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Author Topic: Why all wheel pickup?  (Read 3796 times)
Jim Banner

Enjoying electric model railroading since 1950.


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« on: July 27, 2008, 07:54:35 PM »

Simply put, the more pickup wheels, the lower the odds of losing contact with the rails.  Just for fun, lets play with some numbers.

Suppose the electrical pickup from any given wheel fails only 10% of the time.  Failure could be from dirty track, dirty wheel, dirty wiper, or any other reason, but the other 90% of the time each wheel picks up just fine.

Now suppose that we built a locomotive with only two pickup wheels, one on each side.  Then the chances of both wheels picking up power at any given instant in time is 90% x 90% = 81%.  That in turn means the chances of failure to pick up power at any instant in time is
100% - 81% = 19%.

If we double the number of pickup wheels to 4 (two on each side) then for each side, the chance of failure is 10% x 10% = 1%.  So the chances that both sides will pick up is 99% x 99% = 98%.  The chances of no pickup is 2%.

Continuing in this vein, we can develop a table for number of pickup axles versus failure to pick up.  First lets do it for 90% pickup reliability per wheel.

number of axles     failure, % of time

     1                             19%
     2                               2%
     3                               .2%
     4                               .02%
     5                                .002%
     6                                .0002%

A 2-8-0 with tender pickup is an example of a locomotive with six axles of pickup, four on the locomotive and 4 half-axles of pickup on the tender (they only pick up at one end.)

Ninety percent reliability per wheel is probably about right for clean wheels on clean track with clean, well adjusted wheel wipers.  But suppose both wheels and track are moderately dirty.  Then 50% reliability might be nearer the case.  Then the chances of failure for different numbers of axles would be something like this:

number of axles    failure, % of time

     1                                75%
     2                                43%
     3                                23%
     4                                12%
     5                                 6%
     6                                 3%

Now something amazing comes out of this.  Dropping the pickup reliability per wheel from 90% to 50% increases the failure rate by 15,000 times!  That is, the chance of failure to pick up power at any moment in time rises from .0002% to 3%.

The other day, I pulled an old coach off the shelf and ran it.  The interior lighting had only one pick up on each side and the lights flickered terribly.  I would guestimate they were on for only 10% of the time.  I wondered how much better they would be if I had pickup from 3 wheels on each side or maybe even six wheels on each side and calculated the following table for 32% reliable pickup from each wheel.

number of wheels       failure, % of time
on each side

     1                                 90%
     2                                 71%
     3                                 32%
     6                                 .2%

From this I concluded I would need pickups on each and every wheel, not just each and every axle with the usual one pickup wheel per axle arrangement if I wanted excellent pickup.  Alternately, I would have to add some anti-flicker circuitry and/or better pickups.


 
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japasha

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« Reply #1 on: July 27, 2008, 08:04:35 PM »

well put, Jim.

Many users (young) haven't a clue as to how many pickups their locomotives or cars have.

I did solve the flickering lights by using a 1.5 volt system backed up with small lithium batteries as used in computers. A set of capacitors will do the same thing, once fully charged.

The key here is to purchase equipment with maximum pickups as well as a good power transfer system (Contacts and wiring)
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richG
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« Reply #2 on: July 27, 2008, 10:46:57 PM »

I have converted my Spectrum 4-4-0 and 4-6-0 tenders to all wheel pickup like the new Roundhouse steamers. It does make a difference. Harold has a nice tutorial on how to do this.

Rich
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hminky
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« Reply #3 on: July 27, 2008, 11:16:29 PM »

Since Rich brought my article up:

http://www.minkystrains.org/tender_wipers/



I have found that all wheel tender pickup does the most for steam. The tender wheels have more contact since they are more flexible. I have a Bachmann Oldtyme 4-4-0 with just the tender for pickups that will run over atlas dead frogs with no problems.

Harold
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rogertra


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« Reply #4 on: July 28, 2008, 02:06:23 AM »


http://www.minkystrains.org/tender_wipers

Excellent, well worth bookmarking.


