[Question] : Setup L-motor function with battery box

[darkhorse00]

I am not sure if this has been asked. I have been trying to build a ATSF 4-4-2 (8-wide), with L-motor function and battery box 88000. It seems that a single L-motor might not have enough pull for my train+tender and 2 wagons. It can move, but slowly. I am afraid it might stalls if I add another wagon, especially on curves. I am trying to squeeze all the power functions into the train, so the train do not have space to accomodate 2 motors. Anybody can advise if the types of AAA battery do make a difference? e.g. Does Alkaline batteries give better pull strength than rechargable batteries? If so, does it means that lithium batteries give an even better pulling strength than Alkaline batteries?

[jtlan]

39 minutes ago, darkhorse00 said:

I am not sure if this has been asked. I have been trying to build a ATSF 4-4-2 (8-wide), with L-motor function and battery box 88000. It seems that a single L-motor might not have enough pull for my train+tender and 2 wagons. It can move, but slowly. I am afraid it might stalls if I add another wagon, especially on curves. I am trying to squeeze all the power functions into the train, so the train do not have space to accomodate 2 motors. Anybody can advise if the types of AAA battery do make a difference? e.g. Does Alkaline batteries give better pull strength than rechargable batteries? If so, does it means that lithium batteries give an even better pulling strength than Alkaline batteries?

There are two factors that determine the pulling power of a locomotive:

• Torque is how strongly the motor turns. Torque can be increased by using a more powerful motor, gearing down the motor, or using a power source that delivers more current.
• Traction is how tightly the wheels grip the rail; the locomotive's wheels must be able to push against the rail and not slip. Traction can be increased by using traction tires with a higher coefficient of friction, or increasing the weight of the locomotive carried by the driving wheels.

In my experience, I've found that traction is almost always the limiting factor for Lego models. People running into pulling power problems with their models are usually encountering the limits of traction rather than torque. With that in mind:

Unless your batteries are very dead, I find it very likely that the L-motor would stall unless an axle is actually jammed -- it's very strong. What kind of batteries are you using?

Do the wheels on your model slip when it runs? With something like a 4-4-2, I would imagine it's difficult to get a design that puts enough weight on the drivers.

 

If you could include pictures of your model, that would help us figure out what's going wrong. Without seeing your particular wheel and motor setup I can only make vague guesses as to what kinds of problems you're encountering.

[darkhorse00]

Thank you for the detailed explanation, jtlan!

 

"Traction is how tightly the wheels grip the rail; the locomotive's wheels must be able to push against the rail and not slip. Traction can be increased by using traction tires with a higher coefficient of friction, or increasing the weight of the locomotive carried by the driving wheels."

- I notice I have gotten the 2 x 2 rubber bands, and they become overstretch and thin out to give sufficient traction during motion. The wheels slipping are noticeably lesser after I replaced them with just normal rubber bands. With better traction, the train shows significant speed increase! Haha.

Info: The train engine weighs close to 500g (yet to be completed). The tender (with battery pack 88000 and batteries) weighs ~360g)

 

"Torque is how strongly the motor turns. Torque can be increased by using a more powerful motor, gearing down the motor, or using a power source that delivers more current. "

- I was using the Panasonice eneloop rechargable battery (800mAh). Based on your explanantion, I reckon it should boost the torque by using Energiser Alkaline battery (1200mAh)?? I will be getting some Energiser Alkaline battery later to test out. :) . Might want to get some Lithium batteries to test out too if Alkaline works better, but those batteries are pretty expensive. Haha.

 

[pirzyk]

I believe the standard IR receiver limits amperage to 700 - 800 mAh range, so swapping batteries probably will not show a difference.  But it is good to double check this.  If you want to be sure, you can get yourself a V2 IR receiver from bricklink.

 

[darkhorse00]

Guess I mixed up mAH and mA. Found this link about the performance between the IR receiver and L motor, with different batteries. Looks like this might just answer my question. Haha.

http://www.philohome.com/pfrec/pfcurves.htm

[zephyr1934]

Yeah, I don't think your problem is power flowing from the batteries. A heavier train will drain the batteries faster but it should not be limited by how much current the batteries can deliver. My most powerful trains have two XL motors coming off of a LiPo battery (I think others have reported that the LiPo delivers lower voltage than the AAA box with fresh batteries). In any event, the RC receiver is likely to be the most limiting factor in terms of current. I have other heavy trains where the RC receiver drops out for a second when it overheats and then returns at full power, if you are not getting that, my guess is that you are not having current problems.

In terms of your low speeds it might be that the L motor simply is not turning fast enough for your tastes, but to use gearing to speed it up you will lose power. Simple to test though, does the engine slow down as you add more cars to the train? If yes, then indeed, the single motor is probably too weak, if no, then it is simply too slow.

