What's the secret to proper double heading on the layout?

[OnTheBranchline]

I've noticed in a bunch of YouTube videos that double heading can be a bit difficult in model form.

 

- In one video: two 45xx's haul a load of coaches - it's noticeable that the 2nd 45xx is going at a faster rate.

- In another video: a 42xx and bigger engine (4-6-0 but not sure which one) are running together and the 42xx is dillydallying in front, probably due to the lower gearing, and the 4-6-0 is going like it's trying to break the speed record.

 

It's unclear if these layouts are DC or DCC - I would think that DCC makes double heading a bit easier. Having two of the same engine class would probably be best because then the relative performance is the same.

[The Johnster]

My own layout is DC and I rarely double-head, sometimes I run the coal train with a pair of Baccy panniers, so with that proviso:-

 

.Yes, I think DCC would make this much easier as each loco's motor will be able to react to the load placed on it at any given time, in real time, and the load will in theory be shared between them on Marxist principles, from each according to their ability...

 

.Life is easier when the double-heading is performed by engines with similar mechs and gearing ratios, bearing in mind that the final drive ratio to the driven axle is not the same thing as the extra effect on the overall gearing by driving wheels of different diameters (the same mech with the same motor and gears with different sized driving wheels has the same gearing ratio at the driven axle, but different ratios at the railhead, smaller driving wheels offering lower gearing and greater T.E. at the cost of higher speed.  Compare a 28xx, Hall, and Saint, basically the same boiler and cylinders with different diameter driving wheels).  This is why my double-headed Bachmann panniers work well, but even so no two locos are absolutely identical in performance and one will always be doing more than it's share of the work.  So, if you wanted to pilot a Castle with a 57xx, you would get the best results from trying to match the gearing ratios at the railhead in order to even out the work each engine is doing.  Otherwise the Castle simply pushes the pannier or the pannier tries to pull the Castle, and the overall tractive effort available to pull the train is actually lessened!

 

.This is more important when you are banking in rear, where mismatched locos mean that the wagons in the train either bunch up or are pulled excessively apart, leading to derailments on curves especially if they are of differing weights.

 

.What you are aiming for is a tight coupling between the pilot and the train engine when running, without obvious struggling from either loco,  Banking in rear, you are looking for a generally slackish but not completely buffered up coupling somewhere towards the middle of the train, showing where the load is divided between the locos.  This will be a moveable feast over several wagons.

.

[Mike Buckner]

Perhaps the engine with the tendency to go faster should be placed behind. It will be somewhat impeded by the weight of the train, reducing (or maybe eliminating) the extra effort needed to push the slower loco in front. The coupling between the locos should give a clue as to whether the lead loco is pulling its weight or being pushed.

 

I saw a 4-person tandem cycling along the seafront in Brighton the other day. One of them definitely wasn't pedalling.

 

 

Edited November 6, 2023 by Mike Buckner
Afterthought

[34theletterbetweenB&D]

The real benefit with DCC is obtained by speed matching loco performance. Then you can do the job properly,

 

Adding an assisting engine, typically coupled to the train, first having uncoupled and moved the train engine out of the way, and then backing it down to couple up on front. No track sectioning required.

Make the locos into a consist so that they are controlled together.

And run the train.

When at a stop or destination to break up the double header, undo the consist.

Now drive the leading loco away, and then the assisting engine, and so forth.

Again no need for track sectioning.

 

When DCC was relatively new, it was often suggested that Back-EMF speed regulation be turned off on one of the pair to prevent the two decoders 'fighting'. Never found that necessary with Lenz and Zimo decoders on good mechanisms.

[The Johnster]

1 hour ago, 34theletterbetweenB&D said:

typically coupled to the train,

 

Not always by a long chalk.  The GW insisted on this practice according to legend, but AFAICT it was only done on the South Devon banks.  Assistance by pilot engines from Severn Tunnel Jc or Pilning in the down direction was done by couplng the pilot ahead of the train engine.   In the up direction some passenger trains were piloted as far as Badminton, uphill all the way from the bottom of the Tunnel.  Down trains had an easier ride, but had to cope with over two miles at 1 in 90 from Tunnel bottom.  Assistance was provided in a similar manner in the up direction on Filton Bank.  Abergavenny-Llanvihangel was done uncoupled in rear, Lickey style.

