Concept for gear drive vertical boiler Shay

[jugtown modeler]

For a basic review of concept viability a few basic dimensions would help.  What is the boiler OD and height and what is the offset in the frame?  The boiler dimensions will dictate the maximum motor size and the offset will suggest, at least in part, the room for gears. 

Thanks for the reply. Appreciate your input. For a novice and to minimize my own ignorance... Can you help clarify what you mean by the offset in the frame?
As for the boiler, I was going to go with an inside diameter that would accommodate the smallest useable motor I could find. As others have powered Nn3 with the above Nigel Lawton, 6mm motor, I may start with that. But believe the boiler diameter to be 36-40"+. May be some flexibility here as exact dimensions hard to find.

A double worm would afford the necessary gear reduction for a small motor without using a planetary reduction and because of the vertical motor position, would provide the two shaft direction changes that this requires. 

Glad to hear the planetary is not needed. I suspected but was not sure.  Was hoping the pinion/crown ratio also offers reduction.  Just occurred to me though, I can't visualize the worm gear motions at each end. Can you clarify "two shaft direction changes that this requires." If this is a single shaft, are the 2 worms oriented the same direction or reversed? (Or, are you saying I need 2 separate shafts?)

The motor could be as large as just under the boiler diameter and if there's extra room, the motor could be further offset within the boiler for even a little more gear room.  With those numbers I could quickly figure if there was even a prayer and then more final details could be pursued.  If the basics aren't there...   And finally, assume that the necessary parts, if not standards, could be produced if the basics lay out OK.

Apologies for not following. This is an education for me. I can guess what the offset is but that won't help.  Offset from center?  I was/am/are under the ASSumption that the red crown gear could be centered along with the shaft and worm gears and the vertical motor pinion. Is this way off base?

-Steve

[narrowminded]

Thanks for the reply. Appreciate your input. For a novice and to minimize my own ignorance... Can you help clarify what you mean by the offset in the frame?
As for the boiler, I was going to go with an inside diameter that would accommodate the smallest useable motor I could find. As others have powered Nn3 with the above Nigel Lawton, 6mm motor, I may start with that. But believe the boiler diameter to be 36-40"+. May be some flexibility here as exact dimensions hard to find.

Glad to hear the planetary is not needed. I suspected but was not sure.  Was hoping the pinion/crown ratio also offers reduction.  Just occurred to me though, I can't visualize the worm gear motions at each end. Can you clarify "two shaft direction changes that this requires." If this is a single shaft, are the 2 worms oriented the same direction or reversed? (Or, are you saying I need 2 separate shafts?)

Apologies for not following. This is an education for me. I can guess what the offset is but that won't help.  Offset from center?  I was/am/are under the ASSumption that the red crown gear could be centered along with the shaft and worm gears and the vertical motor pinion. Is this way off base?

-Steve

I was thinking that the boiler is offset right or left in the frame.  Maybe I'm the one that's flaking out here.   Even if it isn't, there may be room to offset shafts to afford the necessary space.  Two 12:1 worms (as small as you should make a gear) will give you 12 x 12= 144:1.  Yes, some will make 10 tooth or maybe even 8 tooth but the mesh becomes pretty bad once under 12 teeth.  In standard gear offerings from stock gear manufacturers (Boston Gear?) you won't find less than 12 tooth and maybe even 14, depending.  More can be read about that with a search for gear design principles.

As far as two direction changes, I'm referring to the 90 degree direction change from the motor shaft to the layshaft and then the 90 degree change from the layshaft to the wheel axles.  And the pinion gear to the bevel gear could afford some gear reduction but nowhere near as much as can be accomplished with a wormset in much less space.  A pinion to a bevel might get you to a 2:1 or so reduction where a worm could easily be 12:1 or more.  That's the reduction that would allow you to use two worms to accomplish a 140:1 or so reduction.  That can be handy if you're trying to use really tiny motors as they tend to make their power with RPM's rather than brute force (torque).  Remember the HP formula: Torque x RPM / 5252 = HP.  With little torque but a lot of RPM's you can still have decent power but now need big gear reductions to get it into a useable RPM range.  Play with that formula and you'll see what happens.