3 Axle Trucks for PF

[Tearloch33]

I am looking at making a MOC of the EMD E-9 engine (if you must know, based on the 1970s BN passenger trains....the "Hockey Stick" ones), which has 3 axel trucks. Looking at the train design, I quickly realized that the wheels are closer together than in a 2 axel truck, so using the PF train motor will not look realistic enough for me. So now I am at the point of using the PF XL motor with a geared truck, like I have seen many folks use. I know the real trick is making one of the axels so that it can move to prevent binding in corners. I found a nice design in RailBricks #6 that looks very doable.

What I was looking for is if anyone else has other designs that work better than the RailBricks version, or have designs that simply look better while working well.

Also looking for suggestions on what to put on the outside of the wheels to look realistic, since the common 2 axel truck "dress up" peice will not work with closer wheel spacing and one more axel.

[peterab]

I am looking at making a MOC of the EMD E-9 engine (if you must know, based on the 1970s BN passenger trains....the "Hockey Stick" ones), which has 3 axel trucks. Looking at the train design, I quickly realized that the wheels are closer together than in a 2 axel truck, so using the PF train motor will not look realistic enough for me. So now I am at the point of using the PF XL motor with a geared truck, like I have seen many folks use. I know the real trick is making one of the axels so that it can move to prevent binding in corners. I found a nice design in RailBricks #6 that looks very doable.

What I was looking for is if anyone else has other designs that work better than the RailBricks version, or have designs that simply look better while working well.

Also looking for suggestions on what to put on the outside of the wheels to look realistic, since the common 2 axel truck "dress up" peice will not work with closer wheel spacing and one more axel.

That Railbricks design came about after much experimentation by a few guys on the Flickr trains group. It's probably the best working of the sliding middle axle variety.

There are two other design types, one with a normal two axle geared bogie, with an articulated third axle. The other has three fixed axles, the middle axle has no traction rubber bands, while the outer ones have slightly thicker traction bands (plumbing O rings) which raise the middle axle enough to avoid binding.

Here are a few examples, be aware they might not be as well tested as the design in Railbrick, or have failed testing and not been updated.

http://www.flickr.com/photos/34338074@N06/3726076426

[roamingstop]

To slightly resurrect this post; I built similar trucks using the technic 12 tooth bevel (6589) but find that the axle easily detaches when powered by a XL motor (direct; as per some of the designs in the link above). Due to design constraints in the model; I also have an axle running perpendicular (underneath) - so there is no space for an axle with stud.

Does anyone know any tricks to help keep the gear on the axle - short of a sport of glue?

Or should I make a chassis using half width technic liftarms; and then include a larger gear wheel; but risk derailing at the points?

Edited July 21, 2011 by roamingstudio

[roamingstop]

And solved my own question. Using the Axle 4 with stop (#87083) solves the problem very well - short enough to be useful in a train MOC; and long enough to keep the bogeys stable under the carriage.

[danim]

are there any sort of these designs for a pf medium motor mounted verticly for a two axel truck

[roamingstop]

are there any sort of these designs for a pf medium motor mounted verticly for a two axel truck

Exactly what I am doing The only issue is that it does not generate a high speed when compared to a traditional 9V / RC / PF train motor. This is because it needs gearing up, but there is not much space for that inside a train and bogey. It is more ideal for shunters / switchers than express locomotives.

To fix the motor, use a 2x2 90 degree bracket, lifted up one plate and it will hold the M motor very well; and drive the wheels. Mind they dont slip though! Vertical gearing could also be a way to improve speed.

Edit: Railbricks #6 has a good section on PF motors for bogeys; and the links above are useful.

Edited July 22, 2011 by roamingstudio

[danim]

is there any pics showing a dissasembled view of the two axel design

[Shupp]

I am looking at making a MOC of the EMD E-9 engine (if you must know, based on the 1970s BN passenger trains....the "Hockey Stick" ones), which has 3 axel trucks. Looking at the train design, I quickly realized that the wheels are closer together than in a 2 axel truck, so using the PF train motor will not look realistic enough for me. So now I am at the point of using the PF XL motor with a geared truck, like I have seen many folks use. I know the real trick is making one of the axels so that it can move to prevent binding in corners. I found a nice design in RailBricks #6 that looks very doable.

What I was looking for is if anyone else has other designs that work better than the RailBricks version, or have designs that simply look better while working well.

Also looking for suggestions on what to put on the outside of the wheels to look realistic, since the common 2 axel truck "dress up" peice will not work with closer wheel spacing and one more axel.

I did an E7 A+B set recently-

It used PF XL motors geared to three axle trucks. I've actually found you don't really need a sliding middle axle unless your wheels have a 2 stud or more gap between them if you do a slight modification. What I did was use the stock Lego train wheels, (the ones with grooves for rubber bands) removed the stock rubber from all of them and replaced the it with #35 plumbing o-rings, as outlined by Tony Sava on Railbricks. I only put the o-rings on the powered axles, that is, the first and third axles, leaving the middle axle wheels rubberless. The difference in diameter between the wheels with rubber and those without is enough to negotiate curves.

