Help with gearing to match...

[edsmith0075]

Greetings crew,

I am in the process of upgrading my 6 wide trains to 8 wide. I have 2 XL, 2 L, and 2 M motors. I would like to utilize all 6 of these in my new Loco builds. I am having trouble with the gearing and ratios. I am wondering if it is possible to match the PF Train motor so that the Locos with regular PF motors and run with the PF train motors when pulling long trains.

Any advice is appreciated. The XL's I would really like to use in my larger diesels like the ES44.

Ed

[marook]

Well, I guess the best is to study gear ratios, and then do some simple testing.

Here is a comprehensive guide telling about RPM's etc., and in case you need it, Sariel also have a great gear calculator online.

[jtlan]

In general, the PF train motor is not as good for pulling heavy loads slowly -- the amount of torque it puts out is low, so it's not as good for low-speed heavy-lifting.

Also, in a lot of cases traction is the limiting factor, not available power -- see this thread (which I keep linking to...). At any rate, if you're not trying to go really fast, a pair of PF motors should be more than enough; for example, Commander Wolf had a locomotive with two PF motors that could

. In general, I've found a 1:1 gear ratio on PF motors works well.

[greenmtvince]

Here's a few videos to give you some ideas about performance with 8-wide trains. I think each test has more details in the comments.

Dual XLs at 5:3

T-3-a Tender WIP by Vinnie Fusca, on Flickr

Single XL at 5:3 -Powered locomotive drivers

M-3-a Haul Test by Vinnie Fusca, on Flickr

Dual Train motors

Glory Days 2015: D-28 by Vinnie Fusca, on Flickr

Edited August 18, 2015 by greenmtvince

[Brickthus]

My Class 14 trip-working loco uses a single PF XL motor in the cab. This has enough torque to drive the loco but not the train as well, so I run it with an adjacent brake van having 2x PF train motors, the IR Receiver and LiPo battery.

The brake van includes pairs of diodes to drop the voltage applied to the train motors, so that the motors are well-synchronised at steady running speed of 40mph, which is the design speed of the loco.

I would use a similar arrangement for a steam engine with any PF motors turning driving wheels on the rails, where an adjacent tender of carriage has PF train motors.

The larger scale has an advantage that I hadn't though of as an advantage: Given that most wheels that are compatible with LEGO track, even BBB large and XL ones, are too small to represent the driving wheels of express passenger steam engines (i.e. larger than 5ft diameter), I have suspended other wheels off the rails. This removes the need for the proportion of power to be matched so closely. A bit of "visible wheel slip" is forgivable when operating a train! So it is with my Hogwarts Express, which has a Hall class engine using 40-tooth cogs for driving wheels and 2x train motors under the tender, with another 2x train motors under the first of 4 carriages. For steam engines like this I set the forward motion to suspended wheel matching speed to about 56mph scale speed (8mm:1ft scale), which is a good long-running speed for exhibitions as it's fast enough to enthuse visitors but slow enough not to burn anything out.

I have more recently tried cut-down Technic wheel hubs to give a smoother appearance the train driving wheels, though these have not yet found their way into a MOC. A suitable model for the 120-degree 3-cylinder arrangement would be an LNER V2 like Green Arrow, or an A3 Pacific. This would work with a similar matching arrangement at 56mph.

It would be difficult (not impossible) to match the speeds of different motors over the full speed range. This would need an electronic circuit to detect the back-EMF of one set of motors and drive the other set of motors in proportion. As I have asked about a slave H-bridge to drive many motors from a single IR Receiver, a speed proportion function could be another feature of it.

Mark

[zephyr1934]

@edsmith0075

My most powerful locomotive uses a pair of XL motors,

I've used this design both in a tender and in a boxcar so that I can use my 9v locomotives with heavy trains and not worry about motor burnout. I have pulled a 50+ car train with this configuration. It is not limited by power, rather, it is limited first by the couplers coming apart (fixed by rare earth magnets) then by the cars pulling off the track in the standard lego curves (no simple solution aside from perhaps ME curves). Key design features: it has a 1:1 gear ratio (simple bevel gears, with technic bushings on any cross axles to help keep the bevel gears in place) for the three axle trucks. The full build has a lot more weight on the wheels to give sufficient traction. The three axle trucks have the aftermarket o-rings on the drive axles while the middle axle just has the standard bands and thus, rides a few mm higher and seems to be fine in the curves but it sometimes complains in switches. I run it clockwise on 9v track to avoid the clockwork issue discussed here.

I suspect a pair of L motors would have plenty of pull and should be sufficient for 10+ heavy cars (but I have not built an L motor locomotive yet)

@greenmtvince

Love those trains, they are all fantastic

@Mark Bellis

Your creations never cease to be amazing