aeh5040

Now that is one strange looking vehicle! You might want to try reinforcing the chassis and the mechanisms a bit...

There might be other ways. Combining a diff with a continuously variable transmission would do it in principle...

Even though it may not be the best for vehicle transmissions, I'm a big fan of this one: - the spur gears on the housing are great for add subtract mechanisms and their many variants...

Nice work! it reminds me a little of Il Tempo Gigante

Well, no wonder your motor is working hard with the additional weight of an orange 6L thin liftarm AS WELL as a 7L black one, and a 3/4 pin to connect them Great work - the orange looks awesome! Indeed, there is not that much torque to spare when it comes to making a turn. Of course, all the mechanisms do have quite a bit of friction (the worms, the differentials, the armatron). I did find that things improved after a careful going over all the mechanisms looking for slightly bent axles and rough gears (in particular I find that the double bevels sometimes have rough spots on the sides). One more technical point to record about this model (if anyone cares!) The 3x3-quarter-circle-liftarm catch that releases the armatron mechanism in response to a command from the brain required quite a few designs (even though the final solution is very simple). It is really crucial that the liftarms have a perfectly circular shape (and this is the first time I have ever used this fact in a model). That way, there is no possibility of the armatron forcing the catch out of the way when there is no command from the brain, yet it requires relatively little force to drag the catch out of the way to give a command (you only have to overcome the friction).

Thanks - these pictures are very helpful. Quite a masterpiece. Where do you get the sails? Indeed. I remember reading somewhere that for many years the only way for a human to travel over 100mph was in an ice-yacht.

The sailboat is amazing! I'd like to see more details... For those who don't like mixing PF with water, another possibility that I've always wanted to try is a land-yacht:

The GBC speedometer is fantastic work. Really innovative use of the differential! (And the ball pump is pretty nice too). When it bottoms out at "Min", what stops the paddle wheel from turning backwards? Just carefully balanced friction in the friction pin versus the clutch wheel? To be picky, I think it does not genuinely give a reading of speed or flow (in balls per minute). Assuming a constant flow of balls, I think it will drift all the way to "Min" if the flow is less than some critical threshold, or drift all the way to "Max" if the flow is greater than the same threshold. Nevertheless, I still say it's awesome! I wonder if there is any way to genuinely get a reading of balls per minute by mechanical means?

Without question, it was this compound of five tetrahedra. Even with a computer model on the screen it is very hard to work out how to interleave them.

That's a lovely MOC. Wonderful mechanics for such a small space!

Actually, there is even more to be said on this point. It is equally important that the upper "brain" does not operate too SLOWLY relative to the lower "drive module". If it did, the drive module could complete its turn WHILE a rocker arm was lifted by one cam. Then it would receive a second turn instruction from the same lifting of the rocker arm, which of course is no good. So the relative speeds of the two halves need to be just right. The time for the drive module to complete a turn needs to be longer than the time that the rocker arm is lifted by a cam, but less than that time plus the "down time" between one rocker actuation and the next. And of course, all these things are not completely deterministic, but subject to some variation, so extra safety margins need to be built in. In fact, this issue is only really important for the earlier cams in the sequence, especially the first one. The later ones move very quickly from one position to the next, as a result of the backlash in the Geneva mechanisms combined with the weight of the rockers acting as a detente mechanism. All this is part of the reason for choosing "sharp" cams (1x3 liftarms) for the earlier Geneva axles. (But "blunt" ones later because of the low torque available). This issue caused a lot of trouble in earlier versions of the machine, when the drive modules were not 100% reliable. Also, I've made a slightly nicer (color coded) version of the "road map" here.

That's a very funny and clever creation! I so wish TLG would do more dinosaurs along the lines of 4958...

Wow, thanks Philo, that was FAST! And great work on the PDF, Blackbird. I really need to learn LPub...

Here ya go!

