# Momentum car



## seadawg (Jan 2, 2008)

I got a chance to pull Bill Payne's momentum car around the Diamondhead oval for a bit, while I was down south last month. Fo some reason I now feel the need to build one. I have SITG back issue #50 on order and even found a picture of David Bailey's 4 axle car on Pete Thornton's website ( I have no idea how the trucks pivot on that one, Bill's was only 2 axle.) Does anyone have any info on momentum cars or possibly even drag cars? I've got some .25 chain and sprokets in hand, turned some quarter inch axles, bearings arrived Monday and the gears are in the mail. I'm looking for any and all input, no detail or tidbit would be to small.

David B., if you get a chance to respond, how DO those trucks pivot? (maybe allowed by the drive belt?)


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## David BaileyK27 (Jan 2, 2008)

Dave, yes the truck pivot as normal, and with reinforced fibrglass toothed belts there is enough flexibilty, but they do take a hammering and I have had to replace them several times because they stretch, especially on the overrun for braking. 
I reckon it adds 20 cars to the consist. 
David Bailey www.djbengineering.co.uk


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## Shay Gear Head (Jan 3, 2008)

Does my memory recall correctly that Larry Bangham had a sophisticated momentum car at one time? Is it in the SitG issue #50 article?


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## afinegan (Jan 2, 2008)

I bet that would make anyone's loco come alive with a prominent exhaust beat, and not have to have a lot of cars,


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## wetrail (Jan 2, 2008)

Ernie Noa built a few of these about sx or seven years ago and I still have one that works like a champ. You might reach him at [email protected]


Jerry


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## Semper Vaporo (Jan 2, 2008)

I made one using an old dial telephone centrifugal clutch mechanism (or is that a centripetal?)... Similar to a "fly-ball governor". This is a device that has a couple of weights on an axle that when it rotates they swing out to to press against a ring that encircles them. The faster the rotation the harder the weights press against the ring and the harder it is for the axle to rotate. 

Springs pull the weights toward the axle when the axle is moving slow thus when starting up there is no braking applied, so starting the car is easy. When the car reaches a few scale miles per hour the pull of the springs is overcome and the weights press against the outer ring. The faster the car moves the more the brakes are applied. 

I only managed to gear it to just one axle on a 2 axle truck on one end of a flat car and found I needed to get a whole lot more axles involved. I painted a stripe on the wheels of both axles on that truck and it was easy to see that the stripe on the free axle would be just a blur, but the axle geared to the mechanism was never rotating above about 3 to 5 RPM. I never got around to getting the two axles tied together somehow, but figured I really needed to get all 4 axles (both trucks) tied to the brake mechanism. I don't think the wheels on that one axle would last very long!

I had to put quite a bit of weight on the car also for it to really do any good applying a heavy load to the locomotive, but I never calculated how much weight I added, I just stacked a couple of 3"x6"x1/4" brass plaques and six 2" diameter 1/4" thick brass disks on it.

I put two magnets on opposite sides of one axle on the other truck and affixed a bicycle speedometer sensor near them to measure the speed and mileage of that car. I had to use two magnets because the particular speedometer I had could not be set to the wheel diameter I needed to get away with just one trigger per revolution. Two magnets did equalize the weight on the axle, but at higher speeds the sensor could not detect the difference between magnets and gaps between them and the speedometer would get very erratic and useless above about 20 scale MPH.


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## Shaymaker (Feb 15, 2008)

Posted By Semper Vaporo on 02/04/2009 7:04 PM
I made one using an old dial telephone centrifugal clutch mechanism (or is that a centripetal?)... Similar to a "fly-ball governor". This is a device that has a couple of weights on an axle that when it rotates they swing out to to press against a ring that encircles them. The faster the rotation the harder the weights press against the ring and the harder it is for the axle to rotate. 

...........

Ingenious though this idea is, it is NOT a "momentum car", but a speed limiter. I think a better name for it would be "automatic brakeman". The difference is that this device will prevent the train running away on a down grade, whereas a momentum car will actually encourage a runaway since, as well as making the train harder to get moving, it will also make it harder to stop.

