Belt drive: through 90 degrees

[Izzy]

Which I have had to do several times over the years when using hollow-ground (brass) worm & wheel drives.......

 

The 12 v. axial-motor and oil-filled planetary gearbox (135-1 ratio) unit has roller bearings on its 3/16" dia. output shaft, so I doubt that lateral forces from the belt will be too much of an issue.

I particularly wanted to have a driveline that would freewheel/coast (if only a litle) without applied power and be quieter than right-angle gearsets (bevel or worm varieties).

 

If you have a high ratio gear reduction of the order you have indicated, even if it's spur gears, then you won't get a free-wheeling effect because of the mechanical loading resulting from the mechanical advantage the high reduction provides.

 

The only way to achieve that is with a fairly low reduction, either through an all spur/bevel gear arrangement, or as Slaters have done for many years, and now Comet, use low ratio crossed helicals with spur gears.

 

However this is not to say ordinary higher ratio worm gear arrangements can't be just as quiet, just that you must use well made/matched gears correctly mated.

 

Izzy  

 

 

 

 

 

If you just want a quiet smooth transmission then I suggest you try a combination of a slightly lower motor/gearhead combo with a crossed helical gearbox. I used such a combination some years ago in a series of S gauge locos I built. Faulhaber with 59-1 head mated to Slaters 3-1 crossed helical final drive.

[Arthur]

Thanks Howard that's clear enough. So, essentially, you can have a symmetrical bi directional drive, but at the cost of poor efficiency.

[Grovenor]

Howard.

Your diagram is making a fundamental assumption that does not apply to the application in models such as the Lonestar locos, ie the use of grooved pulleys.

Since the maximum possible reduction ratio is required, the input just runs on the motor shaft whilst the output side runs on a wide drum on the axle close to the wheel tread diameter. There is no way for the belt to come off and on reversal the position on the motor shaft changes to minimise the length of that part of the belt in tension. The drive works equally well in forward or reverse, in fact there is no way with this arrangement to distiguish forward from reverse.

Keith

[BR60103]

Shortliner mentioned Athearn.  They used what they called the Hi-F drive in almost everything after they went plastic in the mid-50s.  No pulleys, but a wire extension from the double-ended motor and wheels on axles that were plastic cylinders almost up to the wheel diameter. The shaft ran in a metal post with a hole for a bearing. I think the locos used were the F7, GP9, RDC and the Hustler. The drives were very quiet. One comment was that the shivering looked prototypical in the RDC. The rubber bands tended to take up a rearward position while running and shifted when direction was changed.

In a Model Railroader spped survey, the Hustler won top prize at a scale 400 mph.

 

The system may be found in some Lionel HO (made by Athearn), although they had a diagram showing a rubber band from the motor to a double-ended worm shaft.

 

Some Japanese brass units (I know Suydam's interurbans) had a mechanism with a circular coiled spring. There are some in my storage.

[HAB]

Howard.

Your diagram is making a fundamental assumption that does not apply to the application in models such as the Lonestar locos, ie the use of grooved pulleys.

Since the maximum possible reduction ratio is required, the input just runs on the motor shaft whilst the output side runs on a wide drum on the axle close to the wheel tread diameter. There is no way for the belt to come off and on reversal the position on the motor shaft changes to minimise the length of that part of the belt in tension. The drive works equally well in forward or reverse, in fact there is no way with this arrangement to distiguish forward from reverse.

Keith

 

 

Hello Keith,

 

Thanks for the clarification, but I do fully understand what is being described - I was merely trying to show (as a principle) the reason why ANY reversible right angle belt drive must be very inefficient. In the cases you (and the others) have described, the belt runs across the plain shaft / drum at an angle and - as you imply - that angle reverses when the drive reverses for the reasons I have tried to illustrate. BUT it is the belt running at an angle that causes a large amount of rolling frictional loss.  (The efficiency falls off in proportion to the square of the cosine of the angle, and on a small diameter pulley (shaft) the angle is considerable). Worse, very small pulleys are quite inefficient to start with.

 

Debs was asking for for a "coastable" drive at relatively high reduction (one assumes for an industrial loco).  This implies a very high efficiency and - I will say it again - a right angled reversible belt drive can never be that efficient.

 

Note though that I would agree that it might be quite effective AND probably better that the average "model railway" worm and wheel - which is feint praise indeed. And worms and wheels are something that I have not used for thirty years now (RTR conversions excepted!)

 

Of course, I am hoping that one of the proponents of belt drive will prove two hundred years of collective experience of belt drives wrong and actually build a coastable 0-6-0 industrial loco so powered.  When that happens I will show my bare derrière on the Town Hall Steps, on Saturday morning.  (and I volunteer yourself to sell the tickets Keith!)  

 

(Edited for spilling mistook)

 

Best wishes,

[Debs.]

Thank you to all, for the interesting and thought provoking contributions.

 

I`ll do some more research and post again with a progress report.

[Horsetan]

....worms and wheels are something that I have not used for thirty years now ....,

At last! Someone who saw the light!!

[Tigermoth]

I use the following system on all my NG locomotives, not only is it deadly silent but extremely reliable with no belt slip whatsoever. Firstly a double ended Faulhaber motor with a 22 mm dia flywheel on the back, then into a second flywheel 36 mm dia next to a 7 mm pulley, belt drive down to a 24 mm pulley and cardan into a O gauge Roxey mouldings 26:1 gearbox. Can't hear a thing with an 89 to 1 ratio. I have tryed to find a fault with this system but there's nothing, as for the belt slip thats down to plain common sense, it must not be too tight or too loose but there is a lot of tolerance it is a forgiving system. Lastly it works well for all kinds of CD and cassette players so why shoudn't it work in locomotives even heavy ones such as mine, all in brass. As for worm gearboxes, it all a question of alignment and quality. But having said all that i only go along at 5 mph just like the real thing !

[Baby Deltic]

If you don't want to use a worm, and belts are suspect, you could always consider bevel gears or a pair of 90 degree helical gears.

 

[Tigermoth]

one thing to be carefull with is to be sure that you use rubber belts, i have come across to different types of belt, one is matt black which is ok the other is shiny black which is less good .