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Learning how to build Lotus Seven replicas...together!
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PostPosted: February 26, 2021, 10:54 am 
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@marafonets

Thank you.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: March 6, 2021, 5:08 pm 
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I finally did find a rack & pinion vendor who can come very close to meeting all my requirements. I believe I've spent about 6 weeks on various vendors, and I'm so glad to have it in the rear view mirror. I had to make one compromise, but it's small, and not a quality- or function-related compromise.
Attachment:
File comment: This photo is a website of a narrower rack, but mine will have identical architecture, just wider.
Upload Rack & Pinion.jpg
Upload Rack & Pinion.jpg [ 14.71 KiB | Viewed 828 times ]

Th mounting system is also simpler than the others I was looking at, and should allow me to get it lower in the chassis, which may improve bump steer.
Attachment:
File comment: Simple mounting system allows rotation of rack once mounted to adjust the splined steering shaft stub to be rotated to the most convenient angle.
Upload 2-Hole Clamp Mounts.jpg
Upload 2-Hole Clamp Mounts.jpg [ 23.81 KiB | Viewed 828 times ]

I still could not get inner tie rods long enough, or with the metric threads, so I'll need to make an adapter. It's not a huge task, or a difficult one, and I have a small lathe that can do the job.

The red mark in the photo below, added onto a mock-up of a similar product, shows how close the end of the inner tie rod will be to the Lincoln outer tie rods I just bought. I'll need to made an adapter out of hex stock with 9/16-18 female threads on the inner side and M14-1.5R male threads
for the outer end. I'll use the original hex form as the adjuster nut. Final details TBD. The rack should be done and on the way to me in 7-10 days.
Attachment:
File comment: Red mark is approximate location of inner tie rod end for new rack & pinion.
DSC05659.JPG
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Meanwhile, work on the suspension brackets continued. I have a little bit of a fetish about round holes and precision. I keep working to improve as I go through the process. My latest try is building temporary jigs out of scrap material for my drill press to improve consistency of location, and drilling 1/64" undersize and finishing the holes with a hand reamer.
Attachment:
File comment: Crude, but effective, temporary, drill press jig out of scrap.
DSC05649.JPG
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Attachment:
File comment: Consistent set of rough brackets.
DSC05651.JPG
DSC05651.JPG [ 140.92 KiB | Viewed 828 times ]

Attachment:
File comment: Hand ream undersized holes to finished 1/2"
DSC05647.JPG
DSC05647.JPG [ 138.17 KiB | Viewed 828 times ]

Attachment:
File comment: It's definitely a better result than just drilling using a 1/2" drill bit, but takes more time.
DSC05650.JPG
DSC05650.JPG [ 138.24 KiB | Viewed 828 times ]

Attachment:
File comment: I print a 1:1 drawing of the bracket profile using my HP printer (surprisingly accurate) and then trace it out using a sharpie and a scratch awl.
DSC05653.JPG
DSC05653.JPG [ 138.3 KiB | Viewed 828 times ]

Attachment:
File comment: The final shapes are finished up with a bandsaw, burrs in a Dremel tool, hand files plus emery cloth and sandpaper. It yielded a nice little family of finished brackets.

The two upper rear A-arm brackets will require some additional work due to their unique mounting location.

DSC05660.JPG
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The 2"x3"x0.120" RHS does provide a pretty close fit for the poly bushings and compression tubes. There is room for a little movement of the bushings on the tubes, but too little to shim with even a real thin washer, so it's to be lived with, I think.
Attachment:
File comment: Poly bushing and compression tubes. This SAE bolt was just used for tryout. I may have to use AN style bolts to get more smooth shank inside the compression tubes.
DSC05655.JPG
DSC05655.JPG [ 130.97 KiB | Viewed 828 times ]

Attachment:
File comment: Generally, a nice fit of the bushing withing the finished brackets.
DSC05656.JPG
DSC05656.JPG [ 141.98 KiB | Viewed 828 times ]

All-in-all, some progress was made.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: March 6, 2021, 11:23 pm 
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I had my first chance to do a simple trial fit of the lower suspension brackets this afternoon. There are some things I like about the results, and some things I don't like.

For the 6 brackets mounted off the lower frame rails, I modeled multiple versions in CAD as I fiddled with getting the suspension geometry as optimal as possible. Unfortunately, based on what was revealed when trialed, I believe I mistakenly fabricated an intermediate version of the brackets, not my final one.

