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I like this a lot, it seems like a nice tight medium scale build! That drivetrain is super short, not sure anything shorter exists with all the joints and differentials properly included! I also like the steering linkage, I have been planning to try such a setup for a while. Does it have noticeable bump steer? Nice idea with the rubber band to route it to the steering wheel! On the rear, isn't the hub a bit heavy for those soft springs? It seems like it sits in a bit more in the back, although I guess the axle geometry is the same as the front.

Thanks, glad you appreciate simplicity :) In this setup using the soft ones at the front was very weak, because the shocks are angled a lot. In the rear position they are in a more upright position, so it's stronger there. I tried a couple positions in the front, but it was either too soft or the A-arms were too steep or too flat or the travel would have been too short. This angle was the one I liked the most for a buggy.

Hi, My next build is a smaller alternate from the Ford Raptor set. It is a simpler one, but I'd still like to share some insights about it and the set. When I started to experiment with building from this set, I wanted something with moderately interesting suspension, as that's the only technical aspect that could be varied a bit from the available parts (I don't think it's possible to put any real twist in the drivetrain from these parts). My first difficulty was that the set only has two hard shock absorbers and two soft ones, all of them small, with which it is hard to build any sophisticated suspension that has a decent amount of travel. So first I had to find out where I could use the soft ones (front or rear). The design of the rear suspension seemed trivial using the ball-joint for a floating axle, but making the 'trailing arm' longer (as I think it should have been in the Raptor according to the real one). Without weight it was still functioning okay with the soft springs as well, but I knew this would change with the bodywork. In the front, building longer A-arms also seemed possible to make it more interesting, but just could not get the soft springs to support the weight with longer travel. So I just decided to use the hard springs in the front, and keep the soft ones for the rear. Also, the orange body panels of the Raptor are not as good as I first imagined, as most of them are flat and small and I find the wheel arches hard to integrate smoothly (for me, they just stick out as if they were slapped on; and most of the existing alternates don't use them as wheel arches). But the long wing panels seemed good for a nose, and the wheels are perfect for a buggy, so I decided to take a shot at a Class 1 buggy shape (also, it's light, so the soft springs can support the weight). Ridiculously enough, the orange panels were not even enough for building smooth sides (I know I could have built something up from small beams, but I don't like that). So I just used black panels for the sides, and used the orange panels for the roof, at least they were well shaped for that, and could even add some race stripes. As Class 1 buggies have mostly rear engines I put it in the back, so the routing of the drivetrain was a bit of a challenge, given that I wanted to have the ball joint of the rear suspension close to the middle of the chassis to have a long trailing arm for the suspension, and that way the path of the driveshaft had to avoid the HoG steering somehow. Well, they pass really close to each other. Here's the whole chassis, which at least I think is a nice frame with the arches, and it makes it light but sturdy (can be lifted by the roof). In the end, I am satisfied with the shape and the front suspension (the rear one is kind of trivial). I also managed to add a bit of decoration to the rear end. Here are some more pictures. Let me know how you like it! Building instructions are available on Rebrickable. Cheers, Viktor

@1gor That’s one crazy idea (in a good sense)! It seems to have some tension though. But I like you guys are thinking in this direction, such a part is really missing. I proposed earlier some similar parts to 3d print for @efferman (in his custom parts thread), basically that connector with a towball socket instead of the pinhole. We did design a few variants, check out if you are interested, we might together agree on a varient that could be put onto shapeways and tested.

I guess my initial understanding and wording was vague, but it's getting clearer. So I don't propose that it would magically increase torque above the available maximum, but only increase it momentarily on demand within that available maximum to achieve the desired speed. I imagine it works the following way. Suppose the motor has a max RPM (depending on the load), achieved when you give it max power (at max voltage or however that is achieved physically, it's not relevant). Suppose that you want to go with 50% of that RPM. Instead of simply giving it 50% power, what the controller does is that it gives it increasing amount of power, util the desired speed is reached, and keeps regulating the power (in a very fast loop) by monitoring the speed utilizing the position sensor data (this is the PID controller part). The point is that even when moving at low speed, the motor is going to move with *high enough* torque to achieve that speed (within the max torque budget). It's true that theoretically you could do the same with a PF motor by hand, but in practise, you can't be precise enough regulating the power. For example with a heavier off-road model climbing through an obstacle, it could easily happen that you either give it too little power and your model won't move, or you suddenly give it too much power and it will move too fast, so you end up with kind of a binary control, even though the actual motor power can be regulated continuously. So in this sense, it can be hard to move it slowly when higher torque is required to achieve that. When there is little load (for example a light model on a flat surface), then it is fairly easy to do it by hand as well. What I don't understand in this process is how the speed itself is defined. In the PU protocol it is measured as a percentage, but what does 100% mean? It's probably not the unloaded RPM, since that does not mean too much in practise, as usually the motor has varying amount of load. Maybe the motor can measure the load itself (by observing the instantaneous current?) and scale the max RPM accordingly.

