Davidz90

Hubless wheels are amazing. Suprisingly low friction, too.

I have one broken LEGO electric motor waiting to be taken apart. Maybe the motor windings can work as a electromagnet. Alternatively, for example shadow_elenter has incorporated third party electromagnet inside PF motor housing. I'm not planning to directly adjust the pendulum by external force. Instead, the electromagnet will be powered by 1 Hz sine wave (I'm looking for ideas how to do this. Mindstorms is pricey.). Then, the pendulum becomes a driven oscillator, with exactly 1Hz frequency. If the natural frequency of the pendulum is off, then we are away from resonance, and amplitude becomes smaller, but still it has no effect on the rate.

Hour hand is not a problem. Just for the one hour operation, it didn't seem all that usefull. I'm going to keep the current, short drivetrain and make it self-winding. I'll surely try to obtain the lego weights. How much does the counterweight weight? BTW Your clock is a real masterpiece, especially the self - adjusting is very clever. Apart from electric remontoire, another idea I'd like to try is electromagnet in the base impulsing the pendulum directly, at 1Hz rate. Then, the pendulum drives the mechanism. Theoretically, that would be super accurate.

A compact, gravity powered clock. There are many Lego clocks around, but most of them are really huge contraptions, and for a good reason. They are easier to tune, more eficient, work longer... So naturally I took a challenge to make something small but still usefull :P. The key component is the pendulum. Typically, a significant length is needed to get period of one second. Here, a second mass over the pivot point slows the tiny pendulum down, so that it can be many times shorter than usual. The compact "knife edge" pendulum suspension dramatically reduces friction, decreasing the power necessary to run the piece. The low mass of components creates many problems. The clock is reasonably accurate (I got it within 5 seconds per hour), but tuning was a nightmare, and even a sneeze can alter its rate. The power source is 100g weight on a string. Due to only one hour working time, I have decided to use only minute hand. Seconds hand puts too much power demand on the mechanism. 1 by David_Z1, on Flickr 3 by David_Z1, on Flickr Schem2 by David_Z1, on Flickr Many thanks for KEvronista for inspiration to get into this Lego clockmaking hobby :) [EDIT]: embedded the video.

For the record, here's the trigger mechanism. This was the challenging part to make, I guess this connection is non-purist? On a related note, is there any way to reduce axle friction when they are put under considerable load? The friction of the front rollers seems to be the main speed limiting factor. trigger by David_Z1, on Flickr

That 4000 rpm spinning weapon is impressive. How far it is from pulling itself apart due to centrifugal forces?

Thanks! When it comes to lego bows, cable-backed bow is a nice option for pure lego power. Bricks in compression are very strong (as anyone who stepped on a brick can attest :D), its the tension that tears them up. There's my old bow design, nothing really fancy: bow_1 by David_Z1, on Flickr bow_2 by David_Z1, on Flickr

Typically, I use blunt ammo - no need to take risks. The pointed dart goes through 80-100 sheets of paper. It fires very smoothly - the design is overbuilt to take about twice the actual force. The spring strain is reduced on purpose - less shock, less vibration, better accuracy, and the power is ok as is. As a bonus, dry-firing it (firing without ammo loaded) does not destroy the construction.

I always loved lego creations that shoot things, especially crossbows. Unfortunately, the bricks are not so ellastic, so some power source is needed. I decided to use stiff string, as opposed to common ruberbands. Instead, the limbs are moved by steel springs. Reverse draw crossbow by David_Z1, on Flickr This is how it looks unloaded: Crossbow - up1 by David_Z1, on Flickr and here loaded: Crossbow - up2 by David_Z1, on Flickr The limbs are not moving that much, but the draw length is quite long due to the compound system. This has few advantages: -The peak string velocity is 3x the limb velocity -Bolt acceleration is smoother -For the given draw length, limbs can be shorter = stronger and with less inertia. The springs are stretched a lot even in the idle position. Thanks to this, the string force ramps up from 0.6 kg to about 1 kg, greatly increasing energy as compared to going from zero. Moreover, the construction is stiffer this way. The aim of reverse draw construction was to shorten the limbs and move them to the rear, improving balance. The limb movement is synchonised (two grey beams on the front), and the spring tension is regulated (suprisingly, two identical springs were not-so-identical, so this was mandatory). Trigger system: Crossbow - trigger mechanism by David_Z1, on Flickr This is a typical crossbow trigger. After pressing it, the white knob is free to rotate, releasing the string with little friction. The knob can rotate backwards, so that the string can be hooked up by just pulling it over the knob. Okay, for the performance: bolt velocity 20 m/s (about 66 fps). Not exactly blazing fast, but the ammo is quite heavy and stable in flight. The hit effects are usually like this: Penetration test by David_Z1, on Flickr I'd still call it a toy, it is no real danger unless someone is shot in the eye (obviously). Hitting anything beyond 20 m or so is very hard. One can also load lighter ammo such as pencil to reach some 35 m/s, but accuracy becomes terrible.

Hello! I'm Davidz90. I am a physics teacher and Lego fan from Poland. My interests are complicated mechanical systems (such as clocks), medieval siege equipment (catapults, ballistas...) and aerodynamics (no flying Lego model yet, but eventually...). Greetings! :)