Greetings,
I acquired a brass 4-6-0 recently and converted it to DCC temporarily - i.e. I isolated the motor brushes from the frame and wired in a TCS MC2 motor-only decoder to see how well the locomotive ran. CVs 3 & 4 (momentum) were set to a value of "24".
While up on the roller bearing stand and with the boiler off, I made the following observation during any direction change: There is a 2-3 sec delay between the moment the motor shaft begins rotating and the moment the drivers engage. And when the drivers engage it is abruptly - i.e. they jump to the speed step the DCC throttle is set at, or is in the process of reaching. If stopped and started again in the same direction, the motor shaft and the locomotive drivers will move simultaneously w/o any delay.
Does this seem like a thrust washer issue - e.g. too much slop. Or, could it be a Vstart (CV2) issue?
I don't have the locomotive at the moment because I sent it off to have a badly deformed crosshead bracket repaired on the engineer side of the locomotive. I mentioned my observations to the brass repairman making the repairs but wanted to run it past you all, as well.
Thanks for any input...
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
Tom.
A 2 to 3 second delay is huge. What couples the motor to the gearbox? Can you physically push the worm shaft fore and aft? Is this an idler gear box or worm to axle gear only? It sounds like a ton of backlash in the gearbox.
Pete.
As mentioned, Pete, I presently do not have the locomotive, as I sent it off (to MT) to have it repaired for another issue. What I can tell you is that there is a short, white, delrin-like collar that makes the connection between the motor drive shaft and the drive shaft of the gear box. The top of the gearbox is also rounded and shaped like skinny bell so I'm presuming that it is fitted with a worm gear.
If I had thought of it before shipping it, I could have observed whether the axial movement of the gearbox shaft coincided with the delay in the rotation of the drivers. That would have at least confirmed or negated if the gearbox was the issue or not.
wrench567Can you physically push the worm shaft fore and aft? Is this an idler gear box or worm to axle gear only?
I've had a few cases where the idler gear was nearly worn out. I believe some designs used these gears as a "sacrificial" gear so the metal worm gear would wear the idler out which was (more) easily replaceable.
Less common but still a possibility is the idler gear has a worn/broken or missing center pin so the gear flops forward or reverse before the slop is taken up and engages the axle gear.
As Pete points out it should be pretty obvious if the thrust bearings (washers) are sloppy that should be pretty evident.
You'll have to separate the halves of the gearbox to know for sure. Then there's the possibility that the axle gear itself is shifting a little on the axle. It may turn just a bit until it grabs a bite on the axle.
If you haven't studied it already, or for others who may benefit from it, this NWSL informative pdf is packed with valuable information:
https://cdn.shopify.com/s/files/1/0250/4032/2669/files/Gears_1_2.pdf?263
Good Luck, Ed
Any possibility this is some kind of coasting drive?
tstage What I can tell you is that there is a short, white, delrin-like collar that makes the connection between the motor drive shaft and the drive shaft of the gear box.
What I can tell you is that there is a short, white, delrin-like collar that makes the connection between the motor drive shaft and the drive shaft of the gear box.
Based on locomotives I have, I would assume the white delrin collar acts like a universal joint. If that's the case, I would look into replacing that collar/universal joint, as it sounds to me like it's too loose and results in the motor shaft "spooling up" to the programmed speed before finally biting in, which would cause the the wheels to suddenly jerk as you described it. I would suspect that this is your culprit, as I've had similar issues to this and replacing the collar/universal cured it every time.
Wolf,
Unlike a NWSL universal joint, the white delrin collar was solid so it was difficult to determine if it was indeed a real universal joint. IIRC, the delrin collar was outfitted with a set screw but I cannot say that for sure.
I kind of wish I had replaced the collar with a short section of silicone tubing while I had it in my possession. However, the broken crosshead bracket made further testing of the drivetrain precarious.
I am sure if there are any issues, your brass repair guy will get it squared away. I do this for a local hobby shop in my area since they normal repair guy will not touch brass. I find brass engines easy to work on compared to new stuff like from MTH and BLI. I am sure your engine will return in top form. Who is the repair guy in MT? I had a guy out there redo a PFM/United Climax for me many years ago before I learned how to do the work myself. Mike
Silly NT's, I have Asperger's Syndrome
I recall a flexible coupling I once came across that was as if a pair of matching gears, maybe 6 or 8 teeth were soldered on to each shaft end then a splined nylon "coupler" piece was slid over the joint and pinned in place. Effective but near impossible to repair.
In this NYC DES-3 locomotive I was able to use Athearn-style universals and a flywheel out of a Broadway Limited NW-2.
DES-3_gear by Edmund, on Flickr
Another engine I have used this brass dog-bone and cups. It was terribly out of balance and I replaced it with NWSL parts:
PRR_N1_sam1 by Edmund, on Flickr
THIS look into re-powering brass is interesting:
http://schutzer.net/Brass_Clinics/RebuildingBrass2008a.pdf
and this one has some good pointers:
http://shastasprings.com/repower/guide_to_repowering_and_regearing.htm
gmpullmanIn this NYC DES-3 locomotive I was able to use Athearn-style universals and a flywheel out of a Broadway Limited NW-2.
Interesting, Ed. Here's how my DES-3 boxcab arrived:
I replaced the original open-frame motor with a Taneda can motor (cannibalized from a Alco Models H20-44) and installed a TCS MC2 decoder and Keep Alive in it:
The gears growl slightly but I kinda like the sound. It's like having a sound decoder without the speaker...
Those rubber tubes need to GO, way to much flex in that long open area in the clear tube. A Line makes drive shaft kits that work great in these models, or NWSL with their shafts and drive cups. You do NOT want that much open space between the motor shaft and the gearbox shaft when using rubber tubes. The tubes are find for a very close coupling, such as on a steam engine, but that set up is not a very good idea at all.
emdmikeThose rubber tubes need to GO, way to much flex in that long open area in the clear tube.
I have two of these DES-3s, bought one just for parts. When they arrived they were fitted with four "India rubber" couplings with a short piece of intermediate shafting in between:
NYC_DES-3c by Edmund, on Flickr
The above photo shows only one of the live-rubber couplings. They were as brittle as bone china. The silicone tube is a much better choice, of course. A short piece of steel shafting in between would take up much of the torque problems.
tstageInteresting, Ed. Here's how my DES-3 boxcab arrived:
Ultimately, Tom, I was able to install a motor from an old Proto 2000 FA-2 that seems to work beautifully.
Here is is in a trial stage, pre-decoder:
NYC_DES-3b by Edmund, on Flickr
The gear towers do require a bit of fine tuning to find their "sweet spot" but, I agree, the growl is probably pretty close to what they actually sounded like while running with the diesel shut down.
emdmikeThose rubber tubes need to GO, way to much flex in that long open area in the clear tube. A Line makes drive shaft kits that work great in these models, or NWSL with their shafts and drive cups. You do NOT want that much open space between the motor shaft and the gearbox shaft wh
Actually, Mike, the silicone rubber tubing in my photo above has thick walls - 0.05", in fact - with an ID of 0.04". (It's used for fuel lines in RC cars & planes.) So it's flexible enough to compensate for any axial discrepancies between the drive shafts but amply stiff to not collapse while torquing. The small ID of the tubing REALLY bites down on the larger OD of the drive shaft.
Your point is taken though and I might look into adding a couple of 2mm SS rod sections to close up the long gap between each set of drive shafts.
I was thinking coasting drive too.