Powered Up motors: L vs. XL

[2GodBDGlory]

3 hours ago, gyenesvi said:

So the utility of XLs still seem too marginal, though the they could be useful for different applications (for example a single XL motor driving an LA to lift something), but I am struggling to find really good examples, where the XL is a clear winner over the L (for example, the Cat also uses an L for lifting).

Agreed. I don't see the justification for having a motor of almost identical output, but much larger size. Sure, once in a while, the Xl could be helpful, but if Lego is already investing in a second motor, they could at least have made it reasonably different!

I am still intrigued about the fact that the Xl was not used once in any of 2021's three PU sets. Could this motor be being discontinued? Even if not, I'm happy to see as few of them in sets as possible!

[Andman]

1 hour ago, Igor1 said:

The L motor is technically not much different from the XL.

It is, not much, but it is. How would you otherwise explain the difference in precision and backlash, which was not covered in Philos (great!) tests? Otherwise, i agree. I doubt that there is more meaning behind that.

[FoxOne]

Power consumption should be different, but who cares..

 

I prefer L hands down for quite a punch in 3x3 studs. But shouldn't we be puzzled, if there is a puzzle?)) Tinkering is half the fun at least, imo.

[gyenesvi]

4 hours ago, FoxOne said:

1. I believe if one looks for a performance, he might want to switch to Hobby RC.
Lego is a toy set. Yeah, it's slow and not powerful -- personally I'm okay with it. Don't want some crazy 20,000 RPM motor to spin in my kid's hands, nor some serious torque to crash some tiny fingers.

No I am definitely not looking for that kind of performance, and as I said, I think already the buggy motor may be too much. My issue is not that motors are not powerful enough, but that none of them are a good match to the new drivetrain components. That is why I think a 2-3x faster motor would be useful.

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3. Re Zetros -- wheel radius should be accounted for.

That is true, makes a significant difference.

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4. Re practical usage. No, I believe we can't reduce it to max stall torque. As a complication, at least we have different power consumption and also should review cutoff levels. Yes, L can bring some serious torque, but it will swallow so much current it will trigger cutoff. Not the case with XL.

That's an interesting point to consider, thanks, I really asked it because I am not an expert in the field. And that seems to be confirmed by the experiments of RacingBrick.

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As a side note, it would be interesting to see your explanation, sir. We try to guess, true, since Lego has not provided any insights.
But I suppose TLG is neither stupid nor inexperienced, maybe it's just a lack of communications.

Do you mean my explanation for the fact that the XL and L motors are not so different? Could be the result of the redesigned form factor; the old XL seems to have room for a bigger motor (bigger diameter), and hence could have had more torque. Maybe they thought it's not a big deal if the new motor is a bit less powerful for the sake of a better form factor, but it ended up being too close to the L, as it can house only a slightly bigger motor. Maybe the motors were designed earlier than the planetary hubs and their development did not take their interplay into account (though they came out at the same time).

3 hours ago, 2GodBDGlory said:

but if Lego is already investing in a second motor, they could at least have made it reasonably different!

That's exactly what I am thinking. A motor with the same form factor as the L but 2-3x the speed (less down-gearing) could have been more useful than the XL as it is. Another interesting question though is whether that could still work with the position sensor or if it would loose accuracy. Maybe not a problem if it can't be used as a servo for steering, but speed regulation would still be useful (for example slow speed with high torque).

[FoxOne]

6 hours ago, gyenesvi said:

A motor with the same form factor as the L but 2-3x the speed (less down-gearing) could have been more useful than the XL as it is.

Thank you for the clarification. I was under false impression that you'd like to have a motor with no internal gearing at all.

2-3x faster motor in a lineup would be useful, indeed.

[kbalage]

15 hours ago, gyenesvi said:

That's exactly my argument here. I have just rechecked your video about this, and your conclusion was that the XL motor has an advantage for big heavy and slow models (pretty much the description of the Zetros), and especially if higher voltage batteries are used. So if even the Zetros is not big and heavy enough to warrant the usage of XLs, then what is? The Cat? That might have been too heavy for it, as it uses the angular XLs that have 50% more torque (besides their form factor seems to be better for that build).

So the utility of XLs still seem too marginal, though the they could be useful for different applications (for example a single XL motor driving an LA to lift something), but I am struggling to find really good examples, where the XL is a clear winner over the L (for example, the Cat also uses an L for lifting).

I assume there were tests to compare the performance of a single XL versus 2 L motors and the latter combination was better for this purpose. A single XL could be good for slower mid-size builds, but it always depends on the purpose, the weight of the model, performance required etc. 

