portescap. Personally I consider the fact that the motor gears are properly held in the correct mesh well worth the extra cost.

Don

 

I've just received an ABC gearbox for my 4-4-0 and immediately found the problem you describe re the large gear protruding into the cab. I'm not too worried, I'll hide it under a coal spill from an inexperienced fireman or something.

 

The gearbox is beautiful.

 

What did you do to get the custom one - is it a variant shown on the gearbox planner that ABC has?

 

Regards,

David.

[bertiedog]

Hello all,

 

as I said in this post, if we could get skew cut spur gear in these sizes it would cut down gear noise, the reason is that the gears are sliding into mesh rather than arriving into mesh with the full gear tooth.

 

Some of the noise that I am getting will be from the roller bearings, due to me locking the shafts to the inside bearing ring and now allowing NO play between the two. I have always been of the persuasion that if the bearing (roller) is running loose on the shaft (or in the housing) it's not doing it's job.

 

Going back to the whine of the RG4s etc. most of it would be caused by the first set of gears, and not the spur gears.

 

But can we please get back to the O/P is there a gearbox that will drive back in 4mm available?

 

 

OzzyO.

Simple answer is no, there are now none with the withdrawal of Portescap. The Exactoscale is spur and worm combo, but not reversible.

 

On Portescap it s possible to use the plastic gears as masters for metal copies in bronze, I did it once and frankly never again!! Getting Gleason form involute bevel teeth in that tiny size is a deep problem, ( I had to work with a low power microscope!), so I did each tooth in three passes to approx profile, (in engineering terms!), and then ran in the bevels under pressure with optical polish grade Cerium Oxide paste to grind them to the correct form.

 

It worked, a silent Portescap was the result, no noise at all, but a horrible job making the replacement bevel gears I have a second portescap lying un repaired on the bench pending a new bevel, but my eyesight and patience will probably mean altering to other gears.or moving the motor to the side of the Portescap, using spur gears only, possible in O gauge only, there is no space to do it in OO sized units.

 

Stephen.

[davefrk]

All this talk about Portescaps and gearboxes and there's me just put an RG4 up on Ebay....

Co-incidence or what, honest guv.

 

Dave Frk.

[Horsetan]

All this talk about Portescaps and gearboxes and there's me just put an RG4 up on Ebay....

Co-incidence or what, honest guv. ....

 

Cor, strike a light, etc.

[Tickplan]

I have only just come across this thread so apologies if I am "late" and it has run its course. I began reading because of the original title/question - which I think can be summarised as, "are there any available gears that can be back driven in 4mm?". The conclusion reached above is that there are none curently available. Of this I can correct you - yes there is and I know this because I bought one only a few weeks ago, new, from the "manufacturer".

First a little history. One of the posts above shows the Micro Locomotion drive from the 1980's . This was a commercial failure (but I agree with the poster about it being an engineering success). They were taken over by Slaters and some of the products are still used I believe in their 7mm models. However, there is one, catalogue reference number FD1 - see here https://slatersplastikard.com/others/gearboxes.php-

that is a 3 to 1 final drive mechanism. It is suitable for 4mm work as it has a tube reducer for use with 1/8" diameter axles. The gearbox can be back-driven. O.K it is not a complete answer since it needs spur gears (or better still a planetary gear head on the end of a coreless motor at say 15:1) to get the total gearing down to around 40:1. They are also large and would only suit the larger wheeled tank engines. However they are well-suited to tender locos with the motor being located in the tender and connected via a universal drive (available again from Slaters or the nice ones from Branchlines, imported I believe from North West Shortline in the States). I am currently collecting all the parts to do this in a O.F Kirtley but it will be some time before I can report back on success or otherwise. (My concern is that there may be so much torque in the tender that it could topple it off the track - still worth an experiment). If you are still wondering about a suitable motor and gear head try this fellow in the States http://stores.ebay.co.uk/microlocomotion who styles himself as "Grandad Eldon the motorman". he is just making me up a Faulhaber coreless with a 15:1 gear head with ballraces . I hate to think what it will cost but having seen many years ago that Sid Stubbs outside-framed Kirtley coasting along I am determined to have some sort of a go at recreating it.

Happy modelling,

 

Bryan

[Horsetan]

..... try this fellow in the States http://stores.ebay.c...microlocomotion who styles himself as "Grandad Eldon the motorman". he is just making me up a Faulhaber coreless with a 15:1 gear head with ballraces .....

 

He's very good, is Eldon. He's got Maxon double-shafted coreless motors that make very good replacements for the ones in Heljan 4mm diesels.

[bertiedog]

The 3:1 still being available from Slaters is interesting, but would really need a final run of spur gears from Ultrascale or equivalent to reach a decent ratio. The gear head motors offer the best alternative and the States supplier range is good, but they are done by other sources in the UK, and a bit cheaper.

North West may have some gears available but supplies can be very patchy especially to outside the States.

Stephen.