Regardless, there is another important factor not mentioned, namely friction and drag. Look for friction in the mechanism- technic axles have a lot of friction. Then if you have a long wheelbase on the locomotive or traction bands on multiple wheels your engine might be binding in the curves. If you have long cars (over 40 studs long on standard lego curves) those could be causing a lot of drag in the curves. If the train is constantly in curves that too could be adding a lot of drag. Solutions here are to add more power (another motor or XL motor) and/or fight the drag (eliminate friction and/or wider radius curves). Of course fighting the friction might be at the expense of aesthetics, so probably adding more power is the way to go. But that might mean moving the power to the tender. This tender based power plant with 2 XL motors is only limited by the magnets separating (solved with rare earth magnets) and then by its own wheels spinning. I've pulled upwards of 50 cars on standard lego track with it.

 

[dr_spock]

I'm running a L-motor in one of my engines.  It uses the standard AAA battery box with rechargeables and the V1 IR receiver.  It is geared up for more speed but can still pull quite a few cars around standard R40 curves.  Do you have video of your locomotive running and pictures of how it is set up?  Might help to see and hear what's going on.

 

 

 

[jtlan]

7 hours ago, darkhorse00 said:

- I notice I have gotten the 2 x 2 rubber bands, and they become overstretch and thin out to give sufficient traction during motion. The wheels slipping are noticeably lesser after I replaced them with just normal rubber bands. With better traction, the train shows significant speed increase! Haha.

I believe Lego has designed the large wheel to take this rubber band (in red -- in my experience the other colors represent slightly different sizes). On my locomotives I use these O-rings (to better match the black wheels) and haven't had any traction problems.

Edited February 13, 2017 by jtlan

[Carefree_Dude]

Changing O rings did amazing things with even a regular train motor wheels 

[darkhorse00]

10 hours ago, zephyr1934 said:

Yeah, I don't think your problem is power flowing from the batteries. A heavier train will drain the batteries faster but it should not be limited by how much current the batteries can deliver. My most powerful trains have two XL motors coming off of a LiPo battery (I think others have reported that the LiPo delivers lower voltage than the AAA box with fresh batteries). In any event, the RC receiver is likely to be the most limiting factor in terms of current. I have other heavy trains where the RC receiver drops out for a second when it overheats and then returns at full power, if you are not getting that, my guess is that you are not having current problems.

In terms of your low speeds it might be that the L motor simply is not turning fast enough for your tastes, but to use gearing to speed it up you will lose power. Simple to test though, does the engine slow down as you add more cars to the train? If yes, then indeed, the single motor is probably too weak, if no, then it is simply too slow.

Regardless, there is another important factor not mentioned, namely friction and drag. Look for friction in the mechanism- technic axles have a lot of friction. Then if you have a long wheelbase on the locomotive or traction bands on multiple wheels your engine might be binding in the curves. If you have long cars (over 40 studs long on standard lego curves) those could be causing a lot of drag in the curves. If the train is constantly in curves that too could be adding a lot of drag. Solutions here are to add more power (another motor or XL motor) and/or fight the drag (eliminate friction and/or wider radius curves). Of course fighting the friction might be at the expense of aesthetics, so probably adding more power is the way to go. But that might mean moving the power to the tender. This tender based power plant with 2 XL motors is only limited by the magnets separating (solved with rare earth magnets) and then by its own wheels spinning. I've pulled upwards of 50 cars on standard lego track with it.

 

Yes, the train did slow down as I add more wagons to it. 

Specs of my wagons:

Tender ~ 360g ,  studs 7 wide x 18 long

Cargo wagon ~ 360g (450g if I load in a USB power bank to light up my passenger wagon), studs 8 wide x 30 long

Passenger wagon ~ 550g. So with the additional wagons, I am looking at loading, studs 8 wide x 42 long

So, the train is pulling ~1.5kg of load with only 1 L motor and 88000 battery pack. You are correct, it does slow down quite a bit too at curve possibly due to my long passenger wagon. By the way, having rechargable 1.2V batteries compare to alkaline 1.5V batteries does make a little bit of difference after testing them. at least this is what I think so, based on measuring the speed via naked eye.

 

5 hours ago, Goldenmasamune said:

Changing O rings did amazing things with even a regular train motor wheels 

 

8 hours ago, jtlan said:

I believe Lego has designed the large wheel to take this rubber band (in red -- in my experience the other colors represent slightly different sizes). On my locomotives I use these O-rings (to better match the black wheels) and haven't had any traction problems.

Okay will check out the O-rings. Thanks for the great recommendation!

 

9 hours ago, dr_spock said:

I'm running a L-motor in one of my engines.  It uses the standard AAA battery box with rechargeables and the V1 IR receiver.  It is geared up for more speed but can still pull quite a few cars around standard R40 curves.  Do you have video of your locomotive running and pictures of how it is set up?  Might help to see and hear what's going on.

