Hrafn

Well said. DrJB's design is ingenious and very well presented. The animations are particularly helpful in conveying how it works.

Are you familiar with the Lowell Sphere? Bruce Lowell's technique can be adapted to spheroids.

The left-hand design seems somewhat more secure to me, since the pin on has a very strong clutch power in a hole. Still, at high enough speed you could have rotor blades flying out. I certainly wouldn't want to stand next to it! That said, this is very cool.

Thanks! You are correct, the 10L axle is driven by the motor and the (new design) 16t slides on it. It takes a little bit of force to slide the gear - much more than is the case in your design with the clutch gear - but surprisingly the force isn't too great. A properly braced LA can move it without a problem, and it's very easy to slide by hand. I've uploaded a video here. Using a linear actuator works, but there are a lot of problems. 1) it's slow (which could be changed by gearing at the expense of making it bigger 2) you have to watch it to know what gear it's in and when to stop it 3) the LA exerts a lot of force on the structure, which thus needs to be reinforced 4) the horrible jerking and noise that occurs at minimum and maximum extension 5) LA + PF-M = lots of space, and the whole point of the gearbox was to make it small Maybe a captive worm gear would work better, but problems 1 and 2 would still be issues. Technyk32231 is correct about using the wishbone - the axle needs to be able to rotate. You can't pass the axle through the hole in the wishbone, either, since then the wishbone will protrude above the top of the 16T gear and interfere with the 20T gears. Another option is to lengthen the gearbox by 1 stud, allowing for the mechanism that moves the sliding gear to be 3 studs wide (instead of 2, as it is now). That would mean that you could use, for example, 2x to move the gear - the same way Splat does it in his gearbox.

I wonder if maybe Lego didn't include instructions for alternate models with the Unimog set because of licensing concerns. Since the main model was a Mercedes product, TLG or Mercedes might not have wanted a non-Mercedes vehicle as the B-model.

Very nice! I too like the switching - it's always great to see such nice clean mechanical solutions.

Wow! The whole thing is very impressive. I'm also more than a little envious of the number of parts you have. The way you switch between Ackerman and crab steering is very clever - I may have to steal that! How much is the XL geared down to lift the boom? How heavy is the boom, and how long? Is there any way you could gear it down more without losing too much power to friction?

I should have mentioned that my gearbox was very much inspired by Splat's. The fork can be replaced with Technic, Steering Arm with Pins and there are probably other good solutions. Mbmc makes some good points about the advantages of definite control over continuous control; my gearbox was a continuous one because I was trying to make it small and minimize the number of motors used. In theory, it seems like a definite control gearbox with N motors could have 2^N gears since each motor has 2 directions. I suppose you could do 3 modes per motor (forward, reverse, off) if you used a spring and were willing to hold down the motor controller to keep it in a particular gear, but that sounds like a pain and a waste of electricity. Since the servo has 15 positions, theoretically you could have a 15-speed gearbox with just the servo, but given the slop and flex and backlash inherent in the parts, the maximum number of practical speeds is probably significantly lower. Does anyone know of a single-servo design? Of course, a single-servo design would be sequential so you couldn't shift from, say, 1 to 4 directly. I'd like to see Mbmc's multi-servo design, too.

This may not be what Dans lego meant, but in case it's of use to others, I built a compact 3-speed synchronized linear transmission with 20:12 ratios between gears. I have not motorized the gear changing mechanism in the pictures below, but it's easy to do with a linear actuator. The one unusual part is "Technic, Liftarm 2 x 4 Fork with Pin", used to move a sliding 16t gear along the 10L axle. More photos, including a parts list, are here. If anyone finds this useful, please let me know - and if you find a way of shrinking it further let me know that too!

This forum has to be one of the few places on the web where someone can post a string of 4-digit numbers, and members will say to themselves "ah yes, that brings back good memories."

