Power to the wheels

[Redimus]

My first attempt at an Un-Specific Pacific (USP) was met with only partial success, it wasn't very fast or powerfull, it looked too toylike for my tastes and it was mechanically unreliable. The chassis and drive was basically a stretched and bastardised EN chassis and it was clearly not fit for purpose. 

I've been planning a v2 for a long time now, and have finally started. The XL motor is getting replaced with 2 L motors and the gearing has been simplified significantly. This has vastly improved the speed and (i think) the power to the wheels, but the has come at the expence of grip, causing not only significant wheel spin but also it to routinely pop the con rod from the leading wheels. It's powered through the centre (flangless) wheels, which drive the outer (flanged) wheels via the con rod. I did this in an effort to maximize the weight and power applied to the two flanged wheels, but that's looking like a dead end right now.

 

Any ideas, suggestions or tips would be greatly received.

Current build (tender will probably stay largely the same as the original build, although I'm toying with seeing if those little baring will make the standard Lego train wheel assembly a little less draggy).

 

And v1 (before all the bits had arrived).

 

Once I have it mechanically where I want it, I want to give it a smaller boiler and a more tapered cab roof, plus any and all grebelings I can think of.

Edited January 18, 2017 by Redimus

[Redimus]

Moved the weights to directly above the flanged wheels (and under the motors). This has killed the wheelspin, although it did still pop it's con rods once. Will also make it a lot easier when I design the boiler, as there shouldn't be any light grey showing under it now. Might try 2 weights on each side, but that may be overkill, and will make attaching the footplate much more difficult.

[jtlan]

How much stuff are you trying to pull, and how fast?

2x L motors is fantastically strong, but I'd be wary about speed and controllability. Is it geared 1:1 to the drivers?

I can't see exactly how your leading and trailing wheels are attached, but it seems like the height might be off on either the front or rear wheels, which will lift the drivers. Can you post closeups of the connections?

[igordost]

Wouldn't be more efficient to power both pairs of flanged wheels? I think transmission of power through con rod from 1 blind pair to 2 flanged pairs is still charged with some power loss... Are you sure that your solution really maximizes power in this setup?

[ALCO]

It looks to me that you might be able to easily power both your drivers through some bevel gears. This should fix your issue. While theoretical your drive-train can go through the blinds and connecting rods it will be stronger going directly to the flanged drivers via axles and bevel gears. This will keep the weight of the motors over the drive wheels. I think you will also find a smoother transfer of power with this set up. 

[Redimus]

18 hours ago, jtlan said:

How much stuff are you trying to pull, and how fast?

2x L motors is fantastically strong, but I'd be wary about speed and controllability. Is it geared 1:1 to the drivers?

I can't see exactly how your leading and trailing wheels are attached, but it seems like the height might be off on either the front or rear wheels, which will lift the drivers. Can you post closeups of the connections? 

At the moment, 'just' the two Pullman coaches (behind version 1 of the loco), which are both rather long, and heavy, with bogies that have the wheels as far apart as you can comfortably get them. On it's own it's a tad faster, but hardly uncontrollably so, but pulling those it really needs all the pulling power it can muster.

The front bogie and cartazzi axle are both connected in the same way (roughly) as Emerald Night's were. At the moment, the whole front end is held on by a row of 4 studs, so it's probably not fantastically flat. The previous build started with the ride height of the front not being perfect but being OK, then as it got taken apart and reassembled, it got worse and worse until it was a real issue, unfortunately, I don't know of any better solutions right now.

7 hours ago, igordost said:

Wouldn't be more efficient to power both pairs of flanged wheels? I think transmission of power through con rod from 1 blind pair to 2 flanged pairs is still charged with some power loss... Are you sure that your solution really maximizes power in this setup?

 

7 hours ago, ALCO said:

It looks to me that you might be able to easily power both your drivers through some bevel gears. This should fix your issue. While theoretical your drive-train can go through the blinds and connecting rods it will be stronger going directly to the flanged drivers via axles and bevel gears. This will keep the weight of the motors over the drive wheels. I think you will also find a smoother transfer of power with this set up. 

Will that not just add more drag and potential places of mechanical stress? The set up I have now is by far the simplest, and seems to be better than the previous iterations. The issue I see is this, either I power both flanged wheels independently, then you're relying on the con rods to keep them in sync with each other (potentially troublesome, but means less friction between the motor and the wheels), or have both sets of driving wheels powered from the same central point (which would be relatively easy to adapt the current build to), but is that not just adding extra friction for limited power to wheel gain?

The motors are already directly above the wheels anyway, and I've moved the deadweights to under the motors, directly above the wheels too, so this seems like a potential solution, but I'll give your ideas a go in my next session on it. Also, I'll do a few photos at the same time.

[legoman666]

I've connected drive wheels through connecting rods before. Not a good time. When one wheel wants to slip or go faster, the connecting rods bend and bind. They were even properly quartered. I ended up connecting the pair of drive axles with bevel gears inside the bogie. Much smoother. 

 

2L motors should be able to pull an absurd amount of cars. I've got locomotives with 2 L's that can pull about 30' of stock. 

[jtlan]

6 hours ago, Redimus said:

Will that not just add more drag and potential places of mechanical stress? The set up I have now is by far the simplest, and seems to be better than the previous iterations. The issue I see is this, either I power both flanged wheels independently, then you're relying on the con rods to keep them in sync with each other (potentially troublesome, but means less friction between the motor and the wheels), or have both sets of driving wheels powered from the same central point (which would be relatively easy to adapt the current build to), but is that not just adding extra friction for limited power to wheel gain?

For what it's worth, I've never had an issue powering connected drivers through the connecting rods (sample size: 3 steam locomotives). Neither has @Commander Wolf. In most cases the weight of a locomotive is an impediment to pulling power long before the strength of the drivetrain is. I'm not sure why your driving rods are popping off, as I've never used the printed ones.

The pulling power of those locomotives was enough to pull two Umbauwagen at a decent pace, and I wouldn't expect your Pullmans to be a lot heavier (573g each). But perhaps they don't roll as smoothly? For that matter, the wheelbase on the tender looks really long. Do you only have pulling problems in curves?

Aside regarding gears: Generally geared transmissions are very efficient. However, most Lego designs for the frames supporting those transmissions introduce a lot of friction. There is an art to designing a rigid frame that does not overconstrain the axles passing through it.

[M_slug357]

Might I suggest going a bit more technical?

I've been working for a while now on a string engines that use a singular L-motor for power.

 

For your project, this would unfortunately reduce the # of L-motors, but also potentially increase the amount of space you have in the boiler- you could place the weights and Sbrick directly on top of the driven axles.

Let me know what you think/ if you're interested?

[Frank STENGEL]

Nice design. It would be interesting to have a lld /ldraw file to play  and experiment with. I'd love to se what is behind the wheels.