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PostPosted: September 18, 2017, 2:48 pm 
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Location: Carlsbad, California, USA
I'm looking for some feedback on the strength of the design for my version 1 (well probably more like V 0.85) brake pedal setup. As shown above in my build log, I'm using the Wilwood balance bar kit. It's a pretty heavy duty unit. Here's a photo from their website. I can tell you it's been improved since this photo was taken. The main tube that holds the spherical bearing unit is much better steel than the photo, and it's very nicely machined now. It's wall thickness is slightly over 1/8". The clevis's and pins are much better too. Here's the old unit:
Attachment:
File comment: Older version of Wilwood balance bar kit.
Wilwood-Balance-Bar-Sm.jpg
Wilwood-Balance-Bar-Sm.jpg [ 12.89 KiB | Viewed 1016 times ]

My pedal construction looks like this:
Attachment:
Brake Pedal 1.jpg
Brake Pedal 1.jpg [ 18.89 KiB | Viewed 1016 times ]

Attachment:
Brake Pedal 2.jpg
Brake Pedal 2.jpg [ 19.25 KiB | Viewed 1016 times ]

The sides are 14 gauge cold rolled steel plate. The steel cross tubes are 1/2" x 16 gauge (2 places) and 3/8" x 16 gauge at top. I show the pedal pad as 14 gauge too, but that probably wont happen as I don't have a way to roll 14 gauge. Most likely, it will be 19 or 20 gauge with stiffening ribs put into it with a bead roller, and maybe doubled and welded if I don't think that is strong enough after making it.
The balance bar will make up a big portion of the pedal. The pedal proper (above) will be welded onto the 1-1/4" x 1/8"+ tube. An axis of rotation for the unit will be created using a 1/8" flange welded to the bottom of the tube and drilled to suit. It looks like this:
Attachment:
File comment: Flange of 1/8" C/R steel
Brake Pedal Attachment Flange.jpg
Brake Pedal Attachment Flange.jpg [ 14.58 KiB | Viewed 1016 times ]

Putting all the above together into a functioning pedal, it looks like this:
Attachment:
File comment: All pedal parts together. Flange and side plates welded to balancer tube.
Pedal+Flange+Balancer.jpg
Pedal+Flange+Balancer.jpg [ 32 KiB | Viewed 1016 times ]

When I started out, I had a vision of a kind of fancy pedal box structure made up of 16- or 14-gauge plate. However, for simplicity, I wanted to work out all the geometry with a simple prototype unit. For that, I choose 1-1/2" x 1-1/2" x 1/8" angle, which I had a model for, and it's a pretty simple platform to start modeling with.

Subsequently, I'm asking myself, "Why not use the angle for real?" There's only one really good reason not to - aesthetics. The angle is just an unattractive, fairly crude structural piece, but will probably work fine. In the model(s) below, I show the angle unbraced, but in a production piece, it would be secured to the chassis side rails and the 16 gauge steel plate undertray. So, in spite of what you see below, assume the angle is securely attached, and is stable.
Attachment:
Pedal in Context - Small.jpg
Pedal in Context - Small.jpg [ 49.75 KiB | Viewed 1016 times ]

Attachment:
Pedal in Context + Mount - Small.jpg
Pedal in Context + Mount - Small.jpg [ 39.73 KiB | Viewed 1016 times ]

There are some factors that forced me to make certain choices. I could only move some components (the master cylinders, for example) a certain amount, and that was it. To get the pedal ratio I wanted (5.5:1), it further constrained my geometry. I can't move things but small fractions of an inch from where they are now. Here's the setup:
Attachment:
File comment: Geometric constraints shown here.
Pedal Ratios Graphic.jpg
Pedal Ratios Graphic.jpg [ 95.05 KiB | Viewed 1016 times ]


My real questions relates to the operation of the pedal itself. Does anyone see anything that just screams out "failure" in this picture? My main concern is the area of the pedal flange and the 1/8" mounting plates it attaches to. I could use 3/16" plate, and increase the depth of the flange down into the space between them to give more lateral strength, for example. It would be a tight fit, however. I had to downsize to a 1/4" bolt as the pivot for the pedal flange. The geometry is too tight to use 5/16" or 3/8" bolts. Th huge size of the 1-1/4" balance bar tube limits things. However, I don't see much of a chance for a 1/4", grade 8 bolt to fail here.

