So my homework was making a block

"Spanfeller is a twat" (theaspiringengineer)
02/12/2018 at 21:40 • Filed to: TAE VS CAD, shitpost

No idea why any of the parts are like this really, does the connecting rod need to be 9in tall if the engine only has 5in of stroke?
Who knows? not me for sure! Plus, that piston is very weird.

Our graphic design teacher gave us the piston, the rod, and the crank and we had to make our block. needless to say this is kind of wasteful, and such a long connecting rod seems fishy to me, I can’t fathom it’s usage if the engine only has, again 5in of stroke.

Granted, there must be some method behind the madness, after all, he’s the professor and I am the student, I should probably shut up and actually try and understand why he made it that way. it looks almost old timey, like the locomotive connecting rods.

It is very much oversquare; it’s 4 inch bore is smaller than the 5 inch stroke....
You wonder why I use imperial units? well, its because my teacher thinks it’s just fucking dandy to use imperial units. I added a few heat sinks on the outside and I threaded part of the inside to make oil slide up and down the housing easier. If you wonder why the crank housing is so much larger than the crank, it has to do with that connecting rod.

I made a very basic Static Analysis of the parts and I only used 40lbft of force.

Those seem like small amounts of Imperial Units; not that’d know what those mean.

Jesus....

DISCUSSION (28)

shop-teacher > Spanfeller is a twat
02/12/2018 at 21:46

That’s a lot of extra reciprocating weight.

Spanfeller is a twat > shop-teacher
02/12/2018 at 21:48

I guess it could act a bit as a flywheel?

I dunno... I don’t even understand the units this guy’s working with... but a 9in connecting rod? man that’s out of place on a big block! let alone a single cylinder engine!

shop-teacher > Spanfeller is a twat
02/12/2018 at 21:56

Yeah, that’s crazy long. This being just a design exercise, it’s not like it matters. I’m guessing it’s that way just to give you more room to work with to design your black.

Better get used to imperial units, if you’re going to work for someone with US clients.

Spanfeller is a twat > shop-teacher
02/12/2018 at 22:00

But why do you do this to yourselves? They make no sense

How can an foot be contained in 12 inches and a yard in 3 feet?

I swear this is like the.... the third worst thing about the US...

shop-teacher > Spanfeller is a twat
02/12/2018 at 22:09

Because the metric system is for communists ;)

We’re really stubborn. And we’re used to it.

Spanfeller is a twat > shop-teacher
02/12/2018 at 22:13

Hey! The metric system makes more sense than your wierd electoral college!

You know you’re just jealous.

MM54 > Spanfeller is a twat
02/12/2018 at 22:16

I am pretty sure there is a performance aspect to connecting rod length, but which way around is “more torque” escapes me at the moment. It’s been a while since I had any input on designing engine components (aka since I was in college).

shop-teacher > Spanfeller is a twat
02/12/2018 at 22:18

Talk about damning with faint praise!

Spanfeller is a twat > shop-teacher
02/12/2018 at 22:28

Your imperial system makes less sense than the electoral college?

Is thay better?

ITA97, now with more Jag @ opposite-lock.com > Spanfeller is a twat
02/12/2018 at 22:48

Hey now, you’re right about imperial units. As for the electoral college, it makes perfect sense when you factor in the historical perspective that the framers of the constitution didn’t think the citizenry writ large possessed the better judgement to pick a president for the republic. Electors were supposed to be the adult supervision and able to vote independently when their judgement dictated that populism, or any other ism, was going to make a bad choice. It is the same reason that Senators were elected by state legislators and not directly by citizens until the 17 amendment came into effect in 1913.

Spanfeller is a twat > ITA97, now with more Jag @ opposite-lock.com
02/12/2018 at 22:51

It makes sense like that, but now most electors are forced to go the state’s way.

I think the US would be better as a parliamentary republic... But god forbid any similarities with the old country!

