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PostPosted: September 28, 2012, 9:23 pm 
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I managed to get decent results from my Harbor Freight roller by using the weld seam of the ERW tube as a reference and keeping it in line with the top edge of the first roller. It got really tricky when the 20' length started to stick way up in the sky. I also went pretty slow, 1/8 of a turn or less on the top screw each time.


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PostPosted: October 1, 2012, 10:28 pm 
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BARBAPAPA wrote:
BTW, a Porsche 911 steering rack is about 22" and adjustable more or less by screwed in inner mounts, approx 1-2" range Iwould guess. Mine is set to 22" and the mounts seem to be just inward of mid range, I machined some pieces that allow heim joints instead of the rubber bush. You could also use a turbo rack that uses a spherical type inner mount.
The 911 rack is centered which has some benefits.


Do you know which year? Also do you know what the lock to lock is?? I am hoping that not having power steering wont be a nightmare later once the car is moving.

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PostPosted: October 2, 2012, 8:01 am 
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JL1 wrote:
I needed a rack with the same requirements as you. I found online that a '95-'97 Geo Metro rack is rear steer and about 23.5" between pivots. I just go mine yesterday and haven't taken the boots off to get an accurate measurement yet. If I remember correctly, it has about 5in travel but can't remember the numbers of turns it took to get there. I'll post more details later after I measure it.

UPDATE: The Metro rack is 3.7 turns lock to lock with 5.5in of travel.

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PostPosted: October 2, 2012, 8:58 am 
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JL1 wrote:
JL1 wrote:
I needed a rack with the same requirements as you. I found online that a '95-'97 Geo Metro rack is rear steer and about 23.5" between pivots. I just go mine yesterday and haven't taken the boots off to get an accurate measurement yet. If I remember correctly, it has about 5in travel but can't remember the numbers of turns it took to get there. I'll post more details later after I measure it.

UPDATE: The Metro rack is 3.7 turns lock to lock with 5.5in of travel.


SO that would make it 11:1 ratio then?? I don't know if my math is right.

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PostPosted: October 3, 2012, 2:50 pm 
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Finished machining all the upright parts (except steering arm and cv eliminator) and started on the fixture for the front control arms. The machined upright parts will be going out with a batch of stuff here at work that we have for a hard black anno coating. Once the control arms are made, i will need to have them powder coated and then I have to ream the holes so that the bearings can be pressed in and staked.

Attachment:
2012-10-02 06.39.08.jpg


Attachment:
Welding fixture.jpg


I was able to get a steering rack that was 18.75 in, 4in travel and 2.66 lock to lock. The good thing is that I can add spacers into the rack to get the tie rods out to the 22" i need. The bad thing is i need to switch some things around since it is a front steer design.

The other thing I need to figure out is how to calculate Ackerman steering on a Front steer car


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PostPosted: October 4, 2012, 9:51 am 
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So now with the rack in the front.. how do I calculate ackerman in to the steering arm design? It looks like you cannot just draw a line from the steering arm through the center KPI and then to the rear axis... or is that how its done??

The rack in the below is not in the right place for the time being. Just there for reference.

Attachment:
Front steer ackerman.jpg


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PostPosted: October 4, 2012, 11:11 am 
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The rack is close to where it should be, ideally. I think you land up with trying to get the steering arm pivot to be on the same line as the rear steer pivot to the virtual intersection of the left and right side. So those little steering arms would bend the other way towards the brake disk.

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PostPosted: October 4, 2012, 12:26 pm 
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horizenjob wrote:
The rack is close to where it should be, ideally. I think you land up with trying to get the steering arm pivot to be on the same line as the rear steer pivot to the virtual intersection of the left and right side. So those little steering arms would bend the other way towards the brake disk.


First thanks and that's what I was thinking as well. I cant reach the ideal Ackerman point without hitting the rotor.


Attachment:
Ackerman.jpg



I think i may need to do like the At-om does and bolt a rod end to the upright directly with no steer arm. Any issues with this? I have 55° with this so it looks like steering out to be fine.

