T44/URS Strut Mounts - Help Me Help You!

[loxxrider]

Thanks Kevin. I was wondering whether you measured vertically or normal to the strut tower surface, but the picture you took made it look like it was normal to it. I figured that was fine since it's the conservative approach anyway!

I made another surface using your numbers without the hood lining and it clears even at full positive camber.

There still may be some strange situations where a spacer is needed for clearance between the top hat and the custom bearing housing, but it'd be for more obscure settings like full positive camber with negative castor as well. For anything from neutral to negative camber and/or neutral to negative or positive castor, it's good to go as is.

[mushasho]

UrS6 tester here

Sent from my HTC One using Tapatalk

[ringbearer]

I'd test but looks like you want peeps with Billys for now

[loxxrider]

It won't be hard to modify it for konis. I just don't have the measurements needed for them. If you're good with a caliper, go get one and report back with a drawing

[ringbearer]

I should have taken some when I had it apart. I have too much other stuff going on right now to keep playing with it.

[20VAvant]

I took very good measurements of the strut tower bolt pattern (it was pretty close to the one you gave me in your CAD files Nick), the Bicknell hat (you got a little lazy on that one

3) Nick, I'm not sure how much your design which replicates the stock mount, but gets rid of the stock spring perch, etc. raises the strut position in the body, but this design should raise it at least 0.4" more than what is possible with your setup. So that's good news!

Sorry about the Bicknell hat measurements. I used a set of calipers but I must have mis-read some stuff.

I don't really think mine gained any position, very minimal if at all. Mine was more of a 'material friendly' version than a version trying to maximize placement.

Looking forward to running these!

[pilihp2]

If you need a T44 tester with Koni's, hollaaaaa

[WOMBAT]

That's some damn good work Chris!

[pilihp2]

That's some damn good work Chris!

Seriously!


We have so many different copies of AutoCad here at the office, I wish I had some engineering knowledge to mess with it on my free time, I love cad stuff like this.
Unfortunately my knowledge of autocad is limited to setting up the license manager for it and directing everybody to said manager.

[loxxrider]

Thanks guys!

Unfortunately AutoCAD wouldn't be much help with this when it comes to creating surfaces. If it didn't have any of those, it'd definitely work, but I'd sure hate it! I'm using Solid Edge ST7 (by Siemens who makes NX, Unigraphics, etc. which are ~$30k a seat) for this. It's one helluva parametric and synchronous CAD package. I finally found one that works for me for less than $30k a year lol. I spent a long time looking!

[loxxrider]

Progress has not stopped on these mounts. Conceptual design was finished a few weeks ago. Then I was into preliminary design, just trying to get everything to fit into the envelope. I'm not into the detailed design phase where I'm specifying fits and tolerances for the whole assembly. I've never gone into this much detail on a design of my own except for when I designed some parts for the F35 Lightning II jet engines (F135 engine) last year at my previous job. That taught me a lot which should really help make this design work nicely.


There have been a few questions I've had to come up with answers to recently. The thing I'm worried about most (other than strength which I've preliminarily analysed already) is whether this unique design will allow for any rattles. If you inspect the design closely, you'll see that the bearing housing kind of just floats in the "slider," as I'm calling it. Of course there will be a snap ring preventing the bearing housing from downward travel. The problem is that in order to install the snap ring, some clearance will be required. The same applies to the snap ring bearing retention used in the bearing-housing-to-spherical-bearing fit. When I did this before, I didn't notice any unwanted vibration noise from this design, but I think this is something we'll just have to try out and get feedback for, for the first couple of assemblies. I have some ideas to resolve it without affecting the design, but I think tight enough gaps will do the trick.

I just have to get going on a few preliminary drawings and then I can have a quote for getting the parts made in metal

I'd give it a few more weeks at least before I can finalize the design, but we're getting there!

[ringbearer]

Can we please call these drama mounts?

