12" working railroad

Discuss park gauge trains and large scale miniature railways having track gauges from 8" to 24" gauge and designed at scales of 2" to the foot or greater - whether modeled for personal use, or purpose built for amusement park operation or private railroading.

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Pontiacguy1
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Re: 12" working railroad

Postby Pontiacguy1 » Tue Sep 05, 2017 10:05 pm

I would run the hydraulic motors in series. If you run them parallel, when one truck hits a slick spot and "lets go" then more fluid would instantly be flowing through that motor, which would decrease the pressure in the other motor causing it to lose power. In other words, your locomotive will slip more easily and it will be harder to regain traction if you run it in parallel.

If you run them in series then all of your wheels are forced to turn the same RPM all the time no matter how much traction they do or don't have. Think of it like having positive traction in a car. Both trucks get equal flow and speed even if they don't have the same traction.

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BigDumbDinosaur
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Re: 12" working railroad

Postby BigDumbDinosaur » Tue Sep 05, 2017 11:40 pm

rkcarguy wrote:The Dynamic BMPH50 looks like it's more efficient and makes more torque but it's a touch slower at the same GPM. Adding an extra tooth to the output shaft sprocket would make it about equal in RPM at the wheels though to the Prince motor.

As I said, you're approaching it from the wrong direction. :D Design it based upon displacement ratios, not specific flow ratings. Stick with the 1.0 CI/rev per 10 HP relationship in sizing the pump and you will stay out of trouble.

Also, as noted by PontiacGuy, you should series-connect the motors, not parallel-connect them. The latter arrangement will give rise to the same sort of trouble a rear-wheel-drive automobile with an open differential experiences when one drive wheel is on dry pavement and the other is on a slippery surface. If the traction motors are parallel-connected the truck with the lower amount of adhesion will slip first and as the motor accelerates after the wheels have broken traction, proportionally higher oil flow will be consumed by that motor, which means less oil delivery to the other truck. Tractive force will quickly degrade and the locomotive may even stall with the loose truck spinning away.

If the motors are series-connected they are forced to run at the same speed without regard to load, thus assuring that both trucks continue to drive. Assuming no wheelslip, pressure will be split equally across the two motors, which means they'll produce an equal amount of torque.

You are unnecessarily obsessing over pressure and volumetric efficiency. System pressure is largely dependent on loading and for a given pump displacement, will be lower with larger motor displacements. Hence my advice about not using the chain drive to produce additional gear reduction.

Most power transmission designers select hydrostatic propulsion components based upon desired speed ratio (displacement ratio) and maximum input power (system flow). The 1.0 CI/rev per 10 horsepower ratio I use was something that I and another engineer developed years ago in a machine drive that used hydrostatic power transmission. It was close enough to theoretical to efface efficiency considerations.

Overall efficiency is affected by a number of things, some of which are related to your piping design. Quality pumps and motors themselves generally are quite efficient and perform close enough to the theoretical curves to eliminate the need to obsess about such things. What can be a problem is improper piping design, such as using too small a suction line to the pump inlet, or forcing the pump to lift oil from the reservoir. Excessive use of elbows, hoses and (worst of all) pipe fittings can introduce major losses into the system. Pipe fittings are especially undesirable, as they introduce sharp discontinuities in the flow path, causing power-robbing turbulence.

While on the subject of efficiency, one thing that I strongly recommend is that you use a pump with a cast iron body, not an aluminum one. Aluminum pumps' efficiency deteriorates with elevated temperature, primarily due to internal blow-by. Iron pumps are much less affected by system temperature and in many cases, actually become more efficient as the oil temperature increases (within reason, of course). The reason is because they are dimensionally stable with temperature, which is not the case with anything made of aluminum.

As for motors, I use Dynamic BMPH50 motors in my F7, specifically the BMPH100H4KP, which displaces 5.91 CI/rev (you can get Dynamic motors from Surplus Center). These motors are efficient, free-running and tough, with the ability to resist a substantial amount of radial loading on the shaft. During propulsion proof testing, my F-unit was able to haul nearly 8000 pounds up a 2.5 percent grade using the smaller 4.75 CI/rev version of this motor. There were no problems of any kind, even though system pressure was around 1800 PSI as the train approached the top of the grade.