The reason I didn't do a sliding middle axle on these trucks is that I find most sliding axle designs are weaker than those without (This includes my design that peterab posted above. I honestly can't recommend it for heavy pulling). The design I used on my E7s is primarily made up of 3 32324s pinned together and attached with plates on the top and bottom. It's bascially indestructable and the 32324 bricks are just the right size for 12 tooth bevel gears. Here's a mockup-

http://www.flickr.com/photos/34338074@N06/5966342136/in/photostream

Normally you can't put plates on the underside of the technic bricks, but the slightly thicker rubber lets you get away with it. In this case it probably isn't even needed, but why not make it even stronger if you can? If you don't like the bulkiness of the specific design I posted, you could use 1x10 technic bricks for the side frames.

As for dressing up the sides, here's what I did on my MOC-

http://www.flickr.com/photos/34338074@N06/5527713693/in/set-72157625841592802

Using the flex tubing keeps it relatively thin.

To slightly resurrect this post; I built similar trucks using the technic 12 tooth bevel (6589) but find that the axle easily detaches when powered by a XL motor (direct; as per some of the designs in the link above). Due to design constraints in the model; I also have an axle running perpendicular (underneath) - so there is no space for an axle with stud.

Does anyone know any tricks to help keep the gear on the axle - short of a sport of glue?

Or should I make a chassis using half width technic liftarms; and then include a larger gear wheel; but risk derailing at the points?

I see you found a solution but I figure I'll weigh in anyway. The trick to keeping the gear on the axle is making sure it has nowhere to go. The mockup photo I posted above is an example. The axle and gear coming from the motor are stopped by the pin joiner in the middle, and the axles leading to the wheels are also stopped by the pin joiner and the thin bushings on the drive axles. As long as nothing can move, then nothing should fall off!

[roamingstop]

Thanks for the excellent post Shupp.... and what a great inspirational model. Perhaps, for further clarification, the biggest problem was the vertical axle going into the train section / motor - that's where the 4L + stop works really well; and the bogeys dont fall out when you lift the model up.

Edited July 23, 2011 by roamingstudio

[Shupp]

Thanks for the excellent post Shupp.... and what a great inspirational model. Perhaps, for further clarification, the biggest problem was the vertical axle going into the train section / motor - that's where the 4L + stop works really well; and the bogeys dont fall out when you lift the model up.

Well, like I said, the gear cannot move downward with the design I posted there. The other problem could be the axle retreating into the motor, or just upward if it's not directly connected to the motor. An axle with stop would certainly prevent that from happening. I used one on one of my models where the motor was mounted horizontally in the body of the locomotive becuase I was having the issue of the axle creeping upward, although I actually managed to break a gear because of how hard the axle was pulling up on it! If your motor is mounted vertically you can also just make sure there's no room for upward play at all, but that may not be possible depending on what you're doing, I suppose. If I've mounted the motors vertically, I usually attach them directly to the trucks and not to the body of the locomotive. This works especially well with XL motors. Their natural roundness allows them to rotate freely in the right sized space. If the motor is fixed securely to the powered truck, and there's no room for play in the axle, that can also solve the problem. At any rate, I'm glad you found a solution that works!

[Tearloch]

Well, like I said, the gear cannot move downward with the design I posted there. The other problem could be the axle retreating into the motor, or just upward if it's not directly connected to the motor. An axle with stop would certainly prevent that from happening. I used one on one of my models where the motor was mounted horizontally in the body of the locomotive becuase I was having the issue of the axle creeping upward, although I actually managed to break a gear because of how hard the axle was pulling up on it! If your motor is mounted vertically you can also just make sure there's no room for upward play at all, but that may not be possible depending on what you're doing, I suppose. If I've mounted the motors vertically, I usually attach them directly to the trucks and not to the body of the locomotive. This works especially well with XL motors. Their natural roundness allows them to rotate freely in the right sized space. If the motor is fixed securely to the powered truck, and there's no room for play in the axle, that can also solve the problem. At any rate, I'm glad you found a solution that works!

Shupp, amazing build on your E7. It gave me so many ideas. And thanks also for the 3 axle truck plans. B E A utiful! I love the design on the E7. My attempt so far is 6 wide, but your 8 wide version has me really thinking of going bigger. I also love your cars. Excellent work. Thanks again.

[Duq]

There's also Cale Leipharts solution: fix the motor to the bogie:

IMG_3553 by Cale Leiphart, on Flickr

B&O Em1 19 by Cale Leiphart, on Flickr

[Shupp]

Shupp, amazing build on your E7. It gave me so many ideas. And thanks also for the 3 axle truck plans. B E A utiful! I love the design on the E7. My attempt so far is 6 wide, but your 8 wide version has me really thinking of going bigger. I also love your cars. Excellent work. Thanks again.

