TT-Pete Posted May 27, 2014 Share Posted May 27, 2014 A few years back I bought a pair of Mike Chinery M4 12mm gauge power bogies: I had high hopes for them as they could have application in a whole host of possible TT projects, but I have never been able to get them to run smoothly as they both run at different speeds (so I can't put both of them in the same loco), are inconsistent in start and stop speed (sometimes wind up and down smoothly, sometimes stop dead or suddenly burst into speed) and randomly slow down or speed up when running under constant power. I thought I'd give them one last go and so cleaned them up, gave them a good oiling and left them running at both slow and top speeds in both directions for about an hour. All seemed to be well as both then seemed to be running smoothly and consistently. So I put them away, got them out of the box about 2 weeks later and both of them have now returned to their original jerky unpredicatble state. I am on the verge of giving up on them and trying a Halling motor bogie instead, or can they be salvaged and is there something I am missing here? Peter. Link to post Share on other sites More sharing options...
Miss Prism Posted May 27, 2014 Share Posted May 27, 2014 Motors in parallel from the same source impedance (a single controller) tend to 'fight' each other because of their different loads and BEMF. The extent of the problem will depend on the characteristics of the motors and the controller. Mechanically ganging the shafts together will alleviate the problem. Link to post Share on other sites More sharing options...
TT-Pete Posted May 27, 2014 Author Share Posted May 27, 2014 Hmm, I've been running them both separately and in tandem and the results are equally rubbish! My current plan is to use one singly in a 2H DEMU DMBSO that I am currently building with an additional set of pickups on the non-powered bogie. But only if it can be made to run smoothly and reliably... Link to post Share on other sites More sharing options...
PatB Posted May 27, 2014 Share Posted May 27, 2014 Given that they seemed OK and then deteriorated in storage, I'd be inclined to suspect that either the lubricant is solidifying or something is corroding or oxidising a bit. The fact that you've cleaned and relubed them argues against this but mechanical and electrical faults shouldn't return in storage. Oil getting sticky might., Link to post Share on other sites More sharing options...
TT-Pete Posted May 27, 2014 Author Share Posted May 27, 2014 I have used the light oil that you get in those modelling oil pens for years and haven't noticed anything else clogging up before. I used meths to clean off the wheels and pickups prior to running in last time - might that leave a residue? Overall I am wondering if the white-metal chassis might be the problem. The bogies do run better (just about) when warmed up and white-metal might expand/become slightly pliable to make a difference? I am almost tempted to test them to destruction (my first inclination at the weekend (after the naughty words) was to try a "bounce" test off the wall) by just leaving them running at full pelt for hours and hours and hours - and then see what's left at the end! A good loco builder in the 3mm Society once told me that "running in" is not a substitute for building a chassis right first time... (as in you can't polish a turd.) Link to post Share on other sites More sharing options...
