Well, the loco appears to run completely normally with the shell off so, there's your problem. Something to do with the shell being on the mechanism. Oh, and BTW, as far as I'm concerned, both your FM switcher and RS unit are running backward. Doug
That you see an incandescent light bulb continue to shine does not guarantee that you are not having an intermittent electrical issue, especially since the loco manages to keep moving - it does not even come close to stalling. There could be something very subtle taking place mechanically, which might influence whether the wiper arms from the trucks are in reliable contact with the metal plate on the underside of the chassis. I keep focusing on these wiper arms because the rest of the stuff in your Minitrix loco is so simple. I consider my similar Minitrix F9 (bought around 1970-1971) to be bulletproof, except for its wiper arms. I could end up being totally wrong about my theory, but my experience with my Minitrix F9 is causing me to write this. It looks to me like the rear coupler of the FM loco moves slightly higher compared to the lead coupler of the freight car immediately behind it, right after the loco enters the curve. I believe I see this at around the 2-3 second mark of your first video (FM with cover on) and at about the 15 second mark of your video of the FM loco with its cover off. If the loco's rear truck were tilting slightly after entering the curve (where the back of the rear truck went up while the front of the rear truck went down), the wiper for the rear truck could be losing electrical connectivity to the metal plate it rubs against on the underside of the chassis. My Minitrix F9 and your Minitrix FM seem to have almost the same mechanism. I'll bet the trucks on our locos are identical. One thing different is that the total length of your FM chassis is shorter, so that the end of your wiper arms do not appear in your photo of the underside of your loco. They are hidden inside the "gas tank", which appears to be a hollow space on your FM loco. So I can't assess their condition from your 3 photos, and I can't tell if the ends of these arms are bent out of position. It's even possible that one of these 2 arms is out of place and never working at all, and that you are getting only 2 wheels of pickup from that rail on the straight track sections. And then if something additional goes wrong only in the curve, you could then start seeing the slowdown. There are horizontal pins (bars) which hold the trucks in place when you lift the loco off the tracks. You might need to remove these pins, so you can remove the trucks, so you can get a good look at the ends of the (copper?) wiper arms which are attached to the trucks, and get a look (at an angle) at the metal contact plate. I believe your "gas tank" is actually a hollow space, and that the metal plate is where the "ceiling" of this gas tank hollow space. It will be more tricky for you on your FM loco to remove your trucks, and especially to put them back, without bending or harming the ends of the wiper arms. On my Minitrix F9, they are out in the open (they are not inside a hollow fuel tank space). It might be worth trying two additional tests, both with the FM's cover on: (a) turn around the FM but still have it pull the train, in the same direction around the track, as shown in your first video, and (b) Have your FM loco push the train in the opposite direction, with the FM loco at the back of the train.
by looking at the pics of the motor i noticed a very dirty and worn commutator. could it be the motor just no longer has the necessary torque to keep the speed in tight curves ? does the loco slow down on your largest curves ?
OK, so I've had a batch of those. It has pretty much no relationship at all with the F-unit and is a direct cousin of the U28. In fact, I shortened a U28 frame, put FM trucks under it, and made a U25 years before Atlas ever made one. It has the same motor as in the U28 and the 0-6-0, just different shafting and worm position. Mark has good shots of the mechanism: http://www.spookshow.net/loco/h1244.html Now, here's the problem. The truck pivot is at the worm and worm gear. So when it goes around curves, that tolerance at the gear changes, and it effectively tightens the tolerance, causing additional friction, which causes it to slow down. Had the same problem with some U28's. It takes very little to mess this up. The motor is held in by those metal clips that look like staples. The only contact points of the motor are at the bearings, you'll notice that there's no bearings on the motor. So it's kind of cantilevered in there, and if one end or the other is off, then one truck will hang up much worse than the other. If you have test leads, clips, put one on the frame and the other touch to the pickup plate, and move the trucks around and see what you feel and see with your fingers. Is it one truck or both? Turned one way or both? Now, this is one mechanism where 'running it in' really improves performance, because it's brass truck gears with that plastic spur/worm gear in the middle. As that relationship wears and smooths up it gets progressively better. Trix are one of the few mechanisms that get better with age. Another thing that's possible, maybe not likely, is that you've got slightly corroded pickup plates that change contact as the trucks rotate. So the power to the motor is slightly decreased as it goes around curves. So, while you're in there, make sure the pickup wipers are bent to make good contact with that plate - tweezer job - and see how corroded up that plate is. Electrical contact cleaner works well there. They are fragile, but not that bad. I have had them actually fatigue and break off after many years, but it's more common that they aren't solidly contacting the plate. Now other than running the crap out of it and then putting some good Teflon grease on the worm/worm gear after it's worn in, you can take kind of a drastic step. You can attempt to slightly increase that gear tolerance by deliberately taking some material off the top of the bearing when it goes in the frame (or or off the frame) and shimming it up with paper to raise the tolerance about .010 or so. Doesn't take much. You can use a dremel or a hand file,and then experiment with paper shims until you find a sweet spot. That's actually kind of drastic, it works, but I'd only do this if the run-in period doesn't help much. I suspect it actually will. These models were made for a LONG time, and I'm not sure about the FM, but the U28's were showing real signs of mold wear and progressively worse quality and performance over the years. The one's I got in 72-73 were great, and every one after that seemed a little noisier, and you could see metal edges on motor parts, etc. were getting ragged. So tolerances can get messed up. It's a relatively simple and bulletproof mechanism that's wonderful to work on as it's almost all clips and pins, and disassembles and reassembles easily.
Indeed. Remember how dynamic braking works. Motors are generators. Your flywheels store more than enough energy to keep the generator turning, and that creates more than enough current to light a grain o' wheat.
The electronics today is by far superior to the older stuff we played with in years gone by. Today's light bars have built in capacitors to keep the light brilliant during operation of the loco. You can't depend on it to be your built in light tester. Years ago we could but not now. Clean track, clean wheels, clean contacts. As far as slowing down on the curves. That's normal even for the big boys (1:1 foot scale). Give you pesky locomotive a good cleaning, lube job and see what if anything comes of it. Slower speeds are the best speeds. So give it a thought or two.