 

These operations were carried out under the authority of local instructions contained in the appropriate Sectional Appenices, and could vary quite widely between locations.  They are fundamentally differenct from double-heading for the entire length of a journey, which might be done to cope with overloading, common on the LNW* and the Midland, or to save a path with a loco returning to it's home depot (Windward Islands, piloting Princess Anne, both destroyed in the Harrow & Wealdstone crash, was doing this).  In the latter case, it doesn't matter as much if the pilot isn't doing it's share of the work because the load is within the train engine's capacity anyway.

 

Loaded iron ore trains often needed banking and assisting; the Tyne Dock-Consett and Aberbeeg operations  are well-known but the shorter haul Port Glasgow-Motherwell trains with top'n'tailed WD 2-10-0s were pretty spectacular as well, and much less photographed.   But I am more impressed with loaded iron ore between Darren & Deri and Dowlais Cae Harris; double-headed 56xx, 56xx in middle of train to ease strain on couplings, and a coupled pair of uncoupled 56xx bankers in rear.  Brutal and a bit steep; the load was 28 wagons and the noise in the narrow defile of the Bargoed Rhymni valley must have been wonderful!

 

 

*Which often used obsolete singles that could make the speed for the work, which is one of the reasons that Columbine and Cornwall survived to become Engineer's locos. 

[wasdavetheroad]

According to Digital wiki??? with DCC speed matching to within 10% is good enough. I have 2 Hornby 2P 4-4-0's that were within 3% straight out of the boxes. I ran them light engine coupled around the layout with the faster loco in front and observed the tension lock coupling carefully. On 3 sections around the circuit the tension lock slackened and the slower loco was pushing!. Even at 10% difference when pulling a train with the slower loco in front the weight of the train has the faster loco as the slower loco of you see what i mean and the couplings remain under tension for the complete circuit.

 

For DC double heading i remember reading on a US site that it helps if climbing an incline one loco can't pull the train on its own and as long as you don't get wheel spin or skidding you should be OK

 

I don't have much need for double heading but can occasionally just couple 2 x 2P's to pull a 8 coach passenger train. Normally i will just use a Black 5 instead. Another consist i might try one day is a compound 4-4-0 piloting a 4-6-0. In this case i would have 2 or 3 different 4-6-0's speed matched with the Compound.

 

ps- I use battery powered radio control but the principles are somewhat similar to DCC

[pH]

3 hours ago, The Johnster said:

… the shorter haul Port Glasgow-Motherwell trains with top'n'tailed WD 2-10-0s were pretty spectacular as well, and much less photographed …

The reason that there were fewer (actually no) photos of Port Glasgow-Motherwell iron ore trains would be because there were no such trains.

 

The two flows of iron ore in the Glasgow area were General Terminus to Cambuslang or Motherwell (Ravenscraig) on the south side, and Rothesay Dock to Coatbridge on the north side.

 

These trains were almost exclusively handled by pairs of WDs , but both on the front - no banking. I’ve only seen pictures of 2-8-0s on these trains but, given that Motherwell, Hamilton and Polmadie all had allocations of 2-10-0s at various times, I would be pretty sure that these could turn up on the General Terminus trains. Polmadie’s three Stanier 8Fs also appeared at times.

[DCB]

I do a lot of double heading.   You need a decent controller For DC  you need something which gives around 7 volts at half speed off load.  Duettes etc give 20 volts plus. and you can have one loco slipping furiously and another not moving when you try to double head with them  I have Morley, OnTrack and elderly Hammant and Morgan Safety Minor which is an  autotransformer     All give 7 volts on a tester at part throttle.  With these most locos will pair up, Hornby 42XX Bachmann std 5 and a few other odd balls won't play ball as they are too low geared but  most locos will pair up.  My 00  61XX  prairies, 43XX, Halls Manor, Grange, Bachmann 57 and 45XX . Hornby Pannier all happily act as bankers .  As I said with "Resistance" controllers one loco will happily sit there slipping furiously and another not actually move unless they are very similar mechanically  and in a similar state of dereliction.  
DCC is  a conundrum. It should be brilliant, separate control of both locos  but  there just does  anything available which allows rapid fine control to catch a slip,  the sort of thing a 1950s Hornby Dublo controller provides.   Consisting is great for US lash ups which are controlled by a single throttle  but I want to control the locos separately so the banker can drop off a moving train at the summit (which I do with DC, good  judgement and well placed section switches) 
Maybe its about time DCC embraced ergonomics, but if you want to double head bin the resistance controllers, Duettes and the like..