[mushasho]

Ground Control "weld in" mounts?





http://knoxville.craigslist.org/cto/5109969527.html

[loxxrider]

Current events involve trying to get the latest iteration of the design to pass structural analysis. It's really hard to estimate the forces the mount will undergo, but I think I am running it with numbers which are conservative enough. Even so, is proving difficult. I'll get it there though!

Also, I'm currently getting a price quote from a job shop I've used before. No idea what they're going to come back with. I'm hoping under $500 per set, but I'm not making any promises.

[loxxrider]

I've been struggling a little bit to get the slider with the cutout in it to pass the finite element analysis with what I feel are pretty conservative assumptions. That was until I realized I was comparing my results with the yield strength of really crappy steel. I was shooting to have stresses under 36,000 psi. I got it there for the most part, but then realized that regular 1080 steel is around 53,000 psi for yield strength. Now I have lots more room to play, but I'm going to leave the design pretty much as it sits now for extra factor of safety. These should still put the struts up higher with more adjustment with any other mount out there which doesn't require modifying the strut tower.

Here are some details.

The mesh is made with tetrahedrals, with subjective size of 0.1". I didn't spend a whole lot of time on it, but the solution has converged reasonably at this level. Special care was given to the variable radius on the "slider" part with about double the density of tets used there to ensure a good solution in that area.

The outside edge of the mock strut tower part was constrained as fixed in all 6 degrees of freedom (it's connected to the rest of the metal in the car, so this is a good assumption).

A force of 6500 lbf was applied uniformly to the upper snap ring groove upper surface. This is really the only thing I'm not sure how to approximate to be honest. Obviously around 25% of the car's weight will be there on a regular basis, so figure roughly 925 lbs. However, that load can be multiplied quite a bit when hitting bumps, etc. I'm sure it might see the full 3500-3700 lbs of car at times, but there may also be times where it is subjected to a shock or impulse load which can really amplify things. The bearing I have spec'd is one of the higher strength bearings availble in this size, and it can withstand about 7700 lbf safely. When this load is applied to the strut tower, it starts getting close to yielding, so I think what I ran the analysis at is a fairly safe bet. There is room left over of course.

Since I'm running the analysis on the assembly rather than on individual parts (more accurate this way), connections had to be made so that the parts know where they should be making contact with one-another. I won't go into detail, but the contacts were handled as standard.

That's pretty much it from the analysis set up. I ran this probably 20+ times in the past day or two trying to figure out how to modify the design to suit the chosen material.

This shows the overall mesh and a general view of the Von Mises stresses seen in all the parts involved. Notice that the scale goes rather high... that is due to localized stresses in the model which are not "real."

Final_FEA.JPG (129.53 KiB) Viewed 80328 times

Localized stresses along the contact between slider and lower plate

FEA_Localized Stress.JPG (144.18 KiB) Viewed 80328 times

These are the two critical areas for stress in this design. This is the downfall for this type of design as opposed to letting bolts carry the stress from the top. You get a lot of shear and bending stress in the member which crosses the gap in the lower plate.

Slider radius stress

Slider_Radius_Stress_6500lbf.JPG (222.76 KiB) Viewed 80328 times

Slider top hat cut-out stress

Slider_Cutout_Stress_6500lbf.JPG (216.35 KiB) Viewed 80328 times

I may make some more tweaks to this, but at this point I think my analysis is conservative enough that these are not going to fail under any conditions a car will ever see.

I've also just about (97%) finalized all of the fits and clearances for all parts. This should make for a really nice assembly as long as the machinists do their job properly! I just wish I didn't have to make all the drawings. That's a whole project in itself, but I will get quotes in the meantime.

[loxxrider]

Just ran the analysis quickly for 8000 lbf. This is more than the bearing is rated for, and this is a stronger bearing than I used in my previous design which I tested thoroughly by bottoming out the car one too many times haha! The previous bearing was rated for around 6750 lb axial load and I was told by Hoerr Racing that this is a very commonly used camber plate bearing in motorsport. So if you break these mounts, you probably jumped the car off of a cliff!

