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Since a socking great electric motor and gear train has no real business inside a steam loco boiler or tender, I have no prior position on where the mechanism is to be positioned, nor which drive is to be preferred. The sight and performance of the model in action should decide. Provided the eye perceives the loco to be doing the pulling, and a full size load can be hauled, and the appearance of the model has no compromises realting to the drive installation then all is well.

But practically, one can usually perceive where the drive is coming from. Steam loco wheels should sometimes slip a little, and if there is any slack (even the slightest) between loco and tender, the loco should extend the slack in pulling away forward. That makes loco drive my strong preference, especially as present technique will deliver more than enough traction for realistic train loads to be hauled. But if a desireable model type was produced tender drive only as a necesity to prevent the mechanism being on view , and the manufacturer had taken the trouble to make the loco look right dynamically when running, I would have no objection to the purchase.
 

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It is all about performance. A good reliable drive - and like John it is smooth low speed performance that I look at particularly as the biggest contribution to realistic motion - is what matters above all else.

There are however two beneficial aspects of putting the drive into steam locos rather than their tenders that strike me as significant; but possibly of more significance in the UK than elsewhere in the world.

The first relates to the need to loco power tank engines; no prospect of using a tender to power these, and during most of the century plus of steam dominated operation on the UK's railways circa one third of locos in service were of the tank type. So a realistic UK model railway operation needs a significant number of tank types. Thus the RTR manufacturer looking to provide a representative UK range is necessarily locked into loco powering a goodly proportion of their loco product.

Secondly, the very small size of tenders with extremely open underframes found behind many smaller UK loco types. It can be quite as difficult getting a well concealed drive into a tender as into the loco; quite often putting the best possible implementation of the drive in the tender means more unavoidable intrusion of the mechanism into view than the equivalent best drive layout design in the loco.

These aspects say to me, standardise on the drive type that is necessary, and put all the development resource into making this as good and as well concealed as possible. Consistently tackling a problem with a single approach tends to yield the dividend of experience in the longer term, the design team become well versed in the possibilities for getting the best result.

Certainly as far as UK RTR steam loco model productions in OO are concerned, the last dozen years of new loco driven steam model introductions have varied from adequate to very good. The choice of motors and gearing have been fine overall for power, smoothness and quietness; there have been detail design deficiencies, now largely corrected (and readily owner rectified with small modifications), and a lack of weight in quite a few models robbing them of the traction which the motor and gear train had the potential to deliver if only there was enough weight on the driven wheels (again the owner can rectify this, this time with lumps of lead!).
 

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The design of the first 'Silver Seal' units in the class 47 and 9F with all three axles driven were indeed based on a Fleischmann design, and of decent construction, performed quietly and smoothly, and were a significant advance on Triang-Hornby's XO4 chassis and motor bogies, both with worm gears driving axle mounted pinions. Had T-H maintained or even - imagine this - used the new motor as the base for further improvements in drive refinement then I doubt that much of the UK prejudice against tender drive would exist.

There would still though be the difficulty of low tender bodies with very open underframes being heavily compromised by having a tender drive inside them, and there were a lot of such antiques hanging about in UK service into the last decade of steam. Even a can motor in the tender with shaft drive to the loco is far from easy with very open cabs on older types. The fine scale contingent resort to a hard to see 0.5 thick wire as the drive shaft: good for a handbuilt model in the owner or commisioner's care, not a real option for plastic bodied RTR for the general market. So loco drive with motor in loco is the best option in RTR - for the UK. With modern small can motors and mutiple plastic gear train transmission lines, concealment is not a significant problem now.
 

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QUOTE (Digimaks @ 23 Feb 2012, 06:26) <{POST_SNAPBACK}>... About topic - tender vs loco drive. I think there are advantages and disadvantages depending on locomotive type.
When I first got tender driven locomotive, I thought it would derail often because it is being pushed. However this never happened.
Plus there are some locomotives that has boiler suspended high above wheels and frame, that you can see under it. There is no way you would put any sort of gear or shaft, as well as taking it apart would be such a pain.
But Tender is just a box where you don't have to worry about space to fit.
Actually your attached picture of the Dewitt-Clinton illustrates the tender drive problem very well. Whatever the tender that original loco had - I guarantee you without knowing the prototype - there would be clear daylight through the tender wheels and underframe instead of a solid box nearly down to the rail with wheels on the sides. It just looks awful. Whereas a can micromotor and precision gear train could now be manufactured at an acceptable price to be completely concealed in that loco body as it stands. And then the really lightweight nature of the tender would be revealed, and the model would look much more like the prototype.

Tender drive basically just isn't necessary any more. Provided there is some physical connection between the boiler and the frame - and the laws of physics ensure compliance on this one - then there is a route for a driveline between a motor in the boiler and an axle. A good example among UK classes is the 9F, known as the 'spaceship' for the large airspace between boiler underside and frame tops, extending from firebox to smokebox. A drive can be routed through the firebox or smokebox, or just hidden behind some motion tackle as Bachmann have done; good design of the two RTR 9F models with loco drive makes service access really simple, undo screw(Hornby) two screws (Bachmann), lift body off chassis. With competent design, there is no problem at all.

Some of the striong feeling against tender drive in the UK, as I have mentioned already, is because such poor designs were typically used. Hornby, after a decent start with a Fleischmann motor design, put it through many cost down cycles to get it down to a matching level of awfulness to the bogie motor that Lima used; with the results that MMAD so well describes, and to which I fully subscribe. We really don't want anything like that again in OO, not even a high grade well engineered type as used on good quality European HO: it now simply isn't necessary...
 
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