Eurobricks Dukes
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Posts posted by DrJB

  1. I'm in the same boat. I used to follow very closely the new Technic sets and get them as soon as they come out. Now, it seems all new sets are 'variations on a theme' ... but in fact I think it is me, It's like any other hobby, I've had few of them over the years (astronomy, reef tanks, FTA, electronics, 3D printing, ...), and interest 'disappears' after a couple of years. That and lately that the cost of Technic sets has gone way up. The one hobby I have not given up yet on is gardening ... what's the point in having a house/yard if you can't grow some greens?  I'm now contemplating bee-keeping, but not sure the neighbors would approve. 

    Back to Lego, I've reached the point where, just like SR71, I want to sort/clean/pack my many sets and find a good buyer.

  2. Impressive!!! This IS worthy to be front-paged. I like your 'novel' large turntable idea (with the small roller-bearings) and I'm sure once we see the assembly 'moving' we'll get even more appreciation to the inner workings and intricate mechanisms, and even more questions about how you accomplished specific functions. Excellent Job!

    Question 1: In real life, the up/down motion of the arms is accomplished by hydraulic cylinders. Did you use LA, pneumatics, or something else?

    IMHO, some pneumatics with 'sequencing' would be a neat add-on, though maybe a bit difficult to house. 

    Question 2: From the kinematics (your 1st video), it seems each rider-seat has 4 degrees of freedom: rotation of the arm about vertical axis, lifting of the arm up/down, rotation of the 4x2 seats, and then rotation of the seats about their center. I'm sure somehow all seat are connected in 'parallel' and there are a total of 4 motors (or DOFs) for the whole assembly. Now, how many  motors are you using and how many independent controls over the 4 DOFs ?

  3. While I agree with many of the OP's points, this is bound to be a bit of a 'sensitive' discussion as we might get some forum members a bit offended. Yes, I've gotten to a point where I simply 'ignore' many posts (I get an email with every new thread) as after a while, one gets numb to all the 'basic' questions and sub-par MOCs. My approach here is: well, I started there myself sometime back as well and there should be a way to encourage new-comers. If you list all the threads that have 'Ferrari' or 'Lamborghini' in their title, some are worthy of a frontpage, others are, well, ... no need to offend anyone :). Maybe the way to address this is to split the forum further into sub-levels but then it becomes tricky to navigate, and we might miss important/interesting threads/discussions. My 0.02 worth

  4. I remember this discussion ... it was about the time where most of us were getting 'tired' of vehicles with wheels, and wanted to see something different. Yes, would definitely appreciate seeing the progress you've made and how you solved the mechanical 'challenges'. For rotating the seats, maybe flex axles like those used in the ZNAP line could be helpful, as they bend 'easily' and can go through the arms.



  5. A while back I was into salt-water fish-tanks and yes, finding someone who can feed your fish 'reliably' was always a pain. I like what you've done, but am no longer into that hobby as it does require a lot of time. Feeding is only part of the story, then you need to do regular water changes and add chemicals to 'regulate' the tank's chemistry. In that regards, any bit of 'automation' (as you've done) is a very welcome initiative.  

  6. Nicely done. The main issue with these (I think) is the excessive slack from all the links. Conceptually though, this is nice and as you've shown requires a wheel with enough clearance to house all the parts. 

    Have you calculated what the 'scrub radius' is? It is the distance between the center of the tire's footprint and where the pivot axis intersects the ground. In real life, such scrub radius affects many performances of the vehicle, primarily handling and tire wear.

  7. Up until few years back, every technic set had a large collection of 'colored' parts (connectors, flex axles, liftarms, ...). Recently however, most of the vehicles' interior/chassis is typically made up of only monochromatic (black/grey/white) parts and then, a minimum of parts (primarily for styling) are truly 'colored'. There was a time where I 'lamented' as to the lack of colors in Technic as all the SuperCars were issued either in red or black. Back then, the overwhelming answer was the lack of available 'other' colors. Now it seems we're migrating back to 'rare' colors and small number of colored parts for styling ... and yet purely monochromatic parts for the Chassis. This is somewhat the case for many StarWars set as the grey is meant to 'mimic' steel and metallic structures.