This design should keep the material within it's endurance limit under any normal driving conditions ensuring no possibility of fatigue failure unless you bottom out the suspension HARD thousands of times!

Slider radius at 8000 lbf load

Slider_Radius_Stress_8000lbf.JPG (266.29 KiB) Viewed 80328 times

Slider top hat cut-out at 8000 lbf load

Slider_Cutout_Stress_8000lbf2.JPG (283.2 KiB) Viewed 80328 times

I'm pretty comfortable with this.

Now on to finalizing the models and starting to get serious about the drawings

[EDIGREG]

nice job on the FEA... looking good!

[loxxrider]

Thanks Ed.

Did you ever send those mounts my way? I haven't received anything... If not, I probably don't really need them at this point.

I just sent in the request for quote to my vendor of choice. Fingers crossed it comes back reasonable, otherwise I may be the only one running these lol

The only thing I'm really questioning right now is sort of a fundamental design feature of these mounts. It should be interesting to see how it works out with testing. The bearing housing is not rotationally constrained in the slider piece in any way. However, the fact that the strut goes through it at an angle should mean that the bearing housing is always self-centered toward the outside of the car (to the fender) as is intended. Of course if you try to turn the wheels while there is no weight on this part, it may want to turn. I'm hoping this self-centering action will prevent that. If not, I can always add some kind of clocking feature. No big deal. What do you guys think? I think it should work well as-is, but there is a chance it wont.

Here's the 99% finished design.

99percentdonedesign2.JPG (45.5 KiB) Viewed 80304 times

99percentdonedesign.JPG (47.46 KiB) Viewed 80304 times

[mushasho]

These look like the A1 hats... would Bicknell hats sit any different ?

[loxxrider]

Yes, I forgot to mention that. The design will make A1 hays mandatory unless you want to sacrifice suspension travel a lot. The steeper angle of the A1 hat made it better to use once I had to incorporate the lower snap ring groove. The mounts would include modified A 1 hats for minimal price or I can tell you how they need to be modified.

[mushasho]

The design will make A1 hays mandatory unless you want to sacrifice suspension travel a lot.

Oh...

[EDIGREG]

Yeah, I have been on vacation and forgot to ship those to you prior to leaving. I figured at this point they wouldn't be of much help to you.

That looks like an awfully low clearance between the hat and the mount...are you sure there won't be interference there under compression?

I agree the bearing housing should remain self-centered based on directional suspension force, but I'd look into adding a set screw or something to keep it in place. Also, is there a circlip or something planned to keep it from moving downwards? I see a groove there?

[loxxrider]

Yeah, I have been on vacation and forgot to ship those to you prior to leaving. I figured at this point they wouldn't be of much help to you.

That looks like an awfully low clearance between the hat and the mount...are you sure there won't be interference there under compression?

I agree the bearing housing should remain self-centered based on directional suspension force, but I'd look into adding a set screw or something to keep it in place. Also, is there a circlip or something planned to keep it from moving downwards? I see a groove there?

Yes, there will be a circlip on the bottom. The problem with any indexing feature like a set screw or a key is that I'd have to have them in several places on the "slider" part to account for different castor angles.

The clearance between the hat and the mount has been calculated very carefully. Remember, this is an engineered part, not an "engineered" part. I'm coming from designing jet engine parts with clearances down to the gnat's ass There is clearance in all positions. It gets closest at full POSITIVE camber. It still has clearance there, but I haven't truly accounted for the few mils which might be taken up by compression of the mount. That is one reason it's so thick in the area which would affect that clearance, but if there was an issue at full positive camber, a simple washer or a sleeve with a slightly thicker shoulder would be the only thing which needs to be changed. I don't foresee any issues, but I have definitely designed it so that it is easily fixed if there is a clearance problem in any condition.

