Search found 195 matches

by andrew jukes
Tue Apr 18, 2017 2:17 pm
Forum: Control Concepts
Topic: Maximising Adhesion using Electronics
Replies: 21
Views: 4321

Maximising Adhesion using Electronics

A possibly new thought is the use of clever control electronics to maximise the use of available wheel/rail adhesion. I'm not aware of any attempts to do this (perhaps I should check on MERG). Most clever electronics has focussed on running motors as slowly as possible without stalling. A maximum tr...
by andrew jukes
Tue Apr 18, 2017 1:59 pm
Forum: Guest Book
Topic: Flexi Chassis an Appreciation
Replies: 467
Views: 71377

Re: Flexi Chassis an Appreciation

Yes, Andy, what I wrote was ambiguous. Lindsay on April 11th, backed up by Armchair Modeller ('well said'), seemed to think that trying to improve our understanding of equalising beams and things should be consigned to history. Not so I say. An A4 is an extreme case but large boilered locos with hig...
by andrew jukes
Mon Apr 17, 2017 10:24 pm
Forum: Guest Book
Topic: Flexi Chassis an Appreciation
Replies: 467
Views: 71377

Re: Flexi Chassis an Appreciation

On my single-axle weigh bridge, I shim under the scales so it's easy to do +/- 0.8mm from the adjacent track. Hardly relevant for a compensated 0-4-0, though. The A4 in the attached poor quality picture has a test chassis that tried to achieve everything in suspension terms that is current P4 conven...
by andrew jukes
Sat Apr 15, 2017 11:47 pm
Forum: Guest Book
Topic: Flexi Chassis an Appreciation
Replies: 467
Views: 71377

Re: Flexi Chassis an Appreciation

Correction! I got front and rear mixed up in the effective axle load calculations. Going backwards, it should have said 26gm (rear) and 61gm (front). I could also have gone on to demonstrate the drawbar pulls you would have expected if the theory applies. If a 15gm pull is achieved without slipping ...
by andrew jukes
Sat Apr 15, 2017 10:04 pm
Forum: Guest Book
Topic: Flexi Chassis an Appreciation
Replies: 467
Views: 71377

Re: Flexi Chassis an Appreciation

Will L wrote At to the truth of the assertion that equal distribution maximises haulage power, we have had this discussion on the forum before, although on the last occasion it was because I was questioned in my assertion that the pulling power of a coupled chassis is limited by the most lightly loa...
by andrew jukes
Thu Apr 13, 2017 12:25 am
Forum: Guest Book
Topic: Flexi Chassis an Appreciation
Replies: 467
Views: 71377

Re: Flexi Chassis an Appreciation

Will L wrote There is no question that equal distribution of weight will improve haulage power. We can argue the toss over whether our CSBs or your fully equalised chassis are best at this, but compared with many compensated or rigid chassis, they win hand down. I bought into most of this but have h...
by andrew jukes
Wed Apr 12, 2017 11:33 pm
Forum: Chassis and Suspensions
Topic: Articulated beams?
Replies: 84
Views: 15163

Re: Articulated beams?

Russ wrote I agree. It's like an MJT torsion-bar CCU, for example. But it's a significantly different principle, namely where the rotation is in the pitch plane, i.e. 'longitudinal compensation' (and where one could argue the 'triangle' is irrelevant because of its symmetry over the wheelbase), as o...
by andrew jukes
Wed Apr 12, 2017 10:40 am
Forum: Track and Turnouts
Topic: Re: Track and Wheel Standards
Replies: 35
Views: 9456

Re: Articulated beams?

Julian - Yes, that’s right, though you differentiate between the straight and ‘curved’ roads in a way that’s not necessary. In the crossing area, turnouts are generally straight on both roads. If building a turnout with a curved crossing on a curve that’s sufficiently tight to require 0.2mm gauge wi...
by andrew jukes
Tue Apr 11, 2017 11:24 am
Forum: Track and Turnouts
Topic: Re: Track and Wheel Standards
Replies: 35
Views: 9456

Re: Articulated beams?

