Which way Rivarossi motor go in frame?

[mmagliaro]

After all these years of playing around with steam locos, and particularly of late, experimenting with
improving the motor in old Rivarossi/Atlas steam (yes, I'm still working on that), I have come to the conclusion
that I don't really know which way they intended the motor to go into the back of these engines.
The motor can has two cut-outs near the brush holders.  One is a vee shape and one is a plain rectangle.
It seems sensible to me that the Vee shaped cut-out should go at the bottom, because that's where the draw
bar post goes and the vee allows more room for it.
But in fact, the draw bar post will fit even if you put the rectangular cut-out on the bottom, and I would say
from experience that the majority of these engines I've come across have the rectangle on the bottom, which is
the exact opposite of what I would expect.  It's possible that they've all been tinkered with, and people
always put the wrong side on the bottom, but figure the odds of that happening.

Can any of you lend some insight into whether the vee goes on the bottom or not?

This photo details what I'm talking about.

[peteski]

Isn't the V-shape there to identify the magnet polarity (so you can install the motor correctly in the chassis and loco will not run backwards)?

[mmagliaro]

Isn't the V-shape there to identify the magnet polarity (so you can install the motor correctly in the chassis and loco will not run backwards)?

I don't know.   Is that the reason for the Vee?
You are correct, the motor will spin in the opposite direction if you put it in upside down.

I have seen it both ways, and I don't remember if one ran the wrong way or not.

In my case, I'm putting my own magnet in there, so I don't really care.  I'll make sure it runs the right way.

Update:  The "irwin's journal" online page does say that the Vee is to make sure you get the motor oriented correctly so it
spins the right way, and that the vee should go on the side with the "ground" connector, which would be on top, not on the bottom,
as I've been assuming.

But I still don't see how anybody would actually know this.  Are there any brand-new, never-opened Rivarossi engines lying
around to see how the motor was put in?

[wm3798]

I look at the inscriptions on the plastic back head.  As long as "ITALY" is on the right, and "Rivarossi" is on the left, you're good.
That puts the correct pole down to the draw bar pin.  The orientation of the can is irrelevant.  It's the orientation of the back head, because that establishes the polarity.
That reminds me.  I need more old steam engines.
Lee

[peteski]

I don't know.   Is that the reason for the Vee?
You are correct, the motor will spin in the opposite direction if you put it in upside down.

I have seen it both ways, and I don't remember if one ran the wrong way or not.

In my case, I'm putting my own magnet in there, so I don't really care.  I'll make sure it runs the right way.

Update:  The "irwin's journal" online page does say that the Vee is to make sure you get the motor oriented correctly so it
spins the right way, and that the vee should go on the side with the "ground" connector, which would be on top, not on the bottom,
as I've been assuming.

But I still don't see how anybody would actually know this.  Are there any brand-new, never-opened Rivarossi engines lying
around to see how the motor was put in?

Max, when Rivarossi was  manufacturing and utilizing those motors they never considered that modelers would be taking them apart (and maybe even  modifying them, or replacing magnets). That V-notch was made for their own reference.

As for finding reference motors, any motor which still has the original vinyl magnet in the motor housing will be you reference.  I don't think modelers extracted and reinstalled that magnet often (if ever).  The plastic brush-holder end of the motor is asymmetrical, so it only goes into the model one way (the post goes on the bottom and couples to the tender drawbar.  That is your reference.  If you take one of those motors, install it in the loco, power it up so positive rail on the right, and the loco moves forward - that means the motor is assembled properly.  If it runs backwards, rotate the metal housing with the magnet 180 degrees.

[woodone]

WOW, I converted an Atlas (Rivarossi) 2-8-2 years ago and I never noticed that V.
I guess to me it would not make any difference. I would wire to the motor with the leads that make the motor run the correct direction.
If the V notch would make things fit one way or the other, that the way it would go.
Any reason you have reservations has how to mount?
Has I recall, the draw-bar went to the left rail and was the negative post on the bottom of the motor.
The top post has a spring tab that made contact to the frame when you pushed the motor into it mounting and was right rail.

[wm3798]

Again, the position of the metal can don't enter into it.
The polarity of the motor is determined by which contact is connected to the engine frame, and which one is connected to the tender.  The plastic back head is the determinant. 
I'm working on using one of those small replacement motors, and I'm mounting it to the backhead and not using the can at all.  If I have the motor rotated in the right direction, with poles top and bottom, I have a 50/50 shot at having it right.
Lee

[peteski]

Again, the position of the metal can don't enter into it.
The polarity of the motor is determined by which contact is connected to the engine frame, and which one is connected to the tender.  The plastic back head is the determinant.

