Metal front bumper/tow hook mount

[99gst_racer]

Then it'll be bolted in just as the old units were (still working on best way to do that since nuts are integrated into OEM pieces).

You could use threaded tubes for that too. Bascally the same thing we're suggesting for attachment points for the tow hook.

Basically the same thing I did on my 3-pc crossmember. We welded in a threaded tube to gain a threaded attachment point on the underside of the bar. You would just want yours to sit flush instead of protruding like mine.

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EDIT: Too slow AGAIN. I'm going to bed.

 

[snowborder714]

Same way as the tow hook with threaded tubes.

I suppose you could maybe weld nutserts in place but a tube through the center in double shear would be much stronger.

I'm still learning the "double shear" term, but I'm guessing that means welded on both ends, correct?

We had thought about welded nutserts as well as rivet nuts. We'll add weld-in tubes to the list.

 

[Calan]

You would just want yours to sit flush instead of protruding like mine.

You would need to be sure and leave enough clearance on the inside tube to allow the threaded tubes to extend 1/8" or so on each side for a good weld.


at ninja editing. This whole thread is a giant edit in progress. I have to keep going back to the first page just to stay caught up.

I'm still learning the "double shear" term, but I'm guessing that means welded on both ends, correct?

We had thought about welded nutserts as well as rivet nuts. We'll add weld-in tubes to the list.

Correct on the welded at both ends. I'll add the bolt tubes to my FEA model so it will be ready to go when I get the final dimensions.

 

[Bud92gsx]

Ok got that part..But the bolt down part I'm having trouble seeing in my head..

I know your trying to get away from as much welding as possible..But wouldn't it be easier to do it the way I mentioned on page one..And make the tow bar a bolt on process..

I can do it up in paint if your having a hard time understanding the simplicity of it..

 

[knochgoon24]

What if the flat plate at the part that goes into the frame was a 90* piece with the one flange on the outside of the main bar? I don't know how much room there wouldd be under the bumper for that.

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[snowborder714]

Do you see the holes in the square tubing in the picture I posted Bud? There's threads in two of those holes. Those brackets then slide in this hole in the frame.

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You can see the holes in the bottom of there. You use 2 bolts to secure that bracket to the frame. Then you can see the two bolt holes in that bracket where the bumper bolts to. Check out the photobucket gallery link Eric posted on page one to see some pictures of the factory setup that will hopefully help out. Short of making a video or series of "take apart" pictures, I don't know how much more I can describe.

 

[greengoblin]

We are all talking about a true bolt in product.

This unit will slide into the frame rails just l;ike the OEM unit. Then you will use bolts just like the OEM one that go through the bottom of the frame rail and thread into the bumper support to hole the unit in place.

 

[Bud92gsx]

I did aquick thing in paint..

Map..Orange-Bolts/holes
Yellow-Mounting tab, goes on bar..
Black-Bar
Green-back plate/support plate

It's a little smaller than I thought but you should get the picture..

I have also never taken the crash beam off Brian so..I literally had no clue what was behind there..

 

[greengoblin]

You know the real question is will OEM mounts inside the frame rail be able to take the tension(pulling) load of towing the car out of sand etc. Looking that that photo you posted it's clear (at least to me) they where designed to just hold the bumper in place and give way when a compression load is applied(wrecking)Then allowing the load to feed into the frame rail and crumple zones.

Kevin

 

[Calan]

What if the flat plate at the part that goes into the frame was a 90* piece with the one flange on the outside of the main bar? I don't know how much room there wouldd be under the bumper for that.

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That would be much, MUCH stronger if there is room.

You know the real question is will OEM mounts inside the frame rail be able to take the tension(pulling) load of towing the car out of sand etc. Looking that that photo you posted it's clear (at least to me) they where designed to just hold the bumper in place and give way when a compression load is applied(wrecking)The allowing the load to feed into the frame rail and crumple zones.

Kevin

Very good point. I think it would be ok, but it may require some reinforcement and/or better mounting.

 

[snowborder714]

Bud, what's the point in having that "mounting tab" when we could just bolt directly to the "back plate"? But that is essentially like we designed it. So I'm not sure I see what you're trying to get at or suggest.

Kevin, I would say if Drew's setup has held this long without tweaking the frame, then it should be good enough. His setup, as you might know, is fairly similar to this design. His hook has mainly been used to pull the car up on a trailer and from what he's told us, he's only seen a bit of bending in the main bar.

 

[1990AWD]

So your wanting to have this come out at point A in this picture?

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[Bud92gsx]

Well the tab is essentially what holds the bar to the plate..Unless you have some most likely genious idea that will do the same..With no need for a tab..

How can you mount a bar to the plate with no tab being welded on the bar..Yes on the models before you slide the rails right into the frame rail...

I guess I've just never taken a crash bumper out before and said..I could make a smaller one..