I should have said that obtuse crossings require more care because of the need to steer the wheelsets so they don't go the wrong way. It's also important to exercise tighter control in complex formations where there may be common crossings in both rails, opposite each other. In both cases the basic ...
by andrew jukes
Tue Apr 11, 2017 10:51 am
Forum: Track and Turnouts
Topic: Re: Track and Wheel Standards
Replies: 35
Views: 9456

Re: Articulated beams?

Julian - The most important dimension in a common crossing is the check gauge (CG). It needs to position the check rail far enough from the crossing nose so there is no chance of the flange of a correctly gauged wheelset contacting the crossing nose. For a 17.75mm BtoB wheelset, that means a CG of 1...
by andrew jukes
Mon Apr 10, 2017 6:23 pm
Forum: Chassis and Suspensions
Topic: Articulated beams?
Replies: 84
Views: 15163

Re: Articulated beams?

Julian - Let me try to take out anything that I suspect might be confusing. For diagrams 1. and 2., the CofG is 12mm from the pivot(S) and the end axle supporting the weight not carried by the beam(s) is 12 + 24 = 36mm from the pivot(s). If W is the weight of the vehicle, this means 12 x W = 36 x lo...
by andrew jukes
Mon Apr 10, 2017 5:09 pm
Forum: Chassis and Suspensions
Topic: Articulated beams?
Replies: 84
Views: 15163

Re: Articulated beams?

Julian - Doesn't my 10.55am posting answer at least part of your question?

Andrew
by andrew jukes
Mon Apr 10, 2017 11:08 am
Forum: Track and Turnouts
Topic: Re: Track and Wheel Standards
Replies: 35
Views: 9456

Re: Articulated beams?

Why 17.82mm? The MRSG devised the P4 standards in the 1960s and chose a B to B of 17.67mm. The reasons for this choice are not clear but may have included a wish to avoid the ’complication’ of gauge widening. It quickly became obvious that 17.67mm allows lots of slop on straight track (try rotating ...
by andrew jukes
Mon Apr 10, 2017 10:55 am
Forum: Chassis and Suspensions
Topic: Articulated beams?
Replies: 84
Views: 15163

Re: Articulated beams?

Julian - Not sure how you work out the weight distributions but I reckon it’s easiest to do it by taking moments about the beam pivot(s). For diagrams 1. and 2., the CofG is 12mm from the pivot(S) and the end axle supporting the weight not carried by the beam(s) is 36mm from the pivot(s). If W is th...
by andrew jukes
Sun Apr 09, 2017 11:59 am
Forum: Guest Book
Topic: Flexi Chassis an Appreciation
Replies: 467
Views: 71377

Re: Flexi Chassis an Appreciation

I think Andy's 3-axle, 4-beam, 4 fulcrums layout is interesting and I've played around with it myself. If one forgets all the dynamic stuff, then the issue with this layout with fixed fulcrums is that it obviously cannot cope with track twist. Compliance/springs at the fulcrums can be the answer and...
by andrew jukes
Sat Apr 08, 2017 1:23 pm
Forum: Track and Turnouts
Topic: Re: Track and Wheel Standards
Replies: 35
Views: 9456

Re: Articulated beams?

Julian - I set all my check rails with an S4 (18.25mm) Check Gauge. This avoids the conflict you were concerned about. Using Exactoscale P4 check rail chairs, which are intended to give a 0.68mm flangeway, you end up with a little gauge widening in the crossing area, but this has never seemed likely...
by andrew jukes
Sat Apr 08, 2017 12:34 am
Forum: Chassis and Suspensions
Topic: Articulated beams?
Replies: 84
Views: 15163

Re: Articulated beams?