Now, I must look out SitG #50 as a momentum car is on my list of retirement jobs.

Mike Chaney


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## seadawg (Jan 2, 2008)

Very true, the car with the dial governor would not be a momentum car but more like a drag car. I've been thinking about both. I was trying to think of ways to apply more drag as the speed increased using a generator into a variable load, fan, or even some kind of minature centrifugal pump, but the old phone part is absolute genius! Each car has different purposes and different requirements to fill different needs, since I saw Bill's momentum car first I have less design by trial and effort ahead of me. But I think I'm going to an Antique consignment store today at lunch. I did notice the fan blades on the side of one of the flywheels on David Bailey's car.


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## David BaileyK27 (Jan 2, 2008)

I built the car to test the batch of coal fired K27's that I built, it saved getting all my stock out every time, I took it to Diamondhead a couple of times, it needs a big loco to haul it, a Ruby would not move it, it weighs 18 lb. 
David Bailey www.djbengineering.co.uk


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## seadawg (Jan 2, 2008)

Yes, my purpose for the mo-car or drag car is to help tame the CLIMAX I just bought from Trainmax (Richie), the "Bark Box" maker.


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## Chris Scott (Jan 2, 2008)

2 earlier (archive) threads on an inertia or drag car, one with SitG #50 2 diagram pages:

http://archive.mylargescale.com/forum/topic.asp?ARCHIVE=true&TOPIC_ID=8676&SearchTerms=inertia 


http://archive.mylargescale.com/forum/topic.asp?ARCHIVE=true&TOPIC_ID=22610&SearchTerms=inertia


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## Pete Thornton (Jan 2, 2008)

Re: belts. We've been using that 1/8" chain and sprockets for throttles - it might work on the 4-wheel trucks to drive a flywheel. 
*[url]http://www.servocity.com/html/chain.html*[/url] 

I seem to recall from Larry's article (drawing photos linked in the *[url]http://archive.mylargescale.com/forum/topic.asp?ARCHIVE=true&TOPIC_ID=22610*[/url] thread posted by Chris, above.) He mentioned that a flywheel is good for momentum, but a fan acts as a speed governor, rather like Charles' telephone drag. Something about fan/wind resistance being geometric rather than linear. 

The fan approach might solve the weight and chain wear problem that David experienced?


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## lotsasteam (Jan 3, 2008)

Since most of the locos are RC controlled why not using a servo with brake rigging to slow down trains? 
Also Regner makes a brakenzylinder kit(live steam)which would solve the matter! 

Manfred Diel 
SA # 1313


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## Tippi (Feb 5, 2009)

Posted By lotsasteam on 02/05/2009 9:39 AM
Since most of the locos are RC controlled why not using a servo with brake rigging to slow down trains? 
Also Regner makes a brakenzylinder kit(live steam)which would solve the matter! 

Manfred Diel 
SA # 1313

This is what I intend doing on my next loco, but it still won't answer the momentum problem.

Tippi


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## seadawg (Jan 2, 2008)

Posted By Pete Thornton on 02/05/2009 9:27 AM
Re: belts. We've been using that 1/8" chain and sprockets for throttles - it might work on the 4-wheel trucks to drive a flywheel. 
*[url]http://www.servocity.com/html/chain.html*[/url] 

I seem to recall from Larry's article (drawing photos linked in the *[url]http://archive.mylargescale.com/forum/topic.asp?ARCHIVE=true&TOPIC_ID=22610*[/url] thread posted by Chris, above.) He mentioned that a flywheel is good for momentum, but a fan acts as a speed governor, rather like Charles' telephone drag. Something about fan/wind resistance being geometric rather than linear. 

The fan approach might solve the weight and chain wear problem that David experienced?


Yes, about the wear. I wonder if David tried the kevlar timing belts. That might not stretch as readily.


