train efficiency in PF

[Juxtapoisson]

Hello, 

I need to build a train to hall some relatively heavy freight, specifically with as little power as possible.

I would appreciate ANY suggestions about maximizing train efficiency.

The train will be a relatively simple freight train model.  I haven't the experience to do anything especially pretty.  And I am trying to save on weight.  Flatbed cars.  Power functions.

Track is up to me.  Probably a simple loop.  So likely a circle or oval.  No hills.  Max speed isn't a big deal, faster than a crawl.

Any suggestions are great.  Here's the questions that have occurred to me already. Note that power use/requirements is the primary issue.

Is a second motor more efficient?  Given the splitting of the power between them, vs the extra weight and drag.

Where should the 1 or 2 motors be placed?  Front, back, middle?  I don't need them to be in the engine.  The freight will certainly be heavier than the engine.  Would putting the motors under the heavy freight cars improve traction?

Coupling rods and quartering is clearly awesome.   Does it help with efficiency?

Wheel and axle choices?

Is efficiency affected by the length of the cars or the distance between trucks?  Longer cars means fewer wheels (friction) by load volume.  But I can't guess at the trade offs.  Can there be too much weight on 1 truck?  I will have to work out car length and bed support for the weight.   What's the max distance between trucks before it looks dumb going around a corner?  (I don't have to worry about hitting anything.)

Is 1 motor able to pull more weight than 1 magnetic coupling can handle?  I.e.  with a heavy load am I likely to pull away from the cars, and maybe need some other kind of coupling?

I have plastic (modern) and metal track available to me (older 9V system).  I would not be getting power from the metal track. But would the metal track have better traction with the plastic wheels?

I know to use panels to save weight in building the engine.  Any other weight tips?

Would it be more power efficient to use 1 small PF motor instead of a PF train motor? (and have to build my own motorized truck).

[ALCO]

Good questions! Two PF train motors can pull a good sized train especially if you are using ball bearings in your freight cars. I recommend the ball bearing wheel sets from Brick Train Depot. You can find them here.

[zephyr1934]

If you care about power and don't care about looks, you would be hard pressed to do better than a pair of XL motors. I've pulled over 70 cars with this design (plus some weight... a roll of pennies is a good cheap weight). Can be hidden in a boxcar.

If you already have the train and PF parts then the best thing you could do is start with a simple design (e.g., the above link) and see if it works for your needs. It is quite possible that a pair of PF train motors would be sufficient for your needs. If not, then start looking for ways of improving the power.

Definitely keep the track flat.

Using two motors should not be a problem, using three motors off one battery might be. If money is no object, you could add additional power in the form of a second battery box, receiver, and two more motors.

More weight on the motors is usually a good thing. If the engine is too light the wheels would spin. Similarly, less weight on the cars is a good thing.

The motors work better pulling than they do pushing (less friction from the cars trying NOT to follow the track), but putting them under the first car behind the engine probably will not be an issue.

First try with normal train wheels if you have them. If that doesn't work, then consider ball bearing wheels (Brick Train Depot or BMR)

Coupling rods and quartering are for steam locomotives, almost all steam engine designs will bring extra drag. Especially because they use technic axle which are very high friction. If you are looking to push the limits of what you can pull, stay away from technic axle wheels if you can help it.

Longer cars will create more friction in the curves. If you do not care about looks, for best pulling power I'd suggest that you do not go above 28 studs if you are using stock lego curves. Again, best to test your designs and see if they work with your loads.

The pair of XL motors above will happily break magnetic couplings if the train is too heavy. And then if you strengthen those joints (rare earth magnets) it will pull cars off the track on R40 curves.

[Juxtapoisson]

8 hours ago, zephyr1934 said:

I've pulled over 70 cars with this design

Thank you.

I did some searching,and struggled because google just wants to send me to websites to buy lego motors.

I saw how it's done in the Emerald Night, and that's simple enough.

Your picture linked above looks simple.  But I haven't found any guide to what's going on underneath. It looks like the body and the truck pivot on the drive axle (from the motor down to the truck guts).  But my head keeps saying that when the axle meets the resistance at the gears it would cause the body and truck to try to pivot.  That would actually be a huge issue.  So either the build is more complicated, Or I'm too foggy this morning and just wrong about it.  

Please advise?

 

[Carefree_Dude]

I have a design similar to zephyr's inside my big boy. I have yet to figure out what the upper limit is to what it can pull

[zephyr1934]

4 hours ago, Juxtapoisson said:

Your picture linked above looks simple.  But I haven't found any guide to what's going on underneath. It looks like the body and the truck pivot on the drive axle (from the motor down to the truck guts).  But my head keeps saying that when the axle meets the resistance at the gears it would cause the body and truck to try to pivot.  That would actually be a huge issue.  So either the build is more complicated, Or I'm too foggy this morning and just wrong about it.

Yes, the drive axle is also the pivot. In the truck there are 6 or 7 bevel gears to transmit the power to the wheels. The truck does pivot against the rail, so when laying out the gearng you want to set it so that the truck pivots to the left when going forward (the right rail has a small indentation at the rail joints that can serve as a catching point for climbing the rail, especially on 9v track). The bigger issue with the rail joints is a long wheelbase on the standard R40 curves, if you go clockwise around the curves you avoid this problem. Anyway, if you are worried about the truck pushing against the rail, others have built trucks with the XL motor integrated with the truck, so the motor itself serves as a very large axle that the truck and motor rotate around. But again, as long as you have the parts in hand, you can build up a test MOC and see if it meets your performance needs, then adjust it to fix any residual problems.

[ALCO]

4 hours ago, Juxtapoisson said:

Thank you.

I did some searching,and struggled because google just wants to send me to websites to buy lego motors.

I saw how it's done in the Emerald Night, and that's simple enough.

Your picture linked above looks simple.  But I haven't found any guide to what's going on underneath. It looks like the body and the truck pivot on the drive axle (from the motor down to the truck guts).  But my head keeps saying that when the axle meets the resistance at the gears it would cause the body and truck to try to pivot.  That would actually be a huge issue.  So either the build is more complicated, Or I'm too foggy this morning and just wrong about it.  

Please advise?

 

The weight keeps it on the track. I also use the same design.

In your OP, you mention you need to pull some heavy freight. Definitely put ball bearings in the cars with all the weight and you will find they will try to roll away from you on uneven track...meaning the bearings will make the task of moving those cars so much easier for whatever locomotive design you go with.

[Phoxtane]

Mechanically speaking, if you go with a PF motor that isn't the train motor, the fewer gears you have in your drivetrain the better, as each meshing gear will sap some efficiency from the system.

It would probably also be a good idea to lubricate any moving parts in the drivetrain with silicone spray, or some other plastic-safe lubricant.

[Juxtapoisson]

Thanks,

If I am building my own trucks (attached motor, motor in body, etc) should I be gearing all 4 wheels in the truck?  Or just the pair of wheels (axle) to the inside?