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Learning how to build Lotus Seven replicas...together!
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PostPosted: September 23, 2017, 9:30 pm 
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Location: Pemberton, BC
Lonnie,
I wouldn't loose too much sleep over that. Although it is very desirable to have a progressive pedal, I very much doubt that many people can feel the difference of the reduced leverage. Mario, Michael and Rick Mears would know, but most of us wouldn't. As long as the majority of your pedal travel is progressive, the final bit won't make a lot of difference. At that point, you are pushing so hard, your heels will smoke.
https://www.gaskrank.tv/tv/rennstrecken ... ualmen.htm
Your problem will easily be fixed with tilting the pedal forward (or more appropriately backward towards the driver), and adjusting your pedal surface angle.
You'll be fine. :cheers:

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My build log:
viewtopic.php?f=35&t=14520&start=0
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PostPosted: September 24, 2017, 7:02 pm 
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mgkluft wrote:
Lonnie,
. . . Your problem will easily be fixed with tilting the pedal forward (or more appropriately backward towards the driver), and adjusting your pedal surface angle. . .


There's definitely something to both of those changes, Martin, but there's a little more as well.

It takes a little time to do the analysis on some of these things, but I like to feel confident I've made a good, reasoned choice. Most people wouldn't bother much further than a good guess, and that's OK if you're comfy with doing so. I'm willing to push it a little further to increase my confidence level. It's not that hard if you're willing to put a little time into things.

I took a print out of my pedal design, full size. If you have a modern dot matrix or laser printer, these printouts are very accurate. That I glued to some cardboard. You don't even have to do that to observe gross behavior, but I wanted to see how much the pedal moved forward at the pedal pad, and what the angle of the pedal pad would make with my shoe and the "floorboard." You could just draw out a simple vertical bar shape and carefully mark the distances between things. You'd loose visual information like the angle of the pedal pad, however. Using a small finishing nail, I attached it to a small piece of plywood through the pivot hole center mark.
Attachment:
File comment: Accurate print out glued to carboard. Nails were used at the pivot points.
Cardboard Brake Pedal-Small.jpg
Cardboard Brake Pedal-Small.jpg [ 25.69 KiB | Viewed 397 times ]


I cut out a rectangular piece of carboard 4-1/2" long by 5/16" wide to act as the plunger rod. With the card plunger stand-in, I put a brad through it into the center of the balance bar pivot point (the center of the tube/rod combo in real life) on my printout and let the loose end ride atop a small, thin, piece of 1/8" thick wood trim that is flat and square that the plunger rod slid along. So the block of wood stood in for the end of the master cylinder, but the cardboard rod was not restrained.

With the rod level at the start, I just rotated the pedal and could easily observe through tick marks on the rod and plywood how far the rod moved forward as the pedal turned. It was also easy to see when the majority of the pedal movement started to go downward as the rigid card rod started to rotate up off the wood block and you could see the pedal end sink below horizontal. I got about 7/16" (+/-) 1/16" of travel before the "over center" behavior started. That's less than half the full travel of the master cylinder. I don't feel like that's enough for safety.

As you can see from the image above, I started moving the rod up the pedal, increasing the distance between the pedal pivot point and the rod pivot point. I move the block of wood each time so that the cardboard rod was level at the start. This was just a "quick and dirty" way of measuring how much more the rod would move forward into the master cylinder before "over center" happened. That gave me a good idea of the target distance I wanted. Given that the master cylinder control rod height is fixed by the chassis (unless I want to bring the master cylinders inside the cabin, which I don't) and I need to keep the brake pad height inside a certain range, that limits my choices too.

Using the free Calc program from Open Office, I set up a simple spreadsheet to try out some different configurations:
Attachment:
File comment: Simple, 20-minute spreadsheet in Open Office Calc
Distances Screenshot-Small.jpg
Distances Screenshot-Small.jpg [ 118.23 KiB | Viewed 397 times ]


Wanting to keep the pedal ratio at least close to 5:1 for my wife, but realizing I'd have to increase the pedal height some, it looked like a pedal height of 8-1/2" was a good choice. I'd always planned on a heel rest anyway. If I can make an adjustable one, and give my wife an extra "lift" of 1" with that, we'll be effectively back to a 7-1/2" pedal height. Coincidentally, 8-1/2" is just about ideal for me.

I just re-entered the pivot height, increasing it by 1/16" each time and looked at the output:
Attachment:
File comment: Last iteration with 8-1/2" pedal height
Final-Distances.jpg
Final-Distances.jpg [ 50.73 KiB | Viewed 397 times ]


From that I concluded that using either of the 2 circled entries would give a good, all-around solution: significantly more near-linear rod movement before "over center" is reached; a decent pedal ratio; and a pedal height I could work with using a little creativity on the heel rest. The main thing is that I feel I know what is going to happen and that I've balanced out the factors reasonably given the real-world constraints of my build.