PU sets in general use a higher default gearing, and there's a reduction at the end, e.g. with the wheel hubs. I assume the motors were designed to fit this need, compared to the much slower PF XL version.

Regarding the difference between the PU L and XL motors, the performance is very similar, but if you gear the PF L & XL motors to the same RPM you'll also get a somewhat similar performance. So why would you need a bigger motor if you can have a smaller one? As the PU motors have way more pin holes they can act as a structural part of the model, just like in the case of 42099. If the model is big and spacious enough, the XL version can be a better choice. 

[MP LEGO Technic creations]

If I use an XL motor for driving one axle and L motor for another one with the same gearing and wheel size, both connected to the same hub, it shouldn't cause any issues, should it?

[Igor1]

12 minutes ago, kbalage said:

Regarding the difference between the PU L and XL motors, the performance is very similar, but if you gear the PF L & XL motors to the same RPM you'll also get a somewhat similar performance. So why would you need a bigger motor if you can have a smaller one? As the PU motors have way more pin holes they can act as a structural part of the model, just like in the case of 42099. If the model is big and spacious enough, the XL version can be a better choice. 

I built the 42099 with PF L-motors and it didn't cause any structural problems at all. The rigidity of the frame was also not affected in any way. It seems to me that a smaller motor with the same characteristics would be preferable for building anything.

5 minutes ago, MP LEGO Technic creations said:

If I use an XL motor for driving one axle and L motor for another one with the same gearing and wheel size, both connected to the same hub, it shouldn't cause any issues, should it?

Here is an example of such a model.

 

[allanp]

Regards the "good out of the box" argument, doesn't that defeat the purpose of Technic, meaning that you get to build the mechanics? On the case of the CAT bull dozer all you do is connect the motor directly to the reduction hub. So you're not building any mechanism there as it's all done for you. I really like the planetary reduction hub, but I agree that we should have at least one motor with much less internal gearing. Basically the L motor but with preferably no reduction, just a direct drive. I'm not saying all motors should be like that but it would be great to get just one completely ungeared motor, just so we can build the gear reductions we want as opposed to these inefficient and unrealistic "down-up-down" solutions (42099) or mechanically boring plug and play solutions (CAT bulldozer track drives). Personally I'd phase out the XL motor and replace that with the FAF (fast as f@£k) motor! Those who want lots of internal gearing, you already have the L motor, the angular motor and the smaller 5x3 motor to choose from, and there could be more in future maybe. I just think there should be one completely ungeared option, ideally with the same internal motor as the L motor.

[gyenesvi]

59 minutes ago, kbalage said:

A single XL could be good for slower mid-size builds, but it always depends on the purpose, the weight of the model, performance required etc.

I'd love to see such mid-size builds, like the old PF builds of RM8 and Madoca, a single XL and a servo. But I am not holding my breath for it. The PU XL seems weaker than the PF XL even if you account for the RPM difference, and with the huge technic hub it's difficult to build anything mid-sized with a realistic drivetrain / suspension (a slower vehicle kind of hints AWD, which requires a proper drivetrain if it has a single motor); the most difficult part becomes where to put the hub, as putting it into the middle would not work..

1 hour ago, kbalage said:

I assume the motors were designed to fit this need, compared to the much slower PF XL version.

I have doubts about this, and this was exactly my starting point. True that the PU XL is 50% faster, but that's nothing compared to the 5.4x reduction in the hub. And the PU L is actually slower than the PF version. This is why I think a 3x faster motor would be a better match for the planetary hubs. We could get similar speeds as we had with PF and without planetaries, but with much less torque on initial part of the drivetrain where weaker parts like the gearbox and the joints are. Could make it possible to build more realistic and versatile drivetrains and give more playability.

8 minutes ago, allanp said:

Basically the L motor but with preferably no reduction, just a direct drive.

I think that would be too much. As far as I know, there's something like a 36x down-gearing inside the motor, achieved in two planetary reduction stages, so each stage is something like 6x down-gearing. So an ungeared motor would have something like 10,000 RPM, which would be too difficult and space hungry to gear down outside using lego gears only. Furthermore, that 10,000 RPM would also probably melt lego parts. So I think it's good if much of the down-gearing happens inside the motor, but not all.

[AVCampos]

16 minutes ago, allanp said:

I just think there should be one completely ungeared option

LEGO produced the PF E motor, and only found use for it in a single Education set.

[allanp]

@gyenesvi ah yes, 10'000 rpm would be too much. But you can get slower internal motors. The 5x4 ungeared 9v motor had about 4000 rpm? That was a good speed. 

