FoxOne

I'm puzzled over very similar specs of Powered Up L and XL motors, according to Philo's research. I believe I'm not the only one though )). It looks like a good move to invest only in L motors, since they are lighter, smaller and just as powerful. But what's the catch? Are there any insights on the subject? Any additional field test results? Looking forward, thanks!

That's what I was looking for, thanks! @Toastie Thanks for a thorough clarification! One additional note on a case "it holds still.. and suddenly it moves at full speed". As I understand, this might be attributed to the fact that static friction is greater than rolling resistance. First,, motor needs to overcome static friction, so we crank up a voltage, then suddenly there's not much resistance at all with the start of a movement. Explains your gravitation towards field testing )) I was trained as a mathematician, hence my urge to discover a proper functional dependency )). @gyenesvi Point taken, thanks -- granted, it's easier to control a vehicle with support of control system.

I see, and it's completely reasonable. But let me elaborate on what bugs me -- 1) DC motor physics is well known, and we can make certain predictions, e.g. about max power / torque vs. RPM and etc. 2) Control methods are known, too -- PWM, feedback and so on. 3) Now the interesting part -- we mix it together and something magic happens. Like we can independently set RPM and torque (well, kinda), and all other amazing things I believe I miss something. My point is -- can't see [yet] how sophisticated feedback and control could *increase* torque available at low speeds. Given that for DC motor stall torque is the max available torque, already.

Current cutoff, exactly. But how "power setting" control is implemented?

Yes and no, thanks. We share the understanding of max available power and "going under curve". But I can't be sure what means "setting power". As I've mentioned above, I understand manipulating voltage / signal, and maybe constraining current. As for power, I'm not sure. At a glance, seems like a simple term to grasp for users, but need to understand the underlying method.

Sorry to bother, but why you stress PID in this case? As I understand, PID is a method for "smooth" and "proportional" output in control systems (yes it's a simplification). But we're talking on a level below, DC motor physics. So, you can manipulate voltage (incl. PWM and other signals) and can constrain available current. I believe these are only controls available. PID, on the other hand, operates above this and adjusts the control signal. Are we on the same page here?

I suppose you can go *under* that curve, for sure -- supplying less of torque and / or speed available. But if you are to go *above* it, you should somehow override power constraints. Please correct me if I miss something.

Full disclosure -- I'm not quite familiar with all the intricacies of PU protocol. But this case of controlling speed and power seems suspicious. I suppose these are some kind of specially defined metrics, or there must be some kind of underlying constraints. Deep down inside there's still a DC motor. Yes you can do some tricks with a clever control signal and a feedback -- good point, I get it. But you can't beat the physics, for sure -- and for DC motor there is a torque-speed curve (and it's a linear function). See, we even haven't touched upon a [mechanical?] power, completely different function.

I would call it "inertia", because "overshooting" is more specific and implies missing some predefined target end state. Elaborating on this, I can think of 4 possible factors: Moment of inertia, considering "a load" Same, but regarding massive / oversize rotor Gearing ratio Braking method (there are 3 at least for DC motors) My observations on inertia movement of PU L vs XL are the same as yours, and I attribute it to #3 -- L motor is more geared down. But I'm not sure if it's applicable to the case of downhill braking, if we choose to apply active, "electric" braking; would be grateful for explanation.

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! ))

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 ))

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.

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.

In no particular order: 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. 2. 42099's drivetrain may not be advanced -- I agree, not the best choice of words. My point was drivetrain is long, with many gear couplings and ability to tune it by easy swapping. 3. Re Zetros -- wheel radius should be accounted for. 42099 has some monster size wheels to rotate. 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. 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.

I've mentioned "out of the box performance". This means you can just attach a wheel directly and expect some reasonable performance, as a sweet spot between torque and speed. Since it's an all purpose toy motor. Don't see how 42099 is an exception here, because it has rather advanced drivetrain. Ultimately, if you want to kick it up a notch (with planetary hubs...), you always have an option to use buggy motors )). I believe there were 2 or 3 of them. Final conclusions were somewhat more sophisticated, regarding maximum current and cutoff levels.

My guess is that motors' RPM ratio is relatively slow for at least one reason -- to be able to use them right out of the box in most cases, requiring no gearing down. Well, it's a toy set by design. On the other hand, down-up-down method is totally justified: we don't want to have transmission with high torque in between (structural strength concerns). And yes, planetary hubs are for torque in a compact shell, not speed. On the whole "L vs. XL" quest, I do recommend to watch RacingBrick's subsequent videos, it seems he's cracked this puzzle.

I'm working on an autocannon now, and needed some serious gearing up. This is to spin rollers at high RPM. I wasn't satisfied with some combined z36:z12 pairs, due to awkward geometry. Funny I've ended up with those 42099's planetary hubs. The ratio is app. 1:29 (yellow to red). Something like a worm gear with z24; but you can't reverse a worm gear, right? Talking of torque, there's almost none at the output, sure. PF L motor can spin it with Buwizz Ludicrous mode, but hardly with any load. Will test it with two L motors.

Got it! It's hard to beat specifically designed part, but yours definitely has that steampunk'ish looks! I think there's a room for improvement in my mounting rails as well, it's possible to cut 2 studs width-wise.

One level reduction I suppose? What is the maximum ratio in that configuration? As for my choice, I needed something relatively thin but possibly long.

Unfortunately, no -- hub has only 3 pins, no axle hole at all. My fist intention was to ask for the link, but please don't ruin my design experience yet )). I'm not sure I will keep two hubs, too -- but I'm kinda obsessed with linking them in a row at the moment, just want to test it with more power )). Frankly speaking, gear up ratio of 1:9 has already brought me a decent performance with Nerf bullets.

Yep, thanks! That's just a concept; bracing isn't final as well.

One totally non scientific observation to add -- Seems like XL is significantly less geared down than L. Found this while experimenting with steering control -- it was easy to rotate XL's shaft (unpowered) by "steering" front wheels; and nearly impossible to do it with L motor.

Sorry to complicate things, but there's more to take into account: 1. Train remote control will technically work with PF motors / battery box. but it behaves differently. Long story short, if you're going to control a vehicle, you'd better off with another type of remote. 2. To use a remote you will also need to add PF IR receiver into the mix. 3. If you're going to build wheeled vehicles, it's extremely cumbersome (but possible) to control it without PF servo motor for steering function. PF servo is a rare and expensive motor with some known quirks. But there's more -- whole PF system is being replaced by the newer standard, Powered Up. Afaik, PF won't be produced after 2020. If your grandson doesn't posses any PF elements yet, you might want to consider jumping in Powered Up system. Price is roughly the same, there are a lot of different elements, and finally Lego have implemented same standard through different lines -- Technic, Mindstorms and Spike Prime. And L and XL motors also can function as servos, that's a great relief. The only thing to bear in mind is that Powered Up is aimed for controlling via bluetooth with smart devices, like smartphones and tablets. If it's ok with you, there are a lot of possibilities to extend the experience -- e.g. physical gamepad can be easily integrated. Please feel free to ask if you need an additional information on Powered Up, happy to help. In any case, I'm sure your grandson will be thrilled, and it's an excellent choice of the book!

Thanks for the info, gents! @kbalage Look forward to seeing your new tests, Balazs! No hurry though, please take your time )).

@Zerobricks You rock, guys! Christmas is coming early this year ))