Didumos69

You could do that, but you can hardly say it would be compact. Also, the added gearbox would need to add a tertiary ratio that is even bigger than the secondary ratio, so it can not just be a reduced version of the 4-speed depicted above.

Here's the 4-speed half of the Bugatti gearbox, with a few simplifications I did for @jb70's pimped up Bugatti. Black is input, red is output and orange is control. Though I don't like it's modest ratios, this is the most simple gearbox you can make with the orange rotary catch and can thus serve as a very good first study subject. LDD-file here and Stud.io file here. EDIT: In relation to the OP: Why are the ratios of this simple gearbox modest? To keep it simple there are no auxiliary output axles, the clutch gears mash with the main output directly. So having different output ratios is solely based on the use of different clutch gears. Therefore the ratio between the output ratios (= the secondary ratio) is in this case only 5:3, for each driving ring. Based on the OP we know that the secondary ratios need to be bigger than the primary ratio to obtain a useful gear sequence (1-2-3-4 or 4-3-2-1), so the ratio between the input ratios (= primary ratio) needs to be even smaller than 5:3. In this case the input ratios are 1:1 (via a 8:8 mash) and 4:5 (via a 16:20 mash), so the primary ratio is (1:1) : (4:5) = 5:4, indeed smaller than the secondary ratios.

It's in third gear. Transfer follows the low input, so it is in either gear 1 or 3 and it follows the high output, so it is in gear 3. And color the axles as you go, to persist your mental image...

As a whole, just the black part would give unnecessary friction.

That would have been an easier layout to play with, I agree. What's important though, is that I could have used practically any 4-speed sequential gearbox for this explanation. Anyway, perhaps it is useful if I share the whole gearbox, including the gearbox structure. Exploring it in 3D could be very useful, as @Zerobricks suggested. Here it is in Stud.io format and here in LDD format. When looking at it in 3D you can reason how transfer flows by following the engaged clutch gear. Try to reason in which of the 4 gears the gearbox depicted above is.

