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Slaters plunger pickups with beam compensation


dpgibbons
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Do Slaters plunger pickups play well with loco suspension/compensation?

 

I'm building a Finney7 GWR pannier with beam compensation. The beam's vertical travel is constrained to ~1.6mm, which is well within the wheel tyre depth of 2.8mm. So if the plunger is centred on the tyre it should stay in contact whatever the suspension movement.

 

Hopefully somebody can confirm that thinking before I commit to using plungers.   

Edited by dpgibbons
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Posted (edited)
29 minutes ago, dpgibbons said:

Do Slaters plunger pickups play well with loco suspension/compensation?

 

I

 

Answer:  Yes absolutely...if you set them up properly.  Ideally they should be positioned at the centre line of the axles and if using slaters wheels, avoid the `plastic triangle at the back of the wheel tread.

 

315548363_wheeltread.jpg.a3f21fd2696584c43d52db8ec1526e57.jpg

 

I always apply a smooth finish to the backs of wheels.

 

And ALWAYS use very thin and flexible wire. so as not to impede the  plunger movement.

 

DSC02757.JPG.44b754f74e22a4273e63659a130fdb51.JPG

 

They are an excellent product....

 

DSC05765.JPG.84ae6e465f3545a3a08b3d6677d7711f.JPG

 

...the above is set up for DCC.

 

OOps... forgot ...   on beam compensation.

 

DSC04024.JPG.8b47458d0659b923c80228bd1e981b52.JPG

 

 

Edited by ROSSPOP
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18 minutes ago, dpgibbons said:

Do Slaters plunger pickups play well with loco suspension/compensation?

 

I'm building a Finney7 GWR pannier with beam compensation. The beam's vertical travel is constrained to ~1.6mm, which is well within the wheel tyre depth of 2.8mm. So if the plunger is centred on the tyre it should stay in contact whatever the suspension movement.

 

Hopefully somebody can confirm that thinking before I commit to using plungers.   

Oddly enough I was thinking exactly the same question as I contemplate starting a Judith Edge Hunslet 16".  The plungers are a must, the compensation beam optional. I left it out when I built the 15" version.

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I would suggest that compensation or springing is a major improvement to a loco - it's not essential, but I would not build a loco without it.

 

Plungers are perfectly fine, much better than backscratchers, not as good as split axles, ideally, as John says, plungers want to be aligned with the horizontal centre line of the axles, but that may not always be possible.

 

On 4-wheel locos, there will be a fixed axle and a central compensation fulcrum on t'other axle, so not an issue on the compensated axle

On most 6-wheel locos there will be a fixed axle, and a compensated pair of axles - using a single central beam, so there will be room on them. 

There may be some (John's 042 above) where there are a pair of compensation beams, and it is necessary to place the plungers outboard of the beams, or above or below.  Or to have a clearance hole in the compensation beam.

8 wheelers generally have a central beam between one pair of axles and a pair of beams on the other.  The central beam is easy, the pair of beams needs to be arranged for the plungers to miss it.

 

Fitting the plungers around the gearbox will generally be more challenging.

 

Split axles are another approach.  Very good, but lots of work.  See my Garratt "loco loco" thread for a description of Steph Dale's method.

 

atb

Simon

 

 

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Just from interest, could someone explain the advantage of placing the pick up in line with the axle centre. Apart from one or two tender locos with the "American system" all my locos have Slater's plungers.

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29 minutes ago, doilum said:

Just from interest, could someone explain the advantage of placing the pick up in line with the axle centre. Apart from one or two tender locos with the "American system" all my locos have Slater's plungers.

 

Slaters sprung plungers  usually cause minimal  drag but if possible keeping them ( two on each wheel set) on the axle centre line  they will act as a pivot  when the wheel set travels up and down in the hornguides.  Also keeping them in this position will ensure that the plunger has the longest surface wheel tread area  of travel with the movement of the wheels in the hornguides.  Strongly sprung plungers can prevent the compensation movement .

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9 hours ago, ROSSPOP said:

 

Slaters sprung plungers  usually cause minimal  drag but if possible keeping them ( two on each wheel set) on the axle centre line  they will act as a pivot  when the wheel set travels up and down in the hornguides.  Also keeping them in this position will ensure that the plunger has the longest surface wheel tread area  of travel with the movement of the wheels in the hornguides.  Strongly sprung plungers can prevent the compensation movement .

Thanks. I haven't built a loco with horn blocks apart from the Slater's Manning Wardle and that has wipers. Most of my builds have the axle bushes free and just a little vertical movement on the frames. Probably not great engineering practice, but in the main it seems to work. I do however have a couple of locos which have a directional preference for a particular dodgy point!

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If my limited experience of building four locos all featuring Slater's plungers is of any use:

 

All are older LNWR prototypes.    My first effort in 7mm was a Ramsbottom 4' 0-4-0.    It is the only non-sprung loco.    It has classic Sharman compensation: one axle fixed and driven, the other allowed to rock on a central pivot.

 

The Special Tank, Coal Tank and C class all have Slater's sprung suspension,  although only the Special Tank has yet been fitted with springs.

 

Some will say that the plungers work best when at axle level.    That is a luxury not allotted to me with my early locos with shallow frames.   The 4' shunter is a particular example.   

 

Just how rough IS your track, anyway?   I don't expect my axles to move more than half a mm going over my track.    Hard to measure, I admit.     But I don't think the plunger, if set at an exact half of the tyre of the wheel, is going to slide off.    On my Coal Tank I have a fair bit of wheel movement, and the plungers do come right up to the flange, but they don't shoot over.

 

My advice is to not worry too much, get the plunger as low in the frame as you may, get the contact point as close to the center of the back of the metal bits, and forge on.    It will work.

 

Oh, I also always ream out the hole in the plastic a bit, as I found that the plunger could occasionally jam up.

 

Kevin

Edited by bluestag
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I shied away from plunger pickups on this one....stiff phosphor bronze wipers on a fixed axle chassis.

 

DSC06084.JPG.c630ad55bf2e89bd0d2e5696faa8dbf2.JPG

 

 

 

 

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20 hours ago, ROSSPOP said:

I shied away from plunger pickups on this one....stiff phosphor bronze wipers on a fixed axle chassis.

 

DSC06084.JPG.c630ad55bf2e89bd0d2e5696faa8dbf2.JPG

 

 

 

 

Nice model.    Are you picking up from the other bogie as well?

 

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2 hours ago, bluestag said:

Nice model.    Are you picking up from the other bogie as well?

 

 

Yep! There are pickups on all the trailing bogie wheels but are not connected up at the moment as she is still under trials and works really well on the driving bogie...............................

 

 

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