I'm not sure I want to try calculating that! Building time maybe half a day per week for a year? But it's very hard to estimate the amount of thinking time... Surely nonsense I don't know anything about your job, but your Lego creations are simply stunning! If Lego building was my job I would probably be fired - it takes me forever to get anything finished, and many aspects of it I approach in inefficient and illogical ways (e.g. I'd never heard of condition number, although the basic idea sounds easy and natural).

I would welcome Blakbird or others improving the Ldraw file / instructions. I basically did the minimum to make it buildable. If you compare the knobbly tires with those of your 8422, I think you'll find there is no detectable difference in diameter. However, there are some other confounding factors here: 1. The positioning of the wheels in the file may not quite match reality (and I did not try that hard). 2. The tires squish a bit when there is weight on them, changing the diameter. 3. The diameter is only an approximation to what you want - when the vehicle makes a turn, the tires interact with the floor in complicated ways involving friction and deformation of the rubber. (It's possible that THIS part is different with the smooth/knobbly tires). I believe experiment is the only way to get the turn angle exactly right. This is what I did - I kept adjusting the wheel spacing on the real model until I got turns of 90 degrees (as measured by the cumulative effect of several consecutive turns). Then tried to find a combination of pieces to enforce that wheel spacing as best I could. That's right. I toyed with this idea (after the Pendragon 1) but decided it was too difficult, and besides, an add-sub mechanism makes it cooler! I like the current size of the drawing. It's big enough to look impressive, and big enough that it could not easily be drawn by hand, but not so big as to be impractical (like version 1). Quite right. Thanks for the clarification. The earlier post contains a deep link. But brickshelf seems a bit unreliable these days, so here it is in bricksafe too.

It looks as if I got myself confused about this. What I said earlier about it being insensitive to initial conditions was not correct. As you say, the initial set-up in the LDraw file does not match anything in the schematic list of diagrams, and is NOT the correct way to set it up. One possible correct initial setting is to have the cams on one side pointing towards each other in pairs. I will edit the LDraw file to reflect this. Other initial settings will produce DIFFERENT patterns, generally less interesting than the dragon, but also quite nice. E.g. the incorrect set-up in the file (all cams pointing one way on one side) gives a space-filling curve that fills a diamond shape (according to my computer program). Edit: I think the LDraw should be correct now!

Once again, Blakbird has figured out how everything works essentially perfectly! Very impressive without building anything. The armatron animation is awesome! Just a few clarifications: Oddly enough, I didn't give so much thought to this. It's possible a blue 3L friction pin would work just as well. Perhaps it is an axle pin just because of some previous version of the design in which the axle went into an axle hole. (I don't remember exactly). One point to add about the red Armatron wheel: it is important that it is well balanced on the central axle, with the center of mass as close to the axle as possible - otherwise it might come to rest in the spot where the center of mass is lowest, and not rotate any more. The reason for the extra axle with lots of half-bushes is to adjust the weight distribution appropriately. To amplify Blakbird's final point about backlash, the crucial property is that the cumulative error is literally zero. 3000 consecutive actuations of the mechanism on the left side would result in exactly 3000 revolutions of the Scotch Yoke, and exactly 2000 of one wheel and 1000 of the other. As I tried to explain in another post, by happy mathematical accident it turns out that the (considerable) backlash inherent in the transition from a left turn to a right turn does not seriously affect the final drawing. I have put some computer generated pictures here in attempts to illustrate this. One final point about accuracy. As explained, a "turn" consists 2/3 of a rotation for one wheel and 1/3 of a rotation in the opposite direction for the other. We want this to correspond to a 90 degree rotation of the vehicle, but this depends on two things: the diameter of the two wheels, and the spacing between them. Get either wrong by even 2% and the picture will not be so good (see the link above). I managed to adjust the wheel spacing to sub-half-stud accuracy by using a technic plate turned sideways and an old style 8t gear nestled into two axle holes. (The latter trick is also used to get the casters on the bottom of the vehicle the right height). One problem with version 1 of the machine was that the constant turning creates a big sideways force on the wheels, tending to push them off their axles. Even if they don't fall off, this quickly results in lost accuracy. Hence, the two turquoise cantilevers that you see on top of the wheels play an important role.

