Monday, May 30, 2011

Housekeeping: A new Links section

A website without external links is just like a sportscar with an automatic gearbox: it can work, but one just feels something is missing. So as of today, on Legoism you can find the new section with links to the Lego sites I like and recommend. Don't get too excited, though; the fact that you are here, reading this, means you probably know the most of them well.

Monday, May 16, 2011

Lego Technic 8070 Super Car Review: A serious road beast

Supercars have always had a distinguished position in the Technic world, often pushing the boundaries of what was achievable, introducing new parts and techniques, and being among the largest available models. It all began in 1977 with the set 853 which was built without friction pins and dedicated steering parts, continued through a couple of studded models culminating in 8880 and continuing in the studless era with ever more advanced models. The newest, recently launched member of the family is the 8070 Supercar, reviewed here.

Expectations from this type of a set are undoubtedly high, as the supercars are one of the toughest models to design. They need to cramp as many functions as possible within a limited volume, be sturdy, and yet be modelled to look nice, though not as much to hide the underlying mechanics. And above all that, they need to introduce new ideas and concepts, rather than just recycle some previously seen chassis.

This machine did not fail to do so. Already first half an hour into building, it is obvious that 8070 means business. The gearbox in the middle of the chassis and its surrounding area must be one of the most tightly packed systems one can hope to see. The gearbox isn't actually here to provide various ratios for the drive, but to choose between four motorized functions around the car: operating the left and right gullwing doors independently, opening the bonnet, and extending the rear wing. The PF motor serves only these purposes, not the drive or steering which are still manual.

There is a V8 engine under the bonnet powered by the rear wheels, and the car is steered by the knob behind the cabin (a well-known Hand-of-God method). All wheels have fully independent double wishbone suspension. The rear wheels' parts actually theoretically allows them to steer too, but they are fixed in place ― however it may be useful for your MOC's. The rear hood opens manually, and is cleverly designed to allow the wing underneath it to slide freely.

Looks are a matter of personal taste, but I find them fantastic. It is so nicely modelled and features many subtle angles and triangular structures in the bodywork, that I could easily believe it is an accurate model of a real-life sportscar. As usual, the chassis is built very strongly, while the bodywork panels usually connect to an axle or a friction pin, for the possible collisions not to incur too much damage.

With all these functions, there is hardly any remaining free space in the car. As a result, it is not the easiest to build either, with lots of delicate parts and components, mechanisms that need fine adjustments and many moving parts. By no means should it worry an experienced Technic builder (it took me about 4:30 from the unboxing to the finish), but you ― moms who are idolizing your 6-year-olds, please don't just rush buying the 8070 to your children as it doesn't ask just for dexterity, but plenty of patience too. Even more, dare I say.

But it is a great experience and a mechanical lesson, though at first you may be a bit confused about the seemingly unlogical steps you have to make, but after a while, it just comes all together into a great machine. The unusual steps in the beginning are just a normal consequence of the inside-out studless construction.

Therefore, a great set, whether you just like cars, want to play with an interesting one, need useful parts, or want to learn from it.


Fantastic construction ― nice, efficient and strong, though not the easiest to build. So tightly packed with functions, it is almost impossible to put a sugarcube anywhere in the model. Interesting concepts too with the motorized panels around the car controlled by the centralized gearbox. Although there is not anything we haven't seen yet, the feat of putting all that within the given volume (quite small in sportscars) is in itself a very good learning material.

It is not overly difficult for disassembly either, avoiding difficult parts (half-width 2L Technic beams) as much as possible.


You will find some very useful parts for any car, such as the suspension wishbones, hubs, engine, racing tyres, etc., and the set contains also a PF battery pack and a medium-size motor. The rest is a standard Technic building material with plenty of beams, pins, axles and a couple of panels. And with a bit over 1200 parts, it is a good amount, too.


Since the machinery is so deeply integrated, there's not much freedom to modify the car without having to rebuild some components entirely. A most basic addition would be to introduce PF lights in the headlights (this is so obvious that I'm somewhat confused TLG did not do it already). But there's little else to add.


+ Clever construction, great to learn strong and efficient Technic design
+ Lots of functions
+ Considerable supply of parts
+ Really nice to play with
+ Superb looks, very realistic

- Not trivial to build, needs some patience
- Steering wheel in the cabin does not work


With its complexity, advanced ideas and intelligent construction, the new addition to the Technic Supercars line up is certainly up to standard. It is not among the cheaper models, but one really does get a lot in return. Highly recommended, especially if you're into building MOC cars ― in that case you will find some very useful specialized parts here.

