Metal front bumper/tow hook mount

[knochgoon24]

Why is there still discussion about keeping the mustache? I feel most people who have it would be ok cutting it out if they wanted to run this. Unless the bottom of the mustache is the same height as the top of the opening in the 2gb Talon bumper. But I wouldn't worry yourselves with that.

 

[turbosax2]

The bottom of the mustache is the same height as the top of a 2ga Eclipse bumper. Plus, I still have the mustache.

 

[turbosax2]

Can the front tube be a little taller, so that part of could stick down into the opening slightly? Or does it have to be flush with the top of the opening?

If you could use 1-1/2" x 2-1/2" tubing for the front beam, it opens up a lot of options for wall thickness since that is a common size.

The bumper can't be below or even flush with the opening. It has to be slightly above so that it will rest against (or very close to) the edge of the bumper cover at the front of the car. That's why a spacer will be needed for the tow hook to move it slightly down into the opening. This bar is also bracing the bumper, not just providing a mounting point for the tow hook.

 

[snowborder714]

Strange. I would think that if anything, race sanctioning bodies would want a standardized hook ID to ensure that the tow vehicle just drops and goes.

I would think that as well. Make sure they're not flimsy tow hooks, all at least a certain size, mounting locations in relation to taking out shins, etc. I was very surprised to see that the latest docs barely have any regulations.

Why is there still discussion about keeping the mustache?

Eric's being stubborn and won't cut his

 

[turbosax2]

Eric's being stubborn and won't cut his

Why would I want to remove the piece that's effectively routing air through the opening to where it needs to go? Once that mustache is removed, air can go wherever it wants. The sides of the opening lose all shape.

But that's beside the point...

 

[Calan]

The bumper can't be below or even flush with the opening. It has to be slightly above so that it will rest against (or very close to) the edge of the bumper cover at the front of the car. That's why a spacer will be needed for the tow hook to move it slightly down into the opening. This bar is also bracing the bumper, not just providing a mounting point for the tow hook.

Ok.

What about going the other direction? Assuming the bottom side of it is inside the bumper cover and about 1.75" down from the frame rail tube, how tall could it be before getting into the bumper cover or other obstacles on the top side?

 

[knochgoon24]

The bottom of the mustache is the same height as the top of a 2ga Eclipse bumper. Plus, I still have the mustache.

Ok. So 2ga Eclipse/Talon, 2gb Talon, and 2gb Eclipse w/o it cut are all the same height. But with it cut, the 2gb Eclipse bumper is a good bit higher. Gotcha.

 

[turbosax2]

Ok.

What about going the other direction? Assuming the bottom side of it is inside the bumper cover and about 1.75" down from the frame rail tube, how tall could it be before getting into the bumper cover or other obstacles on the top side?

Brian measured the height of the stock bumper at 5". So that's probably a good starting point.

With a 1.5" frame rail tube, the bumper can stick 1.75" from either edge.

Ok. So 2ga Eclipse/Talon, 2gb Talon, and 2gb Eclipse w/o it cut are all the same height. But with it cut, the 2gb Eclipse bumper is a good bit higher. Gotcha.

Right. But like you said, most 2gb people who would use this have the mustache cut, so I'd really like to make it compatible.

 

[ed1380]

I would be careful about using spacers to make the hook lower. That would create a twisting of the horizontal beam.

The bumper can't be below or even flush with the opening. It has to be slightly above so that it will rest against (or very close to) the edge of the bumper cover at the front of the car. That's why a spacer will be needed for the tow hook to move it slightly down into the opening. This bar is also bracing the bumper, not just providing a mounting point for the tow hook.

 

[turbosax2]

Unless the tow hook is centered or straddling the bar, I think some twisting is inevitable. Alternatives?

 

[Calan]

Let's get the structure working first, then worry about the hook.

I would much rather bend a rather inexpensive bolt-on hook, than the structure bolted to the car.

 

[Calan]

Much, much better.

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Material is 1.5" x 3" x .188" wall for the front beam, 1.5" sq x .188" wall for frame tubes; weight is around 27lbs. Max displacement is down to 1/8", and max VM stress in the center of the main beam appears to be around 35k - 36k.

