I got a two-pack of Kato RDCs at what I thought was a reasonable price on eBay. The seller said they'd been tested and ran okay but had not heavily used. He was "changing the direction" of his layout. Yeah... right. One of the RDCs ran just fine but the other stalled as soon as I put it on the tracks. I dismantled it and found that a tooth was missing on an idler gear. I ordered idler gears from Kato. Let's see... $2 for gears and $5 for shipping. I guess I'd better get something else. How about another RS2 kit? $90 later the box from Kato arrives. I set aside the new RS kit and install the idler gear in the RDC. I reassemble the unit and put it on the track without the shell. It runs fine. i put the shell on and it stalls. I take the shell off... it still stalls. I dismantle the thing again and discover that tooth has sheared off the new idler gear. I suspect the worm gear, but don't see any signs of physical damage or distortion. Any ideas... besides why didn't I just spend the $12 and buy a whole truck in the first place? Yet another expensive eBay bargain.
Boy, that's a tough one! I've had my four-car set since they were originally available, and haven't had that problem. Yes, they reach light speed at low voltages, and the motor and gearing are plenty strange to fit beneath the floor. I'd call KatoUSA, explain the problem, and see what they suggest.
These posts are the first that I've heard of this problem. I'd like to hear from others with the same problem. This seems to be unfixable.
I have eight of these things on my non-historic Two---RDC-1s Two---RDC-2s Three--RDC-3s One----RDC-4 (my non-historic hauls large quantities of mail and express, that is why there are so many passenger trains on so short a line) I have never had this problem. All of mine operate well. The speed range is curious: they will creep with very little throttle, do twenty-five SMPH with a flick of the wrist more, a few more flicks of the wrist gets them through the ranges from thirty to forty SMPH, but then the go into warp drive. Try to get them to do fifty SMPH, it is difficult. I suspect that many of us would love to have that problem with certain freight power.
Exactly my experience! I will have to learn how to use the speed tables in DCC. Still, breaking a tooth off of an idler gear seems strange to me. I've never had that happen in 36 years of some of the poorest running N scale engines ever produced. The RDCs do not have high torque motors. A picture of the broken idler gears would help. I'd still recommend calling katousa and finding out about this.
Pete; I'm planning on calling Kato USA tomorrow. I'm also planning on photographing my new TT set tomorrow, so I'll have my lights and stuff up. I'll get some shots of the idlers then.
Pete, et. al.; I talked to Dee at Kato USA today. He said there were a few broken gears on early RDC units, but he's never heard of a gear being broken again after it was replaced. He asked me to send him the unit. Here's the photo, as promised: The gear in the foreground is the one I removed. The mangled new one is still in the gear assy. Best! L
That's strange I have 2 Alaskas (wainting to strip) and my WP and have not had a problem accept for the decoder going wacko about every 6 months.
Whoa! I can't see much from the photo, but that looks like a manufacturing defect. Doh! To be much more un-doh-like, I'm speculating that there was a big bubble or weak spot in the center of the tooth-to-hub interface. I'n no expert on fracture analysis, but it looks like Kato got a bunch of improperly cast gears--either a bubble caused by inadequate pressure or a too-cold set. Happens all the time with low-cost producers.
Kato’s parts list incorrectly calls that gear an idler, but it is actually the worm gear. The worm gear is the gear that is directly driven by the worm. The other two small gears in the truck are true idlers. Pete may be right that it is a manufacturing defect, but a broken worm gear tooth is also a sign of a foreign object being stuck in the gear teeth, either in one of the axle gears or in one of the other idler gears. I have seen lots of broken teeth in various locos, and 9 times out of 10 this was caused by a stray piece of ballast stuck in the web of an axle gear. It is also possible a piece of the original broken tooth was still floating around in the gears. A dark colored piece of ballast or gear tooth can be very difficult to see when it is all the way down in the web of a gear. This causes the wheels to lock up and can cause a tooth to become sheared off. Nelson
I doubt you will want to hear this, but.... I had a bit of ballast in a gear and ended up disassembling the entire power truck. When I had all the gears, idlers, worms, frames, etc. laid out on white cardboard under a magnifying bench light, I finally saw a tiny piece of ballast deep in the crotch (or whatever it's called) of an idler. It was the same color as the plastic and covered in factory lube, so it was virtually invisible. I found it by carefully sticking the tip of a toothpick into every gear crotch until it popped out. Fortunately it hadn't broken any teeth, just jammed the mechanism. From your photo it looks like the truck is almost fully disassembled already, so it should be fairly easy to check every gear tooth.
