Possible motor problem with Bachmann Lyn

Rik, just been through my scrap box and I have an old motor unit, with original motor (I think). The case is in pretty poor condition, as you have identified these are brittle, but its yours if you want it. I also have a few other bits from these early Lyns, let me know.
 
JimmyB said:
Rik, just been through my scrap box and I have an old motor unit, with original motor (I think). The case is in pretty poor condition, as you have identified these are brittle, but its yours if you want it. I also have a few other bits from these early Lyns, let me know.
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That would be great. I can always 3d print another clamshell using the dimensions of the old one and then have it as a spare in case this one goes belly-up (polite version ;) ).

Rik
 
JimmyB said:
Rik, just been through my scrap box and I have an old motor unit, with original motor (I think). The case is in pretty poor condition, as you have identified these are brittle, but its yours if you want it. I also have a few other bits from these early Lyns, let me know.
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The power of the forum :clap::clap::clap:
 
Neil Robinson said:
You can easily tell the difference between original and later locos by looking at the wheel cranks. Original cranks were made from fairly thin pressed steel as per part number 81500-63 in Jimmy B's post number 39. Later cranks are more substantial castings. I don't know if early cranks will fit on later axles. May be an issue if a new replacement chassis doesn't include rods and cranks.
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I did a battery conversion many years ago on an original Lyn, so this is "deja vu all over again" for me.

I think the new cranks are because the new motor only drives one axle. I do not think the old, original cranks, are strong enough to handle a single axle drive. My recollection is that the cranks and pins are very flimsy.
 
ge_rik said:
If I redesigned the casings to take a motor with smaller worms, will that improve the amount of torque between worm and worm wheel? My basic knowledge of mechanics suggests this would work.
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Actually, it probably wouldn't make any difference to the performance of the loco, though as you say it will affect the torque between the 2 gears - the smaller one will chew up the worm gear faster than the big one! The gears are still rotating at the same speed.
Think of the worm taking one revolution. Is that just one tooth of the worm gear, or does it move more than one tooth? With a worm setup, the gear ratio (and thus the torque provided to move the wheels,) is a function of how many motor revolutions for 1 revolution of the axle/worm gear. Changing the size of the worm only affects that if it is a different kind of worm.
 
Yep, commonly called "single lead" vs "dual lead" on the worm, a single spiral, vs 2 spirals one within another.

The dual lead halves the gear ratio, but has the added quality of being able to turn the worm gear (axle) and it will turn the motor. Sometimes a benefit, sometimes makes things worse.

The K-27 Bachmann is a dual lead worm.

Greg
 
Fred2179G said:
Actually, it probably wouldn't make any difference to the performance of the loco, though as you say it will affect the torque between the 2 gears - the smaller one will chew up the worm gear faster than the big one! The gears are still rotating at the same speed.
Think of the worm taking one revolution. Is that just one tooth of the worm gear, or does it move more than one tooth? With a worm setup, the gear ratio (and thus the torque provided to move the wheels,) is a function of how many motor revolutions for 1 revolution of the axle/worm gear. Changing the size of the worm only affects that if it is a different kind of worm.
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I agree that the gear ratio will remain the same regardless of the diameter of the worm - one revolution = one tooth advanced (assuming a single start worm). However, my thinking is that the amount of force needed to push each tooth forward would be affected by the diameter of the worm. In effect, the worm is acting like a lever as it pushes a tooth forward. If the worm is twice the diameter, wouldn't it need twice the amount of effort to push on each tooth?

Rik
 
Greg Elmassian said:
Yep, commonly called "single lead" vs "dual lead" on the worm, a single spiral, vs 2 spirals one within another.

The dual lead halves the gear ratio, but has the added quality of being able to turn the worm gear (axle) and it will turn the motor. Sometimes a benefit, sometimes makes things worse.

The K-27 Bachmann is a dual lead worm.

