Eurobricks Citizen
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About Captainowie

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    Western Australia
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    Technic, Technic and more Technic


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  1. That's one use for it, sure. But you could certainly use a diff in this case too, with one output moving the arm back and forth, and the other output rotating the blade. As long as it takes more torque to rotate the blade than it does to move the arm, then when the motor turns forward, the arm moves out until it hits its stop, then the blade turns - the reverse happens when the motor turns backwards. You could possibly add in a ratchet if you didn't want to have the blade turning when the arm is retracting, but then you stall the motor when the arm retracts fully. Owen.
  2. If that's your motivation, then you're doing it wrong. Build for yourself, pay no heed to a bunch of anonymous strangers on the Internet.
  3. Beautiful. A masterful improvement over the original in every way. Owen.
  4. I am surprised you couldn't find _one_ eleven year old keen to drive a robot around. I would have loved to do that as a kid (heck, I'd probably still get a kick out of it at 35!)
  5. That doesn't look like it'd do much more than back end of a brick separator.
  6. I don't know how much of a problem depth is for you, but I'd suggest using full beams rather than half beams to join the bricks together. Those 3/4 pins are very loose. You might even be able to get some additional strength by running a 1x6 or 1x8 plate under the join. Owen.
  7. Uh yeah. Of course that's what I mean. I'll fix my post.
  8. You're welcome. If you need more friction, I'd suggest swapping out the middle 16T for a 24T and the two outside 16Ts for 8Ts. That should give you more stopping force than you have now (the friction pins are providing the same resistance force, but it'd be applied at a larger radius).
  9. Hey that's a good idea! :-) Yeah, I wondered if that would happen. But I feel that there is still a 1-motor solution. Can you modify your setup so that the XL motor drives the drum as well as the diff cage? Then you're functionally equivalent to your clutch-gear solution, except that now instead of making the clutch gear slip, you're making a friction pin slip - and they're much easier to replace! One problem I foresee is that when you add extra structure to the rotating arm, the extra weight may be more than one friction pin can support. You may find you need to add a second 8t gear + friction pin to the other side of the diff. Good luck! Owen.
  10. That's certainly true in my implementation, but there's no reason it couldn't be improved upon. In your case, you probably wouldn't need to modify your current setup too much. Have the motor drive the diff cage directly, and have the two diff outputs connected to the main rotating arm, and the drum with the peg. If you induce some form of friction into the drum (say, by having it also turn a small gear mounted on a friction pin) then the main wheel will turn until it hits the stop, whence the motion will move to the drum with the peg, until such time as the peg moves around and releases the main wheel. If you continue to use the clutch gear, I worry that you'll wear it down and it'll start to slip at lower and lower torques. Owen.
  11. Sure. The red axle is connected to the motor and moves constantly. The disk and differential serve to intermittently route the motion to the blue and green axles alternately. For most of the time, the diff is prevented from rotating by the axle that's held up by the disk, so the path of least resistance is through the diff and out to the green axle. When the gap in the disk passes under the axle, the axle is free to rotate. Once that happens, the path of least resistance becomes the diff itself, which turns the blue axle. This relies on there being some load on the green axle. In your case, you don't need the blue axle output, you just want the start-stop of the green output. It's then just a matter of gearing it right so that it stops twice per rotation. You could also put a second gap in the rotating disk to double the rate of stoppage relative to the rate of turn of the axle. Does that make sense?
  12. You might be able to use a differential instead of a clutch gear. I made a mechanism that did something similar a few years ago.
  13. Several different hexagons here
  14. Very well. Thanks for an enlightening discussion. Owen.
  15. Yep, in my experience that's what happens when two intelligent people seem to not be able to agree on something! Ah, but this wasn't supposed to be an engineering problem, it was supposed to be an edge case to try to nail down a definition. If fixing the joints in place after the structure reaches equilibrium doesn't change the forces involved, would you still call the resulting structure a truss? If yes, then you could, in theory, construct a structure whose truss-ness depends on its load. This is neither a good nor a bad thing, just a consequence of the definition.