The effect of that is to put the lower wishbone "axle" further away from the centerline than expected, or needed. I'll check all my work tomorrow and see where I went wrong. I'll need to remake those 6 brackets, trial fit them, and then go back to my simulation software and make sure the reality is what's being modeled there, and see how the most critical suspension parameters behave if changes need be made.
Attachment:
File comment: Trial placement of lower brackets on the driver's side. It's not a precise as a jig (which I'll build for installation), but it's pretty accurate, and lets me see how well they'll work generally.
DSC05661.JPG
DSC05661.JPG [ 137.67 KiB | Viewed 808 times ]

Attachment:
File comment: A better perspective perhaps? I expect to move the holes closer to the front frame, which will permit the rear bracket to be placed further inboard - a good thing for welding and trimming to final arrangement.
DSC05662.JPG
DSC05662.JPG [ 146.4 KiB | Viewed 808 times ]

Here's the part I don't care for, and may improve in some way. The Haynes Roadster book indicates that "packing" of the front frame brackets will be necessary. They're talking about the slight gap at the front of the brackets due to the slight twist in members FF2 and FF3 to make fabrication of the front frame practical. I never liked that, and had planned to do things differently some how. Seeing it in steel reminds me of that desire, and I may create a flat 14 gauge plate that goes from the front faces of FF2and FF3 to the suspension bracket instead.
Attachment:
File comment: Gap which the V2 "Book" expects one to pack with a shim before final welding.
DSC05663.JPG
DSC05663.JPG [ 134.25 KiB | Viewed 808 times ]

However, all said and done, it is significant to be closing in on a finish of these brackets, so I can get the A-arms build, and get this thing on its wheels, and on the floor.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: March 10, 2021, 7:33 pm 
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While this looks like the same boring bracket photo, it's actually the new ones I fab'ed yesterday. I did create the initial ones based on an older version of the CAD model. My bad.

The new ones did improve fit. The reason, I'm trying everything is to discover where things will work best in the chassis, rather than in my perfect 3D CAD space, which may not match the actual fabricated chassis perfectly.

That allows me to get actual measurements, and the change the suspension simulation software to see if the best-fit, real-life parameters will attain my design goal.
Attachment:
File comment: Newly revised lower, front brackets.
New Bracket 1.JPG
New Bracket 1.JPG [ 136.12 KiB | Viewed 749 times ]

Attachment:
File comment: Measuring revised pivot points.
New Bracket 2.JPG
New Bracket 2.JPG [ 95.07 KiB | Viewed 749 times ]


In this case, the new brackets moved the pivot points up 3/16" and out 1/4" from the theoretical fit. That was sufficient to change the front roll center from 1.10" to 1.76" off the ground. My design goal is 1" and 1.10" is close enough for me.

By moving the upper pivots up 1/4" (in the software) to compensate that put the roll center down at 1.16", again, close enough for me. Now, I'll have to see where the real-life upper pivots can actually fit well, and see what the real-life measurements of same yield by running a dynamic simulation, looking at all the usual factors such as toe-in, camber, caster, Ackerman, etc., etc.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: March 11, 2021, 12:25 pm 
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Are you planning to use rod ends, or at least separate pivots? If so, there's no need to line up the pivot axis precisely (and when welded, probably will not). Said another way, those brackets could be produced to have the bolts vertical and it would make no difference to the geometry.

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PostPosted: March 11, 2021, 3:38 pm 
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@KB58

Hi Kurt,

Yes, they'll have seperate pivots. I'm using these poly bushings and sleeves on all 8 chassis-side pivots, but with a better suited bolt - more shank, fewer threads. The 1/2" bar is just being used for placement.
Attachment:
File comment: Used on all 8 chassis-side pivot points.
Poly Bushing & Sleeve.jpg
Poly Bushing & Sleeve.jpg [ 44.29 KiB | Viewed 713 times ]


I'd be interested in you opinion on required accuracy in placement of them. Besides the suspension geometry, I'm focusing on having the virtual pivot axis being parallel to the chassis centerline and to the roadway (no anti-dive used) and both sides equidistant from the centerline when viewed from the front. I understand a good alignment job should be accurate to 1/32" (~0.8 mm). Since the lower A-arms will be fixed once fabricated, I'd like them to be as accurate as possible. For a garage shop situation like I'm in, 1 mm of accuracy is pretty hard to achieve.

What did you shoot for in your two designs?

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: March 11, 2021, 3:57 pm 
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Ah, bushings, so non-adjustable... rod ends hide a multitude of fabrication sins... Regardless, what I said still applies, that there doesn't need to be a precise straight-line shot between the two. The suspension's inboard pivot points just need to be set where your math says for them to be.

