Gearboxes that will drive back

[ozzyo]

Hello all,

 

in my J.L.T.R.T. 44xx build thread I put these photos up of two motor & gearboxes that I will be using.

 

Some one said it was a pity that you can't get gearboxes that will drive back in 4mm.

 

So over to yous,

 

OzzyO.

[JeffB]

Hello all,

 

 

Some one said it was a pity that you can't get gearboxes that will drive back in 4mm.

 

So over to yous,

 

OzzyO.

 

Those are probably the two most beautiful gearboxes I've ever seen... Do you know the final gear ratios of each? The thing that makes them "drive back" or back drive, is that instead of a single start worm (which is essentially a single tooth helical gear), it uses a multistart/multi-lead worm, or in the case of the gearbox on the bottom right, a 9 tooth helical gear. You can get a gearbox to back drive with as few as three or four teeth.

 

I've never seen anything like these... I don't imagine that they are even remotely cheap.

 

Jeff

[ozzyo]

Hello Jeff / all,

 

IIRC I think that they are about 26:1. As you assumed there not cheap about £120 a pop. The roller bearing are extras at £20 for the two stage and £30 for the three stage gearboxes, that is counted in the £120 price. The Co. that makes them is ABC gears, the website address is www.abcgears.co.uk

 

The three stage gearbox is going in the 44XX that I'm building in my thread in kit building and scratch building and the two stage in the Castle on the same thread.

 

OzzyO.

[Horsetan]

.....The thing that makes them "drive back" or back drive, is that instead of a single start worm (which is essentially a single tooth helical gear), it uses a multistart/multi-lead worm, or in the case of the gearbox on the bottom right, a 9 tooth helical gear. You can get a gearbox to back drive with as few as three or four teeth.....

 

Yes, but it's encouraging manufacturers to actually make the multi-starts - that the thing. Sid Stubbs wrote about it in MRJ 42, and I think I just about got the hang of what he wrote - there was a lot attached to the importance of pitch angles, etc.....

[ozzyo]

Yes, but it's encouraging manufacturers to actually make the multi-starts - that the thing. Sid Stubbs wrote about it in MRJ 42, and I think I just about got the hang of what he wrote - there was a lot attached to the importance of pitch angles, etc.....

 

 

Hello all,

 

as I mentioned in my 7mm build thread, the gears are industry standard items that are cut / manufactured by Biddle & Mumford (I think). I would think that the likes of High Level Kits or London road Models would be the sort of people to take this on board. Been out of 4mm modelling for a while now so there maybe some one who I've not mentioned.

 

OzzyO.

[halfwit]

Could you tell me what the advantages of this type of gearbox are please?

[Horsetan]

Could you tell me what the advantages of this type of gearbox are please?

 

It won't "lock up" when not powered, so you can still leave the motor in and push the model along by hand when testing, e.g. to see if quartering is accurate, etc.

 

Less resistance to momentum.

[halfwit]

It won't "lock up" when not powered, so you can still leave the motor in and push the model along by hand when testing, e.g. to see if quartering is accurate, etc.

 

Less resistance to momentum.

 

Thanks Ivan.

 

I assume you'd have to adjust your driving style with this set up as surely any loco fitted with one of those gearboxes will coast further when the power is turned off? Especially if a flywheel is fitted?

[Barry Ten]

My kitbuilt 4mm S&D 7F has a gearbox that allows the loco to be pushed along. I didn't build it so I don't know the mechanical details, but I was surprised when I first encountered it.

[Michael Delamar]

I would like it if someone in 4mm did a drop in gearbox/motor, similar to the portescaps.

[Buckjumper]

Thanks Ivan.

 

I assume you'd have to adjust your driving style with this set up as surely any loco fitted with one of those gearboxes will coast further when the power is turned off? Especially if a flywheel is fitted?

 

With an ABC box a 7mm 0-6-0 travelling light engine at a scale 30mph will easily coast its own length.

 

 

I've played with Geoff Stenner's Scale Seven SER O Class which has a Sid Stubbs box and ballraces - running light engine it coasted in terms of feet. When hauling a typical rake it coasted in terms of yards. It's a whole new dimension; cue panic as suddenly you're really driving.

[ozzyo]

Could you tell me what the advantages of this type of gearbox are please?

 

 

One other one that I can think of is if you loose power over a point say, the loco wont just stop, the momentum of the train and the gear train will push it along. So if you have this type of gearbox and a flywheel it will help.

I'm not saying that's is a queuer (is that right for the spelling?) all for bad pick-ups and bad track but it can help.

 

OzzyO.

[Horsetan]

I assume you'd have to adjust your driving style with this set up as surely any loco fitted with one of those gearboxes will coast further when the power is turned off? Especially if a flywheel is fitted?

 

Exactly - got it in one. That's what I'd be looking for, as well as the ability to test without needing electricity.

 

My kitbuilt 4mm S&D 7F has a gearbox that allows the loco to be pushed along. I didn't build it so I don't know the mechanical details, but I was surprised when I first encountered it.

 

You probably have the RG4 in there.

[cheesysmith]

It needs a dynadrive cluch adding between the motor and gearbox. That and a flywheel would give some proper momentum.

Beutiful gearbox`s by the way.

[Horsetan]

It needs a dynadrive cluch adding between the motor and gearbox. That and a flywheel would give some proper momentum.

 

True, but what if there's not enough space for the clutch?