Incidentally, BMPH motors are a bit on the noisy side—they whine, especially when lightly loaded or being back-driven. As the traction motor gearing of the real F7 growled and whined, the noise from the BMPH motor is "prototypical." :D You may find the BMRS motors more attractive, as they have SAE O-ring boss ports instead of harder-to-seal pipe thread ports of the BMPH series.
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rkcarguy
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Re: 12" working railroad

Postby rkcarguy » Wed Sep 06, 2017 12:54 am

Ahh, I was wondering why you didn't use dynamics pump. Makes sense. The aluminum body would grow with heat and have more "blow by".
Also, good call on the "open diff" slippage with the parallel pumps, I didn't think about that.
I'd say to be on the safe side I'll need about a 20-22 GPM pump, just a little smaller than yours?
The 100 series motors aren't much different in price than the 50's, so it's not a big deal. Maybe I'll go with the mid sized BMPH80, I think that is the 4.75 cu/in motor you were speaking of. I'm planning a 4000lb limit for gross weight because I suspect I'll be looking at grades in the 3% range, and if you were doing 2x that at those pressures I should be fine. What do you figure your oil tank + cooler volume is?
I'm stuck with the 2nd run of chain and sprockets because I've already built my trucks and designed everything to be built that way unfortunately, but I can size the sprockets however I want. In my experience chain drive has been pretty efficient, as long as you don't go too small on the sprockets.
As for SAE vs. NPT, I was wondering about that. I know the NPT threads can leak but they are common and easy to work with. Is there a tried and true product for sealing the threads you've had good luck with?

I cut and grooved ties for 30' more track and assembled another 10' section tonight. Time to go to bed!

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BigDumbDinosaur
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Re: 12" working railroad

Postby BigDumbDinosaur » Wed Sep 06, 2017 2:21 am

rkcarguy wrote:I'd say to be on the safe side I'll need about a 20-22 GPM pump, just a little smaller than yours?

From where did you get that number? 20-22 GPM is much too high for what you are doing. As I said earlier, and will say again, you are going it about all wrong with this focus on GPM.

I initially used a Barnes G25-28 pump with a 1.8 CI/rev displacement because I had modified the Briggs V-Twin to produce a stronger torque curve and figured I could use the higher pump displacement. Testing proved that the loading was a bit too high and I subsequently went with the smaller -23 pump, which is 1.4 CI/rev. Maximum governed engine RPM is 2400, so the theoretical flow at full throttle with this pump is 14.5 GPM, versus 18.7 with the larger -28 pump. Think about that, and also consider that I'm working with more horsepower and torque than you are.

The 100 series motors aren't much different in price than the 50's, so it's not a big deal. Maybe I'll go with the mid sized BMPH80, I think that is the 4.75 cu/in motor you were speaking of. I'm planning a 4000lb limit for gross weight because I suspect I'll be looking at grades in the 3% range, and if you were doing 2x that at those pressures I should be fine.

Before you pick a motor, choose a pump and then select a motor whose displacement will give you the desired amount of reduction. You want to use the largest displacement motor that will support the maximum speed at which you intend to run your locomotive.

What do you figure your oil tank + cooler volume is?

The reservoir's interior volume is approximately 4.85 gallons. A full oil charge is 4.75 gallons, which seems like too much until you consider the oil that is in the filter, lines, pump, motors, etc.

I do not use an oil cooler—none is needed. A properly designed oil reservoir will produce adequate cooling in almost all cases (see below).

oil_reservoir.gif
EMD F7 Propulsion Oil Reservoir

As you can see in the illustration, there is a return line filter (10 micron), which is essential to protecting the system from damage. I also have a suction strainer in the outlet on the reservoir, which is the larger diameter one seen in the face view in the drawing. The strainer keeps debris out of the pump.

I'm stuck with the 2nd run of chain and sprockets because I've already built my trucks and designed everything to be built that way unfortunately, but I can size the sprockets however I want. In my experience chain drive has been pretty efficient, as long as you don't go too small on the sprockets.

