Aerotrain rear truck doesnʻt swivel freely - derails on moderate "S" curve.

check and see the wire to the motors allow the motor to rotate freely. Sometimes the factory cuts the wire too short. When the motor turns, the tight wire pulls the motor to the side.

Could be a misdiagnosis. The KNOWN problem with this entire series  of Aerotrain is poor traction due to limitations of a single drive axle with limited weight on the rear truck, tiny secondary guide wheels, and the OTHER known problem the cars are high drag due to the fixed non pivoting axles.

You tie all that into combination, try to run it at low speed under DCS where the front truck has much better traction and weight, but the rear truck has the tachometer, and then you wonder why it derailed in an S curve?

Again minimally, a known thing was to add weight to the engine chassis because of this limitation of the rear truck coupled with the tach sensor and wheel slipping interaction. The weight removes the wheel slip, and since both motors see the same voltage but that voltage is based on what the tach is sensing the rear motor is doing- is now much more likely to match VS be completely mismatched.

I'm not saying you cannot have a binding rear motor truck and or wiring issue, I'm just saying, the symptoms and lack of detail of you making any of the recommended basic mods- more of the problem IMO.

Again, the KNOWN thing that happens- especially at low speed. The rear truck and motor since it is tachometer sensing and control determines the voltage of the front motor too. So you give it slow throttle, the rear wheels slip, but they do not spin uncontrolled- no, they spin controlled to a fixed commanded RPM. The amount of traction (or lack of) determines voltage feeding that motor to achieve that RPM. If unloaded or lightly loaded= very low voltage. Meanwhile the front truck gets the exact same voltage but has better traction. This means that motor does not slip, but may not yet have enough voltage to pull the train. You then have to give more throttle to "get over the hump" where again the back wheels are spinning, but more throttle does raise the overall voltage and now maybe, just maybe the front truck with full traction and not slipping begins to pull the train. At some point- OK now we are moving, but again is the single axle rear truck sitting there slipping the entire time compared to the actual movement of the train?

Now compound this into an S curve. The cars are dragging more, the traction in the engine likely is still slipping that back axle VS the front truck. Again, not surprising without additional weight it wants to climb the rail.

Again from this similar topic the notes https://ogrforum.com/...94#53801014952580894

@gunrunnerjohn posted:

If the engine isn't running smoothly at 4-5 scale MPH, it's broken!  If it doesn't move at all by the time you get to 3-4 MPH on the remote, I'd be very worried.  That is NOT normal!  That's the FIRST thing I'd be looking into.

Mine all had to do with the rear truck, I had to put some very small shims in to allow the rear truck pilot wheels to turn freely, and I had to adjust the bend in the truck part with the pilot wheels on it so it would run properly and not jump the tracks.  I've run it a few times since, several times for several hours, and so far it's run fine.  Oh, it's pulling ten cars, so it's capable of pulling them if it's working properly.

Mine is a PS/3 locomotive, but I bought it used in August of 2013.

Yet another Aerotrain traction topic

https://ogrforum.com/...07#77030152581942207

And again another great topic from @gunrunnerjohn

https://ogrforum.com/...c/154307983526545497

My own personal Aerotrain (a more recent PS3 Run), I added some K-line car weights to the engine frame that hang down and are hidden by the long sides that hang down from the body shell. I also did many of the improvement mods to make sure the tiny wheels roll free and try to get the cars rolling free too.

From K-line flatcars, many had a die cast weight held with 2 screws. Some people remove them (I've not been able to find them just as a single part)

Sorry I do not have my engine handy with pictures, but I mounted those weights 2 stacked) to the frame here hanging down in the hidden space in front of the rear truck but clear of the speaker opening. Again, they are on the bottom of the engine hanging down and completely hidden by the long drop sides of the engine shell.

I realize mine could be taken the wrong way.

If you really have a mechanical bind and the rear truck cannot rotate freely, by all means, that needs fixed- either finding the bur or binding point with the stamped frame hole, or possibly some casting flash or other problem on the die-cast motor mount that is sort of the bearing point to the frame.

But, even after fixing that, then there are more problems you are likely to find due to the drive system limitations and stock weight.

Put another way, I love of the looks of the Aerotrain and waited with my preorder to get my PS3 version and extra cars. This was one of the first trains I really had to wait on.

But like in Chevy Chase Vacation, "If you think you hate it now, wait until you drive it".

After some work and tweeking and running with the shell off to see what the motors were doing- then I got to the real problem solving.

I had to work on the rear trucks of both of my Aerotrain engines to get them to run reliably.  Reliably to me is able to pull the prototypical ten car consist around the layout, including the 2.5% grade.  The one challenge I don't know if they meet is any curves under O72, as I don't have any.

I've often though of taking one of these and fixing the rear wheels solidly and getting rid of the two tiny pony wheels on the front of that truck.  I'd like to see if that would help with the issues.  Again, I think getting that configuration to run any significant load on tight curves may be wishful thinking, but I haven't really tried.

I saw one guy that put a standard truck on the rear to resolve the issue.  Took away from the prototypical look, but sure increased the reliability!

@Vernon Barry posted:

From K-line flatcars, many had a die cast weight held with 2 screws. Some people remove them (I've not been able to find them just as a single part)

My K-Line flatcar cracked in the middle where that weight is located. There was certainly an incompatibility between the weight and the quality of the plastic. I removed the weight and glued the flatcar back together....and leaving the weight off.

Each time I put the Aerotrain back on the rails after a long time sitting on a shelf, the engine shorts out the transformer. I always forget there is a hidden wheel that needs to be on the track! 

@Bruce Brown posted:

Each time I put the Aerotrain back on the rails after a long time sitting on a shelf, the engine shorts out the transformer. I always forget there is a hidden wheel that needs to be on the track!

Wouldn't it be nice to lose those wheels.

Thanks to everyone for all the advice!

I decided to use mini-files to remove the the paint and some metal around the metal motor carrier where it fits into the frame.  I also noticed the frame was bent up and not flat.
All the metal was soft and easy to file/bend.    Added some thicker grease and the engine stopped derailing.  Still jerky going through 036 at speed 10 but okay on a 048 curve.  Added a single coach it started chattering in the 036.

Verdict - "needs more work", but that will have be be for another day.  Beautiful train that I hope to fix or that will run better on my planned 072 upper level. 

Some have been able to stop the chatter of the rear truck by adjusting the pivot arm.  I was not successful, but adding a pound of weight esp centered around the rear truck worked.

Bob