 

[snowborder714]

Yup, position A. It'll look like this.

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[greengoblin]

I thoguht Drew's was welded inplace. Well if it works it works. Just want to make sure all bases are covered.

 

[snowborder714]

I believe his is welded in some way, shape, or form. I have a few pictures but they're of a couple different setups he's had. I don't know what the latest is and how exactly it's mounted/installed.

 

[Bud92gsx]

No criticism Brian...

 

[1990AWD]

In that case, if you were to make it bolt on, would you even have enough room to bolt in on with the fmic there? If it was just a screw in thing where you just spin it in and out, that might work.

A sub-3000 pound car doesn't need that much steel to pull around on wheels, and I doubt if you crash and wheels come off, you'll be wanting to drag it anyway.

 

[snowborder714]

It won't be a matter of want. It will be a matter of necessity to get it off the track, and somewhat quickly most likely (as per staff intentions to keep cars running). I doubt it'd really be up to me to do exactly what I want with my car if I got in a wreck.

What if the car gets into some sand, or even if it was wet? Or maybe some mud. That's going to take more force to yank it out. Also consider the snap forces applied to the car when the tow truck starts pulling. This isn't being built to pull the car around freely on it's wheels.

 

[1990AWD]

True true. Hmmm...I'll have to keep thinking..

 

[Calan]

Yep.. it's going to have to hold up to considerably more than rolling weight. We're going to try to get some real-world numbers with a strain gauge (errr... force dynamometer .

 

[Calan]

Brian...as we discussed on the phone, the preliminary results don't look so hot with the actual tube size you are using. Granted the constraints and loads are not optimized yet and this is a single adaptive pass, but IMO it is close enough to show that there are some issues to work on.

The model is only constrained on the back surfaces of the horizontal mounting tubes until we get more info on how it will bolt up; all other surfaces are free to rotate and translate in 6 DOF. The load is 6000 lb total force, distributed on the front half of the cylindrical surface of the hook's hole. This is a horizontal pulling force only, and doesn't take into account any vertical loads caused by height differences between vehicles. (I basically doubled a typical car weight to account for an angry tow truck driver yanking it out of some sand. The final force target may actually be quite a bit more than that). The material I used is a stainless steel alloy with a stress limit of roughly 60k psi.

Maximum displacement in reference to the constrained surfaces is 1.37 inches at the tip of the hook, and most of this is from the front tube deforming as shown by the transition into greens and yellows.

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I also plotted von Mises stress, which is really just an index showing where maximum combined stresses are located. The maximum VM stress is 365400 psi, which is way beyond the yield strength of any common material. The highest stress is concentrated in the gussets, which was a quick and dirty fix to keep the plates from rotating...so it was somewhat expected. Even so, the light blues and greens shown throughout the center portion of the main tube are well beyond the yield point of anything that you could afford to make it out of, which explains the deformation.

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The bottom line is that the 1-1/2" x 1/8" wall tubing is crinkling like aluminum foil with 6000 lbs of force pulling on it; at least under these conditions. Ok... that is a bit of an exaggeration, but you get the point.

I'll double the wall thicknesses and try some different alloys tomorrow, but I really think there will still be issues with the 1-1/2" square tubing and this design.

 

[ed1380]

Any thoughts on bolting the tow hook to the front 2 crossmember bolts?

I know my fmic sits flush with the bottom of my radiator support, so it should clear most intercoolers. Also I would estimate that 90% of the force will go to the subframe, which will distribute that to the chassis.

 

[turbosax2]

There are a lot of ideas flowing here, thank you all for showing such an interest in helping us make a safe and effective piece!


To answer some questions...
1. Tubes were definitely planned on being welded in for the tow hook to bolt to. I was heavily leaning towards regular tubes with a nut/bolt design rather than a threaded tube. Either would work though, and would definitely be implemented.
2. Gussets on the front of the flat plates will prevent this bar from being height adjustable.
3. Gussets on the back will definitely fit. Our tube will have to stick out a few inches past the frame rail to provide clearance for the FMIC. They will not be flush to the frame rail like the stock pieces.
4. From my measurements, it looks like we're confined to a 1.5" max tubing size to clear the FMIC.
5. The front crossmember bolts were considered. I'm not entirely comfortable with that idea either. Plus, any future hopes of a front splitter could interfere with a hook there.
6. From what I can tell from the pictures, Drew's setup uses the factory frame rail pieces.


I encourage everyone to think outside the box, as well. Most of the ideas are stemming from the original design we made. If anyone thinks of a radically different design that would work better, shout it out. Now that we've pointed out quite a few apparent flaws with this design, I'm trying to rethink the design to see if some other way would be stronger and lighter.

 

[97gst_spyder]

Any thoughts on bolting the tow hook to the front 2 crossmember bolts?

I was just going to ask that.

If the hook was longer so it bolted to the bar and the cross member bolts?