Rhinochugger
Retired Oik
Ah, the worm has turned 
More heat?
More heat?
Possible motor problem with Bachmann Lyn
- Thread starter ge_rik
- Start date
JimmyB
Now retired - trains and fishing
Rik, I think your maths are quite correct.
Neil Robinson
Registered
Get more heat into the worm and flywheel. Use a blowtorch with a fine nozzle. Don't worry about damaging the motor as it's U.S. anyway.
Greg Elmassian
Guest
While your calculations for rotational inertia may be exact, it's meaningless unless you are changing the speed radically on and off and expect the loco to react that way, from 0 to 100 speed in milliseconds.
Inertia has to do with changing speed, and not only do we change speeds slowly, common practice is to ADD MORE rotational inertia to achieve more prototypical operation. (flywheels)
So, reading between the lines, I'm guessing you were unhappy with the performance with the big worms, and I would have to guess pulling power, as your recent mods lower the top speed it seems (but not a lot).
I'm just really curious what was wrong with your first solution, which looked perfect.
Greg
ge_rik
British narrow gauge (esp. Southwold and W&LLR)
No Greg. It's got nothing to do with speed change, it's to do with torque. The larger the worm, the more torque is needed to turn it. That's why the loco performs badly. It slows to a crawl on gradients and on tight curves. Replacing the large worms with smaller diameter ones will improve the torque from the motor shaft.
Rik
Rik
Rhinochugger
Retired Oik
It's all talk 
musket the dog
Registered
Ignoring all the maths and engineering, I suppose the simple way to look at the successfulness of the big worms is to consider why that particular method hasn't really been used on many other models? On paper it looks like a very neat way to get a good sized flywheel and the worm into a compact space. If there really isn't a mechanical downside to having the larger worms in our models, why don't we see it more?
I hope you do manage to find a solution after all this Rik, you've made a fine looking locomotive I look forward to seeing it in useful service on your line.
I hope you do manage to find a solution after all this Rik, you've made a fine looking locomotive I look forward to seeing it in useful service on your line.
maxi-model
UK/US/ROW steam narrow gauge railways 1:1
I suppose an analogy for the large worm gears are the sizeable chainwheels used on track racing bicycles. They require quite prodigious "torque" inputs from the rider to get them moving, or even to change speed (where the track's bankings steep inclines are used to aid) However, they provide the long gear ratios needed to allow prodigious levels of speed to be maintained while still allowing the rider to optimize the use of their power out put, in the near perfect "speed bowl" environment of the track. With a road racing bicycle they are equipped with a wide range of gear ratios (including smaller chainwheels and gear clusters) so the rider can optimise the use of their power output to meet the prevailing conditions rather than applying energy sapping levels of torque to overcome inclines and changes in speed..
Which begs the question - Why is the configuration, as manufactured, so dismal at delivering a usable performance envelope expected in a typical garden railway ? Max
Which begs the question - Why is the configuration, as manufactured, so dismal at delivering a usable performance envelope expected in a typical garden railway ? Max
Rhinochugger
Retired Oik
I remember there was a formula for selecting the gear ratio on your slot car that related to the length of the longest straight on any circuit
............. long time ago, now 
ge_rik
British narrow gauge (esp. Southwold and W&LLR)
I think it's significant that Bachmann have redesigned the mechanism completely. The motor now has a small worm driving an idler which transfers power to the axle. They have put a flywheel on the other end of the motor shaft. The motor used in the new mechanism is identical to the old motor - so it's clearly the large worms which are at fault.
I'm not certain about the maths but intuitively to me it's self evident. The further away from the axis of rotation the force is delivered, the more effort (ie torque) is required.
Rik
ge_rik
British narrow gauge (esp. Southwold and W&LLR)
Rhinochugger
Retired Oik
There's probably a few things that have driven this - 'scuse the pun.
A two-stage gearbox reduces the strain on the gears, thus reducing the chances of stripping the gears, plus a flywheel also helps to reduce the strain on the gearbox when a track-powered loco stutters.
