Fine tuning RTR drives

[Guest Max Stafford]

We now have legions of very nice RTR locos. Sometimes though, probably as a result of being mass produced on a line, individual models don't run as smoothly as they might. I'm talking about things like a tight spot in the gearing which only affects at a certain point in the revolution. I quote the above example as this is a symptom I've come across in my otherwise beautiful 3MT. Some people recommend return to the dealer, but the model otherwise runs smoothly apart from this tight spot and I would rather fix it myself.

I would welcome ideas from those with experience of a good permanent workshop remedy for this problem. I believe it'll require more than a bit of running in. I'm a three kit veteran now, so I possess a little workshop skill!

 

Dave.

[The Fatadder]

We now have legions of very nice RTR locos. Sometimes though, probably as a result of being mass produced on a line, individual models don't run as smoothly as they might. I'm talking about things like a tight spot in the gearing which only affects at a certain point in the revolution. I quote the above example as this is a symptom I've come across in my otherwise beautiful 3MT. Some people recommend return to the dealer, but the model otherwise runs smoothly apart from this tight spot and I would rather fix it myself.

I would welcome ideas from those with experience of a good permanent workshop remedy for this problem. I believe it'll require more than a bit of running in. I'm a three kit veteran now, so I possess a little workshop skill!

 

Dave.

 

I tend to find myself in the same boat with that sort of problem much preferring to try and fix rather than return (though I suppose the fact that I tend to start detailing new locos before test running them does kind of force me to do that...

 

One thing thats worth checking is to completely strip down the gearbox and check each gear for any imperfections, sounds like a couple of teeth could do with some attention.

 

A method I've read about before (but not had reason to try myself yet) is to apply some kind of abrasive paste (such as a whitening toothpaste) to the gears, run for a bit to grind out the imperfection, and then strip down and clean everything before reassembling, and re oiling.

[davknigh]

Dave,

 

A look through this site; http://hackitup.railfan.net/athearn.html might be helpful. Granted it does refer to US diesels but the mechanisms are pretty generic these days and the same principles apply to steam. A rolling road is also a very useful piece of kit if you can manage one as being able to view the running mechanism can often lead you to the source of the problems. There is a thread running elsewhere in RMweb on that very topic so you can get some ideas. I use a Bachrus because it is 1/ adaptable for 00 and P4 and 2/ they are made here in Canada so a better price. :icon_biggrin:

 

HTH

 

David

[Guest Max Stafford]

Thanks for the tip Rich. Dave, thanks also. I do already use rollers, both by Bachmann and also as part of my Masterchassis jig. As Dave rightly states, the rollers are excellent for checking the overall running. They have certainly been of immense value as I enter the world of kit-built chassis. I shall try Rich's suggestion with the gears first in this instance as it does seem from the symptoms noted that the gear train is the issue. I'll have a play around tonight and let you all now.

 

Dave.

[hollywoodfoundry]

Dave,

 

It is worth while taking the time to examine the problem carefully before trying to find a solution. If the binding occurs only once per revolution, then it is most likely to do with one of the wheelsets, as a gear problem will generally occur a number of time in a revolution. The other quite likely place for binding to occur is in the motion gear or coupling rods.

 

I would suggest checking these out before you get into disassembling the gearbox.

[Guest Max Stafford]

Thanks. If what you say is indeed the case, it will doubtless be easier to start from the outside and work in. There does appear to be a 'kick' in the area of the nearside radius rod and return crank area, consistent with the same spot in the revolution. It's also occurred to me that this could also be down to an issue with the axle channel at the base of the chassis casting, perhaps a bit of poor finishing of the casting. Relatively easy to deal with if so!

 

Dave.

[Guest Max Stafford]

Thanks for all the advice lads. I had a partial strip down, a tinker about in various places, followed by some oiling and the chassis is running quite sweetly now. Start-stop speed isn't just as low as I'd like, but it's better than it was and I think several hours' continuous running will probably help as the brushes bed in and starting current reduces.

 

Dave.

[Captain Kernow]

I think you're right to give it a lot of running in, Dave, it often improves things.

 

I found that a Bachmann Jinty wasn't quite as slow running and sweet as I needed, and some tweaking of the pick-ups helped with that.

 

But I find that poor slow running, or a 'once per revolution stutter' is a fairly common feature of many of my Bachmann steam purchases over recent years. Hornby are not immune either, but seem to have fewer instances.

 

It's been suggested that slight problems with the factory quartering could be responsible.

 

What is interesting, however, is that Bachmann's diesels, especially their Bo-Bo chassis (of which I have a few running) always seem to run really slowly and smoothly right out of the box, so perhaps the problem with steam locos is more to do with the rods and valve gear, and wheel quartering, something which doesn't apply to diesels?