Monday, May 9, 2011

Small NXT CNC machine: A bit too ambitious, really

Since the NXT 2.0 set contains three motors, it should be possible to build a Lego CNC machine with a little help from some external parts. Its construction would be quite straightforward and use most concepts we are already well familiar with. Based on those assumptions, I've tried to build one ― or more precisely, its early prototype.

I'm sure it could be built very nicely on a large scale, but the intention was to make it smaller ― that is, small and brick-economical enough to fit entirely on a 48x48 baseplate, yet provide at least 10x10 studs (8x8 cm) of grinding area.

So here it is! Its components are quite self-explanatory. On one end of the platform we've got two motors; each moves a pair of beams along a rail via rack&pinion system, that move the cradle. The X-rail is stationary, while the Y-rail is mounted on the X-beams. Thus, the cradle easily moves in both axes. It is nothing more than a simple little "pool" where I have fitted a thick piece of bakelite, and which slides freely over the surface thanks to the tiles on its bottom.

A bridge is built above the cradle area, heavily reinforced with four rows of interconnected studded beams. It carries a large moveable cradle built specifically for this standard-issue electric drill. The cradle is attached to four strong arms, and there is significant counterweight on the other side, with four large old Technic wheels attached to long arms. The counterweight compensates for the drill weight (approx. 2.2 kg), so the bridge needs to withstand only vertical force, and not the sideways too, which would complicate construction.

The drill is raised and lowered by just a few millimeters at full extents, but it is more than enough for a sheet of bakelite. Its height is actually controlled by raising and lowering the counterweight arms with one linear actuator, connected to an NXT motor. Since the drill and the counterweight are in a fine balance, the actuator doesn't need to produce much force, but I've opted to use it for its precision. (To increase precision of X-Y movements, the motors are also directly connected to the driving pinions ― no gears that would introduce backlash.)

A simple clutch holds the electric drill at a desired power, and a very fine yet hard grinding drill bit with a 0.8 mm head diameter is mounted in it. The NXT module that controls all three motors is resting on the side, connected to a laptop that sends the machining data.

Obviously, this is a quite limited CNC contraption, as the drill can access the surface only from above, so it acts more like a carving machine. The input is really straightforward: a simple script analyses a greyscale bitmap (which is a depth map), calculates the area that needs to be grinded out for each layer, and then "carves" them out, layer by layer. The X-Y resolution is 80x80 pixels, so the pixel amounts to 1 mm ― less would anyway make little sense with the grinding bit of this size, and while the depth could theoretically reach 256 layers, that would be insane ― 10 is more than enough. Or to be very precise, we're not dealing with pixels here, but voxels. Anyway, such configuration amounted to approximately 5500 instructions (motor movements) for an averagely complicated desired result: a tiny physical model of Iceland with scaled altitudes I chose as a first test.

So I've built the prototype (yes, please excuse the horrible colours, but facing running out of beams I've had little choice), programmed the script and happily pushed 'Start'. And quickly learned that the above idealism works only in theory, while in practice, this CNC design has serious flaws, serious enough to classify it as a failure.

Namely, I have terribly, horribly, enormously underestimated the forces that act on the cradle during grinding. Not only does the whole X-Y beam structure bend significantly under lateral forces during the drilling, but the drill itself has the tendency to "dance" around as well, and miss its targets by 2-3 millimeters at least. Of course, the bakelite looks massacred rather than accurately carved.

Theoretically, this problem could be overcome by forcing the drill to always act vertically, and drilling each target pixel separately. Again, this is just a theory: not only would drilling a millimeter from the already drilled area push the drill there to the path of least resistance, but the operation would have to be done for each pixel that needs to be grinded. And that would also last forever, and breach one of the primary rules of engineering ― that the machine should not be as inefficient to actually get the job done slower than an averagely inexperienced person would manually. Finally, even if I was like the Master from the Exile of the Eons (Arthur C. Clarke, 1950) and waited several dozen billion years in suspended animation until it is done, this approach would make very rough, spiky surface on the material.

I guess these problems could be solved by using much more stable X-Y beams, both probably having large pinions on both ends and tighter rails, and attaching a different drill. Perhaps a faster, specialized one would do the job better, but I've intentionally tried to use one of type almost everybody has somewhere at home. These improvements will be the objectives for the second prototype, significantly larger and architecturally different.

P.S. I've tried carving other materials since, such as the brittle spongy plasticky material I've found and can be seen on the photos (a white block), but that didn't seem to solve the mentioned problems.