Greg
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Funny thing, I have noticed with the Bachmann K-27 is that you can roll the loco with little resistance with the power off, unlike most other electric locos I own. When this is done the classification lamps (and headlight) will light up, suggesting the loco's electric motor is acting like a dynamo. I wonder what implications this may have for a battery powered loco where this can occur. Max
 
ge_rik said:
I agree that the gear ratio will remain the same regardless of the diameter of the worm - one revolution = one tooth advanced (assuming a single start worm). However, my thinking is that the amount of force needed to push each tooth forward would be affected by the diameter of the worm. In effect, the worm is acting like a lever as it pushes a tooth forward. If the worm is twice the diameter, wouldn't it need twice the amount of effort to push on each tooth?

Rik
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Yes, it'll effectively halve the gear ratio :nod: :nod:
 
Max, this often has huge implications, besides the obvious mechanical ones (stop the loco on a grade and it can roll away on it's own)

The biggest implication is that the BEMF measured can be so big when coasting to a stop (and really all the time) that certain decoders cannot handle it. Often you must turn BEMF compensation off.

I have a USAT Hudson with this issue, and only a Zimo decoder could handle this well.

Greg
 
Greg Elmassian said:
Max, this often has huge implications, besides the obvious mechanical ones (stop the loco on a grade and it can roll away on it's own)

The biggest implication is that the BEMF measured can be so big when coasting to a stop (and really all the time) that certain decoders cannot handle it. Often you must turn BEMF compensation off.

I have a USAT Hudson with this issue, and only a Zimo decoder could handle this well.

Greg
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Mmm, so I wonder which, if any, ESCs could handle it :think::think:
 
Most (all?) ESC's are robust enough, to not be damaged by a large BEMF.
 
ge_rik said:
In effect, the worm is acting like a lever as it pushes a tooth forward. If the worm is twice the diameter, wouldn't it need twice the amount of effort to push on each tooth?
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Oooo my brain hurts. . .

I don't think so, and I think your 'lever' analogy is wrong. The resistance to the worm gear moving is the same whether the worm is big or small.
Think of a brake pedal that you push with your foot. The pressure needed is the same whether you use a big pedal or a small one, or even a big foot!
As long as the worm gear moves the same distance for one rotation of the worm, it doesn't matter what size the worm gear is. The motor must still rotate once for each tooth pushed/pulled.
 
the "resistance" is caused by trying to convert motion from one axis to another, simple physics.

What is in play is the angles of the gears and how the force is directed, the more angle the more force, but resistance in the motion of the gears caused by side forces (friction) plays into this.

So I think strictly I would have to agree, the size of the gears are not important, it's the angle of the teeth, but that is controlled by the size of the gear from a practical perspective.

Greg
 
I would beg to differ.

Let me put it another way. Would you expect to use the same amount of effort to turn a small diameter screw or bolt as you would a large diameter one? The diameter of the screw thread must have a bearing on the amount of torque required, surely?

Rik
 
ge_rik said:
I would beg to differ.

Let me put it another way. Would you expect to use the same amount of effort to turn a small diameter screw or bolt as you would a large diameter one? The diameter of the screw thread must have a bearing on the amount of torque required, surely?

Rik
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Errrrr......

But the 'tooth' of the gear (worm) you are doing the work on, is at right-angles to the circumference..
The profiles of the teeth of the gears will be approximately the same, so the forces will be similar.. :wondering:
I reckon?? :think:

A single start worm, is a single start worm, no matter what diameter it is..

PhilP
 
OK .....
Let's put it like this

If you keep all other variables constant, but just change the major thread radius in this calculator, then the amount of torque required to advance the nut (or worm wheel) increases ......

Screw Worm Gear Gear Axial Force Equation and Calculator

This calculator will determine the axial thrust or load applied per the applied on a screw (worm gear) thread calculate the axial thrust of a nut. Reference: Schaum's Outline Machine Design. Enter desired data within the boxes, calculations should be automatic.
www.engineersedge.com

Rik
 
So I was probably answering the wrong question? :(

AND..............

I got both answers wrong!! :oops::wasntme:

PhilP.
(Sir, as we are not doing exams (again) this year... Will this affect my grade?) :)
 
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