[kbalage]

1 hour ago, Igor1 said:

I built the 42099 with PF L-motors and it didn't cause any structural problems at all. The rigidity of the frame was also not affected in any way. It seems to me that a smaller motor with the same characteristics would be preferable for building anything.

I didn't say it would cause problems, I also built 42099 with PU L motors. If you check the design, the XL motors are placed in a way to be a structural part of the build. They don't make it stronger or weaker, they are simply used as any other frames or beams. Since the XL motors have more mounting points than the L motors, if they fit then they can be used in a more versatile way. 

[allanp]

6 minutes ago, AVCampos said:

LEGO produced the PF E motor, and only found use for it in a single Education set.

Yeah but that still had lots of internal gear reduction. And if they are going to give us the option between the L and XL motor, which are so similar as to raise questions over why they both even need to exist, then surely they can replace the bulkier XL motor with one that is significantly different. Not just a little bit faster, but waaaaaaaaaaay faster! At least fast enough that even with the cool planetary reduction hubs you still need a significant amount of down gearing to make things more mechanically interesting and realistic.

Edited December 29, 2021 by allanp

[gyenesvi]

14 minutes ago, allanp said:

The 5x4 ungeared 9v motor had about 4000 rpm

That's true, although it was probably weaker as well. I think the 1700 rpm of the buggy motor could also be an okay target. If one stage of the two planetary reductions in the L motor would be taken out (about 6x down-gearing), that would amount to about 1800 rpm. That could be interesting, it's roughly counteracting the 5.4x down-gearing of the planetary hub. Plus I think one less down-gearing stage in the motor would save 1 stud in length (I remember someone took a PF L apart, and it was something like that, 1 stud length per reduction stage; the PU L is 1 stud longer than the PF because of the position sensor taking one more stud).

Edited December 29, 2021 by gyenesvi

[allanp]

4 minutes ago, gyenesvi said:

That's true, although it was probably weaker as well. I think the 1700 rpm of the buggy motor could also be an okay target. If one stage of the two planetary reductions in the L motor would be taken out (about 6x down-gearing), that would amount to about 1800 rpm. That could be interesting, it's roughly counteracting the 5.4x down-gearing of the planetary hub. Plus I think one less down-gearing stage in the motor would save 1 stud in length (I remember someone took a PF L apart, and it was something like that, 1 stud length per reduction stage; the PU L is 1 stud longer than the PF because of the position sensor taking one more stud).

Yes even with taking different rpms into account the 5x4 motor had less mechanical output power than the L motor, which is why I would have liked the ungeared L motor but as you say 10000rpm is too fast for Technic pieces. So I think you're right, L internal motor with one stage of reduction, maybe just nudge it above 2000rpm!

But let's not get bogged down with finer details, essentially I agree with your main point. With new gear train components like the reduction hub and newer diffs, we need a much much faster motor to go with them.

[howitzer]

21 hours ago, gyenesvi said:

<snip> and with the huge technic hub it's difficult to build anything mid-sized <snip>

The Technic hub isn't really any bigger than the PF battery box, just a different shape. And unlike the PF battery box, you can actually use the Technic hub as a structural part, as batteries can be changed without taking the whole unit out. If you need a smaller unit, there's the 88009 hub, which is the same size and shape as the old PF rechargeable battery box though it only has two ports which can support drive and steer with only single motor each.

Granted, the PU lineup would really benefit from a small multi-port hub with rechargeable battery. RI hub is there of course, but it's also similar in size to the PF battery box, so it might be too large for small vehicles.

[gyenesvi]

1 hour ago, howitzer said:

The Technic hub isn't really any bigger than the PF battery box, just a different shape.

The most significant difference is that it's a full stud thicker on the whole surface (5 studs thick instead of 4), and that could matter on the mid scale. True that the mounting points are just placed differently, although the PF was more asymmetric (long-ish, whereas the PU is square-ish), so flipping it to its side made a bigger difference and hence had more different options to place.

1 hour ago, howitzer said:

you can actually use the Technic hub as a structural part

I think using it as a structural part in a car can be a bit of a trap situation even on a large scale, not to mention medium, especially if you want the car to have some technical realism and interior details (I made this note regarding possible mid-scale slower cars possibly with some non-trivial drivetrain, such as AWD using a single drive motor). So where could the hub be used as a structural part? In a truck, it could be standing high in the cabin, but in a mid scale regular car, it needs to be somewhere in the middle, otherwise it would be in the way for the axles/suspension. Now in the middle, if it's a structural part (that is, the shell cannot be removed), in order to let the batteries be accessible, it has to be on the bottom. That means, it blocks the way of any kind of drivetrain. So the only option left is to have and RWD car with the simplest drivetrain, but we already have that (rally car and buggy). So in a car with some nontrivial drivetrain, it has to be higher up. It cannot be sitting horizontally, because then you could not take out the batteries if it's built in (even if you flip it upside down, you'll probably not be able to access the button to turn it on). So it has to be standing, like in a truck. At best it could be used as a B pillar, but it's thickness will take half the cabin space. Another option is the trunk, but then it's not really a structural part. In other vehicles, like construction machines, I could imagine it more as a structural element.

