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Post by cplmickey on Jun 20, 2011 11:47:18 GMT
I've recently bought a Simplex and although it runs well it needs a little work. The rear water tank has a good leak on it and in removing the tank I've had to remove a seriously heavy weight from the cab. Not wanting to question the original owners decision but does it really need any additional weight. Our track is quite long so I don't want to load her up unnecessarily.
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russell
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Post by russell on Jun 20, 2011 12:41:37 GMT
I guess it depends on the weight you intend to pull. I'd try leaving it out and see how it runs .
Russell.
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Post by baggo on Jun 20, 2011 12:48:31 GMT
The weight was possibly to move the centre of gravity of the loco to the centre axle rather than increase adhesion. Unfortunately, a lot of locos tend to be very front heavy due to the weight of the cylinders etc and you finish up with having to have much stronger springs on the front axle to compensate. Ideally, you want the same weight on all the driving wheels.
Adding extra weight to a loco is of benefit if you intend pulling large loads. The tractive effort is usually a lot more than the weight of the loco can transmit to the rails with slipping as a result. Ideally, the weight of the loco wants to be about 4 times the tractive effort.
John
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Post by cplmickey on Jun 21, 2011 18:17:07 GMT
Hadn't thought about balance. I'll check that out as soon as I've repaired the tank. If the existing weight is too much I'll just add enough to balance the loco and then try her out to see if the traction is ok.
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davidm
Seasoned Member
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Post by davidm on Jun 22, 2011 17:04:37 GMT
My Simplex is more or less to the drawings, with no extra weight added. It's a bit light footed on greasy track, for example getting away from the steaming bay area on a slight uphill, and sometimes if I'm a bit heavy handed on a 1 in 80, but otherwise it's fine.
David
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Post by cplmickey on Jul 22, 2011 19:27:59 GMT
A quick update on this topic. When I completed the repairs I didn't put the weight back in place. I have had 2 very successful sessions at the track and even with passengers I had no slipping at all, in fact I've been very pleased with it. I'm still going to look at the balance of the loco but hoping that any additional weight needed isn't anywhere as much as the one I've taken off as the reduced water usage is really noticeable which suggests she's running more happily without it.
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Post by peterseager on Jul 23, 2011 9:07:33 GMT
I assume you have taken into account the "good leak" that was on the rear tank? From my experience with Simplex I am surprised the the weight made a notable difference to water consumption. Now notching back, thats another story, far better coal and water consumption measured in extra laps of our 440 ft track before firing.
Peter
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Post by cplmickey on Jul 24, 2011 10:40:35 GMT
Nail on head Peter. I had taken account of the leak as I'd used the loco beforehand. However, I have improved my driving skills including notching back which I understand has a significant impact on coal and water useage. Having said that the weight is an incredible 8 pounds - over half a stone - so not small.
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Post by cplmickey on Jan 5, 2012 12:47:12 GMT
A quick update on this one. I still haven't added any weight back on the loco and generally it's fine although it slipped a little getting away from the station on New Years Day though with 3 adults and 2 little ones on board. To balance the loco better requires around 4 pounds at the cab, about half of what was there. I plan to add that which should assist slightly with adhesion if all wheels have the same weight on them.
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Post by drjohn on Jan 6, 2012 1:50:55 GMT
Hi cplmickey
Friction on non distorting surfaces (ie wheels and rails) is independent of the surface area of contact - good old rule of physics, so whether all the weight is on the front wheels or evenly distributed will not make any difference to the traction.
DJ
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russell
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Post by russell on Jan 6, 2012 16:11:47 GMT
Friction on non distorting surfaces (ie wheels and rails) is independent of the surface area of contact - good old rule of physics, so whether all the weight is on the front wheels or evenly distributed will not make any difference to the traction. Correct - although the extra weight will increase traction. [Pedantic mode on] If the wheels and rails are non distorting the area of contact will be zero and the pressure infinite![Pedantic mode off] Russell. |
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Post by johnmiller on Jan 7, 2012 20:08:14 GMT
Friction on non distorting surfaces (ie wheels and rails) is independent of the surface area of contact - good old rule of physics, so whether all the weight is on the front wheels or evenly distributed will not make any difference to the traction. Correct - although the extra weight will increase traction. [Pedantic mode on] If the wheels and rails are non distorting the area of contact will be zero and the pressure infinite![Pedantic mode off] Russell. [even more pedantic mode on] Even if the wheels and rails were non distorting - which of course they're not - the area of contact is not even close to zero as the individual molecules in the wheels tend to fit between the molecules of the rails (in the absence of any hydrodynamic film) in such a way as to influence the value of the coeficient of friction depending on the spec. of the materials involved. [even more pedantic mode off] |
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Post by peterseager on Jan 7, 2012 20:17:31 GMT
But the weight has to be distributed evenly to deliver maximum tractive effort through all the coupled wheels else the lightest loaded will start slipping first.
Peter
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Post by johnmiller on Jan 7, 2012 20:33:35 GMT
But the weight has to be distributed evenly to deliver maximum tractive effort through all the coupled wheels else the lightest loaded will start slipping first. Peter How can any wheel slip before the others when they are coupled together with connecting rods and rigid axles? One of the functions of the connecting rod is to provide a self stabilising distribution of tractive effort between each wheel appropriate to the friction parameters existing at that wheel. So even if one wheel was taking 50 % of the weight and the remaining five wheels were taking 10 % 0f the weight each, the tractive effort of the locomotive would be the same as if all wheels were bearing an equal share of the weight. All other parameters being the same. |
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russell
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Post by russell on Jan 9, 2012 19:12:19 GMT
[even more pedantic mode on] Even if the wheels and rails were non distorting - which of course they're not - the area of contact is not even close to zero as the individual molecules in the wheels tend to fit between the molecules of the rails (in the absence of any hydrodynamic film) in such a way as to influence the value of the coeficient of friction depending on the spec. of the materials involved. [even more pedantic mode off] But atoms and molecules are nearly all empty space so how will we define contact? Contact between the nuclei? If that occurs the iron atoms will fuse to become tellurium. I'll leave it as an exercise for the reader to work out the pressure required ;D Russell. |
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Post by johnmiller on Jan 10, 2012 1:24:06 GMT
But atoms and molecules are nearly all empty space so how will we define contact? Contact between the nuclei? If that occurs the iron atoms will fuse to become tellurium. I'll leave it as an exercise for the reader to work out the pressure required ;D Russell. Well no, I would not define contact as contact between the nuclei, because that would require - as you correctly imply - a very large force. I would suggest that a simplified definition would be .... When the outer electron shells of the component atoms of the molecules of the wheels and rails approach coincidence or - in other words - they begin to interfere with each other. After all, it is the depth of engagement between the irregular surfaces described by the electron outer shells of the molecules of the wheels and rails, that affects the value of the coefficient of friction.....  Read more: modeleng.proboards.com/index.cgi#ixzz1j0pbz4Sp |
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Post by alanstepney on Jan 10, 2012 7:51:51 GMT
We are moving away from model engineering, into esoteric areas, so please can we get back to the topic.
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Post by fostergp6nhp on Jan 10, 2012 19:42:54 GMT
We are moving away from model engineering, into esoteric areas, so please can we get back to the topic. Well said that man. |
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russell
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Post by russell on Jan 10, 2012 20:14:32 GMT
We are moving away from model engineering, into esoteric areas, so please can we get back to the topic. Apologies. Russell. |
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