Lifelike SW9 Loksound installation (N scale)

[Jim Starbuck]

Thanks for the offer Daniel. Come to think of it I have an Arnold mech in the parts stash. I’ll check out the blocks to see if they’ll work.
I’m going to run this at RPM Chicagoland next week then I might tear it down and rework the worms using the small diameter brass ones I have on hand. It actually runs pretty well as is although it has an annoying shudder very briefly from dead stop until the worm spins up and finds center.

[Lemosteam]

"It actually runs pretty well as is although it has an annoying shudder very briefly from dead stop until the worm spins up and finds center."

I did not mention this earlier in the thread, but I was going to say that the wire worm has a lot of backlash (gap in mesh) as shown in your image. This is likely the culprit to what you describe above, so if you can find a better mesh worm gear, or a spring with a larger wire diameter it should go away or get substantially reduced.  This would be really apparent when shuttling from forward to reverse as well.

[MK]

Anyway to put that worm in a vise or C-clamp and squeeze it a little to close the gap?  Don't know the material so don't know if you can set some permanent deformation to reduce it.

[peteski]

Anyway to put that worm in a vise or C-clamp and squeeze it a little to close the gap?  Don't know the material so don't know if you can set some permanent deformation to reduce it.

But doing that would change the "module" of the spring coils (which appears to be correct as-is).  John is correct - in order to  eliminate the lash the spring woudl have to be formed from a thicker wire.  Which would also be beneficial, making the spring "worm" stiffer.

[MK]

But doing that would change the "module" of the spring coils (which appears to be correct as-is).  John is correct - in order to  eliminate the lash the spring woudl have to be formed from a thicker wire.  Which would also be beneficial, making the spring "worm" stiffer.

So what?  We're using the worm as a drive screw and not an actual spring.  And  the strength needed for this purpos is overkill so who cares about its Young's Modulus?

[peteski]

So what?  We're using the worm as a drive screw and not an actual spring.  And  the strength needed for this purpos is overkill so who cares about its Young's Modulus?

The gear and worm need to have a matching Young's Modulus number teeth pitch or module for them to mesh properly.  Sure you can fudge things, but it would be good to have a well designed mechanism.  I properly designed worm drive, the worm meshes with more than 1 tooth of the worm gear at  a time.  That way there is solid transfer of force and minimal lash.

If you compressed the spring "worm" like you propose, the compressed spring loops might (will) jam against the other teeth of the worm gear.

EDIT: I misunderstood MK's post. He is talking about "squishing" the worm gear to "fatten the teeth". I still don't think that is a good idea (even if one could do that easily on a double gear). Such process would also likely increase the diameter of the squished gear.

[MK]

The gear and worm need to have a matching Young's Modulus number for them to mesh properly.  Sure you can fudge things, but it would be good to have a well designed mechanism.  I properly designed worm drive, the worm meshes with more than 1 tooth of the worm gear at  a time.  That way there is solid transfer of force and minimal lash.

If you compressed the spring "worm" like you propose, the compressed spring loops might (will) jam against the other teeth of the worm gear.

Huh?  Young's Modulus is the relationship between stress and strain of a particular material.  It has nothing to do with gear mesh.  If two gears have to have similar, not even matching, Young's modulus then there will be no such thing as a metal gear driving a plastic one or vice versa.  The Young's Modulus of metal and plastic is drastically disproportionate.  And I believe gear backlash is not dependent on how many tooth or teeth are meshed.  I'll have to check my text books on that.

My proposal to squeeze the worm is to create slight plastic deformation to reduce the distance between each "gear" of the worm, thus reducing the gap and back lash.  The thickness of the wire used to form the worm also comes into play for back lash reduction as you have mentioned.

[peteski]

Huh?  Young's Modulus is the relationship between stress and strain of a particular material.  It has nothing to do with gear mesh.  If two gears have to have similar, not even matching, Young's modulus then there will be no such thing as a metal gear driving a plastic one or vice versa.  The Young's Modulus of metal and plastic is drastically disproportionate.  And I believe gear backlash is not dependent on how many tooth or teeth are meshed.  I'll have to check my text books on that.

My proposal to squeeze the worm is to create slight plastic deformation to reduce the distance between each "gear" of the worm, thus reducing the gap and back lash.  The thickness of the wire used to form the worm also comes into play for back lash reduction as you have mentioned.

Geez, I just got up right before I read your post and you confused the heck out of me. I was talking about the pitch of the gear's teeth (the distance between the teeth, and you went Young's Modulus on me. That name seemed strange, but I thought that it might have meant the same thing I was talking about.  So just to clarify (and I'll correct my post), I was taking about the spacing of the teeth (their pitch, or module, or modulus of a gear).  I'm awake now - sorry. 

[MK]

Geez, I just got up right before I read your post and you confused the heck out of me. I was talking about the pitch of the gear's teeth (the distance between the teeth, and you went Young's Modulus on me. That name seemed strange, but I thought that it might have meant the same thing I was talking about.  So just to clarify (and I'll correct my post), I was taking about the spacing of the teeth (their pitch, or module, or modulus of a gear).  I'm awake now - sorry. 

Ohhhhh!  Then I must apologize.  I should have known you were referring to the gear's module but since you said Young's Modulus specifically in your post I was wondering "What the????"    See what happens when two  s try to out  the other  on TRW????   

EDIT: I misunderstood MK's post. He is talking about "squishing" the worm gear to "fatten the teeth". I still don't think that is a good idea (even if one could do that easily on a double gear). Such process would also likely increase the diameter of the squished gear.