2 hours ago, howitzer said:

Granted, the PU lineup would really benefit from a small multi-port hub with rechargeable battery. RI hub is there of course, but it's also similar in size to the PF battery box, so it might be too large for small vehicles.

Actually the Ri hub's shape and mounting points are much better than that of the Large Technic Hub. If the technic hub had that form factor with 4 ports only (and at the same 9 stud length as now), that would be great. The Small Technic Hub in the Spike Essential set is promising though (but super expensive now). It has the same form factor as the RI, but much smaller (5x7x4), but only with 2 ports. I'd love to see that in a mid scale technic car with 2 motors though, especially if the steering would be with a small angular servo! So still there's hope :)

[howitzer]

1 hour ago, gyenesvi said:

The most significant difference is that it's a full stud thicker on the whole surface (5 studs thick instead of 4), and that could matter on the mid scale. True that the mounting points are just placed differently, although the PF was more asymmetric (long-ish, whereas the PU is square-ish), so flipping it to its side made a bigger difference and hence had more different options to place.

I think using it as a structural part in a car can be a bit of a trap situation even on a large scale, not to mention medium, especially if you want the car to have some technical realism and interior details (I made this note regarding possible mid-scale slower cars possibly with some non-trivial drivetrain, such as AWD using a single drive motor). So where could the hub be used as a structural part? In a truck, it could be standing high in the cabin, but in a mid scale regular car, it needs to be somewhere in the middle, otherwise it would be in the way for the axles/suspension. Now in the middle, if it's a structural part (that is, the shell cannot be removed), in order to let the batteries be accessible, it has to be on the bottom. That means, it blocks the way of any kind of drivetrain. So the only option left is to have and RWD car with the simplest drivetrain, but we already have that (rally car and buggy). So in a car with some nontrivial drivetrain, it has to be higher up. It cannot be sitting horizontally, because then you could not take out the batteries if it's built in (even if you flip it upside down, you'll probably not be able to access the button to turn it on). So it has to be standing, like in a truck. At best it could be used as a B pillar, but it's thickness will take half the cabin space. Another option is the trunk, but then it's not really a structural part. In other vehicles, like construction machines, I could imagine it more as a structural element.

Actually the Ri hub's shape and mounting points are much better than that of the Large Technic Hub. If the technic hub had that form factor with 4 ports only (and at the same 9 stud length as now), that would be great. The Small Technic Hub in the Spike Essential set is promising though (but super expensive now). It has the same form factor as the RI, but much smaller (5x7x4), but only with 2 ports. I'd love to see that in a mid scale technic car with 2 motors though, especially if the steering would be with a small angular servo! So still there's hope :)

You're right about the form factor difference between the Technic hub and PF battery box, but I believe you could put the Technic hub upside down in the middle, just above the axle powering front wheels, and then design an opening roof in order to access the batteries. The power button can be accessed from the bottom then, as long as you leave some clearance next to the axle. It's true though that it doesn't lend itself well for small cars with complex drivetrains. But as I said before, you could use the other 2-port hub if you're building a car with only 2 motors even if it has AWD.

I also like the shape and mounting points of the RI hub, makes it really easy to integrate into builds. It also helps a lot that you don't have to design it to be removable, as it can be charged on the spot. I'm not that familiar with the hub from the Spike Essential set, looks like I've got to do some searching to find out it's specs...

[gyenesvi]

1 hour ago, howitzer said:

put the Technic hub upside down in the middle, just above the axle powering front wheels, and then design an opening roof in order to access the batteries

I did think about that too, but then besides the opening roof, you are bound to have no interior such as seats, as those would also block the opening of the battery box.

1 hour ago, howitzer said:

you could use the other 2-port hub

Sure, but that's not designed for technic, also difficult to mount to a technic chassis, so I don't really think an official technic set would use that in the future. And for my own builds I just have a BuWizz 3, that solves most problems.

1 hour ago, howitzer said:

I'm not that familiar with the hub from the Spike Essential set, looks like I've got to do some searching to find out it's specs...