What do you think? Do you see an obvious source of difficulties? Constructive input is sought and would be appreciated.

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: September 18, 2017, 2:53 pm 
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Open mouth, insert foot! I see a basic mistake in my layout. The ratio isn't as advertised, but ignore that. Please look at the structural part. I'll fix the ratio issue. The 5.34" measurement should be to the (lower down) pedal pivot point.

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: September 18, 2017, 9:28 pm 
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Location: Fort Worth, TX
That tab at the bottom looks scary. You'll never press perfectly on the center of the pedal so there will always be a side load.

I'd also box in the entire pedal just for additional strength. You can probably make the whole thing out of thinner sheet if its boxed and it'll weigh less and be stronger and stiffer. Here is how I did the pedals for the Sprite from 20 gauge steel:
download/file.php?id=34654&mode=view
download/file.php?id=34917&mode=view
download/file.php?id=34918&mode=view

You will also want some sort of bushing and something to keep the bolt from spinning (a small anti-rotation tab made from sheet metal will work.)

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PostPosted: September 18, 2017, 10:20 pm 
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Lonnie,
I'm with Andrew, that bottom tab is scary. What I dislike the most, is the lack of bearing surface. With a 1/4in bolt, I think you are asking for trouble. I'll try to explain, what I can't draw :BH:
I would make the bottom tab from 1" x 0.125 sq tubing, welded to your angle (which looks to be fine), and then weld in a DOM tube (5/16 to 3/8 ID) for your "bearing" bolt. Then I would make two of your bottom tabs, straddling the tube from the outside. That should provide more support to prevent the pedal from rocking sideways, and increase your bearing support area. I would make those two tabs from 3/16 cold rolled, and if there is room, I'd even go for 1/4. TIG would be my choice to keep the distortion down, but even more so, ensure proper penetration. I hope this makes sense.
I sat in the hairpin at the Long Beach GP in 1980, when Clay Regazzoni's brake pedal snapped off. It was not a pretty sight.

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My build log:
viewtopic.php?f=35&t=14520&start=0
My build video:
https://vimeo.com/143524140


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PostPosted: September 18, 2017, 10:51 pm 
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@a.moore
@mgkluft

Andrew, Martin;

Thanks for the analysis and the ideas. I'll go through both your ideas/suggestions in detail tomorrow afternoon when I have time to try out some new solutions.

It's interesting, but intuitively, I felt the bottom tab might be a weak link. Thanks for the "snapping brake pedal" motivational too, Martin.

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: September 19, 2017, 10:32 am 
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Location: Irkutsk, Russia
Let me give some advice.
Most likely you read this book? https://www.amazon.com/Brake-Handbook-F ... 0895862328
So they write that efforts at a very large pedal and pedal should be very stiff to withstand them. The lower mount of the pedal to the floor will not work it just bent torque to the left or right.
And about the attitude of 5.5/1 is great, but! The pedal is balanced with the diameter of the piston of the brake master cylinder and brake caliper piston? It may happen that the pedal travel would be huge.


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PostPosted: September 20, 2017, 5:08 pm 
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marafonets wrote:
Let me give some advice.
Most likely you read this book? https://www.amazon.com/Brake-Handbook-F ... 0895862328
So they write that efforts at a very large pedal and pedal should be very stiff to withstand them. The lower mount of the pedal to the floor will not work it just bent torque to the left or right.
And about the attitude of 5.5/1 is great, but! The pedal is balanced with the diameter of the piston of the brake master cylinder and brake caliper piston? It may happen that the pedal travel would be huge.


Yes, that's the reference I used. Along with it, I used a Microsoft Excel spread sheet codifying his procedure that was made up by a member here, and then enhanced further by another member. I'm pretty confident in the pedal size (it has to to with balancing between the needs of two different drivers), but thank you for mentioning it.