I am using it as a term to simplify / abstract away the underlying details (as I am not familiar with the correct physical terms), and also because the LWP3.0 protocol uses that term. For me it is sufficient in order to understand the core concept of speed regulation and the ability to move slowly with high torque.

I second that. And they combine well with frames and panels too. Me too waiting fore more lengths to appear, hoping at least for 7L. Though 3-4-5L would also be very useful, but not really holding my breath for those unfortunately. I would not go as far as that. The flip-flops don't work when you need two adjacent pin holes in the same direction (or with any even spacing), which happens quite often. But the two systems would nicely complement each other, given that they both form a complete system (all lengths covered).

That's an interesting question. In a sense, these features are present in official sets, it's just rarely advertised and reviews don't touch on these details; they measure things like max speed and climbing angle, turning radius, but rarely check how precisely it steers or climbs slowly on rocks (as they are meant for indoor use). And also to show the benefits, you'd have to compare them to PF electronics. I think a nice use case could be a trial competition where all these details could matter. It would be nice to see the same build with PU and PF electronics and how they fare agains each other. I think I get what you mean, I had the same feeling. But from the answers above I think it's getting more clear; they trick is that you don't set the actual power (and speed at the same time), but the max power that the controller is allowed to use to regulate the speed. So it CAN use high power to move with slow speed if the load is high, and if not, it uses less power; it does not always use high power to move slowly, only if necessary. I hope that describes it more accurately. Is that what you mean by going under the curve?

Yes, that's what I meant by motor controller electronics, that's in the hub, and makes use of the position data coming back from the motor. But great that you chimed in, as you probably understand the details better. So am I correct that the PU motors can in SPEED and SERVO mode move with slow speed / small angles and with high torque because of this control loop?

I'm not an expert at the physics background of it, but as far as I understand that's only true for PF, but not any more for PU! The key is the position encoder in the PU motors. In the PU protocol, the motors can be run in PWM or SPEED mode (along with SERVO mode). In PWM mode it is as you write, speed and torque is proportional to voltage. But in SPEED mode, you can specify the target speed and the target power at the same time independently of each other. So it can run using high power but low speed, because the speed is regulated through the position encoder by the motor controller electronics (at least that's how I imagine). I tried it with PU models, they can climb firmly at a really slow speed (you can try it with stock models, like the Zetros). It's very useful, and the wheels are also less prone to slip. The same advantage is true for SERVO mode when steering, where you can specify a target angle, and speed and power to get there. So it is able to turn small angles with high torque. That was not true for the PF servo, because the angle is controlled by the PWM signal so low angles resulted in low torque and it could not steer precisely on rough terrain if the model was heavy. But with PU L motor, I never had a problem steering on rocks even large wheels with a heavy (2 kg) model. I think these aspects of the PU system are not well known and appreciated by PF fans who are reluctant to switch to PU. They expected that PU motors would be more powerful than PF, but in fact Powered Up is about more control, not more power.

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.

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. 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. 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:

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 :)

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).

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.. 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. 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.

I love this, looks really nice, and I am blown away by those mini axles and the drivetrain, the sideways shift is a nice detail that seems required for multiple reasons, and the portal gears are a nice touch, the steering linkage is compact, it is a piece of miniature art, I am still trying to figure out all its details.. Amazing work!

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. That is true, makes a significant difference. 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. 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). 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).

Thanks, so if there's 1:3 at the motor, 20:28 = 5:7 at the diff and 1:3 at the portal hubs, then I calculate 5:63 = 1:12.6. Interestingly, that's exactly the same ratio as if you use a heavy-duty diff (12:28) and a planetary hub (1:5.4) with no gearing after the motor..

Nice looking build and the performance is pretty good, both the suspension and the drivetrain. I'd also be interested in the gearing. Is the slow output of the buggy motor geared down 3x before it goes to the diffs? (The image from below suggests that.) If so, I don't get how the 7/45 gear ratio is achieved. Does it need lubrication to avoid damage to some parts near the motor?