Note that I completely constrained the frame tubes now, so there would be some rotation where they join the main beam that isn't shown...but it wouldn't be much with as much weld as there is in that area.

 

[snowborder714]

Care to explain what VM stress and the numerical values represent/mean?

 

[ed1380]

Unless the tow hook is centered or straddling the bar, I think some twisting is inevitable. Alternatives?

Make the hook at the same level as the mounting point.

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straightened out

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if anyone wants the PSD so they can toggle through the 3 pictures, let me know.

 

[Calan]

Care to explain what VM stress and the numerical values represent/mean?

The left plot shows displacement magnitude (or deformation) in inches, and is a rough estimate of how much bending or stretching is taking place, relative to the WCS (world coordinate system) in the model.

The right plot shows stress. VM = Von Mises stress

The VM values are in PSI. The extremely high values at the top of the scale represent tiny anomalies around the joints where the tubes meet, and can be ignored due to the fact that there isn't any weld material modeled, as shown below.

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The areas we are most interested in are in the center of the tube and around the gussets, which actually look fairly decent now.

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[Doubleot]

I just want to say this is an amazing thread, So much great knowledge being thrown around.


I was also wondering if you would consider making these for sale once you get a proper design made up and tested? I'd be interested as i do not have my support bar anymore and would like to have the capability to have a little more reinforcement while being able to have a towing option available.

 

[turbosax2]

Make the hook at the same level as the mounting point.

Please read post 103 again. I explain why that is not possible.

 

[turbosax2]

Craig, keep in mind I'm a man who likes to have his cake and eat it too. That model looks nice and strong, but that is a lot of weight and it's still not adjustable like I want.

 

[Calan]

Craig, keep in mind I'm a man who likes to have his cake and eat it too. That model looks nice and strong, but that is a lot of weight and it's still not adjustable like I want.

You sound like a salesman.

It's always about tradeoffs. There are three basic ways you can lower the weight:

1. Settling for less force applied before the weakest points start bending (and we don't know what that force truly is, even if you decide how much bending is acceptable). The problem with deformation is that once a ductile material starts to bend beyond the yield point (without springing back), it has technically failed and become weaker. Is that ok? Depends on your design criteria. How far can a head stud stretch before it's trash, even if a nut will still thread on ok?

2. Use a more exotic lightweight material. Besides cost and increased fabrication difficulty, most of these materials are more susceptible to fracturing when they fail, rather than bending. So you may get more strength, but at the expense of a catastrophic failure when the load exceeds the yield strength. Airplane wings are designed to bend and flex for a good reason.

3. Come up with a design that better distributes the load, which in turn lowers stresses throughout the assembly. This is usually the best first approach, and is what I have been focusing on. The problem with this is that you are really constrained in the dimensions and shape of this thing.

 

[turbosax2]

Any way to run FEA with this stuff?
40x80 - Bosch Rexroth Corp.

It will roughly cut the weight in third.

 

[Calan]

Any way to run FEA with this stuff?
40x80 - Bosch Rexroth Corp.

It will roughly cut the weight in third.

Yeah, if they have a piece of it modeled in Pro/E, or a sketched and dimensioned cross-section of it. That is one of the strangest and most complicated extrusions I've ever seen.

I'm willing to bet that it would be really hard to work with. Getting good solid welds or even a smooth bend looks like it would be difficult at best.

 

[turbosax2]

Click on the arrow under Solid Model/CAD to download the file. Pro/E is there.

 

[ed1380]

Reasons that i get are either intercooler (which it would clear) or holding up the bumper. In the last case I would recommend making the load bearing assembly as efficient as possible and use foam to hold the bumper

Please read post 103 again. I explain why that is not possible.

 

[Calan]

Click on the arrow under Solid Model/CAD to download the file. Pro/E is there.

Their Pro/E model was imported from something else, so there is no parametric data associated with it; it's just "dumb" geometry. Not sure I can use it to generate a swept (curved) beam.

 

[snowborder714]

I was also wondering if you would consider making these for sale once you get a proper design made up and tested?

Possibly. It's towards the bottom of the list right now with this project, but you can see through the discussion various points on where we're trying to make it as universal as possible. Whether we can do that and make it affordable for the typically cheap masses is another question.

You sound like a salesman.

Don't let him fool you with the cake comment. He also loves pie