Davidz90

Thanks! Really impressive! I've never seen this technique for multiple, coaxial planets.

Thanks! Indeed, the frame holding all gears is pretty minimal, hence the wobbliness. Thanks! It was a bit of an accidental discovery, I knew that the mechanism will do "smaller orbit=faster", but had no idea that it will actually do this perfectly in accordance to Kepler's law. I even tried to derive the equation describing its motion to fully prove that, but eventually gave up.

I figured I could post mine as well. It's a pretty old build, without nice spheres for celestial bodies and a bit clunky overall, but pretty accurate: Gear ratios are: 1. sidereal year: 365.71429 days (should be 365.25636; at that time I didn't know how to do 365, which would be better) 2. synodic month: 29.41165 days (should be 29.450059 days) 3. sun rotation (at equator): 24.9318 days (should be 24.7 days) I also figured out a way to make elliptic orbits with realistic speed variation:

Indeed, the more orreries, the better :) This one is nice and compact. Earth-Moon rotation offset is an interesting feature.

Thanks for sharing this. I'll definitely try to incorporate moon's precession in my mod of the lego set.

From my experience, 2 half width ones. But most impotrantly, bushes have to be new or rarely used - they lose a lot of grip strength over time.

@aeh5040 I think your math is a little off. The central axle is 3 times faster than the moon rotation, not slower, and the crank is another 3 times faster (12:36 in the base, assuming 2 black gear hypothesis is correct). So a period of 3 days (makes sense, hand crank needs to be geared down). Ideally we would want 1:120 gear ratio here. So maybe 1:2 + worm gear to the turntable or 20:60 to the turntable + 1:2 + 1:20 via worm gear?

Yes, this appears to be the case. Pretty clever. So it seems we have 27 day lunar month and also 27 day sun rotation period.

I also wonder if the proper 1:365 gear ratio will be used here, or some approximation. Since 365=5*73, one needs a little differential addition magic to obtain 1:73 gear ratio, but nothing too difficult, really. and for a good measure, lunar month of 29.53125 days is also straightforward: and very close to actual value of 29.53059 days

So excited for this set! IMO the orange rings would look better in gold (and the month names would be more readable as well).

For wheels, there is really no reasonable way to motorize them other than having small motors directly in wheel hubs, unless you want to sacrifice steering.

The motor is almost inaudible, way quieter than Lego ones. There is no power converter, it really plugs straight into the outlet! Power consumption is 4 watts, the amount of torque is enormous. Also, it is slightly more bulky than Lego ones - basically a pancake slightly larger than 40t gear, 2 bricks high (4 bricks with motor shaft). It is buried inside my clock so I can't take photos.

I think that the best option is a synchronous motor. Some of them are powered directly from outlet and rotate at around 5 rpm. They are typically used in microwaves, rotating the platter. Very quiet too. Just google "5 rpm synchronous motor". I have used it successfully in a MOC (clock tower), here you can see the speed: The only thing to figure out is to find the best way to connect lego axle or gear to motor shaft. Simple glue will do if you don't mind gluing bricks. Also, you will need a cable with outlet plug and preferably on/off switch. Should be available in any hardware store. Finally, 230V is no joke so obviously all connections must be secure and not exposed. Very Cool MOC!

Wow, this is super cool!

In my crane, I used 6580 Wheel 43.2 x 28 as the spool. Naturally that would need quite a bit of modification since these rims are 4 studs wide, not 3. String is attached to the rim surface with tape.

Thanks! Subscribed. I've studied various walking machine linkages some time ago, but this one is definitely new to me. Very clever. Looked at the code, it is much simpler than I thought it would be.

Incredible! Very clever idea to have two servos in the hip joint actuating hip and knee, and thus keeping legs very light. Also, amazing job with programming; the motion is soo fluid.

Interesting. For small LA, 71.6 degrees per mm translates to 0.7955 rotations/mm. In my (less accurate) measurements, I got 0.7911. I couldn't find any technical data sheet that would specify the thread pitch of LA, but the number (1.25698 mm/rotation) is a bit odd; does not give a nice, even number in inches as well (0.04949 inches/rotation). Maybe the actual value is 0.8 rotations/mm and 1.25 mm/rotation, respectively? That is one of the standard thread pitches

Amazing! Yes, that's exactly what I had in mind. Another thing worth trying is putting the 2x2 brick between 4 rollers in 4 corners.

Good to know. I mean, 2x2 brick can handle much more than 3 times the torque of regular axle, so the idea was that it could be possible to transfer much more power before reaching axle-melting speeds. But that would necessitate some sort of bearings for 2x2 bricks. To be more precise, I was thinking about something along the lines of the driveshaft in this pneumatic engine: which powered real-life Lego car: but that is total overkill for all but largest builds.

Maybe it's a stupid question, but how about adding a cluth that disengages the gearbox during shift, just like in a real car? As far as I understand, the biggest problems happen during shifting. Second thought, the new splat gears have a huge teeth and can be attached with 2x2 round bricks with technic hole. A large-diameter axle made from 2x2 bricks with regular axle inside can handle some serious torque. Maybe some sort of transmission can be made with that?

Yes, and that's why I think that the only way forward is to figure out a driving algorithm that actually alows for some slip/elasticity and doesn't accumulate error but instead uses that elastic feedback to self-correct.

No, they are tied to a common crankshaft, you cannot move them to 0 separately. You only need to manually check that LAs are not pushing/pulling on the crankshaft (so their positions are exactly matching the intended one) and determine the exact angle of crankshaft.

Yes, the starting, absolute position is known because it is tied to starting crankshaft angle, which I admit, has to be known very precisely.

Yes, the lengths of all 4 actuators are determined by the crankshaft angle. I agree, if we allow for no slip, then the starting angle has to be specified very precisely. Still, I'm wondering if allowing a slip is not a better option? You see, if the LA motor is in some specific phase of motion (specific speed), there is only exactly one crankshaft position that matches it. Allowing motors to catch up depending on feedback from crankshaft seems like a good idea?