Rapido N-Scale FP9A Wheel Gauge Issue

[tehachapifan]

There’s got to be some middle ground here.
You should expect an expensive new release to perform admirably on a layout with 18” radius curves but shouldn’t your expectations be diminished somewhat if you expect the same reliability on 9-3/4” curves?

Agreed. That said, I recall having the wheel hop issue on my 22" 20" min radius curves until I set the wheel gauge slightly narrower. Again, this was with at least one brand of 3 axle truck.

[wazzou]

Agreed. That said, I recall having the wheel hop issue on my 22" 20" min radius curves until I set the wheel gauge slightly narrower. Again, this was with at least one brand of 3 axle truck.

Just curious if that was with one unit or a consist of 2 or more?
I only ask because I wonder if say, the lead unit is being shoved slightly by a trailing unit/s, if this a more common occurrence?

[Point353]

The standard standard. 
Seriously, to the NMRA gauge shown in Doug's photo.

But, for which NMRA wheel type is that NMRA gauge intended?
The flange spacing varies slightly among the three wheel types.

[tehachapifan]

Just curious if that was with one unit or a consist of 2 or more?
I only ask because I wonder if say, the lead unit is being shoved slightly by a trailing unit/s, if this a more common occurrence?

No, this is caused by lack of side-to-side play in at least some 3 axle trucks. I recall this being discussed I believe here at length many years ago where, IIRC, someone drew up a diagram of what happens on a curve with 3 axles and no side-to-side play. Basically, with adequate side-to-side play a 3 axle truck will roll freely around a curve whereas one without side-to-side play will be in more of a binding-type configuration (if that makes sense). However, instead of actually binding, one or more wheels will tend lift instead due the shape of the rail and the wheel/flange. I think that discussion began when someone noticed the center wheel in an Atlas SD50/60 truck hopping when in a curve.

[BCR751]

There is no part number -- I make those washers myself.
I take the appropriate thickness sheet styrene, drill bunch of holes with a #57 (1.13mm) drill bit, then punch the washers out using a 2.0mm punch in a punch set I got from Micro-Mark.

I knew there had to be a catch

Doug

[BCR751]

As mentioned, I was able to set the wheel gauge on the FP9A using the NMRA standards gauge.  I put the loco on the track for a test run.  Just prior to entering a turnout, the rear truck hung up and the unit stopped dead.  Thinking I had something on the track, I did a close inspection and couldn't see anything that would cause the problem.  The problem did occur at the junction of two pieces of track so I did a little filing in case one of the joiners was a tad too tall.  Tried running again and got the same result. 

Also, the loco would hiccup all around the layout as if there was a huge amount of dirty track.  The entire loop was cleaned prior to running the test.

Becoming increasingly frustrated, I wanted to try a comparison.  I put the old MiniTrix FP9 (30+ years old now) on the same loop, fired it up on DC and it ran the entire loop, including the problem spot, with not one issue.  No hiccups and no hang-ups.

Not sure what to make of these results.  Maybe in the quest to be all things to all people, these new offerings are so sophisticated they are just too finicky.  Maybe the old Trix unit is more forgiving.  I don't know.  I'll keep fiddling with the new FP9A and hopefully I can get it to work.  As a previous poster said, however, these expensive units should work well right out of the box.  I don't mind doing a bit of troubleshooting but there is a limit.  We'll see.

Doug

[Mark5]

Traction tires and pick up wires from trucks to frame. N scale locomotive construction is going back to the 1970s.

Traction tires probably are not such a big deal any more as with free rolling trucks and flywheels any electrical conduction gaps caused by the TT is likely not impacting operation. But if the point of the wires is a solid connection so the sound decoder doesn't cut out, and you add traction tires which reduce the number of places to conduct electricity from track to mechanism....

Do those that might be curious, the FP9s include a parts bag which includes a spare geared wheelset - with no traction tire. 

[learmoia]

No, this is caused by lack of side-to-side play in at least some 3 axle trucks. I recall this being discussed I believe here at length many years ago where, IIRC, someone drew up a diagram of what happens on a curve with 3 axles and no side-to-side play. Basically, with adequate side-to-side play a 3 axle truck will roll freely around a curve whereas one without side-to-side play will be in more of a binding-type configuration (if that makes sense). However, instead of actually binding, one or more wheels will tend lift instead due the shape of the rail and the wheel/flange. I think that discussion began when someone noticed the center wheel in an Atlas SD50/60 truck hopping when in a curve.

Yeah, that makes sense.. the middle axle needs to be set slightly narrower than the outer axles... OR.. the needle points need to be filed down on the center axles, to allow more movement in the center axle.   Maybe the wheel profile is designed in a way that in a binding situation, the wheel can walk itself up the flange and lift the wheel off the track, then circling back to 'not enough play in the truck' the whole truck lifts up and derails.

If your removed or shortened the points of the center axle, the problem would be eliminated.

Shouldn't be an issue with 4 axle or inside wiper locomotives though.

[peteski]

There are likely thousands (or tens of thousands) of 6-axle locos from Atlas and Kato out there, and they all use the same pointy-axle design (with all the wheels having the same (very small) amount of lateral play on all the axles, and we don't see any modelers complaining about having problems with them on curves.