That said, I'm being rather hypocritical, since I recommend doing exactly what you're planning, though for different reasons. In my case, it's simply to place the brackets so that you can take your hands off them in order to tack them into position. Whether the rod can still be run through all four holes after the fact is unimportant, which is good, since heat distortion will likely cause the rod to jam.

Regarding you question about accuracy in placement, there is no black-and-white answer. As the placements drift away from what you specified, the car's handling will change "some" amount. Whether that amount is detectable is a subjective thing. What I did in order to try and eliminate variables was to mount the brackets off the built table, not the chassis. That way, any inaccuracy in the chassis can't mess up bracket placement. Or that's the theory...

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PostPosted: March 11, 2021, 11:03 pm 
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@KB58

Thanks for the input, Kurt. Using the build table rather than building a jig, at least for the lower ones, may be more practical. I'll have to take a look at that.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: March 11, 2021, 11:18 pm 
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KB58 wrote:
Ah, bushings, so non-adjustable... rod ends hide a multitude of fabrication sins... Regardless, what I said still applies, that there doesn't need to be a precise straight-line shot between the two.

The compliance in the bushing will allow for a bit of misalignment between the axis of the 2 bushings, but you should still try and align the axis of the 2 bushings as best you can to avoid binding. As an extreme example, look at the diagram below. With the axis of the 2 bushings misaligned as shown, when the suspension tries to travel upward, the axis of one bushing will try and move the lower ball joint upward, and toward the rear of the car, while the axis of the other bushing will try and move the lower ball joint upward but towards the front of the car. If the bushings were solid metal with no compliance, the control arm would bind when trying to move.

The method of running the steel rod through the front and rear brackets is a good way to get the axis closely aligned.


Attachments:
Lower Wishbone.jpg
Lower Wishbone.jpg [ 29.96 KiB | Viewed 690 times ]

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PostPosted: March 12, 2021, 1:41 am 
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If your figure is a top view, it’ll work just fine with no binding.

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PostPosted: March 12, 2021, 3:05 am 
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KB58 wrote:
If your figure is a top view, it’ll work just fine with no binding.

It is a top view. If I widen the angle between the wishbone legs even further, as shown below, does that change your mind? Think about the arc that tube 1 wants to travel in, and the arc that tube 2 wants to travel in, assuming that the bushings have zero compliance. The ends of tube 1 and tube 2 (points A and B) will want to move away from each other, which they can't do if they are both welded to the same ball joint mount.


Attachments:
Extreme Lower Wishbone.jpg
Extreme Lower Wishbone.jpg [ 21.81 KiB | Viewed 672 times ]

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PostPosted: March 12, 2021, 10:02 am 
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To that extreme, yes, I agree that it won't work. The previous example will to some degree, because the bushings do distort. On a related point, because of the distortion, the tire will never be exactly where the suspension software says it'll be, making the goal of getting the desired suspension geometry "exactly right" less important.

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Last edited by KB58 on March 12, 2021, 3:27 pm, edited 1 time in total.

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PostPosted: March 12, 2021, 12:07 pm 
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Soft OE style bushings are designed to non-axially deflect much more than cylindrical polyurethane bushings. Poly bushings will deflect a bit, but if the misalignment is more than slight they'll largely just bind even as shown in the first example. Additionally, it will rapidly lead to some type of failure of the bushing, mount, or arm due to the associated stresses being applied. Just ask anybody with a Fox/SN95/NE Mustang who has run poly bushings, rather than OE or spherical, on the upper (triangulation) links.

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PostPosted: March 12, 2021, 8:51 pm 
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> "packing" of the front frame brackets will be necessary. They're talking about the slight gap at the front of the brackets due to the slight twist in members
----
That falls into the "ugly, but seems to work OK in practice" zone.

An alternative is to use the hacksaw and Dremel or angle grinder and cut a triangular divot out of the face of the frame tube and sink the bracket down into the tube on one side so it lines up with the other bracket.


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PostPosted: March 12, 2021, 10:18 pm 
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Just FYI, the red poly bushings (from Energy Suspension) do not give much. They're pretty darn solid. You can't move them with your fingernail, for example. I haven't looked up any materials figures from the vendor. I do have some Delrin I was working with, doing some machined pieces. They are not as hard as Delrin, but much harder than the factory Mustang bushings.

It's just my nature to try and get things a close as possible, but it's good to hear they can be off somewhat (e.g., welding distortion) and not guarantee a problem. That definitely makes me feel better.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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