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faraway

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« Reply #5 on: July 28, 2008, 02:17:57 PM »

I use a somewhat simplified method. The new pickups are glued in place. From 2-8-0 down to 4-4-0 all my Spectrum steamers got that treatment. They run as if a battery is in the tender Grin

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Reinhard
Santa Fe buff

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« Reply #6 on: July 28, 2008, 05:01:12 PM »

My friend's Daylight 4446 4-8-4 doesn't have any tender pickup wheels, for the 8 driver wheels operate for the power. But a Life-Like diesel, like my GP38-2, has only two pickup axles, and only two traction or driver wheels. For it operates in a 'system'. The front set takes in the current, though wiring, and into the engine. The engine powers lights and then the rear set for power. Looking inside a Bachmann Spectrum F40PH I have, the power is in a 'cycle'. The driver wheels are also the pickups too. They pick  up the power, send  it to the engine, it makes the light, and uses a 'drive-shaft' like turning to move gears and rotate the axles. The 'cycle' is also what is used for the Daylight 4-8-4 and the other steam engines my friend has. Although he does have one Baldwin 2-6-0, with tender pickup wheels, but a wiring connection between the tender and the engine have it out of use. But the good thing is with the 8 tender pick ups, is that you can store some decoders in the tender that wouldn't fit in some small 0-6-0s. But my friends pick up wheels on his 0-6-0 are the 6 drivers. The engine is in the locomotive for no wiring or wires connect the tender, just a 0-6-0 camelback with a simple pin through hole connection.

well put, Jim.

Many users (young) haven't a clue as to how many pickups their locomotives or cars have.

I did solve the flickering lights by using a 1.5 volt system backed up with small lithium batteries as used in computers. A set of capacitors will do the same thing, once fully charged.

The key here is to purchase equipment with maximum pickups as well as a good power transfer system (Contacts and wiring)
I'm 12, but I do know my pick ups, well I think I have more to learn, but mostly, I don't see many kids that know this, but my friend does. Nothing personal, we're okay. Speaking of contacts, the F40PH I have uses the metal frame to transfer power, but it does get dirtly on the connections, so I take it apart and clean it with a dry Q-tip.

Oh, great percents, just like supply and demand. One thing goes down <number of axles>, and something goes up <failure % of time.>
So we could say a 4-8-4 with driver pick-ups, will fail less than a 0-6-0 with driver pick ups. Correct?

Simply put, the more pickup wheels, the lower the odds of losing contact with the rails.


I think I learned something today.  Smiley
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Joe Satnik


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« Reply #7 on: July 28, 2008, 05:30:53 PM »

Dear All,

This might be preaching to the choir, but I'll do it anyway. 

Hey, you guys missed a real important reason to have more pickups in the tender:

It makes more sense to have the DCC receiver close to the most pickups, and close to the motor.  Anyone with common sense would put the DCC receiver in the locomotive, not the tender. 

Guess where they end up?  In the tender, of course. 

Say you have 5 axels of pickup on the loco, and only 2 on the tender (4 half axels).  Those five wheels worth of loco pickup are combined and sent out a connector and across one of two fragile wires to the DCC socket in the tender.  If either wire breaks (usually at the plug), you've lost 5 of your 7 pickups on that side.

If the DCC socket were in the loco, you would only lose 2 of the 7 wheels with a broken wire in the track power umbilical.

Let's put 4 axels worth of pickup in the tender along with 5 in the loco.  Break an umbilical wire and you only have 5 of the 9 wheels dead on that side, with 4 still alive.  Four wheels alive is much better than two.

Hope this helps. 

Sincerely,

Joe Satnik 

Edit: changed "two fragile wires" to "one of two fragile wires" in Paragraph 5 above.  
« Last Edit: July 29, 2008, 07:09:13 AM by Joe Satnik » Logged

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Jim Banner

Enjoying electric model railroading since 1950.


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« Reply #8 on: July 28, 2008, 07:35:40 PM »

... a Life-Like diesel, like my GP38-2, has only two pickup axles, and only two traction or driver wheels.
I have a pair of similarly equipped Life-Like diesels that both run about the same speed.  I permanently connected them back-to-back and wired them motor-to-motor.  Voila.  An eight wheel pickup, eight wheel drive locomotive set.  With the traction tires, it pulls stumps.  Over forty fully weighted cars up a 3-1/2% 36" diameter helix.  Pickup is as good as any other 8 wheel pickup locomotive on the layout.