I finally took the time to write down the things I have come to understand with regard to LEGO 4-speed sequential gearboxes. I am receiving many questions about gearboxes and I hope these understandings can help you reason about a gearbox layout while you're building one or trying to design one. I hope this also answers a question I received from @nerdsforprez more than a year ago, which I did not answer yet. Gearbox layout Let's take a look at this 4-speed sequential gearbox layout. Black is input, red is output and orange is control. The main input is divided over a high input (black) with high input ratio and a low input (white) with low input ratio. The high input ratio is 1:1 (via a 12:12 mash) and the low input ratio is 1:2 (via a 8:16 mash). This makes for a combined ratio of (1:1) : (1:2) = 2:1 between the high and low inputs. I will refer to this ratio as the primary ratio. In fact this ratio is the ratio between the two driving rings. Both driving rings have a high output (green) with high output ratio and a low output (yellow) with low output ratio. For both driving rings, the high output ratio is 1:1 * 2:1 = 2:1 (via a 16:16 mash and a 16:8 mash) and the low output ratio is 5:3 * 1:2 = 5:6 (via a 20:12 mash and a 8:16 mash). This makes for a combined ratio of (2:1) : (5:6) = 12:5 between the high and low outputs of each driving ring. I will refer to these ratios as the secondary ratios. Rotary catch and quadrants Even though I will explain things in terms of the gearbox layout described above, the first understanding I want to address, applies to practically all 4-speed sequential gearboxes with 2 driving rings. Let's take a look at the rotary catch and driving rings from above and divide the layout into four quadrants. Each quadrant represents one of the four gears of the 4-speed gearbox. When we turn the rotary catch clockwise (seen from the left) with 90-degree steps, it will always make the following path through the four quadrants. From the path the rotary catch draws, we can see that it toggles from one driving ring to the other driving ring for every 90-degree step. So if we want to obtain a useful gear sequence (either a 1-2-3-4 sequence or a 4-3-2-1 sequence) along that path, we need to tie gears 1 and 3 to one driving ring and gears 2 and 4 to the other driving ring. Otherwise the rotary catch can never 'toggle' between subsequent gears. Now let's take a look at all distributions of the four gears over the four quadrants that meet this requirement. Starting top-left, this will produce a 1-4-3-2 sequence. Repeating the sequence will give 1-4-3-2-1-4-3-2-etc., which effectively boils down to a 4-3-2-1 sequence. Starting top-left, this will produce a 1-2-3-4 sequence. Starting top-left, this will produce a 3-4-1-2 sequence. Repeating the sequence will give 3-4-1-2-3-4-1-2-etc., which effectively boils down to a 1-2-3-4 sequence. Starting top-left, this will produce a 3-2-1-4 sequence. Repeating the sequence will give 3-2-1-4-3-2-1-4-etc., which effectively boils down to a 4-3-2-1 sequence. Starting top-left, this will produce a 2-3-4-1 sequence. Repeating the sequence will give 2-3-4-1-2-3-4-1-etc., which effectively boils down to a 1-2-3-4 sequence. Starting top-left, this will produce a 2-1-4-3 sequence. Repeating the sequence will give 2-1-4-3-2-1-4-3-etc., which effectively boils down to a 4-3-2-1 sequence. Starting top-left, this will produce a 4-3-2-1 sequence. Starting top-left, this will produce a 4-1-2-3 sequence. Repeating the sequence will give 4-1-2-3-4-1-2-3-etc., which effectively boils down to a 1-2-3-4 sequence. Surprisingly, every distribution that meets the requirement, will produce either a 1-2-3-4 sequence or a 4-3-2-1 sequence. What this tells us, is that it's enough to tie gears 1 and 3 to one driving ring and gears 2 and 4 to the other driving ring, to obtain a useful gear sequence. Nothing else matters! Primary ratio vs. secondary ratios The next understanding I want to address, concerns the relation between the primary ratio (the ratio between the high and low input) and the secondary ratios (the ratios between the high and low outputs of both driving rings). We have already seen that in the gearbox layout at hand, the high and low output ratios are the same for both driving rings. One thing we can say about 4-speed gearboxes in general, is that the ratios between gears 1 and 3 and between gears 2 and 4 need to make a bigger difference than the ratios between gear 1 and 2 and between 3 and 4. Now when we take into account that gears 1 and 3 need to be tied to one driving ring and gears 2 and 4 need to be tied to the other driving ring, and we use the same high and low output ratios for both driving rings, we can say that the secondary ratios, which constitute the ratios between gears 1 and 3 and between gears 2 and 4, need to be bigger than the primary ratio, which constitutes the ratios between gears 1 and 2 and between gears 3 and 4. The gearbox discussed in the beginning of this post has a primary ratio of 2:1 and secondary ratios of 12:5, so it meets the above requirement. Check! Swapping and reversing If we go back to the distributions we listed above, we can see that half of them generate a 1-2-3-4 sequence and half of them generate a 4-3-2-1 sequence. When we study them more thoroughly, we can see that all 1-2-3-4 distributions have a horizontally flipped counterpart with a 4-3-2-1 sequence. In other words, if we flip the distribution horizontally, we reverse the gear sequence. Example: Swapping 1-3 with 2-4 in a 4-3-2-1 sequence produces a 3-4-1-2 sequence. Repeating the sequence will give 3-4-1-2-3-4-1-2-etc., which effectively boils down to 1-2-3-4. Example: Swapping 1-3 with 4-2 in a 1-2-3-4 sequence produces a 4-3-2-1 sequence. What this tells us, is that when we mirror the gearbox layout left-to-right (top-down in the quadrants), which boils down to swapping the high and low inputs, the effect is that we reverse the gear sequence. Practical value: If you find yourself in a situation where you want to swap the upshifting and downshifting directions, simply swap the high and low inputs, like in the image above. Finally, if we take one more look at the gear distributions above, we can see that when we swap gears 1 and 3 or gears 2 and 4 in any distribution, we get a distribution with the reversed order. 1-2-3-4 will produce 4-3-2-1 and 4-3-2-1 will produce 1-2-3-4. When we swap both gears 1 and 3, and gears 2 and 4, we reverse the order twice and get again the same order. Example: Swapping 1 and 3 in a 1-2-3-4 sequence produces a 3-2-1-4 sequence. Repeating the sequence will produce 3-2-1-4-3-2-1-4, which effectively boils down to a 4-3-2-1 sequence. Example: Swapping 2 and 4 in a 1-2-3-4 sequence produces a 1-4-3-2 sequence. Repeating the sequence will produce 1-4-3-2-1-4-3-2, which effectively boils down to a 4-3-2-1 sequence. Example: Swapping 1 and 3, and 2 and 4 in a 1-2-3-4 sequence produces a 3-4-1-2 sequence. Repeating the sequence produces 3-4-1-2-3-4-1-2, which effectively boils down to a 1-2-3-4 sequence. What this tells us, is that when we mirror one side of the gearbox front-to-back (swap the high and low outputs of one driving ring), we will reverse the gear sequence. When we mirror both sides front-to-back (swap the high and low outputs of both driving rings), we won't affect the gear sequence. Practical value: If it's more convenient for the rest of your build to mirror your gearbox layout front-to-back, like in the image above, you can do so without any consequences. If it's more convenient to mirror only the left side or the right side of your gearbox layout, you need to also swap the upshifting and downshifting directions. If you want to inspect the gearbox used in this post in 3D, here it is in Stud.io format and here in LDD format.