The Wilwood "Shorty" master cylinders I'm using (http://www.wilwood.com/MasterCylinders/ ... o%20Outlet) have a very short maximum throw of 1.12" (~28.5 mm). I don't think I'll even need all of that, but we'll see. They make a variety of piston diameters and I'll be able to go larger or smaller on piston size if need be.

Thanks for your response.

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: September 20, 2017, 6:48 pm 
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I would extend the side pieces below the hole for the balance bar and pass a sleeve between them for the pivot (welding the sleeve to the side plates).

The forces from the balance bar will never be centered and impart a twisting force on the single tab.

Ideally you may want to extend the pivot sleeve to the width of the M/C's C/L to best stabilize the pedal.

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PostPosted: September 21, 2017, 12:10 pm 
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Bent Wrench wrote:
I would extend the side pieces below the hole for the balance bar and pass a sleeve between them for the pivot (welding the sleeve to the side plates).

The forces from the balance bar will never be centered and impart a twisting force on the single tab.

Ideally you may want to extend the pivot sleeve to the width of the M/C's C/L to best stabilize the pedal.


I think you're suggesting what I was working out in my head last night. Looking at what I posted, I really know better! I usually do better work.

I think I'm just getting impatient to get some major milestones completed like the pedal box, steering column, dash hoop, etc. I seem to put a lot of time into things, but don't move very far off dead center. Primarily, I've wanted to complete as much design and welding as possible before I put the chassis back on the build table to do the suspension and rear structure of the car. As an amateur welder, having the rotisserie available, so I don't have to weld overhead or vertical is a really big benefit. I'm feeling the need to move on, however.

Thanks for the suggestions. They're much appreciated.

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: September 22, 2017, 8:59 pm 
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Well, here's version 2 of my brake pedal. I've incorporated some of your suggestions, but also focused on materials I have on hand, and as importantly, shapes and parts I can actually fabricate with with the tools I have in my shop.

I increased the side plates from 14 gauge to 12 gauge, which is close to 1/8" material. I've used the same basic, non-boxed architecture as fabricating out of thin material leads to problems with weld-up over distance using my MIG setup. I've made the cross tubes bigger, so I can weld on the outside of the side plates, which will be a lot easier. I'll likely have a professional TIG guy do the machined balance bar. I'll just tack it in place.

The pivot bolt runs inside a 3/8"x~0.0625" tube, which gives excellent fit and very little slop.

The base of the mounts are outside the sides of the pedal for stability, and taking lateral loads on the pedal.

I reshaped the pedal itself. I'm going to use 19 gauge sheet for the pedal pad and bead roll it, which I can do. When I did the gas pedal in 20 gauge with a 3/8" bead in it, it was incredibly stiff. I'll get a even more stiffness with the 19 gauge I have in hand. I can roll it and bead it, even if it has to be done slowly.

Here's the pedal:
Attachment:
File comment: Version 2 of my brake pedal.
Brake Pedal V2.jpg
Brake Pedal V2.jpg [ 61.29 KiB | Viewed 854 times ]


Here's what it looks like in place:
Attachment:
File comment: Version 2 brake pedal in revamped pedal mount structure.
Pedal in Context - V2.jpg
Pedal in Context - V2.jpg [ 56.27 KiB | Viewed 854 times ]


Thanks for all your suggestions.

Cheers,

_________________
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: September 23, 2017, 7:24 am 
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Lonnie - did you calculate for using smaller M/Cs and changing the pedal ratio to something that lowers the pedal pivot closer to the floor? If you lowered it 1/2 to 1", it would improve the strength of the mount and give a lot more clearance. Also, with the short distance between the pivot and the balance bar pivot, it might be sensitive to adjustment so it doesnt go over-center (??)

When you said that you can't mover the M/Cs, i a$$ume that means you can not lower them more, which would obviously be the easiest solution.

