Octan Coach from 7939 Grinds in Bends

[Missing Brick]

Just wondering if anyone else had noticed this problem. Because the Octan trailer has fixed wheels that don't rotate, 11 studs apart, when it goes thru a bend the wheels grind causing alot of drag. Saw some videos of people pulling 10 Octan coaches - so I guess they must have modified their bogeys. But single wheel bogeys would be unstable and cause derailment. So I guess you'd need an extra pair of wheels on each bogey. Either that or they have a mega powerful engine...

[JopieK]

Hmm, not very smart that LEGO didn't think of that! Just modify it indeed I would say!

[Phoxtane]

This is something that's bothered me with every "short" train car I've built. They feel too short to be a proper train car, and I've never seen a full-size train car, real or not, that has its wheelsets like that.

[graafderk]

They feel too short to be a proper train car, and I've never seen a full-size train car, real or not, that has its wheelsets like that.

You mean with just two axles in a fixed arrangement? Like this?:

EDIT: apparently some security measure of the website kicked in...

Edited December 21, 2012 by graafderk

[splatman]

You mean with just two axles in a fixed arrangement? Like this?:

I don't understand what's going on in that pic. And link leads to just that pic. And I don't even know what language the text is in.

[graafderk]

I don't understand what's going on in that pic. And link leads to just that pic. And I don't even know what language the text is in.

It was Dutch. Apparently the website does not like it if you link to their pics... I changed the image now.

[Phoxtane]

Well, I stand corrected. Either way, I don't really like how it's handled on the Lego train cars - they'd have to be extremely short for the wheel grinding to not be an issue.

[graafderk]

Well, I stand corrected. Either way, I don't really like how it's handled on the Lego train cars - they'd have to be extremely short for the wheel grinding to not be an issue.

This kind of rail cars are not that uncommon in Europe and LEGO has produced a lot like these over the years (2126, 3225, 3742, 4536, 4537, 4563, 4564, 10014 to name a few 9V ones.). I never had a problem running the ones from for instance 4564, which I think look good anyway (for a secondary line maybe?). If I remember correctly, they have six studs between the wheel assemblies instead of eight in the Octan car from 7939, so maybe if you modify it like that, you have less running problems?

[Missing Brick]

The 4564 set has 6 studs between all the wheel assemblies so it probably runs OK. The 7939 Octan has 8 studs so it grinds pretty bad. I modified mine to reduce it down to 6 studs spacing using a few black 1x6 plates to maintain the appearance. Doesn't look too bad and runs much better.

I imagine real life carriages don't have to contend with the extreme bends of a lego train track so fixed bogeys aren't such a problem.

[Rustie86]

Most irregular. I've built and run a number of cars with the 8-stud gap between wheelsets and I never seem to have a problem with mine. I have about 7 clones of the boxcar/van from 7897, the aforementioned Octan tanker as well as some smaller tankers, and some gondolas/open wagons all with the same longer wheelbase.

A gap wider than 8 does cause problems, and I've done some experiments to make sure. (Even 9 starts to get problematic!) You may wish to check that your tanker was assembled correctly, just to be sure.

[Hrw-Amen]

I also have several Octan tankers of the official set I have a couple but also some of my own design with the same wheelbase (In fact most of my two axle goods wagons have that wheelbase.) and I have never had any issues with it. I have a few twin axle passenger coaches which have a 12 stud wheelbase and they seem to be OK as well. I have tried numerous wheelbases and anything more than 12 studs I found would encounter problems, but less than that seemed fine.

As an idea to see if it is thew wheelbase causing the problem, you could change out the standard train wheel sets and replace them with Technic axles and wheels, (Like on the train motor.) these can be squeezed in a little further or spread out a little further than the normal wheels especially if you only have three brick widths between the wheels. It may just give you an indication of where the wheels are sticking, or if it all runs OK then show that something else is at fault? Just an idea. You could always just rig up that configuration with some technic bricks and a baseplate to try different configurations?

[Missing Brick]

Thanks for the suggestions. The effect can easily be seen by simply rolling the carriage at a bend. With the default wheel base you can clearly hear the fixed wheels scrapping as they go thru the corner - and the carriage almost grinds to a halt. By contrast, a carriage with articulated bogies experiences no drag or slowdown. Of course a powerful engine can drag the Octan car thru the corners no problem, even if the wheels are grinding - but it adds to the drag and slowdown in corners. Articulating one or both of the wheels is probably the best solution.