All models are wrong, but some models are useful.
September 17, 2022 2:35 PM   Subscribe

Do you think machines are neat? Ever regretted not getting that mechanical engineering degree? Enjoy playing with legos? Can you appreciate things that will teach you stuff without having much other use? Here's something that might tickle your fancy.
posted by nushustu (25 comments total) 52 users marked this as a favorite
 
Dad was a mechanical engineer and the great Thanksgiving debate was Legos vs. Erector set.

I think Lego finally won. nice, thanks for posting.
posted by clavdivs at 2:47 PM on September 17 [2 favorites]


I feel like I just learned more in five minutes about mechanical engineering than my entire life to date. Although I'm having a hard time telling the effective difference between some of these like intermittent mechanism and offset gearing.
posted by BrotherCaine at 3:36 PM on September 17 [2 favorites]


Although I'm having a hard time telling the effective difference between some of these like intermittent mechanism and offset gearing.

They accomplish similar actions, but the Geneva cross is more sudden in it's action whereas an offset gear has a smoother flow as the gears mesh and disengage.
posted by NoxAeternum at 3:41 PM on September 17 [4 favorites]


I used to work on computer I/O that still used cams and stuff like this. My favorite has always been the geneva. (Here called intermittent mechanism)
Ever wonder how a card punch transport could stop moving 12 times a card and still punch 300 cards a minute? Geneva
posted by MtDewd at 4:02 PM on September 17


What, no encabulator?
posted by Wet Spot at 5:22 PM on September 17 [5 favorites]


Why do engines use cams instead of Scottish thinga ma jigs? Scottish dicombulators? Same motion. No?
posted by Keith Talent at 5:48 PM on September 17


I was going to say that Scottish mechanism looked like the craziest one on there. Somehow constantly teetering on the edge of being out of control. He's the uncle you invite but worry about the whole time.
posted by clawsoon at 6:18 PM on September 17 [2 favorites]


Why do engines use cams instead of Scottish thinga ma jigs? Scottish dicombulators? Same motion. No?

Because a camshaft is a form of analog programming. By altering the angle of the cam lobes, you can time the operation of the triggers.
posted by NoxAeternum at 6:19 PM on September 17


Because a camshaft is a form of analog programming. By altering the angle of the cam lobes, you can time the operation of the triggers.

Presumably you could accomplish the same thing by altering the shape of the Scotch yoke, but I think I'd be afraid of the result.
posted by clawsoon at 6:46 PM on September 17 [1 favorite]


Presumably you could accomplish the same thing by altering the shape of the Scotch yoke, but I think I'd be afraid of the result.

You could get an equivalent by mounting Scottish yokes on a crankshaft, but at that point, you're just overcomplicating things.

That said the big difference is where you use them - a camshaft isn't designed to transfer power, while a Scottish yoke is.
posted by NoxAeternum at 7:06 PM on September 17 [2 favorites]


ngl a scotch yoke sounds delicious
posted by Literaryhero at 7:18 PM on September 17 [3 favorites]


Watching at half speed made some of these easier to figure out.
posted by sneebler at 7:29 PM on September 17


Basically, the devices shown fall into one of four categories:

1: Shift the physical direction of a rotating shaft, e.g. CV/universal joints, bevel gears.
2: Convert rotational motion to linear motion (and vice versa), e.g. Scotch yoke, camshaft, rack and pinion.
3: Control/alter the rotational motion of a shaft, e.g. unidirectional linkage.
4: Convert constant motion to intermittent, e.g. Geneva cross, offset gears.
posted by NoxAeternum at 5:17 AM on September 18 [3 favorites]


And related to the OP, a demonstration of the action of various LEGO cams.
posted by NoxAeternum at 5:39 AM on September 18 [2 favorites]


so much better--and more educational--than the latest movie-themed LEGO set
posted by superelastic at 6:36 AM on September 18


This was pretty cool and informatice, except that I guess a torque limiter is just a magic gear.
posted by paper chromatographologist at 8:23 AM on September 18


507 Mechanical Movements

Sadly I can't find the transitioning/easing Bezier, etc. like motion controlling things that produce those nice bounce into place eye candy.

Sadly, no custom cams and rollers. Or slot machine bars and holes randomness. It's all just bog standard translation of energy.

But it was nice to see it put together in one thing in a chain of back and forth. Kudos.
posted by zengargoyle at 9:25 AM on September 18 [3 favorites]


This was pretty cool and informatice, except that I guess a torque limiter is just a magic gear.

It's a clutch gear, a piece LEGO has made for some time. Put enough torque on it, and the clutch slips.
posted by NoxAeternum at 11:17 AM on September 18


Just like the clutch and brakes on a go-kart. Static vs Dynamic friction and centripetal/centrifuga (choose your frame of reference)l force. Managed heat via friction dumping for transferring torque. Calculated energy to heat.
posted by zengargoyle at 11:43 AM on September 18


For the first Easter of the pandemic, we made elaborate baskets for the family. My wife loves birds, so I made a papercraft robin and mounted it on a lambda linkage so it could march straight forward across the front of her basket. (My daughter got two bunnies mounted on opposite ends of a pivoting bar, each kept upright with a parallelogram linkage, so they could have reciprocal hopping motions).
posted by Jpfed at 2:24 AM on September 19 [2 favorites]


From the description I knew what video it was going to be.

I watched the first 30 seconds of that video then set it aside to save for my wife, who I suspected would enjoy watching it with me, later in the evening.

Wife and daughter HATE my YouTube addiction, so I beg them to watch "a thing you will really like".

They do. They are delighted. They loved it. We all did.
posted by Wetterschneider at 8:21 PM on September 19


> Because a camshaft is a form of analog programming.

The funnest thing about camshafts is that the "lobe" which opens and shuts the valve has to be precisely shaped to take into account not only the desired position of the valve but also its acceleration as it opens and closes. If the lobe falls away too fast, the spring which closes the valve can't keep up which means a tiny gap opens up and then slams shut again, destroying your cams and/or valves in short order.

High performance engines are always a hair's thickness away from self destruction.
posted by nickzoic at 3:02 AM on September 20 [3 favorites]


The funnest thing about camshafts

I hear that the cool kids are using camless engines nowadays.
posted by clawsoon at 4:21 AM on September 20 [1 favorite]


^Camless piston engine (Wikipedia). Sounds like a good application for hybrid engines, increasing range and reducing charge time and battery cost.
posted by Brian B. at 9:41 AM on September 20


Lot of potential band names in this video.
posted by neuron at 10:15 AM on September 20 [1 favorite]


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