BLI PRR-P5A In Now

[delamaize]

I am glad I didn’t speculate on the GN or Mil Rd for grins and giggles.

I'm also glad I didn't jump on a Milw unit now...

[Ed Kapuscinski]

If you were to start that and it required folks to re-sign up I'd say pass.  Otherwise, yes.  So far the PM's look like they'll work, too.    There are over a dozen already and they're coming in a few more every time I check so... 

Sounds like you've got something working so no need to mess with it.

But keep it in mind in you ever need a sign up type form in the future.

[bbussey]

I got my drivers today. The bushings float. Looks like a gear-puller is all that is needed should the assembly not a drop-in replacement for the blind assembly. I’m going to wait until I receive the pilot truck fix from Mark @narrowminded before I open up the unit.

[motofavorite]

And it's so easy that even I could install them myself.

Thank you so much for finding a solution and sharing it. The movies were very helpful. I have been hesitant to buy the locomotive. I am not thrilled that it needs a retrofit, but sometimes an easy modification feels like a victory and keeps the modeling flame lit for awhile.

[peteski]

I got my drivers today. The bushings float. Looks like a gear-puller is all that is needed should the assembly not a drop-in replacement for the blind assembly. I’m going to wait until I receive the pilot truck fix from Mark @narrowminded before I open up the unit.

You called those brass things "bushings"?  In  my experience these are the actual axle bearings which are inserted into the frame.  When you mentioned bushings I thought it was the protrusions (shouldesr) that sticks out inwards from the wheel's inner face.

The  design of those axles looks similar to the ones in the BLI's T1 4-4-4-4 loco.  One of the half-axles ends in a metal cup shape (on which the gear is installed).  The other half-axle has a standard end.  Inside of the cup is a plastic sleeve into which the plain half-axle is pressed.  That keeps the half axles separate electrically, yet it results in a very solid connection. Since the plastic sleeve is surrounded by the metal cup, it is not prone to cracking, like in other manufacturer's designs which use plastic axle tuber with integrated gear.   This is actually a very ingenious design I have never seen used before BLI came out with it.  Kudos to BLI!

Here is a photo of the T1's axle design (without a gear) . I pulled the bearing off the plain half-axle. Ignore the turned down drivers -- it's a work in progress.

[bbussey]

That’s what BLI tech support called them. I don’t care what they call them as long as they included them.

[peteski]

That’s what BLI tech support called them. I don’t care what they call them as long as they included them.

I guess a bushing can be a bearing.     I also don't know how they could sell a wheelset without them, since at least the one on the cup-end half axle has to be installed before the wheel is pressed in.  But those bushings aren't really there to limit the lateral travel of the axle - they are there as bearings.  Aren't the the same as the ones on the outer axles?

EDIT: never mind. I found one of the earlier photos.  The center axle has extra "shoulder" on the inner side of the drivers which restricts lateral motion.  Those look to be part of the wheel.   Do the outer axles really freewheel when the shift to one side?!  That is a very odd design.  That would mean that on some really sharp curve the only driven axle would be the center one (which doesn't even touch the rail)!  And since these aren't synchronized gears, there will be some teeth grinding when they get back to center.

[narrowminded]

Stock truck springs from BLI arrived today and new bottle of resin is due tomorrow.  By tomorrow I should have the spring rate for the new spring and can proceed with the final design and testing.  It won't be long now.

[garethashenden]

Peteski, bushings are plain bearings. The inner surface is the bearing surface and whatever shaft goes through the hole is supported by that surface. They are the simplest form of bearing, no moving parts. They are better than just a hole in the part, because you can make them out of a different material, something with lower friction.

[peteski]

Peteski, bushings are plain bearings. The inner surface is the bearing surface and whatever shaft goes through the hole is supported by that surface. They are the simplest form of bearing, no moving parts. They are better than just a hole in the part, because you can make them out of a different material, something with lower friction.

Yes I looked it up -- bushing and bearing are used interchangeably.  I just only recall using the word bushing (like "rubber bushing") as applications that are not bearings.  But put some oil in them and then suddenly become bearings. 

[bbussey]

There does appear to be an extra shoulder on the center wheels.  But that's easily achieved via a number of avenues if the hybrid flanged wheel assembly doesn't stay put.

[narrowminded]

I am progressing on the pickup fix and decided to document the methods used to acquire good information allowing some confidence in each step along the way.  It started with the discovery of the problem but is completed with real information and real understanding of the issue and finally the documented results incorporated in the fix.  It's not all guess work and trial and error.   These videos show how the spring rate on the miniature springs was determined and then how the final proof of the effective change when installed was measured.  It helps to take out the guesswork and have some confidence in the changes made accomplishing the intended end.   I'll add final summary and assembly instructions before to ship.

Edit Add: BTW, the downward force on the trucks as the loco arrived, without the arm support I'm making, was 4.2 grams on the stock spring and with the spring stretched it only increased the force another .2 grams to 4.4.  The arm would just flex, absorbing the spring force that's supposed to be applied as downforce on the wheels.  The stock spring has about 18 grams when set at a serviceable height with sufficient excess travel to compensate for track irregularities, so available +/- 20 grams when the truck weight is added.  That's about perfect.  And with the stretched spring you can get the force high enough that it will cause the loco to tip itself off the rails in a curve when the trucks are pushing up on the loco off centerline.  As it arrived, at 4.2 grams, it never had a prayer.

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[narrowminded]

I finalized the dimensions and the parts are being printed now.  I should be able to figure out the packaging and get them shipped in the next two days, Friday or Saturday.

The final pieces with the stock springs get a very nice downward force on the trucks, between 20 and 24 grams.  That's a little more than the 4.2 grams it had out of the box.   That pretty well maximizes what's available in the spring while still leaving an appropriate amount of travel to absorb track and frog irregularities.  And if the force gets up above the mid 20's to mid 30's it causes the loco to be top heavy and wanting to tip in tight radius turns.  Fortunately that much force isn't available with the stock springs but was available with the stretched spring, which is how I know that it can make the loco top heavy.  

This also underscores what I suspected after finally discovering the issue, that the design selection of the spring force was appropriate and is consistent with the generally very nice quality of the components that can be seen, design as well as execution.  Evidence of very nice tooling and detail is abundant in this loco.  It also underscores what a shame and major oops it is that the arm rigidity slid through all steps of production, finally shipping to customers.  I actually have a little (not tooo much) sympathy for BLI in this.  I hope they are able to handle the issues without too much harm all of the way around.  IMO, it is a very nice loco with this issue fixed.  It's my new favorite... this week.

[peteski]

Sounds like that will be a nice modification Mark.
This also means that about 34 grams less will be supported by the drivers, so there will be less traction.  I don't know the total mass of the model, but I suspect that with the traction tire, this will not noticeably affect its pulling ability.

[narrowminded]

Sounds like that will be a nice modification Mark.
This also means that about 34 grams less will be supported by the drivers, so there will be less traction.  I don't know the total mass of the model, but I suspect that with the traction tire, this will not noticeably affect its pulling ability.

Yes, Pete.  The traction tire still pulls like crazy and I suspect will be desired by most.  With those tires it really pulls strong.  I also suspect that the original design intent was to have approximately the same thing I just did, just that the very flexible arm caused a BIG miss.  I don't think anybody thought that the original 4.2 grams per truck when the truck weighs 3.4 grams by itself was going to do anything except maybe keep the truck on the rails.  I write it off to a pretty big oops.

Edit add: The loco weight is 108. 6 grams and the trucks now take about 20 grams each from that so... it's still got a decent load on the main chassis and with the traction tires it should pull about anything you'd want it to.