I know that there is no extra lateral play on the middle axle because I have serviced dozens of them, and the bearing cones are all the same depth, and the wheelsets are all the same (and interchangeable).

[peteski]

As mentioned, I was able to set the wheel gauge on the FP9A using the NMRA standards gauge.  I put the loco on the track for a test run.  Just prior to entering a turnout, the rear truck hung up and the unit stopped dead.  Thinking I had something on the track, I did a close inspection and couldn't see anything that would cause the problem.  The problem did occur at the junction of two pieces of track so I did a little filing in case one of the joiners was a tad too tall.  Tried running again and got the same result. 

Also, the loco would hiccup all around the layout as if there was a huge amount of dirty track.  The entire loop was cleaned prior to running the test.

Doug, are you saying that after you regauged the wheels, the loco still climbs over the frog of the turnout (in the same exact spot as before regauging).

And that it also now runs very poorly (as if there was electric pickup problem ) over tangent track?  Did the loco run smoother over  those areas before regauging?

[BCR751]

It's NOT bumping over the frog, it is doing it prior to entering the turnout at the junction between two pieces of flex.  I can't find the reason for it.

This morning, I decided to see if the pick-up issue was happening on the layout trackage due to some unforeseen grime that I wasn't able to remove.  So, I hooked up a piece of brand new spotless (I cleaned it with IPA) ME Code 55 flex track to the DCC system.  I set the FP9A on the track, fired it up and it made it down the track about an inch and died.  When I touched it very lightly on top of the body shell, it would come alive again and when I removed my finger, it would die.  I got it to move along down the track but it would die frequently and touching the shell would bring it back to life again.  I gotta believe there is a pick-up problem inside the shell.  I tried calling Rapido to see if they have had any similar situations with other units but their answering machine says "due to COVID, we will not be answering the phone".  HUH?  Anyway, it looks like it may have to go back.

Doug

[Chris333]

Checking locomotive wheel gauge has always been a thing. If I checked a loco that was in-gauge I'd say out loud "Holy $hit".

[tehachapifan]

Yeah, that makes sense.. the middle axle needs to be set slightly narrower than the outer axles... OR.. the needle points need to be filed down on the center axles, to allow more movement in the center axle.   Maybe the wheel profile is designed in a way that in a binding situation, the wheel can walk itself up the flange and lift the wheel off the track, then circling back to 'not enough play in the truck' the whole truck lifts up and derails.

If your removed or shortened the points of the center axle, the problem would be eliminated.

Shouldn't be an issue with 4 axle or inside wiper locomotives though.

All not necessary, at least in my experience. I've solved any issues I was ever having by simply setting the wheel gauge SLIGHTLY narrower than the slots on my MT wheel gauge (I only ever noticed some center wheel hopping on curves in a couple Atlas 6 axle locos). In most N scale diesel loco designs, setting the wheel gauge slightly narrower shortens the distance between axle points. Aesthetically, having the wheels gauged slightly narrower than according to Hoyle doesn't bother me in the least. Now, if the slightly-narrower gauge setting was causing any type of running issues, that would be another story. One possible issue could be the axle points aren't making as good of electrical contact with the axle cups or there are problems running through turnouts, etc., as someone mentioned earlier in this thread.

...it's worth mentioning that I believe Kato has perhaps tried to add some more side-to-side play in their more-recent 6 axle trucks with a revised truck contact strip design, where the centermost axle contact point is on it's own spring piece as opposed to one solid contact strip containing all 3 axle cups. Plus, I believe they're now going with a thru-the-hole contact point design vs. the more common axle cup concept.

[BCR751]

Well, I've eliminated the pick-up problem on the FP9A.  I buffed up the pick-up/axle contact spots and changed out the wheelset with the traction tires to a regular one with no tires.  Runs all the way around the layout loop like a top now, no hiccups.  Thanks to Rapido for including the tire-less wheel set in the extra parts bag.  I also tightened up a bit on the wheel gauge based on some of the replies in this thread.  I also found out that the "bumping" of the rear truck was being caused by a slight difference in rail height at the track joint.  The rear truck was the one with the traction tires and that little bit of rail height was digging into the rubber tire just enough to cause it to hang up.  I filed that down and no more issue with that.

Thanks for all the help with this.

Doug

[dangerboy81]

I have been way deeper into these locomotives than I should be, but I would rather work the problem out myself (if possible) than send it back and risk having it come home with the same problem.
I have some contact issues, some times it is fine for an hour, then suddenly stalls here and there. I will try really cleaning the contacts. On paper, I think this pick up system should be great. The GMD-1's look the same, but  my 2 GMD-1's run really well, and quiet.
 The problem I am having sounds like gear noise. Like a grinding or clicking now and then. I would like to pick the brains here. I have found the gears have a lot of movement on their shafts. They don't move enough to dis engage from each other. Do you think that could be a problem? I have put very thin shims in to keep the gears in place. I wonder if the gears should have that movement in them? The shims don't seem to have improved anything, but there are still 1 or 2 gears in the truck that could get a shim. I told you I am way deeper into this than I should be!
another thing, look at the top gear (closest to the fuel tank. It seems to wobble on it's shaft. That can't be helping! You can see my little plastic shims to keep the gears in place.

Click the picture. I have the video hosted on Flickr.

Looking for advice. by Leon Richard, on Flickr