Just wondering if anyone else has tried to make a car indexer for a rotary dumper and if so how did you deal with the different lengths of cars. Cars of E&C heritage, (LBF, Huberts, now Intermountain) are shorter than Walthers, Athearn and Tangent cars (I don't have any Exactrail, Atlas or Scale Trains coal cars). As near as I can tell, the trucks need to move .036" toward the end and the distance between the truck screw and coupler screw needs to be .022" more for a total of .060" extra length on each end. Intermountain has complicated the issue by retooling the bolster/draft gear and end insert as one piece. My indexer is on the exit side of the dumper and has an arm that moves the cars. There are also two brakes to hold the string of cars in place for dumping. After the arm advances the car, the first brake grabs an axle on that car and another brake grabs an axle on the car about to enter the dumper so there are 4 cars involved, one that was just advanced, the one just removed from the dumper, one in the dumper and one about to enter the dumper. 6 car ends times .06" is a almost 3/8 inch and things don't line up. An imperfect solution I've applied to pre-Intermountain cars is to remove the bolster and reattach it .060" toward the end. It is imperfect because then, while the car is the correct overall length, the axles are too close to the ends and the second brake can have trouble grabbing its axle. I think a better solution is to make a new bolster/draft gear and cast up a pile of them.
How digital is your indexer? If it's controlled by an Arduino or computer, is there a way to import settings to tell the motors where to position the trolley? If you keep the cars in the same order, you could write some kind of program that defines the car length to tell the indexer how far to move. You could also try to correct the length of shorter cars by using long-shank couplers. It may not look as nice, but it would give you more accurate car intervals. I'm not sure if that's the principle your indexer works on, but it was an idea I thought of. You could also try some kind of detection method, using an IR sensor or magnet to detect the axle of the car. The indexer could then locate any car type. It sounds like you have two problems to solve. One is the indexer not being able to grab shorter cars because the arm doesn't line up, and the other is the axle brake not being able to grab trucks of different spacing. To fix truck centers, I like the idea of new bolsters. Your issue stems from inaccurate models, and to me, that's an issue I would fix. 3D printing could pretty easily solve your problem. Do you have any photos or videos of how it works right now? That may help us understand how it works and what improvements can be made.
It is a very analog facility, Mr. Trainiac. Maybe someday but electronics are magic to me. It is powered with a N20 size gearmotor. It is a 12V motor, but I am running it on about 3V. There is more reduction after that and it will drag an entire 35 car train with 3 SD60s sliding along at the head end. The clamps are also animated by N20 size motors. Here is an overview, loaded trains move left to right. The white square in the track at the left is the loaded side clamp, the middle bit is the rotary dumper followed by a rerailer. The empty side clamp is in the track near the yellow arm on the indexer trolley. The indexer trolley rides on a linear bearing: Here is the empty side clamp and indexer trolley. The notched square brass moves up and down to grab the car axle, obviously shown in up position. It is needed so the car doesn't move when the indexer arm raises and the car stays in place so the arm stops in the right place to grab the next coupler. When dumping a long string of cars, they will roll back toward the dumper when the arm raises and then are not in place for the next movement. The trolley is stopped by SPDT switches it runs into at the end of its desired travel. And the loaded side clamp. It raises after the empty side clamp is up. It is mostly to keep tension on the rotary couplers while dumping, they work a little better that way, they are less likely to twist apart. The dumper is to the right. There are a couple videos on YouTube, here is an overview, minus the clamp action: And finally, V1 of a proposed solution, a new bolster/ draft gear with proper spacing:
On the prototype they manually position the arm. On a model you could use a set of optical sensors to "find" the coupler and engage it.
Dave, you mentioned on the prototype the arm is manually positioned. Do you know how? It looks like the operator is far away. Maybe just paying attention to where the car is in the dumper is close enough to allow the car clamps to hold the train in position. The difficulty to me seems to be where to stop the trolley on its return to grab the next car. As far as other people crazy enough to attempt to model an indexer, not counting Barney type movers, I have seen 4. Doug Nagel built the model of the Sommerset dumper facility and the other two were single modules.
