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2nd Radius curves?

2549 Views 16 Replies 9 Participants Last post by  Sir Galahad

Does anyone else have the problem of locos slowing down through second radius curves?

I have a Mallard that slows down through 2nd radius curves and it annous the hell out of me.
Is there a fix?


Sir G.
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QUOTE (Sir Galahad @ 29 Oct 2007, 08:30) <{POST_SNAPBACK}>Is there a fix?

Third radius?

Seriously I don't have one currently but none of my friends have mentioned it.
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I mean, the track is down. Forgot to mention.
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My locos are fine going through 2nd radius curves and they don't slow down one bit.
This tends to affect locos with traction tyres on smaller wheels. Is your Mallard an older Hornby tender drive version?

The sideways force on the outer flange when a loco enters curved track will put additional strain on the motor. Beyond this traction tyres are very grippy and the the lateral forces imposed on traction tyred wheels in corners also put additional strain on the motor as the wheels are going to slip a lot less that those fitted without traction tyres to compensate.

Also small wheels are affected much greater than big wheels so modern outline and tender drive steam outline with traction tyres will suffer the most.

One solution is to increase weight as increased mass reduces the effect of the lateral forces on the wheels. This though can be difficult on steam locos with tender drive but less so on modern outline. Once the mass is increased you can then replace the traction tyred axles as the hauling power of your heavier loco should not drop significantly in these circumstances..

Happy modelling
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Slowing down on curves is caused by increased friction and train resistance. The energy required to pull the train round a curve will always be greater than to do so on the straight. The longer and heavier the train and the tighter the curve the worse it gets.

If you run the engine light round 5' radius curves there won't be any problem . This isn't the answer you want to hear...

Unfortunately this is a property of physics operating here, and attempts to avoid the laws of physics don't work - otherwise teleportation devices and faster than light travel wouldn't be confined to TV Sci-Fi

The only remedy I can suggest is increasing the energy supplied to the loco as it enters the curve, and decreasing it as it leaves. There are 2 ways of doing this - turn the knob on the controller, or possibly a feedback controller

Sorry , but I'm afraid there isn't a real fix here
QUOTE (Ravenser @ 29 Oct 2007, 09:27) <{POST_SNAPBACK}>Sorry , but I'm afraid there isn't a real fix here

Unless you are using DCC with back emf enabled.
You are up against laws of physics as Ravenser wrote. But despair ye not, because railway modelling is in part about engineering, much of which is about understanding the problem, then finding a way of overcoming or mitigating its' effect.

The Back-EMF facility found in both DC feedback controllers, and the better DCC decoders, offers at least part of the solution. This technique attempts to keep the motor turning at constant speed when the load varies. If that does the job then you are sorted.

However, if the load behind the loco is enough that the driven wheels slip badly when on the curve you may still not maintain speed. To overcome that requires more weight on the driven wheels. That will usually be enough to do the job.

If speed is still not maintained then either the power supply system or the motor capability may not be up to the job. In which case operate long enough applying the stress, and one of the components will fail. Replace failure with a higher grade component (this is a very respectable technique, and was the principal basis of leading edge aviation development until relatively recently!).
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Thanks for all the replys.

I am running the loco (It's a new Mallard, DCC ready) with no rolling stock on it. The sontroller is ancient, so that maybe the problem.
QUOTE (Sir Galahad @ 29 Oct 2007, 19:12) <{POST_SNAPBACK}>Thanks for all the replys.

I am running the loco (It's a new Mallard, DCC ready) with no rolling stock on it. The sontroller is ancient, so that maybe the problem.

Just a thought...

To get locos around curves, I presume that there must be some sideways play in the coupled wheels with the centre wheel outside the front and back wheels so that they align to the curve. So it may be worth checking the sideways play on this particular loco and compare with others - is it free to move?
I personally haven't noticed this but do use a feedback DC controller.
No, I don't think there is much play in the wheels. And do you get this feedback thing on Hornby DCC?
what is the order of gauge widening on these curves? In fact,is there any?
I dont think there is. Its just a right angle.
QUOTE (Sir Galahad @ 29 Oct 2007, 19:52) <{POST_SNAPBACK}>No, I don't think there is much play in the wheels. And do you get this feedback thing on Hornby DCC?
You will need to read the documentation with whatever decoder you have, or plan to install in the loco. If the decoder has the feature, it will work irrespective of the DCC command station.
Yeah. I read up on the Hornby decoder and it has it. Was asking 'cause now is the time to decide whether I need to rethink my layout before it is all layed and ballasted.
Quite seriously, if you do have the option to lay larger radius curves, including moving to flexible track to escape from fixed radii, it is all gain. The trains look better, particularly long locos and coaches, running reliabilty improves and longer trains are possible. I went systematically testing this in preparation for the layout I am building and concluded that in OO the 'break point' was from a 30 inch radius up. Using a RTR diesel like Bach's 66 or Hornby's 31, or the Bach 9F, I can fill the scale half mile circuit with 37 Bach mk1's, and they will take it away. And it doesn't pull off on the corners.
Yeah. I suppose if its slowing then there must be exsessive wear on part of the wheels. I'll see how much play I have with the cormers. I should turn in earlier and run the corner smoothly round shouldn't I? It is already flexi track.
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