I can't find the detailed specs on lego.com, but someone did post a link here a while ago. The only downside is that the battery is something like 7.4V, and the small motor was described to be for low torque tasks. Could still be okay for steering a mid sized car (and for controlling gearboxes), and as most rechargeable batteries are 1.2V, the Technic Hub also often ends up being used at 7.2V and is still fine.

I did find a thread about the small motor though:

 

[FoxOne]

Gents, as much as I enjoy this discussion, one might note that we have gone far away from the original topic. Which was dedicated to a comparison between PU L and XL motor, hope someone will find it helpful.

As a personal note, I think more productive way (to have models compact, performing and realistic to a degree) is to stray into hybrid constructions, not to harm some purist motives.
Interestingly, BuWizz guys even found a way to legitimate this ))

[nerdsforprez]

Admittedly, I have not read the entire discussion.  But I read enough to think that this has not been discussed yet.  If it has, please ignore this comment.  

All the comments above appear to be concerned with how vehicles are powered by XL or L for FORWARD movement, which typically for the vehicles we are discussing involves UPHILL movement (trial trucks, rock crawlers, etc).  I see no discussion about the motors and how they play a part in such vehicles as they go DOWNHILL or are involved in BRAKING.  

As someone who has rock-crawled in real life I can tell you that going downhill is every bit as important as going uphill.  Real vehicles have brakes.  For Lego Models, the motor is the brake.  And sometimes the limitation of a crawler/trial truck is not insufficient power to climb up but its inability to navigate or brake going down.  

This may one benefit for the use of XL over L for the above reason.  Not due to power per se but rather braking.  I have built and experimented with many crawlers to find that the benefit of an XL over a L is in its resistance.  Even if this resistance is only slightly greater than a L motor, it can save a lot of crashes.   

[gyenesvi]

Indeed we strayed away, so let's get back to topic.

@nerdsforprez did you test that with PU or PF motors? I think for PU, this should not be a difference, because they have position/speed control. In the PU wireless protocol, there are 3 modes to stop the motors: COAST, BRAKE and HOLD. COAST does not try to prevent the motors from moving, BRAKE does put some resistance on them, and HOLD tries to actively hold the position in which they were stopped (that means moving it back there if you move it away by hand). While in COAST mode the resistance of the motors may be different, in BRAKE and HOLD mode they should behave similarly (though the force they can exert could be different, I think both the L and the XL should have enough force to stop a model from moving downhill).

I can never really push around my PU models even when they are turned off, and I think the official Control+ profiles do use braking in some models (though cannot be sure). My experience is that with PU motors, you have really fine grained control for slow crawling both up and down, they can move precisely with high torque!

One more note, often when you release the acceleration for a PU model, it feels like it's running free for a bit. The PU protocol can also set an acceleration/deceleration time for the motors, and I believe they do use it, so that it does not start or stop abruptly.

[nerdsforprez]

1 hour ago, gyenesvi said:

Indeed we strayed away, so let's get back to topic.

@nerdsforprez did you test that with PU or PF motors? I think for PU, this should not be a difference, because they have position/speed control. In the PU wireless protocol, there are 3 modes to stop the motors: COAST, BRAKE and HOLD. COAST does not try to prevent the motors from moving, BRAKE does put some resistance on them, and HOLD tries to actively hold the position in which they were stopped (that means moving it back there if you move it away by hand). While in COAST mode the resistance of the motors may be different, in BRAKE and HOLD mode they should behave similarly (though the force they can exert could be different, I think both the L and the XL should have enough force to stop a model from moving downhill).

I can never really push around my PU models even when they are turned off, and I think the official Control+ profiles do use braking in some models (though cannot be sure). My experience is that with PU motors, you have really fine grained control for slow crawling both up and down, they can move precisely with high torque!

One more note, often when you release the acceleration for a PU model, it feels like it's running free for a bit. The PU protocol can also set an acceleration/deceleration time for the motors, and I believe they do use it, so that it does not start or stop abruptly.

PF motors.  I have not played sufficiently with PU motors.  

[FoxOne]

1 hour ago, gyenesvi said:

My experience is that with PU motors, you have really fine grained control for slow crawling both up and down, they can move precisely with high torque!

One thing to consider --

DC motors RPMs are controlled by voltage changing (or PWM signal, but that's the same effect). Problem is, if we want some precise action at low speed, we need to reduce our voltage -- hence the low torque. Granted, max torque is achieved at stall state, but that's not the same as a controllable low speed / high torque action. That's just motor trying to do its best at the very edge of performance envelope.

Ironically enough, precise and powerful crawling is achieved through massive gearing down -- either in drive train, in motor, or both. Finally, it's not so bad to have some reduction built-in! ))
 

 

 

 

Edited December 30, 2021 by FoxOne