Chain drive efficiency isn't the issue. Getting the best efficiency from your hydrostatic components is what should be your main concern. That is why I STRONGLY recommend you develop all of your "gear reduction" in the hydrostatic circuit. Run your chain drive at 1.0:1 and size the hydraulic motors to produce the desired ratio. Using smaller motors and implementing additional reduction in the chain drive forces the motors to run faster, which is less efficient.

As for SAE vs. NPT, I was wondering about that. I know the NPT threads can leak but they are common and easy to work with.

In the fluid power industry, pipe threads are avoided as much as possible; you will seldom find them in aircraft hydraulics, for example. SAE ports use an O-ring seal—no thread sealant is required—and are essentially foolproof. Commercial grade SAE to JIC fittings have a working pressure rating around 5000-6000 PSI, far higher than what is used in hydrostatic propulsion. These fittings are inexpensive and are readily available from many sources, Surplus Center being one of them.

Speaking of fittings, JIC -8 is a good size to use in the high pressure sections of your propulsion system. Avoid elbows and if you have access to a precision tubing bender and a JIC flaring tool, hard-pipe as much of the high pressure system as possible. It will be more efficient than using hose, won't burst and will act as a radiator to control system temperature.

I used type-K 3/4 inch copper pipe to make up the suction and return circuits in my F7. These runs see no pressure, so use of copper is practical and convenient. A large suction line to the pump will prevent damaging cavitation when the oil is hot and the pump is working hard. I used commercial grade acid-core solder to solder the joints, not the lead-free stuff sold at the hardware store. You could also silver-solder the fittings, although that isn't necessary and is somewhat a pain if all you have is a propane torch.

Is there a tried and true product for sealing the threads you've had good luck with?

I have used Loctite's no. 545 anaerobic sealant on hydraulic pipe thread parts for many years and have had minimal problems with it. A less expensive, but not as reliable, substitute is Oatey's Teflon-infused pipe dope, which you can get at most hardware stores. This is the white gooey stuff that comes in a bottle with a brush applicator in the lid. You stir it up real good, liberally apply it to the male threads and immediately wrench the parts. I don't use it in hydraulic work because of its potential to get into the oil flow (plus it's messy), but do use it in compressed air systems.

What is good about using Loctite 545 is the parts don't usually have to be super-tight in order to seal. With the Oatey stuff, you have to crank things down tight to get a reliable seal when the pressure gets into the 1000+ PSI range.

While on the subject of pipe thread sealants, don't even think about using Teflon tape on hydraulic pipe fittings! :evil: Pieces of it often shred off when wrenching the parts and subsequently migrate into the system, plugging up valve ports. Some manufacturers of hydraulic components will not warranty a failure that is traceable to use of Teflon tape as a thread sealant. That is the worst damned stuff ever invented! :D Don't use it!
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rkcarguy
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Re: 12" working railroad

Postby rkcarguy » Wed Sep 06, 2017 4:28 pm

Ok that makes sense, thank you!
No progress today, in fact I woke up in the middle of the night to searing left abdominal pain and had to go to the ER....Kidney Stone!
I'm waiting for this sucker to come out, and in the meantime I'm on pain meds and flow-something but I'm throwing up nearly everything. I think I finally kept a popsicle down.

rkcarguy
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Re: 12" working railroad

Postby rkcarguy » Wed Sep 06, 2017 4:47 pm

I'm going to say that the BMPH100 will be about perfect. The 125 would also be a possibility, but my top RPM would be near it's max continuous RPM. Going with the BMPH 100 leaves me some wiggle room.

rkcarguy
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Re: 12" working railroad

Postby rkcarguy » Wed Sep 06, 2017 4:57 pm

So I'm looking at the 5.87 cu/in per Rev motors here. A BMPH100-H4-K-S, will get me that motor with 7/8" SAE threads and a 4 bolt SAE flange.
For comparison, the H2-K-P, would be a 2 bolt SAE flange with pipe threads.

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BigDumbDinosaur
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Re: 12" working railroad

Postby BigDumbDinosaur » Wed Sep 06, 2017 5:32 pm

rkcarguy wrote:So I'm looking at the 5.87 cu/in per Rev motors here. A BMPH100-H4-K-S, will get me that motor with 7/8" SAE threads...