Try it Lee.  Take one of those motors out, and rotate the metal can (with the magnet still inside) 180 degrees (in relation to the plastic back cover), then reinstall the motor back into the loco. It should now run backwards.

[wm3798]

I don't follow that logic, because regardless of the position of the case, the orientation of the armature and the brushes along with the connection to the track power would determine the polarity and therefore the direction of rotation.
I have some motors I can experiment with to prove my theory, and I'll repert my results.
Lee

[mmagliaro]

What Lee, and others may also be assuming, is that you take the plastic back off with the brush holders in it.   But you don't have to.
In fact, I usually pry the holders, brushes and springs out before I remove the back.  That avoids the possibility of ruining the springs or losing the brushes when you pull the back off.

Lee, if you take the motor out and rotate it 180 degrees and put it back in, you will have to reverse the locations of the brush holders because the drawbar one always has to go on the bottom.  You will have then connected the tender lead to the opposite side of the motor, and the direction will reverse.

In fact, that black plastic back DOES go on either way, with the "Rivarossi" down the left side or down the right side.
Believe me, I've been taking these things apart and putting them back together for a few months now. 
The back can go on either way, the brush holders can go in either hole, and the drawbar post can be on either one.  All that really matters is that the drawbar post is in agreement with how the magnet polarization is on the inside.  Since the magnet is virtually never removed by anyone (as Peteski pointed out), the rotation of the can DOES affect the direction because it rotates the magnet 180 degrees (or not), and reverses its orientation to the polarity of the brush connections.

I guess there is no reason to really care which way it goes as long as one is consistent and the motor spins in the correct direction.

[woodone]

Max, if you are asking where the draw-bar attached to the motor with the long pin arrangement, it goes to the bottom bare pin.
The other metal sleeve is a spacer.
I don’t recall if it made electrical contact with the brush holder.
The last time I worked on one of these was over 10 years ago.
I since have sold all the older Atlas loco’s.

[peteski]

I don't follow that logic, because regardless of the position of the case, the orientation of the armature and the brushes along with the connection to the track power would determine the polarity and therefore the direction of rotation.
I have some motors I can experiment with to prove my theory, and I'll repert my results.
Lee

Lee, when you rotate the metal case with the magnets 180 degrees in reference to the back of the case (which has to remain in the same orientation) then the magnetic field inside the motor is flipped (in reference to the brushes and electrical connections which remain unchanged. That will reverse motor's direction.  Try it.  Again, the plastic rear part of the motor has to remain in its original position (just the metal front of the motor case gets rotated.

[wm3798]

I hadn't considered that magnet is fixed to the can.  (or in most cases, melted and fused to it!)
With that in mind, what you're saying makes sense.
My assumption was that since the magnet is circular, that the field would be consistent regardless of how the can is oriented.  I'm not sure why that design would be different from the typical open frame motor with two different magnets top and bottom.
But I'm suddenly reminded of the the Model Power/Mehano motor that Peteski retooled for me, which has a single magnet that transfers the field through two metal plates to rotate the armature.  Obviously, that single magnet design would be reversed if one were to flip the motor over and connect the contacts in the original orientation, so it stands to reason that Rivarossi would behave the same way.

Ah, the miracles of science.
Lee

[SkipGear]

I look at the inscriptions on the plastic back head.  As long as "ITALY" is on the right, and "Rivarossi" is on the left, you're good.
That puts the correct pole down to the draw bar pin.  The orientation of the can is irrelevant.  It's the orientation of the back head, because that establishes the polarity.
That reminds me.  I need more old steam engines.
Lee

The orientation of the magnets is what determines the direction. The brush hood is just how the current gets to the armature. The orientation of the magnets determine what is done with that current and how it interacts with armature.

For a brushed motor to work, it must have two poles to work against. Those rubber magnets are just one long magnet which has, just like every magnet, two poles, one at each end of the strip.

[mmagliaro]

What Tony says is correct.
And when you wrap that rubber magnet around into a ring and stuff it in the can, you can think of it as two magnets, a "N" and an "S", on opposite sides of the can.  It would be no different than if you put two separate magnets in there on either side of the armature.
In my case, I am replacing that thing with a solid neodymium ring that is "diametrically polarized", which achieves the same end.  If you look into the ring magnet (like you're looking into a tube), the half on the left is one pole (say, "N") and the half on the right is the other "S".   It would be just like putting two semicircular magnets into the can on opposite sides of the armature.

And holy cow... is that magnet strong, especially compared to the old rubber "refrigerator magnet" thingy.