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About Davidz90

  • Birthday 01/09/1990

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    <p> Technic </p>

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  1. Davidz90

    Fast Robot Dog

    Very impressive! I guess this had to take a lot of trial and error, stable walking cycle is a challenge on its own, springs make the dynamics even more complex.
  2. Nice. I think that the problem with the tail rotor is more about the size and thickness of the rotor blades than the size of the mechanism (which seems to be hard to make any more compact); Maybe rotor blade 99012 would be better? I agree that the nose is a bit off; too flat, too long. But overall, very nice job!
  3. Absolutely amazing piece of engineering and coding! Very creative solution with two black background/white background sensors. On the photo, it looks like a giant artillery piece XD
  4. Thank you very much! Indeed, getting proper gear ratios and arranging them in compact enough form was one thing, but then making sure that everything is properly aligned and runs with little friction was another. Very quickly I realized that auto-rewinder is a must here; grandfather clocks and wall-hanging ones have the advantage of large space below, where the hanging weight can drop. With this form, getting more than one hour working time was all but impossible (and having two pendulums to keep in motion instead of one doesn't help the efficiency). Thanks!
  5. Thanks! Frankly, working out the correct gear ratios made my brain hurt too. In the end, I wrote a computer program to find them. Then, I "only" had to scan through a list of about 300 combinations to find the most convenient ones.
  6. Maybe you can disable the striking mechanism but keep it running? Or the ticking is the problem? The amazing thing is that not only you can make a Lego clock, but actually you can match the efficiency and accuracy of "real" grandfather clocks, at least the lower quality ones.
  7. Thank you very much! I agree, that is what Lego Technic is for, at least for me. I'm not a fan of cars or vehicles in general, but always liked clocks and other contraptions with complex gear ratios. Thanks! I was afraid I might have gone too far with the music XD
  8. Seeing so much positive feedback and nice comments in my recent clock topic, I decided to revive this one (I hope it's OK) with some new mechanisms. Grasshopper escapement This is a type of clock mechanism invented by John Harrison in 1622. The name comes from the fact that the moving parts resemble legs of a grasshopper. Its remarkable property is the fact that the pendulum is in constant contact with the mechanism, so it is driven all the time, instead of short pushes that most other mechanisms deliver. In my Lego rendition, I tried to simplify the design by tying it directly to the pendulum. The result is a remarkably simple and efficient design: You can see that the escape wheel (40T gear) moves mostly forwards, but goes back (recoils) for a brief moment. This recoil, caused by the pallet engaging the tooth, causes the other pallet to disengage. To allow this recoil, the resting points of the pallets need to be movable - this is acomplished by the black T-brackets. And here is an even simpler rendition, designed for very small swing angles: My goal here was to find out how efficient it can be; I wanted to make a clock that runs for 1000 hours on single rewind. This proved to be a bit too ambitious, in the end I settled on 170 hours:
  9. Thank you very much! I'm afraid not, for several reasons: 1. That would take a lot of time 2. Clock needs several custom pieces (steel nuts for pendulum weights, steel block for driving weight, printed dials) 3. Mechanism is a horrid mess of almost 100 gears, with axles going in various directions and questionable building techniques to get some gears to mesh together. However, I have a series of videos where various components are shown in detail:
  10. Maybe there is some simple way to advance 20 tooth gear by 2 teeth at a time.
  11. Thanks! John Harrison was a genius, no doubt about it. Grasshopper escapement is an uncommon mechanism, but actually one of the simpler ones to pull off in Lego. Also, it can be extremely accurate; this clock is not made for accuracy and keeps time up to 5 minutes/day, but under 10 seconds/day is possible with a regular, long pendulum, temperature expansion compensation and fine-tuned escapement. Thanks!
  12. A dual-pendulum clock with grasshopper escapement, inspired by John Harrison's H1 clock that was intended to be used aboard a ship, for accurate navigation. Two pendulums swinging in opposite direction cancel out forces due to the ship moving on waves. My model includes several extra complications: -separate seconds hand -moon phase indicator accurate to 1 day in 19 years -calendar, with year length of 365.2484 days (accurate to 1 day in 170 years) -star map (planisphere) showing the night sky at the given date and time -equation of time (the difference between mean time and solar time, which is +-15 minutes depending on the time of year; accurate to 2 minutes) -time of sunrise/sunset, accurate to approx. 15 minutes -motor powered self-winder Video:
  13. Davidz90

    Half beam problems.

    Yes, they tend to break all the time, even when not stressed at all. It seems that better structural solution is there arleady - I've never had issues with the shortest half beams (with two x holes).
  14. Davidz90

    [MOC] Trebuchet

    Maybe a battery box? The black bricks are around 50g each, AFAIK a full box is 250-300.
  15. Davidz90

    [MOC] Trebuchet

    I believe it would definitely help with jumping - ideally, with sufficiently long rope (and maybe heavier projectile), the trowing arm brakes almost completely, with no energy left for any jumping. Lightening the arm is an option too - that would also help with throwing power. Motorized rewinding would be cool, waiting for results [EDIT] You inspired me to make some experiments. Here's a quick and dirty prototype: I have used longer rope and there is dramatic difference when firing with and without projectile. The counterweight is somewhat overdone - it is over 2x heavier than the rest of the machine :D As You said, there is a lot of physics involved - light arm allowed me to move pivot point closer to the weight and get more velocity despite shorter drop.