Stereo

I don't think they're as finicky as the 2L liftarms pushing 3L axle with stop that's pretty common design, lots of MOCs I've tried from the 42093 Corvette need tiny adjustments to the axle locations before they'll even roll. Also you can run them flat or upside down rather than only in a V or inline. But yeah, in situations where one doesn't work, the other won't either.

Would it be ok to space the pistons out more? You could alternate 1x1 bricks and 1x2 bricks with 1 hole so they're 1.5 studs apart, and then use entirely the crankshaft "Type 1" inserted with all the axles in a straight line, so the pistons only rise 1/2 stud, don't drop 1/2 stud.

I don't have the new driving rings yet irl, but maybe you can use hollow 1x1 plate instead, possibly with a minifig skate or something in it? On the old driving rings it looks like it's 1/2 plate thick, so 2 plate constructions like this will fit. I don't know if the pins on the black piece are already engaging the ring either.

Here's one option, makes it a bit taller physically, I built it in 7x11 frames to make it easier for me to locate stuff. (20:16/16:28 = 0.71 in low gear, 20:16/24:20 = 1.5 in high gear) The red output is only active in low gear, blue one in both gears.

If you add another 20t gear meshing with one or both of the red 16t gears, for your front wheel output, that would do it, right? So the bottom shaft goes to the rear in both gears, and then another one only connects the fronts in low gear. If you could replace the 20t with a differential, that seems like it should also work - the higher ratio would be feeding into one side of the diff (and thus not power the thing sticking out the other end) and the lower ratio would drive the diff directly, and thus do both outputs. I'm not sure what gear spacing would make a diff work there though. Maybe use 20t clutch to the 16 end of an old style diff? Or use a clutch piece to connect the pinhole 20t gear to one side of a diff, with the two pieces pushed together so it's just always engaged.

If you just want to move it by 1/2 stud, maybe use the 1x5 plates with an axle hole in the middle instead of technic plates. I'm not certain but I think they also have stronger clutch on the underside than standard plates.

With something that small, maybe you could just have a rubber band drive to the other axle, on the half bush. I'd be inclined to build something all technic for rigidity. The motor has a good number of pinholes to attach plates anyway. I'm using the 4277 3x5 liftarm with alternating holes here. You could build it in a 7x11 frame though that's sort of large

If the axle's the same length as the upper/lower control arms, shouldn't it work fine? The 3 joints won't be in line with each other at either end, but they move in parallel.

Here's one way you could do it - the red 3L beam goes to the motor, the grey 3x3 turns 90 degrees back and forth as it spins. Middle shows one extremity, bottom shows the other. Depends what space you're fitting things into. The yellow 5L and grey 3x5 can be made longer if that works better.

When it came out, the original Aquazone felt like space to me. I think Lego was more vague on lore back then, so there's nothing actually tying it to Earth, unlike Atlantis. But I do have a pretty narrow window of Lego Space as a kid, 1993-1995, after that I was all in on Technic, I probably still glanced through the catalogs but I was saving my money. So they'd have to get pretty specific to hit my nostalgia (Space Police 2, Ice Planet 2002, the neon yellow Blacktron), hasn't happened yet.

The method used in, for example, windshield wipers, is you have a shorter spinning arm connected to a larger arm that only moves back and forth. For the angle to be 90 degrees, the ratio of the two arms is around sqrt(2) times longer. Though if they aren't aligned exactly parallel at the center, it changes the ratio. Blue dotted line showing that the center of the circle is aligned to the endpoints of the arc, thus the linkage arm moves exactly 2R side to side for both. If you keep the longer arm pivot point and move the shorter one up and down, it'll increase the angle moved by the long arm.

I woke up more clearheaded and probably putting clutches in both sides of a modern gear is the sensible solution. One permanently, one controllable. Though that makes it a 2 1/2 wide thing, and probably needs something to hold the clutch in place (put it on full bush + 1/2 bush instead of axle connector?). So if there was a gear that works directly that's still more compact.

I was thinking about this topic again, pulled out my bucket of gears to see what fit with what, and found an interesting interaction. (vertical gears are the same type as the one sitting in front of them - 6542a, 6542b, 4019, 94925) Still on the topic of "1:1 output connect to input via clutch", the obvious solution is the old 16T clutch gear (left) with old 1/2 bush. Easy to find parts, though the 1/2 bushes are at this point 25+ years old and a lot of mine have split. That said, when their teeth are meshed to another part, they're pretty stable. But the old 16T axle gear turns out to also secretly be useful! The 4 nubs it has are the same diameter as the axle-connector that the clutch slides on. So the old 6539 clutch can actually engage onto it. The newer clutches don't have interior ridges all the way to the end, so they probably don't work. Engagement distance is a smidge less than 1 plate with this build. Which I should note, due to the axle with stop, is actually a bit more than 4 studs long. The other geometry of note is that bars spaced 1.5 studs apart on center engage with the outside ridges on clutches. Just a tiny bit farther than 24t gears (which have holes sqrt(2) apart). If there was a part that could put 2 or 4 bars on a 1.5 stud circle, or a piece a bit smaller than a bar (minifig lipstick? I don't know) it might be possible to engage that way. Thinking logically, the reason the 16t gear nubs work is they're actually antistuds in disguise - just like the axle connector, they're intended to be able to attach directly onto a plate between 4 of the studs, while having a 1 stud outer diameter. So maybe there are other antistud-sized parts that work. I seem to remember the old palm trees had something like that in their base. Palm tree bars maybe? I definitely don't have one at hand the way most of my Technic is, but maybe tomorrow I can dig one up. Also it turns out splat gears have antistuds and can be engaged by the clutches... maybe not useful, maybe a splat gearbox would be fun.

