I once was going through a huge phase where everything I had needed to be tested for stall current, since I was really high set on DCC (now I am utterly confused - as I am sure many others are - on the true advantages of DCC over DC, but that is a subject long worn out and for another, braver soul to start up again). I went around pressing down on every locomotive I had until I could measure the correct stall current. Unfortunately, the worm gear on my IHC 0-8-0 slipped right off the drive shaft. I stopped imediatly, since I defenatly did not want to do any damage to my other locomotives. Now the drive shaft spins in the worm gear. I certainly hope this is not the end of my little locomotive, as it had been one of my top performers before the "incident," so now I ask for any personal experience with the issue and how to repair a problem like this. Any help would be greatly appreciated! Also if anyone has a better method to measure stall current, it too would be appreciated!
Thanks in advanced,
Ghonz
- Matt
ghonz711 wrote: I once was going through a huge phase where everything I had needed to be tested for stall current, since I was really high set on DCC (now I am utterly confused - as I am sure many others are - on the true advantages of DCC over DC, but that is a subject long worn out and for another, braver soul to start up again). I went around pressing down on every locomotive I had until I could measure the correct stall current. Unfortunately, the worm gear on my IHC 0-8-0 slipped right off the drive shaft. I stopped imediatly, since I defenatly did not want to do any damage to my other locomotives. Now the drive shaft spins in the worm gear. I certainly hope this is not the end of my little locomotive, as it had been one of my top performers before the "incident," so now I ask for any personal experience with the issue and how to repair a problem like this. Any help would be greatly appreciated! Also if anyone has a better method to measure stall current, it too would be appreciated!Thanks in advanced,Ghonz
I'm not familiar with that particular model, but I'm guessing you're working with a plastic worm on a metal shaft. Look closely at the worm and see if there's a split in the worm itself. If this is the case, you'll need to replace the worm. They're normally just a press fit (a tight one). If the worm isn't split, you can try to epoxy it fast to the shaft, but your best bet overall would be to replace the worm.
Why do you have to know the stall current? The current draw on most all motors these days is so small, I don't see any reason to put the locos through any abuse like this.
The overall weight and Drawbar pull are the most important specifications to know of each loco.
Modeling B&O- Chessie Bob K. www.ssmrc.org
I would imagine it depends on how new said 0-8-0 is.. while the newer motors might be really good, and draw less than an amp, I'd personally still wanna know "for sure"...
-Dan
Builder of Bowser steam! Railimages Site
IHC typically uses plastic worms. If it's not split, I would degrease the shaft & worm, then put a drop of CA inside the worm and quickly push it into place. I've installed plenty of NWSL gears & universals that way.
Nelson
Ex-Southern 385 Being Hoisted
NeO6874 wrote:I would imagine it depends on how new said 0-8-0 is.. while the newer motors might be really good, and draw less than an amp, I'd personally still wanna know "for sure"...
Most of my locomotives still have open frame motors, but I still agree with bogp40. Trying to find the stall current of an installed motor is almost a guarantee of over-heating a motor or damaging a gear train sooner or later. Stall currents can and often do exceed the maximum current rating of the motor. The Tortoise switch machine is a notable exception where a motor can be safely left in a stalled condition all day.
When building a locomotive, the goal is to get maximum weight for maximum traction, but still have the drivers slip before the motor reaches its maximum current rating. When properly setup as described, stall and maximum currents will never be seen, except in a very unusual derailment configuration that locks the drive wheels with power still on the motor. If published maximum current is reached before the drivers slip, there is either or both of 2 choices - reduce weight or install a more powerful motor. It is rare in HO and smaller to get enough weight into a locomotive to prevent drivers slipping prior to maximum current without the use of traction tires.
The above assumes no traction tires. If traction tires are used, current really needs to be monitored to prevent motor overload until one knows how many cars can safely be pulled. Even then, derailments can burn out a motor.
Current when the drivers slip then becomes the criteria for decoder selection. The test for motor slip current is to block the locomotive's horizontal motion while the drivers spin, not by pressing down on the locomotive. Choose a decoder rated greater than the driver slip current, and you will be fine.