[Horsetan]

.....the Micro Locomotion drive from the 1980's . This was a commercial failure (but I agree with the poster about it being an engineering success). They were taken over by Slaters and some of the products are still used I believe in their 7mm models. However, there is one, catalogue reference number FD1 - see here https://slatersplast.../gearboxes.php-

that is a 3 to 1 final drive mechanism. It is suitable for 4mm work as it has a tube reducer for use with 1/8" diameter axles. The gearbox can be back-driven. O.K it is not a complete answer since it needs spur gears (or better still a planetary gear head on the end of a coreless motor at say 15:1) to get the total gearing down to around 40:1. ...

 

The gears appear to be crossed helicals. In 4mm scale, only ever seen that type of gear used on the FIA LMS "Twins".

[34theletterbetweenB&D]

...My concern is that there may be so much torque in the tender that it could topple it off the track - still worth an experiment...

If the motor is mounted on a vertical axis hinged beam from the rear of the loco so that it sits within the tender body void but is not physically supported by the tender, that potential problem is eliminated. Seen this arrangement once in a very small 4-4-0, the motor hanging off the rear of the loco counterweighting the mass in the boiler and smokebox forward of the driven wheels. Tractively this model just ran away with a huge train of four and six wheel carriages, lovely piece of work.

[Tickplan]

Here are some photos of the 'box. No doubt someone with better engineering knowledge than myself can advise if they are indeed "crossed helicals".

 

Can Stephen tell us where the gearhead motors can be purchased from more cheaply here in the UK.

 

I like the idea of the motor being supported on a hinge held in the vertical plane and can understand the reason for so doing. Are there any more details (photos/diagrams?)

 

Bryan

[Tickplan]

OOps - still got the hang of adding attachments. Second attempt.

 

Bryan

[bertiedog]

Crossed helical gears are usually one to one, the type by Slaters are multi start worms with low ratio. Davall, HPC, and other gear factors supply small 1:1 types at about 8mm diameter minimum with HPC in steel.

 

On gearhead motors, Ebay is full of them most times, the tiny camera lens ones are very powerful, medium coreless show regularly in the auctions. I got a Maxon 1:100 medium size motor for £9.95 recently.

 

I will look up other suppliers, the ref's are on an old computer drive.

Stephen.

[ozzyo]

Hello Bryan,

 

if the photos were a bit bigger it would help.

 

But if these gearbox's are the Slater's gearbox's they are the crossed helicals and will drive back. All this normally means is that the gears are cut at 45Degs.

 

OzzyO.

[Tickplan]

Dear Ozzyo - quite right - they were small. Hopefully this will resolve matters. As you can now hopefully see they are cut at 45 degrees

 

 

Bryan

[bertiedog]

Try :

http://www.precisionmicrodrives.com/

(no connection),

 

For UK supplied motors and gearboxes,some conventional motors, some coreless types. They do a good range of ratios on some models, see the full listings.

 

Other than that, Ebay is very good, the US supplied ones are often Maxon motored etc., and top quality, but at higher prices.

 

On Crossed Helicals, the pitch angle is only 45 degrees for 1:1 ratio, other ratios generate a different tooth pitch to match the PD of the gear.(Formulae are in the HPC manual, (on-line PDF), or the "Mechanics Handbook" gear cutting tables.)

 

(On considuration the Slaters could be 45degree due to the small pinion, number of teeth and the final ratio at that PD, resulting in a 45degree pitch).

 

The Slaters are not 45 degree cross helical gears, as with 1:1 type, they are "low ratio multi start gears", but still reverse just the same for our purposes. They are not quite as efficient as 1:1 cross gears though, the slight loss can be disregarded for most users. It may affect 4mm locos more than the heavier 7mm locos they are really intended to fit.

 

All gear systems with crossed helical gears(or any worm gears), require really good bearings, and end thrust to be taken into account, or things will not work well. It should also be fitted with a flywheel to further take advantage of the smoother action of the gears. The Slaters would be best fitted with thrust collars on each shafts , bearing on the gearbox casing, simple brass collars would do, with a precision steel washer between the faces.

 

Usual practice is to make the loco quite heavy as well, to help with inertia sustaining the smoother motion on over run.

 

Stephen.

[goodmayes]

Even back EMF control is only trying to keep the voltage and current stable, and as the load on the motor changes the voltage may remain constant ,and the current is forced to stay the same, but the simple force of gravity will speed up and slow the loco all the same, albeit under far better control than without the feedback

Stephen.

 

Reading this late but just one point about bemf control. It works to keep the motor speed constant regardless of load. Not the running current. So bemf locos do not tend to speed up going downhill and vice versa.

 

Ted.

[bertiedog]

But the point was made, it is with a reversible gearbox, gravity does overcome the BEMF control with this type of gearbox to an extent.

More stable BEMF control works with ordinary gearboxes much better, that's all that was implied.

[bertiedog]

BEMF is not like a digital stepper motor, or DC motor under digital control, although the back EMF gives control there is lag, tolerances, mechanical losses etc., to take into account, and all BEMF locos will react to a slope, they may not slow, or speed, so much, but do respond to conditions to an extent. A free running spur gear driven loco running on BEMF will still speed up and slow under both load and gravity, the current control is not perfect or in total control of the motor, it is just a lot better than plain DC.