Another obvious difference is that it is WAY quicker to turn an idea into physical reality (at least a prototype mechanism) in Lego than any other medium I know (even other toys like Meccano). In particular, trying out a small variation can take only seconds. It means that hands-on trial-and-error design is a far more realistic option than elsewhere. By the way, I am definitely in the inside-out camp.

Thanks for saying that! I was worried most people might be getting bored...

That's a really neat and effective design (and awesome filming as always). Although from the title I was expecting this

Very practical (but messy)! Does it always get the stone, or can it "miss"?

I am looking forward to seeing Victor's life size working fallout shelter MOC... Once I have the idea for a MOC, I usually start by trying to get the hardest / most complicated bit working. (E.g. a gear box, or an unusual mechanism.) I do lots and lots of trial and error, sometimes working on squared paper to get the layout clear. The many possible uses of modern technic pieces always surprise me. Often when I'm stuck a particular point, I'll browse other people's MOCs, or even just sort through my own pieces, until I suddenly realize "that it is the perfect piece / combination for the job".

Awesome work so far, Blakbird. Actually, the Geneva mechanisms move quite easily, so there is not so much need for torque here. (The locomotion requirements of the lower module are what prove to be the limiting factor in terms of torque). Much more important here is that the Geneva wheels turn slowly enough that the lower module has time to do a complete operation between "instructions" from the upper "brain". That said, the Geneva mechanisms ironically involve some gearing UP - in your lovely animation, you can see that the orange wheel actually moves faster than the purple one, at its moment of maximum speed. Consequently, the last few Geneva wheels provide very low torque, no matter how hard you push the first one. Therefore, all moving parts of the brain layer need to be very light, loose, and low friction. (Thus: the round rollers, and the counterbalances on the rockers). And the lower layer will need to do a lot of "signal amplification" to do its job properly... No, 2:1 gearing would not work at all. Think about the last axle - it is turning at an average speed of (maybe) 1 turn every 30 minutes. If it did so at a uniform speed, as would happen with gearing, then it would hold a rocker in the up position for maybe 5 minutes at a stretch, and furthermore the precise time interval would be very unpredictable. Throughout that time, the bottom would be receiving constant instructions to turn. We don't want that! No, there is not. The "rest position" for all the axles is with the cams at 45 degrees to the vertical. Because the cams line up with the 2 pegs of the peg wheel, whenever an axle advances from one 45 degree position to the next, it either actuates one of the rockers itself, or it advances the next axle (but not both). Again, no, there is not. (If there was, it would result in the machine moving straight ahead for a step). The effect of the last special cam is that whenever this last axle would cause the next axle to advance (if there was a next one), we instead get a right turn. (The last cam does not just provide lift 3/4 of the time - it provides 3 separate lifts, with gaps between them.) This is what causes the curve to join up and form a twin dragon. It's nothing to do with the shape of technic axles specifically (except in combination with the shape of the cams), but your second explanation is essentially correct. Good idea, I'll try to set this up at the weekend (with the real model). In the mean time, perhaps this picture will help. Each row on the right is an illustration of the cams viewed from the left side of the vehicle (with the triple cam at the end), at a point in time between steps. From each row to the next, the first axle advances 90 degrees clockwise, perhaps causing some others to advance. The little red vertical line shows that exactly one axle actuates a rocker at this step. It will be the left side rocker if the cam moved across the top, or the right side rocker if it moved across the bottom. This corresponds to a right or left turn respectively, and you can see the corresponding place in the dragon curve.

That's a fascinating creation, and very playable! Pity it's not pure Lego, but I understand the difficulty. I'm interested and surprised that rotating the propeller cowlings works so effectively for steering...