If forced to choose, I think I'd rather fry the decoder than the motor. Like I said, it would have to a rare derailment situation that locks the drivers to cause the damage. If the decoder fried first in such a situation, it might protect the motor from a similar fate as it sits there stalled with power on. Replacing a decoder is normally easier and less time-consuming.
nobody asked me, but my thoughts anyway
Fred W
bogp40 wrote: Why do you have to know the stall current? The current draw on most all motors these days is so small, I don't see any reason to put the locos through any abuse like this.The overall weight and Drawbar pull are the most important specifications to know of each loco.
Weight and drawbar pull are important, to be sure. BUT, there's always a but somewhere, if we want to add weight to a loco to increase the drawbar pull, I would want to know so I could keep the weight down so that wheel slip would occur well before that loco reaches a damageing current draw. Wheel slip is a built in safety valve, you could say. Food for thought here. Ken PS If that is a metal worm a tiny dab of Loc-tite may do the trick.
Sorry for some of the confusion, but the worm gear is plastic and is driven by a metal drive shaft connected to a can motor. As for measuring the stall current, it seemed pretty important to me since if you don't place a decoder with the correct max current you could end up with a melted wad of plastic and metal all burnt up on the track. At least that is what some good people at my LHS told me. I think I will try what Nelson had to say and degrease the drive shaft and ad some CA, since the worm gear is not split (thankfully). If not I will come back here and look for some other ideas. Also thanks a lot to Fred W. Your information was very helpful! And Gary, quite an interesting idea. I understood correctly, I should add groves running horizontally along the drive shaft using a file? Seems like it could work, and maybe I'll give it a try if all else fails. Thanks to all others who put in their own ideas and experiences. Also, would a metal worm gear be a better choice? Since I have the shell open already (and sitting on my workbench), should I replace it with a metal gear instead of the plastic one? The plastic gear is not split or cracked, but would a metal worm gear save me from future trouble?
ghonz711 wrote: Sorry for some of the confusion, but the worm gear is plastic and is driven by a metal drive shaft connected to a can motor. As for measuring the stall current, it seemed pretty important to me since if you don't place a decoder with the correct max current you could end up with a melted wad of plastic and metal all burnt up on the track. At least that is what some good people at my LHS told me. I think I will try what Nelson had to say and degrease the drive shaft and ad some CA, since the worm gear is not split (thankfully). If not I will come back here and look for some other ideas. Also thanks a lot to Fred W. Your information was very helpful! And Gary, quite an interesting idea. I understood correctly, I should add groves running horizontally along the drive shaft using a file? Seems like it could work, and maybe I'll give it a try if all else fails. Thanks to all others who put in their own ideas and experiences. Also, would a metal worm gear be a better choice? Since I have the shell open already (and sitting on my workbench), should I replace it with a metal gear instead of the plastic one? The plastic gear is not split or cracked, but would a metal worm gear save me from future trouble?Ghonz
As far as I'm concerned the plastic worm is just as good as brass or metal would be. My guess is the the gears it drives are plastic also so wouldn't make much difference. Just keep in mind that any lubricant used must be "plastic compatible". By "knurling" the file's teeth will sink into the metal shaft, forcing metal to be raised causing the shaft diameter to grow larger. Go easy with this and trial fit often. Too large and you will split the gear. The idea here by rolling we don't take any metal off that shaft, just enlarge it ever so slightly. Ken
My IHC diesel did the same thing. As mentioned-check for cracks, degrease and use CA glue. Make sure you push the worm on the shaft the correct amount. Not too much or too little. That ruffing up the metal shaft with a file is a good idea too.
If I have to take a loco apart for maintenance, I usually pull all the worms and drive couplers joints and do this to them while it's apart.
Knurling with a file is an option, but as ErieDiamond said, too much and the worm could split. I've use the CA solution for that reason, and because I want something that sets up quickly. It's probably best to use the standard CA to give you some working time, though I tend to use the thin stuff. Just don't glue the worm to your fingers! (Been there, done that. ) Scrape away any excess from the shaft and worm.
Acetal plastic is a fine material for gears. I recently discovered that NWSL had changed one of their regearing kits from a steel worm/brass worm gear combination to steel/plastic, and figured at first that it was a cost cutting measure, but I think the the steel/plastic combo may actually be better. These plastics are self-lubricating, but brass will wear.