Back to martin's points quoted above. I'm rotating the pedal pad downward to increase shoe/pedal contact as the pedal nears the over-center point. I won't be increasing the distance back towards the driver, as the face of the pedal is just where it needs to be based on our heel location and the angle our feet can make comfortably. We developed those measurements from mock-up, wooden pedals we did some months ago when the chassis was on blocks and it had a seat (my old Mustang seat cushions) and floorboards using plywood clamped in place.

Anyway, V3 of the pedal design will be done with much better information and assumptions.

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 27, 2017, 10:56 pm 
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Location: Carlsbad, California, USA
To finish my pedal bracket setup, I needed to finalize my clutch design. I had originally planned to keep and modify the Mustang cable clutch. However, when I started to look at the engineering involved, and the space it would take up, I started to investigate using a hydraulic clutch instead. Cluth conversions are pretty expensive, but I found a nice, simple one from Modern Driveline.

It mounts externally on the bellhousing. You need to drill a couple bolt holes in the bellhousing, but that's not real hard. Below are some photos of their example installation, not ones of my build.
Attachment:
File comment: Laying out the holes with the supplied bracket.
Modern-Driveline-3.8L-Clutch-Slave-Kit-#4.jpg
Modern-Driveline-3.8L-Clutch-Slave-Kit-#4.jpg [ 13.16 KiB | Viewed 365 times ]

Attachment:
Modern-Driveline-3.8L-Clutch-Slave-Kit-#5.jpg
Modern-Driveline-3.8L-Clutch-Slave-Kit-#5.jpg [ 12.75 KiB | Viewed 365 times ]

Attachment:
File comment: Bracket and slave in place.
Modern-Driveline-3.8L-Clutch-Slave-Kit-#2.jpg
Modern-Driveline-3.8L-Clutch-Slave-Kit-#2.jpg [ 96.95 KiB | Viewed 365 times ]


The required master cylinder is slightly different that the two Wilwood "Shortys" I'm using for the brake MCs, but that's OK. It's still very compact and has the same flange size and mounting holes. It's the classic Girling style with a built in reservoir. It does have a shorted rod that the other two, so that will have to be accounted for. But, all-in-all, pretty simple compared to a mechanical layout with cable.
Attachment:
File comment: Matching MC for clutch slave
Wilwood 260-6579 No Markup.jpg
Wilwood 260-6579 No Markup.jpg [ 10.67 KiB | Viewed 365 times ]


So, on with finishing the design.

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: November 11, 2017, 9:08 am 
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Lonnie, I am looking at your pedal design and cads, and mock ups,(your like the mock up guru). Your patients level is off the chart. There is no Forking way I could do this to the level that you design parts. WOW!.
Stuff is looking really nice by the way. I just had to tell you that. Have a good weekend :D

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My build : viewtopic.php?f=35&t=17160


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PostPosted: November 13, 2017, 11:51 am 
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Hi Steve,

Thank you for the nice compliments and for giving me a nice "Atta Boy." I actually enjoy the whole process. There have been a number of times that creating a design, and then making a cardboard or foamcore mock-up for it, has motivated me to go back and do a much better job. It's a nice way to reason things out on the car with out the time and expense of fabricating something in metal. There have been a couple of times where it saved me from spoiling some large and expensive pieces of metal too. :roll:

I've been working almost full time on a big community project lately, and I'm getting real anxious to get back on the car again. It will probably be another 2-3 weeks before that's possible for me. I've been vicariously enjoying all the progress you've been making.

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: November 16, 2017, 1:01 am 
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Lonnie, Is that one solid shaft from the slave piston all the way past the clutch fork? It is kind of hard to tell from the pics.

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PostPosted: November 23, 2017, 1:06 pm 
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rx7locost wrote:
Lonnie, Is that one solid shaft from the slave piston all the way past the clutch fork? It is kind of hard to tell from the pics.


Hi Warren,

Sorry for the delayed response. I've been on a sort of sabbatical (I think that's Greek for unexpectedly distracted) from Locost stuff for a few weeks and not checking in here.

Yes, it's all one shaft. They have a few different kits for different years and bellhousings and that part varies with the corresponding lever arm you have for your model year.

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: December 10, 2017, 3:57 pm 
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As an aside, when Hyundai introduced the 2005 Tucson, I went to technical training on it. They had found people in emergency stops were not pressing the brake hard enough, so they went with an over center effect for the mast cyl/booster. Might put you into the ABS, but you stopped faster (pro driver's excepted, one supposes).


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