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## David BaileyK27 (Jan 2, 2008)

The weight was added to get the wheels to grip, even so I had to reduce the amount of reduction in the pulleys as the original design was much too hard to move due to the low ratio, there are also two fans as you can see in the picture, the main problem is stopping, if you shut off too quick the car tries to overtake the engine due to the momentum in the two flywheels, hence the problem with overloading the drive belts. 
It makes a good "Governer" when going downgrade and is ideal for an R/C controlled engine on a graded line. 
The whole lot sits under a Gold Belt Box Car and has caught a few people out when I have been asked to lend the consist to be pulled by another engine, they cannot understand why they cannot pull it, until I take off the body and show them. 
David Bailey


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## Pete Thornton (Jan 2, 2008)

The weight was added to get the wheels to grip


I picked up a couple of xmas cars from Star Hobby with the candy cane the swizzles around as the car moves, and a couple of gnomes that wander back and forth. I wanted to see if the drive from the trucks could be used for a momentum car. 

The wheels had rubber tires to make sure the mechanism got driven. But the whole thing is too flimsy to drive anything serious, so they are delegated to their original duty - looking seasonal at Xmas. Oh yes - the trucks didn't even pivot; the non-drive axle had a huge amount to side play to get around curves! 

The rubber tires are definitely a useful option, though I don't know of any freight car wheels with grooves.


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## Dan Pantages (Jan 2, 2008)

"I don't know of any freight car wheels with grooves" how about a lathe and little work.


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## Guest (Feb 7, 2009)

Grooves won't help. How about serrations, or knurling . . . but then you'll have to deal with "hum" . . . and track owners who want to know, and rightly so, "Which one of you sods is chewing up my bleedin' rail!?" Perhaps the best solution for all concerned I have found is to sandblast the wheel treads. 

It would be informative to know, if anyone knows beyond a wild guess, exactly what the difference between a drag car and a momentum car mechanism is, if there is an actual difference. I have an Pannier, my favorite running loco, which can be sprightly when left to its own devices and its track performance benefits greatly from what I reckon is a momentum car to smooth out the peaks and valleys. This car is essentially a flywheel on bogies and in theory should not limit speed, although from my racing days Horsepower = Speed, so it does have some speed limiting capability as the Pannier reaches its horsepower limit and can no longer increase the speed of the flywheel.


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## Semper Vaporo (Jan 2, 2008)

Posted By Curmudge on 02/07/2009 8:29 AM
Grooves won't help. How about serrations, or knurling . . . but then you'll have to deal with "hum" . . . and track owners who want to know, and rightly so, "Which one of you sods is chewing up my bleedin' rail!?" Perhaps the best solution for all concerned I have found is to sandblast the wheel treads. 

It would be informative to know, if anyone knows beyond a wild guess, exactly what the difference between a drag car and a momentum car mechanism is, if there is an actual difference. I have an Pannier, my favorite running loco, which can be sprightly when left to its own devices and its track performance benefits greatly from what I reckon is a momentum car to smooth out the peaks and valleys. This car is essentially a flywheel on bogies and in theory should not limit speed, although from my racing days Horsepower = Speed, so it does have some speed limiting capability as the Pannier reaches its horsepower limit and can no longer increase the speed of the flywheel.


I think you gave the correct definition of a momentum car. It is a car with a flywheel to maintain momentum, whether that momentum is zero or some other value. They are harder to get started moving because the flywheel takes energy to overcome the inertia of not moving and once moving the energy stored in the flywheel getting it started is released back to maintain the motion of the car. It does then smooth out variation in speed. 

The brake car, drag car or speed limiter, whether a mechanical braking mechanism or a fan working against air, just limits the upper speed and has little flywheel effect.

This was argued a couple of years ago on some forum (don't remember which one, probably 'SitG') when, I believe, Larry Bangham did his momentum car. I then asked about some way to apply brakes after the car got started and someone suggested the telephone dial mechanism (again, I don't remember who, sorry... it was a good idea and I wish I had saved all those old dial telephones I once had, but since I didn't it cost a lot of money to buy just one at a Junque store!).