 

 

 

 

13 hours ago, pirzyk said:

I believe the standard IR receiver limits amperage to 700 - 800 mAh range, so swapping batteries probably will not show a difference.  But it is good to double check this.  If you want to be sure, you can get yourself a V2 IR receiver from bricklink.

 

Thanks for the recommendation. I am sure the V2 IR receiver does make a difference. But seems like it might be too pricy for me to get one from bricklink. KIV for that. :) By the way, I have try swapping the rechargable 1.2V batteries with those alkaline 1.5V batteries. It works much much better too. Will see if I can post some videos on the differences in the train performance speed after I get some O-rings.

[jtlan]

13 minutes ago, darkhorse00 said:

Thanks for the recommendation. I am sure the V2 IR receiver does make a difference. But seems like it might be too pricy for me to get one from bricklink. KIV for that. :) By the way, I have try swapping the rechargable 1.2V batteries with those alkaline 1.5V batteries. It works much much better too. Will see if I can post some videos on the differences in the train performance speed after I get some O-rings.

The voltage of fresh alkaline batteries drops off pretty quickly, so they won't actually deliver the full 1.5V for most of their usable life. I would compare against freshly charged Eneloops (be sure you're using a good charger, like the one that Panasonic supplies with them), and see how they behave.

 

Any chance we can see pictures of what you're working on?

Edited February 14, 2017 by jtlan

[Shupp]

I agree with zephyr that friction is usually the limiting factor. 1 L motor should be able to pull an engine of that size and a few cars without too much trouble. In my experience, the best way to check for friction is to remove the motor for a while and check things by hand. Pick up the locomotive and check that the wheels spin freely. Push the locomotive through curves and switches by hand and see if you feel resistance. Sometimes a gear will just be too tight on an axle and prevent free spinning. Sometimes the way you have connected the pilot or pony truck to your drive wheels will cause binding in curves or switches. As you also say, friction in your other cars could also be an issue.

I disagree that if adding cars makes the train slow down a lot, it must because the motor is too weak, though. If friction in the drive and articulation is not a problem, a lot of the motor's power can be lost if it is able to move or flex at all. I think this is usually more of an issue than lack of power in the motor itself. Motors need to be securely attached to their driven axles. I like to check for this by stalling the motor. Basically by picking up the locomotive, turning it on to full power and stopping the wheels slowly with my fingers. Does the motor twist or lift up from the frame? Do the gears start slipping? If so, that same thing is probably happening when you're running, and you're losing a lot of power there. Note that you can twist axles and break gears doing this, but I think it's worth it!

If none of that works, I think you would be best off getting one (or two if you have room in your tender design) PF train motors and putting them under your tender instead of the L motor. Change the stock rubber on the LEGO wheels to plumbing o-rings and make the tender as heavy as you can. You can pull pretty heave trains at high speed with one of those motors.

Echoing what others have said, electrically, the IR receiver is the weak link, and is limiting current to the motors. V2 IR receivers are a little expensive, but worth it in my opinion. Sbricks have the same motor driver circuits as V2 receivers if I recall, and also allow much more current through. Plus in an sbrick, each channel has its own driver IC, so the overall current limit is higher. I think your issue can be fixed with mechanical tweaking though, and you probably don't need to change electrical parts. I typically only hit the IR receiver current limit running 2 XL motors.

[darkhorse00]

4 hours ago, jtlan said:

The voltage of fresh alkaline batteries drops off pretty quickly, so they won't actually deliver the full 1.5V for most of their usable life. I would compare against freshly charged Eneloops (be sure you're using a good charger, like the one that Panasonic supplies with them), and see how they behave.

 

Any chance we can see pictures of what you're working on?

I managed to do up a video on the comparsion on my MOC 4-4-2 using AAA 1.5V alkaline vs 1.2V rechargeable. Notice any difference? I do feel that the alkaline 1.5V do give better performance. Sorry for the long video. Each test run is around 1min. Feel free to skip to every 1min interval. For each test, the train are tuned to run at max speed. Do note that the lightning in the passenger cabin is powered by a USB power bank in the cargo wagon instead of the PF battery pack itself.

 

Edited February 14, 2017 by darkhorse00

[M_slug357]

((I'm a bit defensive of L motors since I use them quite a bit in my engines))

My theory is that mechanically, you only have the motor turning one axle in your 4-4-2 build?

If so, I would recommend powering both drive axles instead.

Check out my Class 08 shunter:

https://www.flickr.com/photos/94581721@N06/30732265640/in/album-72157643243395285/

This engine is powered by a single L motor, but 2 out of it's 3 axles are powered.