    What are your thoughts on this and how has this affected your 'MOCing' options ?   

    Oh Yes,  miss seeing an official Technic Car in RED  ... the last we've seen is 8070, and then 'smaller' attempts since then, as in the customizable truck and the fire truck. The latter though has more grey than red.




  8. What would happen to all the FLL programs (worldwide) that use MindStorms as an introductory 'Robotics' course?

    As many might recall, Mindstorms started out from a robotics course at MIT 6.270 (late 80's) and then the first brick (RCX) was developed jointly by MIT and TLG. Many schools (Highschools and Universities) have then adopted the format and started offering introductory courses. If MindStorms is to go away ... many schools would need to 'scramble' for new content.  

  9. There are multiple good sources on 17 groups on the web. The one I thought was most 'enjoyable' to read/study is an app (iOS/Android) called iOrnament. I got the screenshot below from it. It explains in a very compact form what the 17 groups are ... 

    For example, the first square is a pure translation along 2 axes. The second is a translation plus a rotation. The third is a mirror reflection ...


  10. 2 hours ago, aeh5040 said:

    Several things are a bit confused or potentially confusing here ...

    Agree, need a bit more clarity here ...

    2 hours ago, aeh5040 said:

    3. DrJB: Not quite.  In any number of dimensions that a rotation is a composition of two reflections ...

    You're right. Intuitively it makes sense. I was thinking of it initially from a mathematical standpoint, and was not sure a rotation matrix can 'always' be written as the product of two reflections matrices. It might very well be that the solution could at times be not unique.

    2 hours ago, aeh5040 said:

    4. Lastly, it's true that rotations do not in general commute in 3 or more dimensions.  But in 2 dimensions rotations about the same point do commute.

    When I mentioned 'commutativity', I has in mind full rotation in 3D space, and there, for sure the rotations do NOT commute i.e., rotation about x then y axes is NOT the same as rotation about y then x. Thinking of rotation matrices again, if we change the order of matrix multiplication, we get a totally different result. Now, all of this is true in 3D space (and beyond if we're comfortable with that). In 2D space, there is only one axis of rotation (Z, normal to the 2D plane). There, when a rigid body is subjected to two rotations, they are both about the same axis, and as such, they do ADD. In 'my' terminology, one cannot speak about commuting rotations in 2D ... again, pure terminology.

    PS. Thanks for a trip back in time ... This reminds me of a graduate course in Dynamics many years ago, and of all the subjects, 3D dynamics is often NOT intuitive ... especially when you include gyroscopic effects. 

    2 hours ago, aeh5040 said:

    So for example, a 3L axle going through a 27940.pngshould be avoided ...


    That's not fair ... what am I going to do with all the parts I ordered from BrickLink? :(

  11. The other option, which I find rather slick, is to use a gimbal-stabilized camera. I got the DJI osmo recently and rather pleased with the 'stability' of movies it produces. Careful though, as the 4k videos it produces won't run on just any PC/laptop.

    DJI Osmo 3-Axis Gimbal and 4K Camera (No Handle)

    Now, if you're into building your own little camera (forget zoom and other features), you can try a Raspberry PI with a Camera Module. Be prepared to invest some serious time programming, to get it to do exactly what you're after. Again, both options (Raspberry Pi and Osmo) have no mechanical zoom/Tele capability. 

  12. 9 hours ago, JonathanM said:

    The 1 dimensional analogue of the wallpaper groups are frieze groups - 2D with repetition in just one dimension. There are 7 of those - no rotations allowed, other than by 180 degrees (two reflections at right angles) as all axes must be parallel or perpendicular with the axis of repetition - thus just translation in the axis of repetition, and reflection in the parallel and perpendicular axes (and the corresponding glides).

    I believe these apply only to FLAT patterns (i.e, 2-dimensional only). Once you move to the third dimension, no succession of mirror reflections can produce a rotation. It only works in one special case, when the pattern has one plane of symmetry. Translations are commutative (can change the order without changing the outcome). Rotations however are NOT commutative, the specific sequence of rotations CANNOT be altered.

  13. The GoPro Session (small cube) is ideal for many such applications. It retails for around US $150, and it includes both an SD card and a handheld stick. Not sure about the price in Australia though :(.