The lack of flywheels in our large scale locos has long surprised me - it's simple enough to do and is entirely beneficial. Bachmann woke up to this solution pretty late, but other manufacturers still persistently ignore it, despite it being used extensively in the smaller scales.
ge_rik
British narrow gauge (esp. Southwold and W&LLR)
I'm wondering if the idler might be to allow for clearance between the motor and the worm wheel. The problem I've encountered with trying to fit a smaller worm is that the can of the motor prevents me from putting the centre of the worm over the centre of the worm wheel - I'll either need to extend the shaft or place an idler between the worm and worm wheel. My engineering capabilities don't extend as far as adding an idler so I might have a go at extending the shaft. I'm having to use copper tube as a reducer on the worm so that is possible.
The modulus of the new gears are 0.5 which means the teeth are smaller than those on the original gears. This makes meshing them a lot trickier - less wiggle room. I've redesigned the casing to bring them a tiny bit closer (0.2mm) but I'm not sure of they are up to the job. I've sent off for another set which are 0.8 Mod so I'm hoping they will make meshing easier.
Rik
Rhinochugger
Retired Oik
Yeah, the theory of the two-stage gearbox is to deal with greater loads - putting one together is an art form.
Apart from the ready-to-run offerings in Bachmann locos, I have two different two-stage gearboxes, but they were both expensive
Greg Elmassian
Guest
Again, while takes more (you choose, torque, energy, horsepower, ergs, etc.) to turn a larger mass, the extra power needed to turn it at constant or slowly changing speeds is minimal between these 2 worms... back to inertia again, only makes a difference if you try to change speeds rapidly, which we do not.
The laws of physics won't be bent to suit an analogy.
So, while you disagree with me, you note that a flywheel has been added to the newer design, again, more rotational mass.
But I'm asking what was wrong with the first solution, and it seems that the current solution is no better. What was the source of the effort to make the change?
But, this may be flogging a dead horse, I asked several times... really all I am curious about is what happened, I have a degree in physics, I don't need a refresher on the laws of kinematics, this stuff I do indeed comprehend.
So I give up my curiosity...
Greg
The laws of physics won't be bent to suit an analogy.
So, while you disagree with me, you note that a flywheel has been added to the newer design, again, more rotational mass.
But I'm asking what was wrong with the first solution, and it seems that the current solution is no better. What was the source of the effort to make the change?
But, this may be flogging a dead horse, I asked several times... really all I am curious about is what happened, I have a degree in physics, I don't need a refresher on the laws of kinematics, this stuff I do indeed comprehend.
So I give up my curiosity...
Greg
ge_rik
British narrow gauge (esp. Southwold and W&LLR)
OK Greg
I wasn't aware that I had disagreed with you.
Unlike you, I don't have a degree in Physics so I can only use my powers of observation and apply a fair degree of common sense. As I have stated previously, I have three of the original Lyn motor blocks and they all perform in the same way. They simply don't have enough power to haul even a modest train up a gradient and visibly slow on tight curves. One of these blocks has been re-motored with a Buhler motor which I assume is better quality than those supplied by Bachmann and yet it too performs in exactly the same way as the other two. The common factor is the mechanism with the large diameter worms. At first I redesigned and 3D printed the motor block housing as the quality of the plastic on the originals is poor. It made no difference to the poor performance - lending even more weight to the idea that the mechanism is at fault.
I don't have the maths to back up my suppositions, but it seems to me that the large worm must be the culprit. It seems obvious to me that the further away from the axis of rotation the force is applied from worm to worm-wheel, the more effort, force, torque (call it what you will) is required. So, if I redesign the gearbox to use a smaller diameter worm - then surely the motor will have to do less work to turn the worm wheel.
This, to my reasoning, would explain why Bachmann have scrapped the original motor block and replaced it with one using a smaller worm.
I am not knowingly bending the laws of physics - I'm merely trying to find a way of explaining myself in layman's terms. As it happens, teachers use analogies all the time - eg using water flow to explain electricity.
Rik
Greg Elmassian
Guest
Wasn't really disagreeing, I apologize if that came across.... just was going back to my original question, and it seems that the motors just don't have enough torque. That's the question I have been asking.