I like the speed limiter because I run Live Steam and a Steam Engine has enough trouble starting itself! I don't need to have to overcome the inertia of the flywheel at the same time. Once the Steam Engine gets the train started it is easy to keep it going. My speed limiter car is easy to start, but makes it hard to go fast and that makes the locomotive work hard once it has had an easier time getting started. I get good "chuffing" sounds while starting and can maintian the sound when running.

Unfortunately, my mechanical abilities are pretty poor and my car is not well constructed, and like I wrote earlier, needs more wheels connected to the brake mechanism... LOTS more wheels! I would like to see it built into the axle and then I'd put it on every axle of every car I have! Have to work at getting the spring pressure "just right" so there is no brakes at starting and all of the brakes get applied at some certain speed... maybe have axles setup for a freight speed limit and another set for a passenger speed limit. EDIT: the variable resistor would enable the end-user to adjust the amount of speed limiting at each axle to balance them all to the same value.

If each axle could contribute a small amount of braking, maybe the wheels would not wear down too badly. The car I have now shows severe wear on the wheels of the one axle that has the brakes on it and I have not run that car very much at all.

Instead of a mechanical brake mechanism, maybe a tiny electric motor on the axle (or geared to it) and a variable resistor might work like "Dynamic Brakes" to do this.

I have several tiny motors but I have not figured out how to get them attached to the axles to try it.


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## Pete Thornton (Jan 2, 2008)

Instead of a mechanical brake mechanism, maybe a tiny electric motor on the axle (or geared to it)


Hmmm. I like that idea. I did a lot of work on winding small electric motors n my slot car days, and on wiring "dynamic brakes" (short the motor when you release the power and it will try to act as a generator - the dead short makes it work harder and thus it slows down.) I even built a controller with a generator in it that applied a reverse voltage when the throttle was released - super-charged braking! 

Maybe a lot of tiny electric motors/generators would cure the wear and grip issue. R&T had an article about battery-electric cars last month, and the 'regenerative' braking was quite effective, they said, on some of them. 

Thinking about it, we could send power through the track and tell all the motors to pull the train in the opposite direction...


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## lotsasteam (Jan 3, 2008)

Look what i found: 
http://www.narrow.gauge.btinternet.co.uk/lads1.htm

Go to May 01 NO 12

Manfred Diel
SA #1313


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## Shaymaker (Feb 15, 2008)

Ee! That's reet gradely, lad.


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## Pete Thornton (Jan 2, 2008)

Manfred's link is to Dave Wilding's 'governor' wagon, and I agree with Shaymaker (and couldn't have said it better, by gum!) 

Dave's wagon has rubber wheels (useful) and is geared 3:1, which is doubly interesting, as that's the ratio of your average slotcar. I was mulling over the facetious post above, but realised it wasn't that ridiculous if one can find the motor/gear combo off the shelf. 
I might have a couple of old 5-pole slot car motors with 3:1 bevels driving the axle - shouldn't be too difficult to change out the axle for a wagon type with (rubber) wheels. Let's see if this pic (item on eBay) works:


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## seadawg (Jan 2, 2008)

How 'bout a R/C nitro car's clutch where the bell is held fast, then as the car speeds up more pressure is applied to the bell. Check out this picture and allow you mind to wander. (I imagine you would need a smaller spring.)Clutch


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## lotsasteam (Jan 3, 2008)

Tamyia has 3:1 gears(some kind of casting metal,pretty tuff)they use it in 1:10 trucks and cars ! 

Manfred Diel 
SA # 1313


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## wchasr (Jan 2, 2008)

Posted By Pete Thornton on 02/09/2009 2:09 PM
Manfred's link is to Dave Wilding's 'governor' wagon, and I agree with Shaymaker (and couldn't have said it better, by gum!) 

Dave's wagon has rubber wheels (useful) and is geared 3:1, which is doubly interesting, as that's the ratio of your average slotcar. I was mulling over the facetious post above, but realised it wasn't that ridiculous if one can find the motor/gear combo off the shelf. 
I might have a couple of old 5-pole slot car motors with 3:1 bevels driving the axle - shouldn't be too difficult to change out the axle for a wagon type with (rubber) wheels. Let's see if this pic (item on eBay) works:














Ok So i've got an old motor and frame like that and I've even got some old toy wheels that have rubber treads. I'm sure I can mount that all up some how even if it was to a 2 axle car. Now tell me the rest of the secret? What do I need to attach to the motor?