BTW, you still are missing part of the point I'm trying to make by suggesting squishing the worm gear.  It is not to fatten the teeth or change the worms diameter.  It basically changes the pitch of the worm to better match the plastic gear to lessen the gap that causes back lash.

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The diameter of the wire that forms the worm will not change in the gentle squishing.  I'm not saying mash the two ends together in an arbor press.    To look at it in a different way, you are changing the spring constant while keeping everything else the same.  In other words, you are making the spring weaker by making the coils closer together.  In John's picture above, the coils are apart a little too much.  I'm just suggesting getting them closer together for a better fit between the teeth.

Engineering Mechanics in a DCC/Electronics forum.  I love TRW!   

[peteski]

Ohhhhh!  Then I must apologize.  I should have known you were referring to the gear's module but since you said Young's Modulus specifically in your post I was wondering "What the????"    See what happens when two  s try to out  the other  on TRW????   

BTW, you still are missing part of the point I'm trying to make by suggesting squishing the worm gear.  It is not to fatten the teeth or change the worms diameter.  It basically changes the pitch of the worm to better match the plastic gear to lessen the gap that causes back lash.

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The diameter of the wire that forms the worm will not change.  To look at it in a different way, you are changing the spring constant while keeping everything else the same.  In other words, you are making the spring weaker by making the coils closer together.  In John's picture above, the coils are apart a little too much.  I'm just suggesting getting them closer together for a better fit between the teeth.

Engineering Mechanics in a DCC/Electronics forum.  I love TRW!   

LOL!  Good think I wasn't drinking anything when I read your post - I would have spit it out laughing!   

I still say your squishing idea would not work the way you think.  Even if we could put the gear in a press and squish it, the teeth would get a bit fatter, but the entire squished gear would also increase in diameter.

You could do an experiment:  Using some soft material (like butter, pudding, or something like that) sculpt a gear-shape on a flat surface (like a kitchen cutting board). Then take something flat and transparent (small pane of glass would be ideal) place it on top of that sculpture and press it down to squish it.  You will notice that as you are squishing it, the teeth will get thicker and the entire gear will get larger. At least that is the "Peteski logic". 

[MK]

Hey Peteski, what is your phone number?  My wife wants to talk to you.  Something about wasted butter and a messed up cutting board.   

I know what you're saying but look at that picture.  There's so much space that the increased in diameter is negligible given how little we are going to squish it.  For all practical purposes the diameter is the same.

As for the thickness of the "teeth", i.e., the cross sectional diameter of the wire used to form the spring, that does not change unless you compress it beyond its plastic limitation.  For some stupid reason I still remember that factoid from engineering school many years later.  I must have been paying attention that day or wasn't drinking the night before!    So the teeth will not get fatter.

Dang it Peteski, now you're going to make me find my engineering text books and actually read through them...again...years later!   

We'll discuss more at Winter Fest...

Now back to your regularly scheduled thread.... 

[peteski]

Hey Peteski, what is your phone number?  My wife wants to talk to you.  Something about wasted butter and a messed up cutting board.   

I know what you're saying but look at that picture.  There's so much space that the increased in diameter is negligible given how little we are going to squish it.  For all practical purposes the diameter is the same.

As for the thickness of the "teeth", i.e., the cross sectional diameter of the wire used to form the spring, that does not change unless you compress it beyond its plastic limitation.  For some stupid reason I still remember that factoid from engineering school many years later.  I must have been paying attention that day or wasn't drinking the night before!    So the teeth will not get fatter.

Dang it Peteski, now you're going to make me find my engineering text books and actually read through them...again...years later!   

We'll discuss more at Winter Fest...

Now back to your regularly scheduled thread.... 

LOL! 
I guess we still have a misunderstanding.  When talking about the spring "worm" I thought you wanted to permanently compress the spring slightly, not to increase the diameter of the wire, but to decrease the distance between the turns of that spring's coils.  That would change the "module" of that spring's coils and jam the worm gear.

But if a new spring was made which had the same distance between each turn of the coil but made from thicker wire (closer in diameter to the width of the worm gear's teeth), that would make a better "worm" with less slop meshing with the worm gear. Plus as an added bonus it would be stiffer, so there would be less flexing without it being contained in some sort of channel.

But you're right, time to go back to the regularly schedule thread. 

[Jim Starbuck]

So I worked out mechanism v2.0 this afternoon.
I ran the engine quite a bit at RPM last weekend and it ran well but this setup is much better.

The Tomix brass worms have a 1mm shaft as does the Bachmann motor. I made motor coupler sleeves for each end by reaming out pieces of brass tubing I had on hand. The worms are press fit and run true without end bearing blocks. They also match the teeth on the stock Lifelike truck gears. I trimmed off the excess length with a Dremel cut off wheel.
The brass worms are slightly larger in diameter than the flexible spring worms resulting in the motor only riding .017” higher in the chassis which I think still affords enough room for the decoder.

This new setup starts much more smoothly and runs very quietly. I put this motor in a spare frame and ran it for a couple hours around the test loop on DC. We’ll see how it does when fully installed.

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Jim

[tehachapifan]

Now you've really got me interested! The previous concept was good, but the spring worms seemed like a potential trouble spot. Are these worms readily available?

[Jim Starbuck]

Now you've really got me interested! The previous concept was good, but the spring worms seemed like a potential trouble spot. Are these worms readily available?

I got these off eBay from PlazaJapan.
There are multiple listings for Tomix worms. I think the only difference is the plastic carriers and the actual brass worms are all the same.

Jim