Speaking of contacts, the F40PH I have uses the metal frame to transfer power, but it does get dirtly on the connections, so I take it apart and clean it with a dry Q-tip.
A small drop of conductive oil on the contacts, where the rings touch the frame pieces, helps the connections stay cleaner longer.  (I am assuming it is a Bachmann F40PH.) The oil suppresses arcing which creates a paticularly nasty type of dirt.

So we could say a 4-8-4 with driver pick-ups, will fail less than a 0-6-0 with driver pick ups. Correct?
All else being equal, yes.

I think I learned something today.  Smiley

I think we all did, thanks to the links to Harold Minky's excellent article on adding all wheel tender pickup.  I wonder if anyone has tried the stock pickups for the uninsulated wheels combined with Minky pickup for the insulated wheels.

To add to Joe Satnik's argument for putting the decoder in the locomotive, this also reduces the number of wires between the tender and the locomotive to three - left pickup (black), right pickup (red), and tender light (yellow).  For the tender light common connection, you can return it to one rail for half wave operation or return it to both rails via diodes for full wave.  The fewer wires between locomotive and tender, the lower the likelihood of derailing the tender.  The number of wires can get right out of hand when you start adding a light inside the cab to let the engineer read his orders, lights under the cab for oiling around at night, and a flickering light or two in the firebox.  It also leaves more room in the tender for a sound system, if so inclined.  I managed to stuff a Digitrax DZ125 decoder into an H0 Bachmann CN Mogul, using the space normally occupied by the smoke generator.  I want to try a Sound Bug in the tender, which should leave lots of room for a speaker.  I modified a tender frame from a Connie to fit under the Mogul's tender just to get extra pickups.  Now I am thinking of modifying it again by adding Minky pickups, either alone or in combination with the stock Spectrum tender pickups.
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Rashputin

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« Reply #9 on: July 29, 2008, 07:01:58 AM »

   Thanks for an interesting post.  And, you know, you seem to post a lot of interesting stuff, so thanks for all the ones I read and didn't thank you for.  Oh, and forget that one blooper of a post, no one will remember it by now Wink.

   Regards
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Jim2903

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« Reply #10 on: July 29, 2008, 02:26:21 PM »


http://www.minkystrains.org/tender_wipers

Excellent, well worth bookmarking.



I agree. However, while mounting the wiper to the truck seems straightforward, what I'm unclear on is how to wire the wiper to the loco.

Also, did you use Neolube just because you wanted to paint the backs of the wheels? I'm sure you can pick up power from the bare metal wheel.
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Jim Dudlicek
Hoffman Estates, IL

Cascade International Ry.
Santa Fe buff

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« Reply #11 on: July 29, 2008, 05:15:26 PM »

... a Life-Like diesel, like my GP38-2, has only two pickup axles, and only two traction or driver wheels.
I have a pair of similarly equipped Life-Like diesels that both run about the same speed.  I permanently connected them back-to-back and wired them motor-to-motor.  Voila.  An eight wheel pickup, eight wheel drive locomotive set.  With the traction tires, it pulls stumps.  Over forty fully weighted cars up a 3-1/2% 36" diameter helix.  Pickup is as good as any other 8 wheel pickup locomotive on the layout.

Speaking of contacts, the F40PH I have uses the metal frame to transfer power, but it does get dirtly on the connections, so I take it apart and clean it with a dry Q-tip.
A small drop of conductive oil on the contacts, where the rings touch the frame pieces, helps the connections stay cleaner longer.  (I am assuming it is a Bachmann F40PH.) The oil suppresses arcing which creates a paticularly nasty type of dirt.

So we could say a 4-8-4 with driver pick-ups, will fail less than a 0-6-0 with driver pick ups. Correct?
All else being equal, yes.

I think I learned something today.  Smiley

I think we all did, thanks to the links to Harold Minky's excellent article on adding all wheel tender pickup.  I wonder if anyone has tried the stock pickups for the uninsulated wheels combined with Minky pickup for the insulated wheels.