Attachment:
Ackerman Spherical.jpg


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PostPosted: October 4, 2012, 12:53 pm 
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Woodward Precision Power Steering company has an excellent article on ackermann and bump steer.

http://woodwardsteering.com/images/cat0 ... 064-79.pdf Bump steer at pg 7 and ackermann at pg 10.

The main concern is the angle between the steering arm and the tie rod. Front steer has an angle less than 90 degrees and rear steer the angle is greater than 90 degrees. Moving the rack rearward in a front steer vehicle will increase ackermann. This may allow decent ackermann without hitting the rotor with the outer tierod.

Actual steering ratio must also take into account the length of the steering arm.

Hope this helps. JMTC JMR

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PostPosted: October 5, 2012, 7:03 am 
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I would suggest that you look at a desgin that attaches the steering arm to the inboard machined face of the spindle. That gives you a little more clearance to the disc and wheel plus it appears that the arc will be closer to duplicating control arm travel. It will also give you less bump steer the with the short steering rack and longer steering arm would have a better ratio. Dave W


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PostPosted: October 5, 2012, 8:41 am 
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You are a brave man to machine your uprights before you have the design done. :cheers:

Two things I think I see, 1st) By my numbers, you have only 9 degrees of steering if you mount the heim directly to the front of the upright. Maybe I'm missing something. And your steering will be dangerously quick.

2nd) your earlier front view shows you will have bump steer. The angle of the steering link is wrong. (I think). If you decide to continue with your steering mount, moving the line upwards where it should be might give you slightly more space to work with. You might begin to fall inside the brake disk hat, giving you more clearance?

Attachment:
steering angle.JPG

Attachment:
new steering link.JPG


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PostPosted: October 8, 2012, 8:54 am 
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davew wrote:
I would suggest that you look at a desgin that attaches the steering arm to the inboard machined face of the spindle. That gives you a little more clearance to the disc and wheel plus it appears that the arc will be closer to duplicating control arm travel. It will also give you less bump steer the with the short steering rack and longer steering arm would have a better ratio. Dave W



I am not quite following that.. any way you can clarify?

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PostPosted: October 8, 2012, 9:00 am 
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rx7locost wrote:
You are a brave man to machine your uprights before you have the design done. :cheers:

Two things I think I see, 1st) By my numbers, you have only 9 degrees of steering if you mount the heim directly to the front of the upright. Maybe I'm missing something. And your steering will be dangerously quick.

2nd) your earlier front view shows you will have bump steer. The angle of the steering link is wrong. (I think). If you decide to continue with your steering mount, moving the line upwards where it should be might give you slightly more space to work with. You might begin to fall inside the brake disk hat, giving you more clearance?

Attachment:
steering angle.JPG

Attachment:
new steering link.JPG


I am a very brave (stupid) man! I made the design adaptable to some extent so that I could move things around as needed but yes there is some situations where it could have not gone to plan.

1) yeah I am looking a that now.
2) That was corrected a bit back but I didn't re-post any thing that showed it. I tired moving the ball joint originally into the hat space but it was still to big but maybe it will work with a spherical end.

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PostPosted: October 8, 2012, 11:02 pm 
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So there is no situation that solves the tie rod bump steer position and ackerman. I think the best things to do is to get the outer tie rod joint in the right location for bump steer then see how ackerman will affect the car and move the rack if need be.

The rod end that works for full steer and bump is a high misalignment 3/8.

Attachment:
Ackerman.jpg


Attachment:
Bump steer.jpg


additionally the tir rod arm is inline with the rack at full lock.

Attachment:
full lock.jpg


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PostPosted: October 9, 2012, 3:25 pm 
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So I am in the process of trying to get the driver lower in the vehicle but the only thing i can think of is tilting the seat back (which in turn rasies the front of the seat on fixed backs) or using a reclining seat which is not race approved unless I fix the rear to the chassis. Below is a pic with the seat in normal position and with it in a more reclined position.

I would prefer to be a little more tucked down but that may raise my knees too high and I am not sure if you can tilt a seat that much. I know Ar-i-el makes custom seats to do this in the A-tom.

Yes I will adjust the roll bar height once I get the seat layout closer and I probably wont even make them until an actual seat is in the car.

Attachment:
Untitled.jpg


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