I decided to park this project for now. I don't regard it as failed, because I learned a lot from it. I will most likely split this project into two, a model with dual diagonal drive and a model with a 4-speed gearbox that can run through all gears at speed. I already have an idea for a 4-speed gearbox with automatic clutch, which disengages the entire gearbox during shifts. Both RC models of course.

Nice! I would not go further. Gear rack travel is now at the level of the A model and I think LEGO was also careful with the max steering angle. @rekreK, I can't see the images

For my 10th anniversary at work I got a second 42099 set. So I figured I might as well experiment with another B model I have in mind. This is still work in progress and there is no guarantee whatsoever this is going to be a success. This time I did want to do a WIP-topic, simply because that fits me better and I can use the feedback. The idea: Gear up as much as possible. My believe is that when you want to use XL motors with differentials in a speedy model and you don't want the differentials to slip internally, you need to reduce torque by gearing up the differentials and then gear down towards the wheels. With the new portal hubs that come with 42099 the gearing down part has already been taken care of, so what rests is the gearing up part. To gear up, I will be using the turntables as gear. I could fixate the grey side of the turntable directly to the motor house and connect the black side to the motor output, but then I would get quite some friction from the two turntable halfs. So I ended up using the turntable as one big gear. Next I tried to mash a 12 tooth gear with the turntable. I used a 2x4 (center to center) distance (similar to a 2x1 distance which can be used to mash a 16t gear with a 20t gear), but the distance is slightly too small (4.47L instead of the ideal 4.5L for a 60t-12t gear mash) and made the mash suffer from too much friction. So eventually I opted for a 60t - 20t gear mash with a 3x4 distance (which matches the ideal 5L distance). Overall the gearing up ratio is 5.95:1 and with the portal hubs gearing down by 1:5.4, the effective ratio will be 1.1:1. The whole model at this stage. Now the challenging part will be to brace the motors and gears well in a rigid chassis. I plan to put the battery / control unit in the back, behind the motors.

Thanks for your report! Yeh, also for me it felt like it could be brought further, but not with the constraints of this being a B-model. I am glad however, that the differential suspension ides, which is the core of the whole concept, is a success.