Edited November 7, 2023 by DCB

[kevinlms]

2 hours ago, DCB said:

Consisting is great for US lash ups which are controlled by a single throttle  but I want to control the locos separately so the banker can drop off a moving train at the summit (which I do with DC, good  judgement and well placed section switches) 
Maybe its about time DCC embraced ergonomics, but if you want to double head bin the resistance controllers, Duettes and the like..

There is absolutely no reason why you cannot do this with DCC, most controllers are capable of controlling 2 locos separately easily.

[wasdavetheroad]

Banking would be a more complex problem than double heading or piloting which can have both locos using the same throttle but 'putting a sock on it' requires careful monitoring of the banker to avoid pushing too hard and causing a derailment. My solution for DC would be to use a battery powered radio controlled banker not coupled and having say a Hornby medium coupler bar without hook to push on the train brake van with a hook less coupler and not a wobbly narrow tension lock.

 

The problem with a radio controlled banker, say a 2-6-4T is finding space for the battery but apparently you can take power from the rail. I just googled it and other locos were used including a A4! and an interesting story about a 9 car DMU assisting a stalled Black 5 on a mixed freight outside Preston

[Chris M]

So long as the speed of the locos is somewhere near double heading works very well with DC. You can even put a helper in the middle because the drag of the wagons effectively keeps the speed of the helper down.

 

 

Edited November 7, 2023 by Chris M

[Chris M]

Here's a vid I made a few years back regarding double heading and banking with DC

 

[Chris M]

Just prove I'm no luddite here is a little vid I made showing how useful DCC can be when banking is required.

 

[34theletterbetweenB&D]

8 hours ago, wasdavetheroad said:

According to Digital wiki??? with DCC speed matching to within 10% is good enough.

Very much for the operator to choose I feel. I operate a lot, much more than most, and most UK OO RTR product has plated tyres. These wear through with normal single loco operation, I wouldn't choose to accelerate wear by having one or both locos slipping against each other when using two or more coupled up. (My main use of locos running coupled up is 'trots' moving between KX loco and KX to reduce track occupancy, rather than hauling trains; what with the GNR, LNER and BR(ER) being agin this sloppy midlandish tendency.)

 

Matching performance is so easy on DCC anyway, why not go for ideality instead of 'that'll do'?

[GONK43]

OK

Heres what I do. Right or wrong. All in dcc. I take my locos, and disconnect the worm wheel and driveshafts.

Then it becomes a towed load behind the powered locomotive. I

[GONK43]

Sorry something happened there.

Then it becomes a towed load behind the powered locomotive. It is difficult in dcc to consist the locos for me.

This does not affect lighting, which can still be operated under the towed locos address.

And before anyone posts a reaction saying `no its easy`, It may be for you, but some others like me start getting into all sorts of loco running issues by adjusting this and that. When you want, put all the parts back where they came from.

Just my two bits worth, and it works for me.

[melmerby]

12 minutes ago, GONK43 said:

Sorry something happened there.

Then it becomes a towed load behind the powered locomotive. It is difficult in dcc to consist the locos for me.

This does not affect lighting, which can still be operated under the towed locos address.

And before anyone posts a reaction saying `no its easy`, It may be for you, but some others like me start getting into all sorts of loco running issues by adjusting this and that. When you want, put all the parts back where they came from.

Just my two bits worth, and it works for me.

Difficult that way if you are double heading for a reason and not just appearance as you appear to be doing.

[GONK43]

Yes melmerby, just for appearance.

Onthebranchline`s thread states that one loco travels at a different speed to the other because of slight difference in loco motors/gears etc. That was my way of eliminating that, and giving him/her one solution I use.

My train lengths will never need both power units to haul the train.

Have a good un.

[sncf231e]

Who needs DCC when you can double head with clockwork

Regards

Fred

[rogerzilla]

If you take the front couplings off tender locos, as I do, the slower loco has to go at the front.  I have two Hornby Kings (James II and Henry II; I mean to renumber Henry as William III as an in-joke).  Even though the models are otherwise identical, Jim is a bit faster than Billy.

 

I'm not sure how many trains would have needed two Kings, but that's another question!

Edited November 14, 2023 by rogerzilla