Technical Engineering question, a serious one

It was so good...brought back ghosts re: fear of snoring in class!

 

Now that's a fact. I was in school from 69 to 73. Most all the engineering buildings had been built in the 40's and had no air conditioning. Get a class after lunch, about 80* outside and 85* in the room, along with one of those professors whose lecture was a monotone drone, and staying awake was about 5X harder than the course material.

 

If can't find it here Id be surprised....http://www.hubcityinc.com/documents/7R-HubCityFarmProductsAndAccessories.pdf pg 11 to 14..

 

Oh, Oh. Did we lose 31Vicki? or is he sleeping in the back of the classroom?

 

Nope, stuck fixing something else today
Front end parts changing.

 

I could probably do the math, but wouldn't have any idea what the answer meant. I sure hope someone translates the answer so us not so smart guys can understand what the real answer is, will this work? Gene

 

... plus instantaneous impact (ie, turning hard while hitting a nasty pothole), plus tolerance.

Yeah, I think this is probably pretty acceptable "math" for the application , 31. However, there also will be some weird diagonal rotation on the shaft end points not typically seen in a steering setup because the shaft isn't in a linear application like it would be for steering (as in, all forces are in a pure rotation). Make sense?

 

Yep!
There's also some bending force getting redirected into rotation

 

Grainger sells Hub City splined shaft and couplings. I'm certain Hub City has all of the specifications you want. There are many sizes an number of splines. You use a bearing at each end instead of a bushing.
https://www.grainger.com/category/s...nd-adapters/power-transmission/ecatalog/N-i9g

 

for the engineers: in this application would a bearing be better than a bushing?
most king pins are bushings- take a beating and still work when worn. most crankshafts/rods "bushing" for the same reason and embedability.[?] wheel bearing handle loads smoothly and with limited friction.
so what would be better?

 

I could set it up with tapered wheel bearings too.
I'll have out source some of that, it's not really convenient any more.

 

In most cases, it's about the speed of the shaft. Something that turns very slowly or in a limited range doesn't require bearings. Bearings are used on splined shafts because they don't have the smooth surface area.

 

Rough mock up.
Tube length and shaft should get shorter after I start the figuring

 

Bearings or bushing's splined or dd? I'm no engineer where math is concerned. 31Vicky and all those that have thrown out the numbers I envy all of you and I see where your all coming from. But here's what I take from all this. Is a panic stop going to have the same affect as a ball peen hammer striking a solid stationary piece of steel. The Wrecking Ball affect is how I'll describe it. Isn't there going to be same give that will decrease the load? Things like the drivers angle, flex at the pedal lever, absorption at the brakes pads and or shoes, flex brake lines expanding? Can math answer these visuals and make this re-engineering more comfortable to accept in regards to a good nights sleep?

 

I was told there'd be no math on Friday!

 

DDDenny, the math was yesterday. We can't help it if you skipped class and had to do the make up test today.

I believe the concern of a catastrophic instant failure would be pretty remote using the steering components. The effects of the pivot point bushing wear and the cross shaft work hardening and becoming weak at the bushing edges over time may be a different story. The advantage that exists is that there is pretty limited rotation involved.

I wonder where they get the 200 lbs of pressure. I'm a pretty big guy, I can assure you, in a panic stop, I would put a whole lot more pressure on that brake pedal then 200 lbs. Way back in high school I could leg press 3.5x my body weight. Figure 1.75 my body weight for one leg, your at over 450 lbs of pressure, and that would be on the pedal. You would need to add in the numbers for the additional leverage of the pedal arm length. Maybe some destruction testing then stress crack inspections are in order here?

I still think the steering components will hold up fine! Gene

 

This has always fascinated me in top fuel.

 

I doubt anyone around here looking at that mock-up would be sucking their teeth thinking that's not gonna work.

I ran the scenario past an engineer and pro mod racer/engineer buddy of mine whos son is also a skilled engineering designer and the feedback was that the calcs would be no problem but to give a proper answer there would be so much data required, much of which wouldn't necessarily be available eg the exact materials and what had been done to it eg case hardening of splines and to what spec etc etc. Real world he tells me he knows of nobody who's doing that even in Top Fuel applications.

Chris

 

Thanks Happy!
A little confused- "he knows of nobody who's doing".... What? In depth analysis of exact materials ?

 

Mock up or just after a 300mph run?

 

Who's "they" ?
I guessed a panic stop could generate 500 lbs pressure.

 

The picture isn't exactly what I was looking for but was the best close up of what the saddle and clamp mounts I've seen so often on top fuel cars. So to answer your question, "after a 300mph run".

 

You can always do what we did in the spacecraft industry, build it and proof-load it. Build a stub frame with the tube and bushings, make your pedal assembly, anchor the M/C end and apply a thousand or more pounds to the pedal and see what happens.

 

There seems to be a lot of good technical information on this thread that can be put to good use.

Personally, trial an error have done me well. Look at this Ford pedal assembly. There has got to be as much pressure on a clutch pedal as a brake pedal, maybe more given the opposing force of the pressure plate springs. These seem to do ok with a round shaft, thin bushings and a 1/4" pin holding it all together.

 

Yep, but it's a clutch. The principal and idea come from there.
It's always better if your clutch works but lives don't get involved if a clutch pedal broke or if the pedal lost communication with the pressure plate.
That's why I think it's important.

 

My point is that small clutch pin has more force applied to it more often than that brake pedal does. I’d hazard a guess that the amount of force and elapsed time that force is applied between the brake pedal and clutch pedal are about the same. I haven’t heard of the factory ford clutch pedal setup breaking being a problem.

 

The forces out of a typical clutch pedal are pretty constant; an example would be about 300 lbs, given a 50 lb input and 6:1 ratio. The linkage, clutch lever and release arm take up the remaining forces necessary for release, normally around a 10-11:1 overall ratio from pedal pad to T/O bearing.
Brake pedal output forces could vary from under 100 lbs to well over 1200 lbs with that same common 6:1 ratio, depending on constantly varied pedal input.

 

bchctybob is saying what I'm thinking. Build it, put it in a fixture, and test it.

 

Let me pose a what if...My thought when I was tractor pulling was to use aluminum 1x1-1/8 tube to hold the weights...I put one end of a 24" long piece in a vise and hung my 200# off the end and it didn't bend..I put an 18" adjustable wrench on it at the end and again my 200# couldn't twist it..Push rod to MC is only 5/16 dia; you'd think it would bend..Race car pedals that use two MC with a threaded bias adjusting bar; the bar is only 3/8ths dia. and doesn't bend..Look at Hub city stuff..

 

The thing about brake pedals that you find in cars and trucks, is that it's always one piece that has the pedal on it, and pushes the mc pushrod.

As if it's done that way, on purpose.