Chas


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## Dan Pantages (Jan 2, 2008)

How about a “paddle” wheel in a sealed box that is about half full of a liquid. That way there would be almost no drag when you started but it would increase as the speed increased. You could change the dynamics of it by changing the amount and the viscosity of the fluid. 

The other thing I had thought of using is a mercury switch set so when you started down a hill it closed a circuit that made an electric motor into a generator. You could use a load of a string of lights so the faster it went the more of a load the lights would put on the generator. Running on the flat or up a hill there would be no load. 

Larry Bangham’s original idea of a flywheel was to stop radical changes in speed. Going downhill your engine would not be able to speed up enough to get out of control and when going up a hill the dynamic energy built up in the flywheel would help push the engine so you don’t have to open the throttle more.


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## Semper Vaporo (Jan 2, 2008)

You just short the motor leads to each other! You can get less braking if you put some resistance in the circuit and that might be a good idea to try to limit the possible burning up of the motor windings due to excessive current flow. I am GUESSING anywhere between 5 to 100 Ohms.


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## Old Boy (Feb 9, 2009)

How about a “paddle” wheel in a sealed box that is about half full of a liquid. - Dan Pantages

This has jogged the memory. Have any of you heard of the Baker fan? The Baker fan was invented by Abner Baker (1861-1953) as a static load for running-in new steam traction engines and they are still used at traction and threshing meets to load engines for demonstration running (you know . . to make them bark.) The power consumption of the Baker fan is provided by atmosphereic pressure, the resistance of air to movement, and varies with the cube of the rotational velocity. In non-mathematical terms, as the fan turns faster the resistance to being turned, thus the load, increases sharply. There is little momentum effect to speak of as the only weight involved is in the relatively light fan frame and vanes. 

At least one so-caled "momentum car" I have seen uses a vaned fan, a Baker fan, rotating in air. Now, it appears, we do have two distinct mechanisms to choose from or combine, one primarily momentum, and one primarily load. The question that would need to be answered however, before declaring that a miniature Baker fan would be effective, is whether there is scaling effect? That is, will a 3" diameter (or so) fan have the same relative loading behavior on a model as a 4ft diameter fan will on a full size engine. My guess is that it will not, unfortuantely, because nature (in this case the resistance of air) cannot be scaled. So then, if the medium were changed to liuid, as Dan suggests, would that behave in the same way air does? Lacking a member with a PhD in fluid dymanics who can run the calcs, that would make for an interesting experiment. 

Also, FWIW, I am the user formerly known as "Curmudge." I have retired that name and will henceforth post under the name "Old Boy." When I chose the former username I was unaware that there was already a "Curmudgeon", whose username selection preceded mine, so to avoid confusion and to insure that he doesn't suffer from something I might say, I thought it only fair that I no longer use that name. 
Cheers, 
Old Boy


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## Pete Thornton (Jan 2, 2008)

i've got an old motor and frame like that 

You just short the motor leads to each other! 


As Charles says, you apply a dead short across the motor, as it is being driven as a generator. 

Chuck, after many years running slot cars with 'dynamic braking' (a dead short when the power is off) I can assure you there is absolutely no chance of burning out the motor! The wiring in an electric motor isn't the same as a generator, and it makes miniscule amounts of power. Enough, however, to cause a drag. 

If it shows any promise, I'd probably rewind the armature with many turns of fine wire to improve the generator action. 

And yes, one could theoretically turn the short on and off via r/c. With it off (braking effect off) the motor will free-wheel and all you get is drag from the weight. When you get to the top of a hill, switch them on to limit the downhill speed. 

What do I need to attach to the motor? 


How about some wheels? I'd try mounting the motor vertically on the axle of a truck, sticking up in the air (inside the body of a boxcar eventually.)


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