Nelson, Hank, I've seen this once: a bit of ballast or detritus breaking off a tooth. Or actually just wearing it down. But that occasion was with a pretty high torque motor. The RDC does not have a high torque motor. It's still as likely an explanation as a faulty gear, perhaps more likely even. My experience is that gear trains just jam with foreign objects, rather than shearing off a tooth. Even with marathon running on my Bachmann F-7s, there was negligible gear wear, although the axle gears did crack.
Upon rethinking this a bit, there is a scenario for a foreign object to break off a tooth. These things will run at light speed. Something introduced into the gear train at high revs could break off a tooth. The stress on a gear tooth is probably the square of speed, or maybe more due to a rotational factor. So one of these zipping around at top speed, which is about 200 MPH, would have 25X the stress on gears of my normal speed of 40 MPH. While I still think the train would come to a screeching, or in this case sudden jumping, halt, I can't see it breaking a tooth off without a defect. I need to learn "what's after the bakery?"
Foreign objects in gear trains usually make a "thunk, thunk, thunk" sound. The sound might be hard to hear if the ambient noise in the room is loud, or the motor is noisy. The noise from the bit of ballast I described above was not constant, I assume because the ballast may have been moving slightly as the gear rotated. The "rotational factor" that Pete described has another consideration....momentum and shock. A slowly rotating gear will ease the tooth onto the foreign object allowing the tooth to adjust its position slightly. But a rapidly rotating gear will slam the tooth into the object with much higher momentum, square of the speed as Pete said. The higher momentum will create a high shock to the tooth because the tooth will not have time to adjust its position. This repeating high stress will cause the base of the tooth to fracture as your photo shows. The tooth base is the weakest area in a gear. Note that "ease" and "slam" are relative terms, but I think you get the point.
Pete, et. al.; It's hard to see, but the new gear has been sliced up by the worm screw, it's not as clean a break as the original gear. If you look carefully you can see that it looks like two teeth have been sheared off of the new gear. There was no foreign object in the worm, I not only visually inspected it, I ran a tiny screwdriver down the groove to be certain before I reassembled it. I did notice that the ridge of the worm felt unusually sharp in one area but not being an expert on such things didn't give it much thought. In retrospect I suspect that the sharp area was slicing the plastic. Nelson; Thanks for the correct terminology. I don't have an extensive background in things mechanical.
I know I am reviving an old thread, here, but I have had this same exact problem. I have two used RDCs, one of which has this very same gear busted. I am trying to avoid spending $12 on a new truck, but if Kato calls this gear a worm gear I think I will go ahead and buy four of them so that I have one for each time of the other three trucks for when they go, too. (the photo in post #8 above shows exactly what I found) I put a decoder in my other RDC last night. I am definitely going to be wanting to program a very SLOW speed curve there.
I'm curious to know if Lownen was able to resolve his breaking worm gear tooth problem, either with Kato or by himself.
My gear tooth was already broken. I had thought it just needed some run time to get back into shape, but after nothing seemed to improve I started looking for answers. That's when I noticed that the drive shaft was moving but the wheels on one truck were not, and then I found the broken gear. I am trying to get away with not ordering a whole new truck, but if I have to I will. Someone above mentioned that Kato (incorrectly) calls this a worm gear. If that's the case I'll order that.
I've got the Budd demo unit, with DCC installed. Only problem I've encountered, was a broken drive shaft to one truck. And NO, it was NOT declared a broken driveshaft, at the pass at Lizard head!!* . *C.W McCall, Galloping Goose