Sorry if this all seems a bit unnecessary but I have a vivid recollection of a very nice GW Castle which would simply lift one of its rear drivers high off the track when it tried to pull anything. It was torque reaction doing it combined with a poor choice of compensation layout. With compensated 4...
by andrew jukes
Fri Apr 07, 2017 1:43 pm
Forum: Track and Turnouts
Topic: Re: Track and Wheel Standards
Replies: 35
Views: 9456

Re: Articulated beams?

Without being too pedantic, it's twist that is the real problem. A canted circular curve has no twist and should pose no problems however much cant is applied. But you can’t connect a canted circular curve to an uncanted straight (often described as tangent) track without introducing twist. The tran...
by andrew jukes
Fri Apr 07, 2017 12:20 am
Forum: Chassis and Suspensions
Topic: Articulated beams?
Replies: 84
Views: 15163

Re: Articulated beams?

Are you saying it is the fixed axle chassis that has poor stability compared with one where no axle is fixed? No. I’m saying that some compensation layouts are less stable than others. Compensation usually is based on the idea that a 3-legged stool will not wobble as it will sit firmly on all three...
by andrew jukes
Thu Apr 06, 2017 6:45 pm
Forum: Track and Turnouts
Topic: P4 vs S4 - Pro's and con's
Replies: 164
Views: 34850

Re: P4 vs S4 - Pro's and con's

Tony Wilkins said S4 stock will run on P4 track . While this is what's said in Digest 1.2 (which generally I think of as our bible) I think it is misleading. An S4 wheelset with a 17.87mm BB running through a turnout built to P4 standards i.e. using a check gauge of 18.15mm violates condition 2 of t...
by andrew jukes
Thu Apr 06, 2017 3:08 pm
Forum: Chassis and Suspensions
Topic: Articulated beams?
Replies: 84
Views: 15163

Re: Articulated beams?

Probably my fault, for simply reacting to points as they arise without worrying about the thread heading. But I'm not sure what the correct etiquette is. If a reference is made to the Snooze 199 article and I want to comment on that (which is where I came in), should I have started a fresh thread? A...
by andrew jukes
Thu Apr 06, 2017 2:23 pm
Forum: Track and Turnouts
Topic: Re: Track and Wheel Standards
Replies: 35
Views: 9456

Re: Articulated beams?

Julian Forget speed for the moment - providing a running clearance for wheelsets is important whatever the speed. The design parameters I use on my own layout are: minimum radius 1200mm; all curves to have transition curves; track to accommodate Pacifics with scale 6’ 8” drivers and fairly limited s...
by andrew jukes
Wed Apr 05, 2017 11:10 pm
Forum: Chassis and Suspensions
Topic: Articulated beams?
Replies: 84
Views: 15163

Re: Articulated beams?

Julian I am getting confused! The compensated tender and which axle is fixed doesn’t seem related to the question of whether extra load on the leading axle is helpful or not. There are a whole lot of reasons why a three axle chassis with one end axle fixed is a bad idea. If you compare a fixed end a...
by andrew jukes
Mon Apr 03, 2017 2:36 pm
Forum: Chassis and Suspensions
Topic: Articulated beams?
Replies: 84
Views: 15163

Re: Articulated beams?

I read the reasoning in Snooze 199 with some interest but didn't really accept it. There are lots of reasons for derailments, wheelset under loading being just one. It is probable anyway that the wheelset most likely to derail is a leading wheelset but to jump from that to a conclusion that over-wei...
by andrew jukes
Fri Jul 17, 2015 1:58 pm
Forum: Track and Turnouts
Topic: Plastic Chairs suppliers.
Replies: 17
Views: 4765

Re: Plastic Chairs suppliers.

I think the thing you really need is the large table to be found in the download ‘General information on use’ under the Special switch and crossing chairs heading. Go to: http://www.finescale.org.uk/index.php?route=information/information&information_id=36 for this Seems like a lifetime ago that...

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