PatB Posted May 27, 2014 Share Posted May 27, 2014 I have used the light oil that you get in those modelling oil pens for years and haven't noticed anything else clogging up before. I used meths to clean off the wheels and pickups prior to running in last time - might that leave a residue? Overall I am wondering if the white-metal chassis might be the problem. The bogies do run better (just about) when warmed up and white-metal might expand/become slightly pliable to make a difference? I am almost tempted to test them to destruction (my first inclination at the weekend (after the naughty words) was to try a "bounce" test off the wall) by just leaving them running at full pelt for hours and hours and hours - and then see what's left at the end! A good loco builder in the 3mm Society once told me that "running in" is not a substitute for building a chassis right first time... (as in you can't polish a turd.) Fair enough. It was a long shot at best. I doubt if meths would leave any kind of residue (although, it can take the shellac insulation of motor windings so it pays to be careful with it). I hadn't clocked that the bogies were whitemetal. Yes, it's entirely possible that it's expanding when warm and altering things like gear mesh and bearing clearance. Tight clearances could certainly lead to the symptoms you describe. If they open up when warm it would explain why everything seemed OK after an hour's constant running. The two critical clearances I can see are the mesh of the spur gears off the motor shaft and the mesh of the worm on the axle (can't see if both axles are driven). Try shimming the motors up with a slip of thin paper (Rizla Blue cigarette papers would be my first try; a thousand engineering uses so I always keep a pack handy, even though I haven't smoked in 20 years) to ease the spur gear mesh and see if it improves matters on a cold bogie. I'm not sure how I'd adjust the worm's mesh. If they were mine I'd probably clean all the oil off the worm and wormwheel, relubricate with a dash of toothpaste (very mild abrasive) and run the unit, preferably under load, for an hour, followed by a thorough clean and relube with oil. Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted May 27, 2014 Share Posted May 27, 2014 By the time you get them running right, the axles will have worn their holes oval, if they are running in the whitemetal. My jaundiced experience from near fifty years ago, back in the day when such construction was more common. I would suggest taking the motors out, testing them off bogies. Another potentioal explanation for all this variable running is oil soaked into the brush carbons. Run fine once all warmed through and the oil on the commutator contact patch all volatilised away, but it comes back. Degrease motor in a solvent you can no longer buy like carbon tet or freon, fit new brush carbons is the cure. Link to post Share on other sites More sharing options...
TT-Pete Posted May 28, 2014 Author Share Posted May 28, 2014 Thanks for your replies guys, it's given me something to think about. I did a little experimentation last night; thinking this through logically first I soldered some cables to the motor contacts so that I can power the motor directly to try to work out if it's a mechanical or electrical issue. The answer: both! Most of the time it does power up and down smoothly, but every now and again it hangs and you can hear that electrical "hummm" of a stuck motor and I have to twiddle the flyweight to unstick it. Unfortunately I can't see a way to take the bogie apart, and I have my suspicions about the end bearings of the shaft that carries the worm gears, there are no bushes so it's just a hole in the whitemetal: But I think suspect that it's the pickups that may be the worst offender here: (Does it look like the white wire might have a dry join?) One last try. I will give it another clean with meths, re-solder that wire, "lubricate" with toothpaste ("a very mild abrasive" - Genius!) and then run it for an hour in both directions. Fingers crossed... Link to post Share on other sites More sharing options...
BlackRat Posted May 28, 2014 Share Posted May 28, 2014 The wheels look a bit tarnished, dunno if that will affect the pickup? Also the top two pics above the motor and worm look to be off set, could just be the pic angle but they def look out by a fair bit? Link to post Share on other sites More sharing options...
PatB Posted May 28, 2014 Share Posted May 28, 2014 One last try. I will give it another clean with meths, re-solder that wire, "lubricate" with toothpaste ("a very mild abrasive" - Genius!) and then run it for an hour in both directions. Fingers crossed... Not original to me, I'm afraid. I originally picked that tip up from an ancient Meccano Magazine article on building a Riko slot-car kit. Link to post Share on other sites More sharing options...
TT-Pete Posted May 28, 2014 Author Share Posted May 28, 2014 @BlackRat: Oooh, well spotted Sir! I hadn't noticed that and comparing the bogie against the other one the motor is indeed twisted in the frame, which would explain the dodgy running and sticking. As the mounting is part of the whitemetal frame I had a quick fiddle to see if I can straighten it, but decided I would rather go with a pristine bogie than soldier on with one that has known issues, especially as I agree with 34C's mistrust of whitemetal. So I have soldered some pickup extension wires to the motor and ran it directly from the power source: sweet as a nut. It has also occurred to me that the bogie does not have the weight of the unit or loco body pressing down on it, so I blu-tacked some lead weight to the top of it which must have improved the contact of the wheels on the track as it runs much better that way. If I then have the second bogie on the unit also with pickups on all wheels, that should ensure a constant power supply. Thanks! Peter. Link to post Share on other sites More sharing options...
BlackRat Posted May 29, 2014 Share Posted May 29, 2014 Only glad to help! Link to post Share on other sites More sharing options...
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