If you need the bushing TIG'ed, i would be happy to do it for you. I am not a pro, but a pretty good amateur. I have done a couple of those, too. I am on the wrong coast.....but the price is right :)


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PostPosted: September 23, 2017, 10:40 am 
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Lonnie,
I think that this is a good design and looks to be strong enough. I would furthermore box your bottom mounts, for both pedals. Although they will be welded to the angle, there could still be a bending load induced, because you cannot torque up the pivot bolts. It's overkill for the clutch pedal, but I think it would just tidy it all up.

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My build log:
viewtopic.php?f=35&t=14520&start=0
My build video:
https://vimeo.com/143524140


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PostPosted: September 23, 2017, 10:41 am 
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Sean in CT wrote:
Lonnie - did you calculate for using smaller M/Cs and changing the pedal ratio to something that lowers the pedal pivot closer to the floor? If you lowered it 1/2 to 1", it would improve the strength of the mount and give a lot more clearance. Also, with the short distance between the pivot and the balance bar pivot, it might be sensitive to adjustment so it doesnt go over-center (??)

When you said that you can't mover the M/Cs, i a$$ume that means you can not lower them more, which would obviously be the easiest solution.

If you need the bushing TIG'ed, i would be happy to do it for you. I am not a pro, but a pretty good amateur. I have done a couple of those, too. I am on the wrong coast.....but the price is right :)


Hi Sean,

I tried several combinations of pedal ratios and MC diameters using Puhn's suggested assumptions about level of effort on the pedal. I used the Excel spreadsheet that SeattleTom fixed up from an earlier version by the original author (sorry, I can't remember his name, and thus give him credit) some months back. I'll have to go back and look at the printouts to see which ones I tried. However, the two overall limiting factors for my particular situation are the fixed height of the MC plunger rods (I can't get them lower) and the height of the brake pedal itself. It's just low enough for my wife to drive the car, while being just high enough to work for my big feet. "All design is compromise", is so true, isn't it?
Attachment:
File comment: My toes practically scrape the cross tube.
My Feets.jpg
My Feets.jpg [ 89.48 KiB | Viewed 814 times ]

Attachment:
File comment: She's about 2/3rds of the way up.
Her Feets.jpg
Her Feets.jpg [ 115.77 KiB | Viewed 814 times ]


I needed to keep the level of effort reasonable for her, and I think this setup will do that. That's what the spreadsheet told me way-back-when, anyway. You're right about the short distance between the pivot center and the center of the balance bar tube. There is a danger of "over center" and I need to make up a little cardboard model to check it out graphically. The MC has a maximum throw of 1.12" and I don't think I'll need but half of that, but "never say never" is my watch-phrase. I need to test that out before I build something. Thanks for reminding me. I can raise the pedal height for myself, but it's pretty well maxed out for her.

Thanks also for the TIG offer. It's much appreciated. However, when I actually do build something, I'm one of those guys who wants it done yesterday [LOL]. There's a shop in a neighboring town that promises good work at a reasonable price. I've been looking for a chance to test out their claim. We'll see!

Thanks for your suggestions.

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: September 23, 2017, 10:45 am 
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mgkluft wrote:
Lonnie,
I think that this is a good design and looks to be strong enough. I would furthermore box your bottom mounts, for both pedals. Although they will be welded to the angle, there could still be a bending load induced, because you cannot torque up the pivot bolts. It's overkill for the clutch pedal, but I think it would just tidy it all up.


Thanks for your suggestion, Martin. A little extra metal and weld bead for some additional insurance is OK in my book. It's a street car, not an F1 racer, so ounces don't matter much in my application. Besides, if all other weight-saving measures fail, I could stand to lose 30 pounds [LOL].

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: September 23, 2017, 7:41 pm 
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I did an experiment with a full size mock-up of the V2 pedal profile. Long story short, the about of useful travel before the pedal goes "over center" isn't adequate for safety reasons. I'm going to need a version 3 pedal, and I may have to raise the pedal height to make the pedal ration reasonable, making it awkward for my wife to drive the car. I preemptively explained that to her today and showed her why it was so. I'll do my best to make something workable for her, and something that I can live with too.

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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