Stephenson Valve Gear > Spanfeller is a twat
02/12/2018 at 23:08

It isn’t very intuitive, but there are differences in how the piston accelerates and decelerates with a long rod vs/ short rod. I seem to remember reading an article years ago where they took an engine, did baseline dyno runs, then swapped out the rods & pistons for longer connecting rods & pistons with a higher wrist pin location to accommodate the longer rods. With no other changes, the engine made more power. I won’t pretend to be able to understand the dynamics of how that worked! However, like anything, I’m sure there is a balance to the engineering... shorter rods allow a more compact engine, longer rods might increase power up to a point, but then the extra mass would start to rob any of the minimal performance gains that were being made.

Now, reverting back to my steam locomotive tendencies, those glorious external combustion machines tend to have a much larger rod length-to-stroke ratio than an internal combustion engine. A typical steam locomotive has the connecting rod driving a crankpin directly on the drive wheel. If the rod is too short, the angle of the rod will tend to direct the force down toward the rail, causing excessive movement in the suspension and unwanted vertical movement of the drive wheel. I’ve seen small steam locomotives with short connecting rods that would actually induce a very noticeable rocking motion to the engine when working at full throttle. There are enough balance problems inherent in a typical two-cylinder steam locomotive as it is, so long rods with their resultant shallower angle at mid-stroke (compared to a shorter rod) helps to minimize vertical movement caused by the forces being transferred from the piston through the connecting rod to the crankpin. An internal combustion engine - with its crankshaft held firmly in place by a rigid engine block - won’t have that same type of issue, although I can see how a longer connecting rod might lower the pressure on the side of the piston to the cylinder wall, thus reducing drag a bit.

Thanks for posting your homework... it is interesting!

benjrblant > Spanfeller is a twat
02/12/2018 at 23:17

I hate imperial measure. Hate. Haaaaaaate.

Spanfeller is a twat > Stephenson Valve Gear
02/12/2018 at 23:19

My teacher is a peculiar man, he said that the rod length was the “torque of the engine” but one wouls be lead to believe that torque is distance from axis times the force times the cosine of the angle... Meaning that what would givr it torque would be increasing the distance from the crankshaft’s center (more stroke) or increasing the force (more bore) not necessarily keeping the piston so far away...

I think that the longer rod does keep the angle to the crank closer to 90 for a longer duration but it could be a mere coincidence....

Aremmes > Spanfeller is a twat
02/12/2018 at 23:36

Long connecting rods reduce side loads on the pistons by keeping the rod angle closer to vertical when the crank web reaches the halfway point between TDC and BDC. This allows the engine to run at higher speeds and power levels.

The Wärtsilä-Sulzer RTA96 doesn’t just have long connecting rods — it has split rods, with the piston rods going through bulkheads that limit their horizontal movement.

Kinja'd!!!

Spanfeller is a twat > Aremmes
02/12/2018 at 23:49

“angle closer to vertical”

This would increase torque...

Is this a general rule? i`d think it’d depend on stroke too...

Aremmes > Spanfeller is a twat
02/12/2018 at 23:55

Stroke length has greater influence on torque as it’s directly related to the lever arm of the crank webs.

PS9 > Spanfeller is a twat
02/12/2018 at 23:57

Homework instructions: Make a block.

Result;

More than one object has been made

Does not appear to be square at all

Moving parts???(wtf)

FAIL. Student...you had one job. Listen. Just make a block. If you need inspiration, check the masonry section of Home Depot. Or the side of your house. Or a construction site. Anything but whatever you’re trying to do here, and I’m not even gonna address the Technicolor stuff you also did. Just. Make. A. Block.

AND DON’T BRING ME ANOTHER PICTURE OF THAT HOONIGAN RALLY GUY OR I WILL FAIL YOU FOR EVERY CLASS YOU WILL EVER TAKE GOING FORWARD, STARTING WITH THIS ONE

Spanfeller is a twat > Aremmes
02/13/2018 at 00:00

yeah, it is what I am thinking about, you add torque by making more bore or more stroke

Each have their downsides... but never thought about the whole connecting rod thing...