On that topic, the power a motor makes is basically the electrical power it draws. Besides the obvious more voltage applied, and not being current limited, the impedence of the motor is a big factor.
So, I propose the motor is limiting you, unless it is being "starved" for power.
On the subject of inertia:
Yes, you are right about the torque to get the worm moving, but the difference between different worm diameters/weights to keep the worm moving is much less. If there was a huge constant drain in energy, no one would ever use flywheels. All your assertions are true when spinning up or slowing down QUICKLY (and I mean a lot more quickly than your train could ever do, like revving a souped up motorcycle in neutral).
Remember that flywheels are used to "store" energy, and neglecting air friction (not a factor in this case) and neglecting differences in motor bearing friction (not a factor in this case), flywheels store energy losslessly.... so any difference in mass or diameter of the worm makes no difference in this case.
So, the extra weight or size of the worm is not a factor here, only gear ratios, and if there is some extra friction in the gears in one case or the other.
If you would like an analogy or real world example, cars normally have flywheels, attached to the rear of the crankshaft. Racing cars, where very rapid transitions in RPM are needed have lightened flywheels.
I really liked your larger worm setup, because the friction between the gear teeth was spread over a larger area, so that should have had reduced frictional losses.
On the subject of gear diameter:
Also, if you study gear mechanics, (and this is also part of basic physics), when you translate force 90 degrees, you have much more loss (like a car differential), and the larger diameter worm should have less loss.... I won't go into all the vector force diagrams that show this, but in virtually all cases, larger gears have less loss from this situation.
Bottom line, I think checking to see if you are "starving" the motor (current limiting, too low voltage) or just getting a higher torque motor are your possible solutions to better pulling power.
Regards, Greg
On that topic, the power a motor makes is basically the electrical power it draws. Besides the obvious more voltage applied, and not being current limited, the impedence of the motor is a big factor.
So, I propose the motor is limiting you, unless it is being "starved" for power.
On the subject of inertia:
Yes, you are right about the torque to get the worm moving, but the difference between different worm diameters/weights to keep the worm moving is much less. If there was a huge constant drain in energy, no one would ever use flywheels. All your assertions are true when spinning up or slowing down QUICKLY (and I mean a lot more quickly than your train could ever do, like revving a souped up motorcycle in neutral).
Remember that flywheels are used to "store" energy, and neglecting air friction (not a factor in this case) and neglecting differences in motor bearing friction (not a factor in this case), flywheels store energy losslessly.... so any difference in mass or diameter of the worm makes no difference in this case.
So, the extra weight or size of the worm is not a factor here, only gear ratios, and if there is some extra friction in the gears in one case or the other.
If you would like an analogy or real world example, cars normally have flywheels, attached to the rear of the crankshaft. Racing cars, where very rapid transitions in RPM are needed have lightened flywheels.
I really liked your larger worm setup, because the friction between the gear teeth was spread over a larger area, so that should have had reduced frictional losses.
On the subject of gear diameter:
Also, if you study gear mechanics, (and this is also part of basic physics), when you translate force 90 degrees, you have much more loss (like a car differential), and the larger diameter worm should have less loss.... I won't go into all the vector force diagrams that show this, but in virtually all cases, larger gears have less loss from this situation.
Bottom line, I think checking to see if you are "starving" the motor (current limiting, too low voltage) or just getting a higher torque motor are your possible solutions to better pulling power.
Regards, Greg
JimmyB
Now retired - trains and fishing
Greg you may have a physics degree but your mechanical engineering information is incorrect, it has been mentioned a number of times that the larger the worm, the less power output, or correctly torque. I am not going to explain it again, the maths are simple especially, if you have the appropriate degree.
Rik has informed us of what he has done, why he has done it and the result, which speak for themselves. I think the worm size matter is closed.
Rik has informed us of what he has done, why he has done it and the result, which speak for themselves. I think the worm size matter is closed.
Greg Elmassian
Guest
Jimmy, you are confusing gear ratios with what I was talking about, losses.
