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Reply to "Legacy Conversion Williams Brass N&W J Class #611"

@JohnActon posted:

Sid, you need to carefully count the ratio of your gearbox there are two solutions depending on the ratio of your gearbox..  Put a mark on one drive wheel and another on the flywheel in a location that you can see both from one viewing angle. It is also nice to have those marks line up with a fixed detail on the loco as a reference point. Then start turning the 42:1 takes a while.  Before you put your marks on the wheel and flywheel turn the flywheel in the direction you wish to turn while counting to make sure all the slack is taken up.  The 42:1 can have a bit of slack.  I have owned over twenty Williams locos and only found two gearboxes in the Samhongsa made locos they are basically the same gearbox one has a double helix worm and one is single. The single helix worm gives the gearbox a 42:1 ratio. The double helix worm has a ratio of 21:1.  Williams imported some locos from Ajin and I have yet to count the turns on any of their gearboxes. That may be the source of the infamous 44:1 box. Not that there would be any significant difference between 44 and 42:1.  Hopefully your "J" has the 21:1 box. However if it has the 42:1 box there is a solution to keep the motor from screaming like a siren at anything above 30smph.  The nice thing about the Pittman is the closed case keeps the noise inside for the most part however if you want to drive your J at anything about 30smph your going to need more rpm than the 12v Pittmans deliver.  One of the values you need to ascertain with whatever motor you plan to use is the static resistance of the motor that will determine the stall current at whatever the maximum voltage you drive the motor at.  A stalled motor obeys ohms law so if you want a 6A stall current at 12V your motor will have a static resistance of 2 ohms.  A quick and dirty way to determine static resistance is to first run the motor at a low voltage for a couple of minutes to remove any oxidation from the commutator segments.  then disconnect the power connections or any other electronics such as an electronic e-unit, driver-board etc. connect your VOM set to read ohms and take a reading. Spin the motor again take another reading. Do this 5-6 times and average them.  On a new motor you need to run it long enough to fully seat the brushes. Ten minutes should be enough. I have no experience with Legacy motor drivers but most TMCC drivers can deliver 8A for a short time in a stall situation so the lowest static resistance should be no lower than 1.5 ohms and your pressing your luck at that, it will be an amp hog too boot. Try and stay above 2 ohms. So your looking for a 2 ohm motor at what ever rpm your driver diameter and gearing give you for your desired top speed.  Driver diameter X 3.1416 = ? .        Divide  1320" (scale mile in inches) by this number to find the wheel revolutions per scale mile. Then multiply this number by the ratio of your gearbox. That is the rpm you will need for 60smph.  You can use a simple ratio to find speeds over 60smph.  X 1.5 would give you the rpm needed for 90smph.  I am always happy to have a top speed on a model of 60smph for passenger locos and 40smph for freight locos.  Now what to do should you be lucky enough to have that 42:1 gearbox.  A similar discussion to this started a couple of months ago and it prompted me to pull out what Williams and early Weaver Samhongsa locos I still have.  I had forgot what gearboxes I had.  I still have five of the Sam. locos two have the 42:1 gearbox and three have the 21:1 gearing. Luck would find that the two locos I wanted to run fastest, a Williams "J" and a Weaver PRR M1 Mountain,had the 42:1 box.  The gearbox on all of these locos can be swapped easily as the bottom cover comes off and the gear on the axles are all the same. I also have a Williams PRR B6 switcher 21:1 and a Williams PRR L1 mikado also 21:1. I am not all that concerned with the top speed on either of those locos so I took their 21:1 gearboxes and swapped out the 42:1 boxes on the "J" and the M1.  I then put the 42:1 boxes on my B6 switcher and the L1  2-8-2 Mikado. Though 30smph is not a problem at all on the B6 I would like the Mikado to be useable at 40smph without the siren sound of a Mabuchi 500 series motor spinning a 12,000rpm.  The solution, at 42:1 motor torque is not an issue but rpm is and the 300 series Mabuchi motors can go to 12k without too much whine and if you line the inside of the firebox/boiler with foam tape you can suppress most of the whine. So I am using a Mabuchi 385 with a static resistance of 2 ohms and 12,500rpm at 12V that will get the loco to about 55smph at 12v I mounted a MTH flywheel on it and had to machine a sleeve out of brass rod to step down the flywheel hole to the 385 shaft took me four tries to get the thing concentric.  Well the things runs great I have only put 22 cars behind it but it seems that it could pull at least 30. The wheels and gearbox make far more noise than the motor. If their is a problem it is that any motor running over 10k, even with no load, is going to generate heat and the 385 runs hot I have run it over an hour with 20 cars and it gets warm but you can still hold it without having to let go. I bought it from Mops Electric on eBay and perhaps one of their 385 Mabuchis with 8500rpm at 12V would be plenty fast at 40smph and run cooler.  I am going to have to stop here but I have been working on this Mikado for about two months now and plan to post here what I have done I may not finish but I will put something up by tomorrow.  Link to the 385 I used   https://www.ebay.com/itm/Mabuchi-RS-385SH-Motor-Knurled-Shaft-12V-12500-RPM-Powerful-Hobby-Motor/284065816087?hash=item4223a45e17:g:IN4AAMXQrvpRE~hp.

I would still rather have any of the Mabuchi 500 series motors in it and if I ever find a Sam. gearbox with the 21:1 gears I will pull the 42:1 and the 385 out in a heartbeat.          j

While everything you said is true, I am installing legacy and the stall voltages of the Mabuchi motors are to high will trip the legacy boards into stall mode.

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