Davidz90

Ah, ok. Yes, if the input voltage is varying, some "intelligence" is needed to keep voltage constant. However, if the voltage variations are not great, it is sufficient to ensure that LED always gets more than minimum needed voltage. For example, let's use the above mentioned system with 2 LEDs, 3V each and 1kOhm resistor. If the supply voltage is increased from 9 volts to 11 volts, then: -LED voltage is still very close to 3V, because current increasing exponentially with voltage also mean that small changes of current make almost no difference in voltage. -Resistor voltage is now 11V-6V = 5V -Current is now 5V/3kOhm = 1.67 mA, which is perfectly acceptable in most cases.

Again, just use a proper resistor in series. It does just that - cuts the voltage (in addition to limiting current). Learned about LED variation hard way when I was building a toy lightsaber. Wired 100 LEDs in parallel and powered them with 3 volts. In theory, with so many LEDs, internal resistance of batteries should be sufficient. What I didn't anticipate was that some LEDs reached full brightness at 3.1 volts and some at 2.9 volts, so my lightsaber turned out uneven. The 2.9 volt ones burned out few weeks later.

Yes, and the remaining voltage is the voltage drop in the resistor. So for example, you can have two LEDs in series (6 volts) and a resistor (remaining 3 volts); to get 1 mA current, you need 3 kOhm resistor. LED calculator says the same: https://ledcalculator.net/#p=9&v=3&c=1&n=2&o=w

That is likely to burn them. LEDs have a very little resistance, the current will be much more than 1mA. You always want to have a resistor in series.

More specifically, they pass zero current until some minimum voltage is applied, and then the current starts increasing exponentially (as opposed to linear relation for reistors). Also, the operating voltage can vary slightly from led to led, even in the same batch so it is very hard to just set the voltage for proper current. That is why current limiting resistor is always needed with LEDs. If you don't want to bother with calculations, but have a decent selection of resistors, you can just start from the highest resistance one and keep decreasing it until LED lights up. However, the formula is simple: (Supply voltage) - IR = (LED Voltage) where I is the target current and R is the necessary resistor. Here's a good tutorial: https://www.electronics-tutorials.ws/diode/diode_8.html

Yes to this, with one caveat: at the small scale/speed Lego models are operating, typical airplane-like profile as depicted is not optimal. Very thin, curved surfaces (like in first airplanes such as Wright flyer or small birds) are better. If symmetrical profile is used (for reasons you described), a flat, thin plate may still be better than "proper" airfoil, but overall zero curvature profile all the way from blade tip to root would severely hurt performance.

A pneumatic motor would either need one or several pistons (like the mentioned axial piston pump; howevet, it comes with all the complications of making them airtight) or some sort of turbine (but that would be extremely high speed/low torque unless large gearbox is added). Since nothing else really uses pneumatic pistons (as opposed to electric motors which are off the shelf parts packed in Lego casing), it would not be exactly "mass" production and certainly much more expensive than electric motor. Besides, it would really be useful only as a pump, unless used with significantly larger air tank than the one currently available. Or electric motor driving a pump, but then why bother?

You would need an enormous air tank. One can get more mileage out of pullback motors (better energy density than air).

32+8=40 so it would need the same spacing as other combinations that sum up to 40, like 20+20.

It would easily mesh with other spur gears. Most importantly, it would result in easy 1:4 reduction with 8t gear. An example of custom 3D printed 32t gear:

A 32 tooth gear.

Amazing! The power and speed are terrifying. Overall shape reminds me of the game "rollcage"; with slightly flatter chassis it could drive upside down.

Slight offtopic but that is so cool! I considered this career path, but ended up teaching physics at university because I didn't want to focus on only one field . Got into Lego Technic at the age of 12 and at first, it was all about pushing the limits of bricks, mostly with various shooting contraptions. After breaking many pieces, fev velocity and energy records and poking few holes in my home's walls (my parents had to be super patient), learned a lot about mechaniscs and structural integrity. Finally settled on building mechanical clocks. Apart obvious things like gear ratios I learned a lot about astronomy and physics of clocks in general - in fact I published two papers on the subject, one of them has experimental data measured with Lego clock. I use Lego models in my lectures as well, students love it.

Thank you! That's why I love mechanical clocks - they allow me to build all sorts of interesting contraptions unlike anything else.

Currently not, but that would be pretty straightforward to do here. February is represented by a gap on the ring, allowing the skipping arm to fall as far as it can go. A small cam attached to an axle rotating once per 4 years would stop it 1 day earlier on leap years.

The ring gear idea worked. Now the calendar is finished. I believe it's world's first mechanical Lego calendar.

Nice! Instantly recognizable despite the small scale.

I think I got a workable design for 12-sided cam: 20230101_230920 by David_Z1, on Flickr it is based on the small ring gear. Radius can be easily controlled by adding plates. The ring will double as attachment point for the dial with month names. The ring has 60 teeth, on the back side I have a 20T gear and knob wheel on a common axle. Advancing 20T wheel by quarter of a turn moves the ring by 1/12.

I don't know what is more impressive: the telehandler, the control panel or the skillfull driving!

Still working on a proper Lego cam, in the meantime I tested the rest of the mechanism with a cardboard cutout.

Cool! Interesting use of these unusual wheels. It could be fun if the hand crank at the front was functional, rewinding the pullbacks.

That's great idea! Thanks!

Thanks! I hope this design won't be a dead end.

Another attempt at calendar that doesn't need huge wheel with all 365 days. The biggest problem to solve is to build a 12-sided cam that encodes the length of the months (or more specifically, how many days to skip at the end of 32-day dial; 1 for january, 4 for february etc.). Also, the design would be so much simpler if 32 tooth gear existed...

Interesting project. The results are pretty consistent. The problem with steel wire was insufficient motor power or just bricks bending?