[flubrush]

Could you tell me what the advantages of this type of gearbox are please?

 

Apart from other advantages given, it is a more efficient gearbox when compared with a worm drive gearbox, so a locomotive fitted with one tends to be more controlable.

 

Jim.

[ArthurK]

The Micro Metalsmith's gearbox of years gone by was a drive-back system. The final drive was a 3:1 skew gear driven remotely by a coreless motor through spur gears. It was similar to the Portescap in performance but was in my opinion much better. It was much more flexible than the former and could be adapted to drive on virtuall any chosen axle. More important it doesn't have that awful whine so common witrh the later Portescap gearboxes (why were the earlier ones much more quiet). Fortunately I acquirede several of these whilst they were still available and still have a couple awaiting locos.

 

I believe that the system was taken over by Slaters but it was qickly abandoned.

 

ArthurK

[ArthurK]

I am not sure if my description of the Micro Metalsmith's as being 'drive back' is strictly accurate but is can be driven in reverse from the axle as can the Portescap. For those not familiar with the Micro Metalsmith's sytem I offer the following photo. Whereas this is not to the engineering standard of the gearbox described earlier it is nevertheless a well made and a very attractive system. Total reduction is 42:1.

 

ArthurK

[hollywoodfoundry]

There are an awful lot of gears in that gear-train, I would be surprised if it was not quite noisy. The primary reason most designs use a worm as the first stage is to quickly reduce the speed so that following gears are not so noisy. And a worm drive produces a compact gear box.

[Donw]

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

[Guest jim s-w]

 

 

Some one said it was a pity that you can't get gearboxes that will drive back in 4mm.

 

So over to yous,

 

OzzyO.

 

Porterscaps do (did?) and they have been arround for decades. They sound pretty horrible though. How quite are these ones? Do they have the same horrible whine?

 

Cheers

 

Jim

[Guest jim s-w]

With an ABC box a 7mm 0-6-0 travelling light engine at a scale 30mph will easily coast its own length.

 

 

Cool but think about it, the real thing wouldn't stop that quick if it was having an accident! With a simple dcc decoder you can coast for scale miles if you want to but with a panic button if you suddenly realise you have got it wrong. The other advantage is when the gimmick wears off and you realise that it's a royal PITA on an exhibition layout you can turn it all back off!

 

Cheers

 

Jim

[Horsetan]

....The primary reason most designs use a worm as the first stage is to quickly reduce the speed so that following gears are not so noisy. And a worm drive produces a compact gear box.

 

Half the point of this thread was to encourage the finding of a multi-start worm that could be used in 4mm scale, and which would permit drive-back.

[bertiedog]

The 1:1 skew gears needed are made by Davall,(and other gear factors), in a size (8 to 12mm dia) that will fit a lot of 4mm designs, and another solution are the crown wheels made by Ultrascale.

 

The Davall gears do need sleeves to fit the 2mm and 1/8th shafts, they have large bores as standard. They are moulded in plastic in these sizes, as well as in steel.

 

HPC can supply small crossed helical gear down to 6mm or smaller, in plastic.and steel

 

A point about the helical skew gears that is worth correcting, they are not actually more efficient than worm gears, the angle of the teeth lead to less efficiency at 1:1, but improving at 2:1 etc. They may be reversible but forward efficiency is poorer than equivalent spur gears or worms,, this is why more complex skewed bevel forms are used in car rear axle transmissions to get the efficiency nearer to a crown wheel or worm drive.

 

In larger size skew gears te inefficiently is due to sliding contact between the gear faces, it causes extra friction, which requires constant lubrication in an enclosed gearbox. Also skew gears require considerable resistance to end forces built in to the transmission, which in smaller size transmission simply means friction and heat, albeit small in model transmissions.

 

The fact it is "reversible" is more a by product, than just desirable, crown gears and bevel gears are reversible, as are all spur gear designs, which are the most efficient form of gear transmission.

 

Crown wheels are efficient, but are noisy, and have back lash issues, which complex form helical skew gears do not have. Better would be bevel gears but small bevels are costly to make in metal and to be economic have to be moulded. The Gleason bevel machining system can make small bevel faced gears but cost would be very high indeed.

 

But noise is not normally an issue in tiny models, and with the Ultrascale crown wheel, then a chain of spur gears, (they do helical spur form), a quiet and efficient drive is possible. The crown wheel is plastic, and quiet, and the whole gearbox could be sealed and grease filled.

If a Portescap whines or is noisy, then it needs fresh lubrication, or the bevel gear is well worn or even badly moulded, as the later ones were made in worn moulds, resulting in the fine standard of finish required, not being met. Regrettably I don't think new bevels are made for the Portescap any more.

 

Hope these notes help, getting the gears is easy in 7mm, but 4mm is a problem for higher standard transmissions, they are going to be costly, not much short of the 7mm versions, and most 4mm modellers will not like spending 150 quid plus on a transmission and motor.

 

Stephen..

[bertiedog]

The page shown is from the 850+ plus page HPC catalogue, which is available free on line as a PDF, and is shown here for reference purposes only, no infringement of HPC copyright is intended, or any sales purpose whatsoever.

 

The smallest of the .04mod crossed helical gears are small enough for 4mm uses, and have 3mm bores, which could be sleeved for smaller or reamed out to 1/8th or bored to 1/8th.

 

Stephen.