    GoPro HERO Session Waterproof HD Action Camera

    4 hours ago, Splat said:
    1. GoPro Hero 4 Session.  This camera is great for attaching to your Lego model to get that shot where it looks like you are riding inside/beside your model.  I have used this on remote controlled cars/trucks/tanks, as well as attaching it to Lego trains, etc.  There is a vast array of attachments for this camera, and these can be mounted to Lego, but I tend to just use a piece of strong double sided tape (the stuff that is used to stick down carpet - link).  This is strong enough to stick to the Lego and keep the camera in place, yet easy enough to remove after use.

  14. 1 hour ago, Didumos69 said:

    @DrJB, you started the same discussion before.


    You're right ... obviously your memory is better than mine :). Though in all fairness, the older thread was primarily about panels vs. no panels. In this new thread, I was motivated by another reason (highlighted in the first post)

    The reason for this 'newer' thread is that I was a bit 'frustrated' by connectors becoming rare (my other thread you're contributing to). I'm ok with panels, but I do not want them to come at the expense of other parts/connectors.

    1 hour ago, PlastiBots said:

    I too have been around the block for many years (since Technic was first introduced). I dont mind the progress to date, but I also like the idea of seeing complex mechanisms at work.  I would pay top $$ if LEGO came out with a custom set with transparent outer panels and beams to allow the inner working (engine, gearbox, suspension) to be seen.. i.e the Porsche where all orange bits are clear.  Not the best example (or maybe it is ;-) but this is what I am talking about:



    Yes, I agree fully that a clear/transparent' model would be a nice offering. The picture you chose clearly illustrates that what's inside a car matters a lot ... ;).

    In fact there are already 'few' technic parts available in Trans colors (15L beam, few connectors, and 1 panel). I wanted a while back to ask that same question (in a dedicated thread) but we do not have a large collection of parts yet. 

  15. I'm old enough (like many on here) to have seen Technic 'evolve' through many stages. It all started with a rather bare/studded chassis 8860 and 'minimum' functionality. Then came the Super Street Sensation 8448, the Mission 8450, and the Off-Roader 8466. They all used various connectors and flex axles to define the main 'lines' of the vehicle. Lately however, more emphasis is placed on more 'realistic/boxy/closed' looks and extensive use of panels is seen. I think panels have their place, but doesn't that take away from the Technic theme itself? What's the point in building often intricate mechanisms to, in the end, cover it all with 'non-functional' panels? The other 'side-effect' is that now, we see fewer flex axles and connectors, and when we do, they're often available in primarily monochromatic colors (black/white/grey). What are your thoughts on this?

    8448-1.png 8450-1.png 8466-1.png 

  16. Very nice, I like those. Thinking of the wallpaper groups (simplifying the math), the only 'transformations' allowed/possible are:

    1. Translations

    2. Rotations

    3. Symmetries (mirror images) about 1 or more planes

    It appears the rotations/translations are relatively easy to achieve. The symmetries however are not so trivial.

    Here are three more, I call them 'Variations on a Theme'. The first is symmetric (three planes), and the other two are its 'twisted siblings' (i.e., no longer symmetric). Yet all three of them still obey translation and rotation.


  17. 1 hour ago, Erik Leppen said:

    What's interesting about this one is that it fits. I was looking at it for a bit until I realized it's not an exact fit, but close. This can be proven using some mathematics. For those wanting to know:

    A hexagon consists of 6 equilateral triangles, So, for a hexagon, the "radius" (center-to-corner distance) is equal to the side length. The yellow hexagon has sides of length 3, so the radius is 3 too. The blue hexagon has sides of length 8, so the radius is 8. The height of the blue triangle (side-midpoint-to-center distance) can be found using Pythagoras as height^2 + 4^2 = 8^2, hence height = sqrt(64 - 16) = sqrt(48), wuich is about 6,93. So the red rod, whose endpoints are 3 and 6.93 from the hexagon's centers, has mathematical length 3.93; so the piece used is 0.07 too long.

    Yes, I did the math too and, surprisingly, this works very well in LDD, no complaints whatsoever.