Sorry about the hats OB! I thought they would be better to use too, but the way the design panned out, I just can't use them.

[EDIGREG]

The problem with any indexing feature like a set screw or a key is that I'd have to have them in several places on the "slider" part to account for different castor angles.

Why? You don't need the threads to go into the bearing housing, just have the set screw drilled through the slider and press onto the bearing housing (or cut a small channel into the bearing housing for it to ride in).

The clearance between the hat and the mount has been calculated very carefully. Remember, this is an engineered part, not an "engineered" part. I'm coming from designing jet engine parts with clearances down to the gnat's ass There is clearance in all positions. It gets closest at full POSITIVE camber. It still has clearance there, but I haven't truly accounted for the few mils which might be taken up by compression of the mount. That is one reason it's so thick in the area which would affect that clearance, but if there was an issue at full positive camber, a simple washer or a sleeve with a slightly thicker shoulder would be the only thing which needs to be changed. I don't foresee any issues, but I have definitely designed it so that it is easily fixed if there is a clearance problem in any condition.

I wasn't questioning your engineering abilities and it's not a matter of dealing with small tolerances. I realize you've designed it to have clearance in all positions while static, I was referring to the increase in positive castor that occurs when the suspension is compressed. Unless you've modeled the full sway bar/control arm/strut assembly for simulation, or measured those angles in real world scenarios, then it is difficult to know. Plus, it depends on the ride height and spring rate.

Agreed it would be easy to fix by spacing the hat further from the mount, just an observation.

[loxxrider]

The problem with any indexing feature like a set screw or a key is that I'd have to have them in several places on the "slider" part to account for different castor angles.

Why? You don't need the threads to go into the bearing housing, just have the set screw drilled through the slider and press onto the bearing housing (or cut a small channel into the bearing housing for it to ride in).

I was thinking about more of a positive engagement feature, so I hadn't really thought about a set screw just yet. I think that might be the solution. I will add that to my design unless we can come up with a better option which doesn't increase machining costs substantially.

The clearance between the hat and the mount has been calculated very carefully. Remember, this is an engineered part, not an "engineered" part. I'm coming from designing jet engine parts with clearances down to the gnat's ass There is clearance in all positions. It gets closest at full POSITIVE camber. It still has clearance there, but I haven't truly accounted for the few mils which might be taken up by compression of the mount. That is one reason it's so thick in the area which would affect that clearance, but if there was an issue at full positive camber, a simple washer or a sleeve with a slightly thicker shoulder would be the only thing which needs to be changed. I don't foresee any issues, but I have definitely designed it so that it is easily fixed if there is a clearance problem in any condition.

I wasn't questioning your engineering abilities and it's not a matter of dealing with small tolerances. I realize you've designed it to have clearance in all positions while static, I was referring to the increase in positive castor that occurs when the suspension is compressed. Unless you've modeled the full sway bar/control arm/strut assembly for simulation, or measured those angles in real world scenarios, then it is difficult to know. Plus, it depends on the ride height and spring rate.

Agreed it would be easy to fix by spacing the hat further from the mount, just an observation.

I didn't mean for that to come off as defensive. I was just explaining my reasoning for the design features. To answer your question, no it doesn't account for much in the way of this kind of movement directly, because noone ever gave me any specs for it. However, all of the clearances were done with the strut at full extension. At full extension, all of the angles involved would be amplified compared to at full compression or anywhere in-between. For that reason, I *think* it should be OK. If not, different spacers will be made

Here is the way it is constrained at the bottom. There is a sleeve which allows for vertical movement of the strut and rotation along the transverse axis of that little sleeve. This is as close as I could get to emulating a worst case scenario of suspension movement without having more information. I realize the point that sleeve is constrained at can move a little bit, but it should only pose a potential problem when the mount is at full POSITIVE camber which I don't think too many people will use. At neutral or negative camber, there is pleeeenty of space!

full camber.JPG (24.68 KiB) Viewed 80231 times