No problem. I think we may need to make an updated PF building resource at some point. Sava has posted some good guides on Railbricks, but we're all still learning new things with each build. A lot of people dump their truck designs in the Lego Train Ideas group on Flickr, so there way be more things hiding in there as well.

There's also Cale Leipharts solution: fix the motor to the bogie:

This is what I would recommend when you can do it. I didn't do it on my E7 because I wanted to gear the motor up for a little more speed before powering the trucks. With the small train wheels there's not much you can do to change the speed within the truck design, because you can basically only use 12 tooth gears in there reliably. Anything bigger will be wider than the diameter of your wheels.

When the motor is not directly connected to a free-moving truck, the truck will want to spin in place a bit from the rotation of the drive axle. You can see this if you pick up something you've built this way while it's running. That means a little lost power and possible problems going into switches. Connecting motor and truck directly eliminates this issue, and also makes it harder for the motor to pull apart from what it's powering. Cale's engines, especially that second example you posted, are absolutely reliable. So his truck designs there would be a fair bet as well, though I still think it's best to use the 4x4 technic box brick when you can. Also, the sideframes on his EM-1 were a big inspiration for what I did on my E7.

Edited July 28, 2011 by Shupp

[Tearloch]

So if you fix the motor directly to the truck, how to you fix the entire truck/motor assembly to the base (or body) of the train?

[roamingstop]

So if you fix the motor directly to the truck, how to you fix the entire truck/motor assembly to the base (or body) of the train?

As in the photo links above - you build a large rectangular tube which the motor sits inside; with the body resting on the tiles of the truck. The 3/4 technic pins help keep stop the motor + bogeys falling out when the model is picked up.

I had been playing with some different ideas; testing PF-M motor direct to the bogey's and whilst it drives well, it is relatively slow. Faster speeds can be found by using the normal PF train motors; but then 3 axles are no longer possible.

I saw a link (somewhere) where the PF XL motor is used to drive a jacobs bogey (i.e. it connects between two base plates / cars) - this allowed larger gears to be used, but whilst I can visualise the photo, I have not found it again. I somehow think it was in a Tram model...

[Shupp]

So if you fix the motor directly to the truck, how to you fix the entire truck/motor assembly to the base (or body) of the train?

Here's a picture to help illustrate it:

S2 Tender Interior by Shuppiluliumas, on Flickr

In this case, I used 5x5 square holes for the motor to sit in. The XL motor is perfect for this because it's a 5x5 cylinder, and rotates freely in the square opening. As roamingstudio said, the weight of the tender just rests on top of the trucks, and the technic pins keep the motor from dropping out when you pick the thing up.

I had been playing with some different ideas; testing PF-M motor direct to the bogey's and whilst it drives well, it is relatively slow. Faster speeds can be found by using the normal PF train motors; but then 3 axles are no longer possible.

The speed issue can be a problem. Direct-driven XL or even M motors with small train wheels are pretty slow. My experience is, if you're going to gear up for more speed, use XL motors. When I gear up (or even gear down) M motors there just isn't much power left there. My current project uses two heavily geared up XL motors and yet it's still a pretty good puller.

Depending on how you want to build the side frames, it's sort of possible to have three axles with a train motor. PF train motors have the same weird sorta-hole in the middle that every train motor has had, and you can make use of it. I don't really have a great photo, but the tender for this 2-4-0 steamer I made uses one of the RC train motors, which is the same shape.

Prussian P 3 Locomotive 2-4-0 by Shuppiluliumas, on Flickr

The middle wheel is attached by a 2 length technic axle just resting in the hole in the side, and is kept from falling out by the red plate with hole piece. Depending on the design you could probably use a 7 length thin technic liftarm as well. I've been planning a locomotive that would use two PF train motors for the tender, so we'll see if I can make the 3 axle thing work with them.

[Tearloch]

Sorry to rehash a subject, but just checking in to see if there has been any new and innovative development in the 3 axle truck world? I finally have put my BNSF GP-38 MOD to bed, so now I am looking at starting on my BN E9 passenger train project.

[Shupp]

Cale's design posted above is bulletproof, and can be built several ways with basically any spacing between the axles you can think of and either an M or XL motor. Here's what I did on my E7s:

EMD E7 powered trucks 1 by Shuppiluliumas, on Flickr

Lego Power Functions train wheels by Shuppiluliumas, on Flickr

I picked this way of building them because it seems to be the absolute strongest. Cale also recently came up with a really great geared up truck design:

IMG_7301 by Cale Leiphart, on Flickr

I haven't seen it adapted to 3 axle yet but it's doable. You could just put an axle/pin in the technic pin hole Cale is using to attach the side frames in this design, and put a wheel on it. It's probably also possible to build this sort of truck longer, but I haven't tried it.