I only have a few sets (8841 Dune Buggy, 3806 Gigamesh, 3808 Shadowstrike, 8455 Back-hoe, 8043 Excavator, plus 8376 Hot Flame RC car and 8001 Battle Droid). 8043 is impressive for how much stuff is crammed into the superstructure, but for me the 8455 back-hoe wins for sheer complexity and realism. Admittedly, given the rest of my collection, those two sets don't have much competition...

The boxes also serve as in-store advertising; the larger the box, the more impressive the set looks. I'm just speculating here, but it's possible that one factor in Lego's decisions on how big a box to put each set in is the 'billboard' effect. They may want to make customers more aware of (and eager to buy) certain sets, and thus may make those sets' boxes larger than necessary. Or it could all be pretty much ad-hoc

I have also had nothing but good experiences with Lego customer service. It sounds like your initial mix-up was a rare failure, but them giving you a refund and letting you keep the extra set is very much in keeping with their practices. I may gripe about a few things Lego does wrong (like inconsistent colors within a set) but they do a good job on customer service.

Thanks for sharing those photos! Do you know if that was the final shaft design? I'm having trouble seeing how they avoid having the shaft fail in torsion where the bricks grip each other - stud/anti-stud connections can be reasonably strong, but I'm surprised they're strong enough for this application.

The Lego Car Blog just posted a life-sized, pneumatic engine driven, Lego hot rod:

I agree entirely, though I'd add that sometimes black's being hard to see can be an advantage - sometimes you want to hide certain things. I like the chassis to be dark and dull so it doesn't compete visually with the bodywork, but dark gray would work just as well and would be easier to work with. Sadly I have only a few pieces in that color, and loads of black.

I would do every chassis entirely in black if I had the parts to do so. Otherwise black can be good for highlights sometimes. Madoca's SUV is one of the very few all-black MOCs I've seen that I thought looked really good, for the reasons others have already mentioned.

I may be a math nerd here, but I always use the teeth-to-spacing rule. Two gears mesh perfectly at a distance (in mm) equal to the average of the number of teeth they have; and 1 stud = 8mm. So two 8t gears mesh at 8mm = 1 stud, a 16 and 8 mesh at 12mm = 1.5 studs, etc. I find it especially helpful when I'm meshing one of the spur gears (8t, 16t, 24t, 40t) with one of the double bevel gears (12t, 20t, 36t). Once you get into mixing studless with studded (where a plate = 1/3 of 9.6mm = 3.2mm), though, it gets messy.

He probably means a micromotor. They are very slow but have decent torque for their size.

Sariel's book helped me a lot when I came back to Technic and had to adapt to studless; he talks in the book about the strengths and weaknesses of each and how to combine them. It is a steep learning curve, but worth it since studless opens so many possibilities and can be used to build so compactly. A lot of studded parts are still quite useful even if you move to building mostly studless - the 4L differential works nicely as a longitudinal central diff, the studded beams can be used to stiffen up a frame, etc.

I agree. Maybe the new part was designed to solve some other problem that couldn't be solved with existing parts, and then they used the part in the snowmobile because it was available? Maybe we'll see the part in a 2H 2014 model in a context where it makes more sense.

22 years old! Wow. He says he's around machinery a lot at work; I wonder if he's in engineering or manufacturing? Certainly he's got the skills to make a living off of mechanical design if that's what he wants to do.

I have intentionally not bought any of the 5L xooox thin liftarms because I know that as soon as I get a few, I'll find them indispensable and have to spend way too much money on Bricklink building up a stash.

It does answer my question, thank you. I'm not planning on using it for a structural connection; instead I want to use it to create friction between two other parts. The full details are in my continuously variable transmission thread, if you are interested; I'd be using the leech to replace the ball joints in that construction. I will probably have to modify the leech by cutting off the parts that protrude from the sphere, though. Thanks again!

Thank you! As long as it's approximately the same size as the ball joints, it should work for what I want to do.