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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Topics may include: antique park gauge train restoration, preservation, and history; building new grand scale equipment from scratch; large scale miniature railway construction, maintenance, and safe operation; fallen flags; track, gauge, and equipment standards; grand scale vendor offerings; and, compiling an on-line motive power roster.
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Re: 12" working railroad

Post by rkcarguy » Wed Feb 19, 2020 2:24 pm

I'm pretty much ready to start retrofitting everything onto the dozer to get it rolling on it's new rubber tracks. I need to trim away some of the old plate ribs that were under the engine where the front axle will now reside and move in a slot under spring tension, match drill the channel frame rail bolt holes through the body and then start welding in the rear axle, gussets, and spring perches.
I've also decided (If you didn't notice by the bolt pattern in the output shaft plates) I'm going to go hydraulic drive. The belt system on these is just too hokey and high maintenance to be of interest and getting it all in good shape would have only saved me ~$200 compared to going hydraulic. Plus it gives me the freedom to position the engine wherever I like as I don't have to line up any pulleys. The GX390 is already like trying to cram a watermelon into a mailbox in the dozers 16" wide body.
I ran some calculations based upon a .75 cu/in pump and two 6.15 cu/in hydraulic motors(from their flow charts):
Hydraulic reduction: ~16:1
Final Drive Chain Reduction 2.6:1 (I can also go from -2 to +6 teeth here on the 14 tooth driver).
Total Reduction ~41.6:1
"Big Block" GX390 or GX390 Clone 18ft/lbs torque x 41.6 =748ft/lbs x .88(advertised efficiency) = 658 ft/lbs of torque(potential).
Top speed at low pressure 2.4 MPH
Top speed at max pressure 1.6 MPH ( set max to 1,800 PSI).
Sprocket + track thickness comes out to 12-1/8" total "wheel" diameter, close enough to 1' that I'm calling that 1:1 for torque calcs.
Torque peak on the GX390 motors is actually around 2500 rpm, so peak torque should be around 1.1 MPH and should be a good "dirt pushing" speed.
That said, the max continuous torque on these hydraulic motors is about 120ft/lb which gives me 312ft/lb at each axle. Above that, and the relief is going to kick in on the hydraulic system. Should be good utilization of the engine without stalling it out at max pressure.

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