If it stays more vertical for longer it means that it stays closer to 90 degrees... The formula for torque is

D(stroke)*F(bore)*sine(angle of rod against crank)

The engine has the most potential torque at around 70 degrees (if zero degrees is TBC) because it’s then that the rod and the crank are perpendicular.

If you can keep them as close to 90 as possible for longer, you will generate more torque!

Spanfeller is a twat > PS9
02/13/2018 at 00:03

How can you ask me to make a block! Do you know how hard it is to reach true level?

random001 > Spanfeller is a twat
02/13/2018 at 06:35

So many stroke jokes, so little willingness to engage is such tomfoolery...

shop-teacher > Spanfeller is a twat
02/13/2018 at 07:07

“Damning with faint praise” is a saying that means what you said is true, but you said something is better than something that isn’t very good.

So yes, the metric system does make more sense than our electoral college, but the electoral college is a hot mess, so that’s not saying much :)

After I posted that comment last night, I realized there was a good chance you didn’t know what that saying meant. But then I fell asleep.

shop-teacher > Spanfeller is a twat
02/13/2018 at 07:16

Believe it or not, you kind of just hit the core of why we still use imperial units. Schools made a big push to move us to the metric system in the 70's and 80's. I have old wood working curriculum with everything converted to millimeters. Old enough that the stuff was mimeographed.

Our system wasdeliberately designed to be difficult to pass laws, and the political will to actually pass the necessary laws to actually switch us over to metric never developed. Eventually the metric push just petered out, although our science classes all still use it.

Fun fact, we don’t call them Imperial units. We call them SAE units, which stands for Standard American English. I find it funny because they’re nobody’s standard but ours anymore, certainly not the English.

punkgoose17 > ITA97, now with more Jag @ opposite-lock.com
02/13/2018 at 09:09

Having Senators selected by the state legislators was also a check that the state governments had on the federal government. It is something we are missing now.

Schaef_Camaero Z/28 > Spanfeller is a twat
02/13/2018 at 09:58

Lay your thumb flat on the table. That’s roughly an inch wide.

Measure your foot. It’s likely close to 12 inches.

Take a step. That’s approximately a yard.

Imperial measurements are closely related to the human scale, and as such are much easier (in my american mind) to deal with when it comes to building things meant for human use. The scale of feet and inches are geared much better to houses and buildings than metric, in my opinion. For example, this room is 11'-6" x 14'-0" rather than 3500mm x 4260mm. Now I do think metric is better suited for science and mechanical engineering, where smaller units are beneficial.

Spanfeller is a twat > Schaef_Camaero Z/28
02/13/2018 at 10:14

I wouldn’t know if it’s very useful in architecture, we all work with meters here!

I was taught to use the system in elementary school... Iknow an inch is 2.54cm and a foot is about 30.1; I know that connecting rod is huge!

But it’s a system that is not very congruent, think of it this way, intrinsically I know that 4260mm is 426cm or 4.26m of the top of my head because tables of ten are natural.... Tables of three, twelve, and such aren’t as easy!

But the argument that it’s based on human metrics, well, it’s a candid one

Spanfeller is a twat > shop-teacher
02/13/2018 at 10:17

I thought SAE stood for Society of Automotive Engineers...

I remember there was a brief change to metric... One president tried it and everyone hated it for some reason

I guess that kilometerage doesn’t sound as cool as mileage

shop-teacher > Spanfeller is a twat
02/13/2018 at 10:37

That’s a different SAE, but you are correct. We like to make things confusing around here. In actual practice, we just refer to our measurements as “Standard.” If you went to the hardware store to buy a socket set, you would find “Standard” sockets and “Metric” sockets.

People hate change. I can objectively admit that the metric system is better and far more logical ... but I’m used to inches and fractions, so I’d rather not change. Now, if the government mandated it, I’ll get over it pretty quickly. A lot of people will pitch a damn fit, so the political will never has and never will materialize.