The gear ratios are a given of course.... although you can have a physical worm with the same final gear ratio in different sizes. The gear ratio is the combination of both the worm and worm gear... not the worm alone.
Again, we are discussing things way beyond the simple gear ratio....
Rik is talking about inertial losses due to the effect of diameter (and of course mass), which do exist, although they manifest mostly during quick acceleration and deceleration.
Honestly, I don't think you are reading my post at all, or really trying to understand.
Besides stating how things work, and doing Rik the courtesy of addressing exactly what he is asking, I'm trying to be helpful to explain why the pulling power is not better.
The electrical investigation, i.e. the power delivered/consumed to the motor is in question I believe, as it's torque output.
Greg
The gear ratios are a given of course.... although you can have a physical worm with the same final gear ratio in different sizes. The gear ratio is the combination of both the worm and worm gear... not the worm alone.
Again, we are discussing things way beyond the simple gear ratio....
Rik is talking about inertial losses due to the effect of diameter (and of course mass), which do exist, although they manifest mostly during quick acceleration and deceleration.
Honestly, I don't think you are reading my post at all, or really trying to understand.
Besides stating how things work, and doing Rik the courtesy of addressing exactly what he is asking, I'm trying to be helpful to explain why the pulling power is not better.
The electrical investigation, i.e. the power delivered/consumed to the motor is in question I believe, as it's torque output.
Greg
ge_rik
British narrow gauge (esp. Southwold and W&LLR)
Hi Greg
I've tried increasing the number of li-ion cells from three to four, thereby increasing the nominal voltage of the pack from 11.1v to 14.8v and it made negligible difference - the most noticeable being that the motor block was tangibly warmer, nay hotter, after I had tried testing it.
I agree that my use of rotational inertia is probably a red herring, but that's because I'm not a physicist and so was trying to find some mathematical means of explaining what I was experiencing.
To help inform my understanding, I asked for clarification on an Engineering forum. To be honest, other than a gut feeling, I had no real certainty that the contributors would support or confound my implicit theory. The resultant response seems to suggest that the torque (Mw) required to turn the worm is directly proportional to the radius of the worm Rw
engineering.stackexchange.com
This is persuasive enough for me to continue with my experiments. As indicated above, the teeth on the new gears are very small and so it's difficult to get them to mesh reliably - and even when/if I do I think they will probably wear quickly given the loads I'll be placing on them, I've sent off for larger modulus gears and so will have to wait for them to arrive before I can redesign the gearbox. Life would have been so much easier if I could have found smaller worms which mesh directly with the original worm wheels.
Given that I have three of these mechanisms, I'm determined to find a way to get them all working.
Rik
I've tried increasing the number of li-ion cells from three to four, thereby increasing the nominal voltage of the pack from 11.1v to 14.8v and it made negligible difference - the most noticeable being that the motor block was tangibly warmer, nay hotter, after I had tried testing it.
I agree that my use of rotational inertia is probably a red herring, but that's because I'm not a physicist and so was trying to find some mathematical means of explaining what I was experiencing.
To help inform my understanding, I asked for clarification on an Engineering forum. To be honest, other than a gut feeling, I had no real certainty that the contributors would support or confound my implicit theory. The resultant response seems to suggest that the torque (Mw) required to turn the worm is directly proportional to the radius of the worm Rw
How does the diameter of a worm gear affect the amount of force needed to turn it
Can anyone help inform a discussion I'm having with fellow modellers on a model railway forum? I have a locomotive powered by an electric motor turning a 20mm diameter worm gear meshing with a spur...
This is persuasive enough for me to continue with my experiments. As indicated above, the teeth on the new gears are very small and so it's difficult to get them to mesh reliably - and even when/if I do I think they will probably wear quickly given the loads I'll be placing on them, I've sent off for larger modulus gears and so will have to wait for them to arrive before I can redesign the gearbox. Life would have been so much easier if I could have found smaller worms which mesh directly with the original worm wheels.
Given that I have three of these mechanisms, I'm determined to find a way to get them all working.
Rik
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