You would use a fitting with -8 JIC male flare on one end and -10 SAE male ORB (O-ring boss) on the other, such as Parker part number 8-10 F5OX-S. This part is available from Surplus Center, their item number 9-6400-8-10.

...and a 4 bolt SAE flange. For comparison, the H2-K-P, would be a 2 bolt SAE flange with pipe threads.

Go with the 4-bolt mounting flange, not the 2-bolt one. The 2-bolt mountings are intended for applications that don't subject the motor to radial loads.

Below is an illustration of the motor mount bracket I designed for my F-unit, which is for the 4-bolt SAE mounting. It'll give you some ideas on how to mount your motors.

motor_mount.gif
Traction Motor Mount Bracket
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rkcarguy
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Re: 12" working railroad

Postby rkcarguy » Wed Sep 06, 2017 5:41 pm

As for piping, typically I'd use hoses from A to B and put a loop in them for the flex but this is not a typical project. This is where the TIG welder comes in along with the tubing bender at work. I've made a few hard lines before, and can TIG them from stainless pipe.
You think hard lines from the rear of the cab to the center of the locomotive, then have the hoses form 180* bends upward from the center and down into the motors on the trucks?
I'm going to mount my control on the "sitting car" behind the locomotive, so I'll need hoses here as well as at the flex points so the trucks can pivot obviously. It's a shame I feel so bad today, I have a pile of aluminum in the garage waiting to become a body.
I have access to a lot of pipe scraps, what about several large stainless pipes mounted vertically with each end boxed in for a tank?

rkcarguy
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Re: 12" working railroad

Postby rkcarguy » Wed Sep 06, 2017 5:47 pm

Ok, last question lol, the pipe threaded BMPH's are $133, where as the SAE models are $167. If I'm buying adapters anyway, could I use a Male NPT to JIC adapter on the motors and the Loctite 545 for a reliable connection?

https://www.fastenal.com/products/details/423015-131280

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BigDumbDinosaur
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Re: 12" working railroad

Postby BigDumbDinosaur » Wed Sep 06, 2017 8:09 pm

rkcarguy wrote:You think hard lines from the rear of the cab to the center of the locomotive, then have the hoses form 180* bends upward from the center and down into the motors on the trucks?

It's best to not continuously bend high pressure hoses in that fashion. If you can hard pipe enough to keep the hose bend angle at or below 120° you will not have to worry about premature failure. Also, the minimum allowable bend radius for -8 hose is 3-1/2 inches. Contrast that with 1/2 inch OD seamless or DOM tubing with .049 inch wall, which can be formed on a 1-1/2 inch radius.

I have access to a lot of pipe scraps, what about several large stainless pipes mounted vertically with each end boxed in for a tank?

Can't pass judgment on that without seeing a drawing.

Ok, last question lol, the pipe threaded BMPH's are $133, where as the SAE models are $167. If I'm buying adapters anyway, could I use a Male NPT to JIC adapter on the motors and the Loctite 545 for a reliable connection?

Yes, if you thoroughly clean the mating parts. I use Brake-Kleen for that purpose.
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rkcarguy
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Re: 12" working railroad

Postby rkcarguy » Sat Sep 09, 2017 1:47 pm

Well I'm still alive, I ended up having to have surgery and a stint put in my kidney tube. "It burns burns burns, the ring of fire" is an understatement!
Thanks for all the feedback on everything, I feel like I can build this thing and have it be a success now with some minor fine tuning.
For the tank, I'd simply form up and weld a pair of gage metal boxes, and weld pipes vertically between them. Allows me to use what I've got available and increases the surface area. I'll have room inside the body for it to be about 14" tall and 13" wide...maybe 13" deep as well, so probably 4 vertical pipes in a square format. Would it be better to have it mounted behind the grille up front where it will get air, or back by the engine closest to the pump, but would be near the exhaust?
Also, I think the pumps fluid intake will be higher than the bottom of the tank, unless I make the tank a shorter height and mount it on legs on the frame? I may sub-frame under the whole locomotive body anyway for more mounting points for it and hose-pipes-accessories, so not a big deal.


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