Thank you @Philo, for sharing your experience. Great to know the instructions are workable. The model is slow, by design obviously, and yeh, the turning radius is quite poor. Maybe I have been too protective towards the new CV joints. I have been in debate whether to drop the levers tying together the upper and lower suspension arms (the black and yellow levers), but thought it would serve two goals, a stronger setup and a limited steering angle, which implies more protection for the CV joints. However, the model can do without the levers, because the tow balls and wheel hub are one piece (so now tow balls can pop out) and downforce is only applied to the upper suspension arm. Long story short, you might try to improve the turning radius by dropping the black and yellow thin levers close to the wheel hubs. You will also need to recalibrate the L-motor for steering of course. Btw, I'm curious to know what you think of the rigidity/robustness of the whole model.

Excellent work! Incredible how many functions you manage to pack in such a clean build! Thanks for sharing!

By switching the roles of ball and socket, you could make a lever that actually operates something.

Btw, what a few of you might have noticed in @kbalage's video, is that it's hard to demonstrate the spring suspension while the model is standing on the ground. This is because when you compress the suspension by pushing down the cabin, the wheels rotate relative to their frames, which causes them to drive the motors. This is also why the model doesn't easily return up after pushing it down. When the model drives around, it easily returns to its ideal spring compression level, which is about 40% of the overall spring travel. To demonstrate or get a feel of the spring suspension, the best option is to lift the model with your hands underneath the front and rear differentials and let it bounce a little.

Based on what @kbalage did in his video, I updated the instructions on Rebrickable. It now has two options: Option 1 with open differentials and options 2 with locked differentials. Both options stay within the parts list of the A model. People that already bought the instructions should be able to download the new version.

Okay. If it had been okay with 12t gears, that would have been the better option. But since it's not, you're right to fall back on knob wheels. Apparently something is causing substantial friction, otherwise gears would not slip. Your gearbox uses clutch gears as intermediate gears to pass drive from the engaged clutch gear to the output. Even though many others do that, I can guarantee it's not a good idea and will induce friction. But maybe that is not the biggest cause. To find out the friction source, I always put in torque manually up to the point where the drive train almost starts moving. At this point I check wit my other hand all axles involved to feel if they are stressed in some way. An axle that is not stressed, will still slide and move a little when you touch it, but axles that are stressed feel as if something has a grip on them. The stressed axle is likely the axle that suffers from friction directly.

You are right, but I don't see anything like that possible within the other parameters such as a pre-defined parts list and compactness of the axles (ground clearance, front and back clearance, i.e. the tires need to stick out to the front and to the back). So I'll stick to the option to build it with open or locked differentials. Yeh, people probably have the parts needed to build it with locked diffs. But I saw a challenge in building it with locked differentials with only parts from the set and I found a way. I will simply add this as an alternative build track in the instructions.

Yes, I think you should.

The willingness to refactor in order to solve seemingly minor issues is what Technic design is all about , imo! The knob wheels won't slip, but do generate more friction, especially under higher torque. (EDIT: The knobs rub while turning. The more torque, the more friction this rubbing suffers from.) You could try with 2 12t gears first. The way they are enclosed in a 5x7 frame should be enough to avoid slipping. In fact 2 12t gears are less likely to slip than 2 thin 12t gears or 2 thin 20t gears, as long as they are braced well. Flatter gears bend more easily.

@kbalage, I think I will add the diff locks as an option to the instructions. If the locks can do without the half bushes, it can actually be done with the stock 42099 parts list by moving a few things around.

Just watched it again. I like the section starting at 4:00 the most. Is suffers, but manages. (new page, so embedded it again)

Steering is fairly limited with and without diff locks. Max 20 degrees I think. The reason for that is explained in the OP.

Awesome video! Thank you very much @kbalage! We watched it with the whole family and my kids now want to go on vacation to Hungary !

Cool! So you were close to this already.

Thanks! Finally did a real slope test. The default longitudinal tilt angle is 3 degrees (leaning forward) and the max tilt angle in a climb is 44 degrees (leaning backwards), so overall it can climb 47 degrees, which is about 107%. Not quite as fast as my previous buggy : https://youtu.be/ek-_36MBD9k