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). Hmm, this is exactly my problem; if you build such a thing with the recent drivetrain components used nowadays for stock RC cars, the result is too slow. First, a wheel is rarely attached straight to the linear motors. Usually there is at least a diff and a wheel hub in between, and TLG seems to push the heavy-duty diffs and planetary wheel hubs / portal axles for good reason: with them things are less prone to break because the high torque only manifests itself at the end of the drivetrain. Second, the Zetros is an example of a straight to the wheel drivetrain in this sense; the motors go 1:1 to the axle diffs after coupling (the central diff is irrelevant). But the result is such a slow speed that is hardly playable and the torque is almost too much (for a trial truck that setup is acceptable, but for other kind of vehicles?). To get a sweet spot with these components, faster motors would be needed. The other option is to build without planetary hubs. It is faster then, but then there's too much stress on the drivetrain that can break some joints or skip some gears (not to mention that steering angle is worse if the front is driven as well). Also, about other RC functions like LAs, stock models are often criticised for being too slow to operate. I would definitely not call the drivertrain of 42099 advanced. It's one of the simplest possible, the motors go almost directly to the diff with some gearing that is needed for routing the driveshaft because of the high build of the chassis (and can be also used for adjusting speed/torque). No coupled motors, no gearbox, no floating axles, it's not even a realistic AWD (separate motors front and back). It's okay though for an RC car, I just don't really see it advanced. That's where it gets interesting. For one, the buggy motors (or Buwizz motors) are faster by 4x-6x, which is too much, it will damage the parts if you build a realistic drivetrain with it (not straight to the wheel). Second, its form factor makes it far from easy to use inside the chassis, (not inside the axles or in place of the diff in an independent suspension), typically, it would have to be put into the middle of the cockpit of a car to get the output where it should be. Actually, that is the motor that has been designed to put a wheel straight onto it, but that's also somewhat limited usage. How does that translate to practical usage? Isn't that just proportional to max stalled torque?

That's something quite useful indeed, I have missed this new part so far, thanks!

Well, sounds like a nice idea, but the very first set that used them (42099) is already an exception, as it needed up-gearing. Of course a single kind of motor will never be enough for all models without some gearing. That's why it seems odd that all PU motors have roughly the same speed. How is that justified? I understand what you say about less torque in between, but if you have a faster motor with less torque to start with, you'd have the same effect for the transmission but with less loss off efficiency due to the gearings that cancel each other and only add friction. Sure, I have seen them long ago. As I remember, the conclusion there was that the XLs are a bit better for high torque applications. Well, the Zetros seems to kind of defy that argument, as it needs high torque, but uses two L motors. Even the Cat does not use linear XL motors, and as I have read it struggles with raising the blade (it is too slow as it is, and if geared up, it does not have the torque). 42100 uses XLs for drive, but with a lot of down gearing, and the technique has been kind of enhaced by the Cat's planetary drivetrain. Then there's 42114 that uses one XL for drive, which is a bit weak. So all in all, I don't see great usages of the XL motor.

I had the same observation when trying to write custom control app for PU, the L motor was much more precise. As if the XL is not really designed for steering, only for crude positioning such as for LAs. The internal gearing is also something that has puzzled me for a while, as it does not seem to be a good match for all the recent drivetrain parts, like the planetary hub’s massive down gearing. When the XL motor (and the hub) was first introduced in 42099, it had to be geared up to achieve proper speed, which looks a bit strange, given that inside the motor it is geared down, and all the down-up-down gearing probably loses significant power. I thought the reason was that in other models, like 42100, it needed higher torque, but that could have been achieved by gearing down outside the motor. Even the buggy used a bit of up-gearing (if I remember well), and the Zetros also has very slow speed at 1:1 gearing, that could only be made faster by up-gearing. It seems to me that the motor speed does not well match the rest of the parts in recent sets (planetary hubs and heavy duty diffs), and that with faster motors, a wider range of speeds could be achieved with less power loss (it’s kind of impossible to build fast models with PU and planetary hubs, as significant up-gearing of the motors looses all torque because of too much friction). Does anyone have an explanation for this? Could this be intentional design, or just lack of compatibility between the design of PU motors and other drivetrain components? I think the PU system leaves significant power on the table because of this misalignment. Or is this the wrong way to think about it?

That’s an ingenious mechanism, I like the idea of logarithmic representation and the overflow/carry mechanism! It seems to be really reliable too, does it ever miss a ball or is it built in a way that it’s kind of impossible?

That's a pretty cool mechanism, kind of like a small GBC that's actually got some real-life utility! Interesting use of the Buwizz motors, didn't think it would be possible to build it with such a reasonable speed out of lego.