It's a funny shape, one big and one small bead, the small one does actually fit the current size tires. Though it's some tiny amount different (1LDU? 2LDU? Eyeball can only say less than half a plate for sure) I don't know if mounting tires that way is secure enough for powered stuff though, it might start spinning on the wheel.

Baker valve gear. Kinematically it's doable, the problems are downsizing it to something that would fit in a MOC, making it sturdy enough to transmit any force, and having enough travel to actuate a pneumatic switch. To a lesser extent it was difficult to figure out how it even works, from 100 year old scanned documents. All the individual components are amenable to being made from Lego, as it's just straight and L shaped bars, the problem is that they're all stacked - green inside light blue inside dark blue inside red - so the minimum thickness ends up around 4 studs before including mount points on either side. How it works is the pivot at the middle of the red bar is "fixed" for a given mode of operation, so the blue bars pivot around that point as the crank pushes front to back, which rotates the bell crank. Having the red pivot left of the bell crank pivot makes the crank and valve go opposite directions, right of the bell crank pivot, they go the same direction, which lets you reverse the operation of the pistons. (or stop the engine by putting it in the middle) When they're running in opposite directions, light blue and green overlap on the bottom of the bellcrank so potentially the whole stack is actually red, blue, lblue, yellow, green, yellow, lblue, blue, red. On real steam engines they use a S-shaped light blue bar to help with this issue, and have a bit different vertical location of the joints.

I suppose they're aesthetically questionable, but maybe the new city worm gear could be used for a decent amount of linear actuation. Since you can just keep stacking them, you could have 16 stud worth of travel from 3, fitting in about 18-19 stud vertical space when compact.

I suppose my argument is that you can always place a virtual 3rd part in the slider and it'll join to the 2 parts as it would if it existed. It's not the easiest thing to find good reference on but the ball bearings in Rzeppa joints are actually splitting the angle between input and output in half, and acting like a double U joint. They don't stay fixed relative to either component. And now I'm questioning the old 8880 "CV" balls too since that other thread brought them up. Unfortunately I don't have that set to look closely at how it works. I do have 8444, not sure it's the same part for its swash plate offhand.

Oh, I never looked closely to the small/large ones to notice they swapped the "male"/"female" parts, so the one with the axle-holder has the nubs on the large version, and the axle has the slots. They're still mechanically the same universal joints, just with sliding instead of a 3rd moving part. Just to confirm things I wiggled the 948L skidder around, since it uses a single one instead of a center differential, and as expected at 0/90 to the steering axis they stay in phase, but if the CV joint is at 45 degrees, steering it will make one of the axles roll forward while the other stays still. It's lego so there's enough slack in the gears it doesn't really matter for driving of course.

It's effectively inside out from the U-joints, so you want to match these pins to the orientation of the holes on the U joint, on the intermediate shaft with joints at both ends. (same as 2 U joints want them to match) I think that means your picture is correct.

I somewhat thought so as well, but actually the key for fast builds is change as little as possible from your usual methods. I've built MOCs from sets like 8818 a hundred times over, I know the rack and pinion steering, so that's what I use when I need it to design and work first try.

Ok, here's a Bricksafe gallery with higher quality photos. Particularly, these are the moving parts: The linkage goes all the way through the cab so it doesn't really have interior details. An elastic band on the rear axle helps it to "latch" into the raised/lowered positions. Overall, it's 30.5x11x11 studs, or 29x11x12 with the rail wheels down.

I'm fairly dependent on natural sunlight to take good photos, so here's the best I can do with it currently overcast and snowing. 1990s Ford F350 Hi-Rail. Featuring steering, opening doors and side compartments, hood, and a lever that switches the rail wheels up and down. I'll do a more complete write-up when I get a sunny day and can do better photos.

Better look at the linkage (grey plates). In the forward position the corner plate hits the crossing 1x10. Then, sliding it backwards, the plate doesn't block the steering anymore, and the thin liftarm is the steering stop. Made some changes as I went, had some unanticipated intersecting parts around the front tires, and I wanted a higher roof. The truck cab's essentially done so I think that's a good stopping point for today. Little bit of fiddling on the doors and more white parts if I can find them.

I did end up with a half stud extension on the linkage to get both working together, using engine crank parts, not ideal, but it's not in the way of anything I planned to build. With the black lever forward, the train wheels are down and locked. It also locks steering in the centre. Pulling the lever backwards, which is somewhat tricky with just the bare chassis, raises both up. The front wheels go straight up and the rear ones swing backwards because I'm controlling opposite parts of the linkage; rear moves the 5L thin beams, front moves the 3L thick beams. On flat ground the road wheels end up a stud off the ground, it's pretty sturdy. The 2x8 plate that bridges stud to studless will of course get sandwiched between Technic bricks later, and fix the bend in the middle. I just had to tackle the function before covering everything up. If you're not familiar with LEGO Technic TRAINS on YouTube, it's worth checking out. I don't have the space or budget to do it properly, but I built a 4-2-0 pneumatic locomotive (and then had to add a counterweight for it to have traction + flywheel inertia). 1:25 is about halfway between minifig and Technic fig scale, average people are 7.5-8 studs. So the minifigs are 1m tall and Technic are 2m. And even the smallest locomotive dwarfs a regular pickup truck.

Bit of a sunk cost thing on the design where I don't like the half-stud gap between cab and box anymore (wheelbase is 15.5 studs, which does help with a half stud clearance for steering) but everything's connected so I don't want to do it over. The grey lever on the side of the box controls the train wheels by sliding forwards, and there are a couple cabinets on the side that don't have any interior surfaces yet. There's some amount of unintended geometry in the train wheels (hypotenuse 4, height 1, length 3.87 while stored) so I'm going to go ahead and build the chassis, see how everything actually functions at the moment.