[Guest Max Stafford]

Thinking logically Tim, that would indeed make sense. I'm not quite sure of the optimum way to tackle a quartering issue in RTR however. Like you, I once had a jinty with that problem, but it appeared to be cured after a very unscientific manual twist of one of the drivewheels on its axle!

 

Dave.

[bertiedog]

It may not apply here, but this is a very vital bit of information, model electric driven steam locos with outside rods will never run in a balanced fashion, even when correctly quartered. The side rods are out of any balance, not at 180 , but 90 deg, so will always be out of any possibility of static balance.

 

This is not usually a problem with OO, as the mass of the rods is relatively low, but if the drag of the valve gear is added, then the issue may raise it's head with an audible surge and rise and fall in noise as the gearbox rotates the wheels. The drag of the pickups can also add to the problem, split frames are better here, if correctly done.

 

This problem is most noticeable on higher end drives like the Portescap, where the lack of general noise may make the slight surging more obvious.

 

But it can be as obvious on a RTR chassis, where the gear noise is higher, and the surge makes a rhythmic beat. Diesels simply do not have the problem at all, except where side rods are used.

 

The only answer is to make sure the drive is as loose and run in as possible, the drag of the pickups is at a practical low, and the quartering is perfect.

 

So a long run in is very definitely required, along with a bit of common sense mechanical attention to the details of the valve gear, making sure there are no tight rivets or screws adding drag, and all parts are properly in line.

 

Stephen

[Horsetan]

It may not apply here, but this is a very vital bit of information, model electric driven steam locos with outside rods will never run in a balanced fashion, even when correctly quartered. The side rods are out of any balance, not at 180 , but 90 deg, so will always be out of any possibility of static balance.

......

 

Somebody somewhere must come up with a machine for balancing, just like on the real thing.......

[bertiedog]

Somebody somewhere must come up with a machine for balancing, just like on the real thing.......

 

Trouble is the "out of balance" is small, very small. But it is enough to make noise, and render the gears audible, an effect dampened by the grease on the gears, and the fit of the teeth.

 

So a well sealed enclosed gearbox full of grease would be the best choice overall, no noise from the balance problem, it should be suppressed.

 

A far bigger source of noise generally on RTR is the wipers of the wheel pickups, not from them as such, but the constant drag they put on the transmission, aggravating the noise from loose fitting gear teeth and balance noise and surges.

 

Pickups should be set to a minimum pressure contact, not excessive, or should be done away with on tender locos, or have split frames on tank locos, no problems with most diesels as one bogie will pick up on one side and the other can be the return circuit, without any pickup at all.

 

Stephen.

[Jol Wilkinson]

Trouble is the "out of balance" is small, very small. But it is enough to make noise, and render the gears audible, an effect dampened by the grease on the gears, and the fit of the teeth.

 

So a well sealed enclosed gearbox full of grease would be the best choice overall, no noise from the balance problem, it should be suppressed.

 

A far bigger source of noise generally on RTR is the wipers of the wheel pickups, not from them as such, but the constant drag they put on the transmission, aggravating the noise from loose fitting gear teeth and balance noise and surges.

 

Pickups should be set to a minimum pressure contact, not excessive, or should be done away with on tender locos, or have split frames on tank locos, no problems with most diesels as one bogie will pick up on one side and the other can be the return circuit, without any pickup at all.

 

Stephen.

 

Another answer is to maximise external noise, e.g. turn up the radio, operate your models/layout at an exhibition or add DCC sound. For example, my layout has two Fulgarex point motors to operate ground signals. In the quiet of the workshop they sound deafening but at a show cannot be heard over the background noise.

 

A bit like the philosphy of having very loud car audio systems, so you blank out the road/wind noise.

 

Jol

 

p.s. grease also causes drag, so a sealed gearbox with a modern "dry" lubricant might be better.

[bertiedog]

The point of using grease is the damping effect, not lubrication in a gearbox, dry lubrication will work, but is usually in a grease medium anyway as with Labelle grease, to make it handle and stick to the gear surfaces.

 

A dry gearbox, however well lubricated and friction free will still have undamped back lash, which the grease version has in a dampened form.

 

Hard Nylon, Delrin and PTFE gears can operate without lube, or with dry lube, but they are quieter because of the damping of the more flexible plastic having "give", and this helps dampen noise.

 

It is not over all noise we are talking about here, but the low background rhythmic noise that should not come from a conventional gear set. Such noise also indicates potential extra wear and tear on the gears.

 

We are talking about fine tuning, and all this helps with getting the best from the mechanisms.

 

Stephen.