To add to Joe Satnik's argument for putting the decoder in the locomotive, this also reduces the number of wires between the tender and the locomotive to three - left pickup (black), right pickup (red), and tender light (yellow).  For the tender light common connection, you can return it to one rail for half wave operation or return it to both rails via diodes for full wave.  The fewer wires between locomotive and tender, the lower the likelihood of derailing the tender.  The number of wires can get right out of hand when you start adding a light inside the cab to let the engineer read his orders, lights under the cab for oiling around at night, and a flickering light or two in the firebox.  It also leaves more room in the tender for a sound system, if so inclined.  I managed to stuff a Digitrax DZ125 decoder into an H0 Bachmann CN Mogul, using the space normally occupied by the smoke generator.  I want to try a Sound Bug in the tender, which should leave lots of room for a speaker.  I modified a tender frame from a Connie to fit under the Mogul's tender just to get extra pickups.  Now I am thinking of modifying it again by adding Minky pickups, either alone or in combination with the stock Spectrum tender pickups.



You guessed it!


My friend's Daylight 4446 4-8-4 doesn't have any tender pickup wheels, for the 8 driver wheels operate for the power. But a Life-Like diesel, like my GP38-2, has only two pickup axles, and only two traction or driver wheels. For it operates in a 'system'. The front set takes in the current, though wiring, and into the engine. The engine powers lights and then the rear set for power. Looking inside a Bachmann Spectrum F40PH I have, the power is in a 'cycle'. The driver wheels are also the pickups too. They pick  up the power, send  it to the engine, it makes the light, and uses a 'drive-shaft' like turning to move gears and rotate the axles. The 'cycle' is also what is used for the Daylight 4-8-4 and the other steam engines my friend has. Although he does have one Baldwin 2-6-0, with tender pickup wheels, but a wiring connection between the tender and the engine have it out of use. But the good thing is with the 8 tender pick ups, is that you can store some decoders in the tender that wouldn't fit in some small 0-6-0s. But my friends pick up wheels on his 0-6-0 are the 6 drivers. The engine is in the locomotive for no wiring or wires connect the tender, just a 0-6-0 camelback with a simple pin through hole connection.

well put, Jim.

Many users (young) haven't a clue as to how many pickups their locomotives or cars have.

I did solve the flickering lights by using a 1.5 volt system backed up with small lithium batteries as used in computers. A set of capacitors will do the same thing, once fully charged.

The key here is to purchase equipment with maximum pickups as well as a good power transfer system (Contacts and wiring)
I'm 12, but I do know my pick ups, well I think I have more to learn, but mostly, I don't see many kids that know this, but my friend does. Nothing personal, we're okay. Speaking of contacts, the F40PH I have uses the metal frame to transfer power, but it does get dirtly on the connections, so I take it apart and clean it with a dry Q-tip.

Oh, great percents, just like supply and demand. One thing goes down <number of axles>, and something goes up <failure % of time.>
So we could say a 4-8-4 with driver pick-ups, will fail less than a 0-6-0 with driver pick ups. Correct?

Simply put, the more pickup wheels, the lower the odds of losing contact with the rails.


I think I learned something today.  Smiley
But sadly, my Life-Like GP38-2's wiring has broken off, and I don't have any soldering tools. And when I was lubing my F40PH, a screw that connects the two metal frames, fell off, and I lost it. When I was lubing my normal Bachmann F9, my dog side swiped me, and it fell, the loss trunk caught, and tore the wire off, yet again, I need soldering tools for that too. My final engine I have is my Life-Like F7, which is so terrible, I have to pushing is and get is a winding start just to get is to move, so yeah, I have no engines now.  Sad

I think I might just buy a new one, or call it up, but my dad will have to do it. The life-like one is under warranty, the second one they sent me, so we can get a new one easy. Now that F40PH, we might find that screw in my room. Oh forget it, I'm getting an GE Dash-9-44CW anytime soon, and my dad can fix that GP and the F9. That PH is okay, I can find the screws.
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- Joshua Bauer
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