Board Logo
Go To Bottom

Printable Version  
[ Total Views: 163128 | Total Replies: 173 | Thread Id: 23861 ]
 Pages:  1  2  3  4  5  6
Author: Subject: Rack and Pinion Steering
MemberBrad
Wolfsburg Elder
*******


No Avatar


Posts: 3764
Threads: 332
Registered: August 24th, 2002
Member Is Offline

Location: SE QLD, Mt Nebo
Theme: UltimaBB Pro Blue ( Default )
Mood: Manx Buggy Building

posted on July 7th, 2004 at 10:43 PM


"Wes,For tie rods I use heim's with adapters and C/molly tube, or 3/4" alloy bar, gun drilled to 5/8". Much stronger than standard and I'm not sure but you could take the material spec sheet to the governing body when you take everything else"

Nice idea but not an option with the rules the way that they are.

The aim of this exercise, besides letting Wes play with his cool computer is to design / develope and make availible a FULLY LEGAL Rack and Pinion Steering setup for VW's in particular Beach Buggies.

After talking to Wes and begining to build the design he has settles upon I am pretty confident it will work and work very well.

Onya Wes :cool:




Brad
Why copy when you can own an original ?
Meyers Manx Australia
MemberFlintstones
Custom Title Time!
*****


Avatar


Posts: 1077
Threads: 69
Registered: August 27th, 2002
Member Is Offline

Location: Sydney
Theme: UltimaBB Psyche Blue

posted on July 8th, 2004 at 09:47 PM


Wes, great spreadsheet you generated, after i got over being bombarded with all the numbers.

Cheers
MemberBaja Wes
Bishop of Volkswagenism
V6 Baja Pioneer
******


Avatar


Posts: 3119
Threads: 94
Registered: August 26th, 2002
Member Is Offline

Location: Brisbane
Theme: UltimaBB Pro Blue ( Default )
Mood: Content

posted on July 9th, 2004 at 08:16 AM


Quote:
Originally posted by Flintstones
Wes, great spreadsheet you generated, after i got over being bombarded with all the numbers.


:D , try writing the equations in the first place :D

I will make it more user friendly, and I'll get Excel to draw a top, side and front view of the beam as a chart. Should be able to animate it too. :)




Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... :)
www.taylorcycles.com.au - My DH MTB racing brothers shop.
MemberMikeM
Custom Title Time!
Buggy Head
*****


Avatar


Posts: 1429
Threads: 71
Registered: August 7th, 2003
Member Is Offline

Location: Brisbane North Side
Theme: UltimaBB Pro Blue ( Default )
Mood: :duh

posted on July 9th, 2004 at 11:03 AM


Quote:
Originally posted by Baja Wes
I will make it more user friendly, and I'll get Excel to draw a top, side and front view of the beam as a chart. Should be able to animate it too. :)


Cool. Very cool.

I've looked at the XL equations to try and figure out what's going on...... intense...... got to hard, I'll have to look into them a bit more when I have time.




Membernbturbo
Veteran Volks Folk
*****


Avatar


Posts: 2170
Threads: 89
Registered: December 19th, 2002
Member Is Offline

Location: Whyalla Sth.Aust.
Theme: UltimaBB Powder

posted on July 9th, 2004 at 03:52 PM


Some one has probably come up with this already- what about getting a steering box from a LHD Beetle,remove the input shaft and welch plug the holes-mount it up on the LH side of the beam,then fit a short track rod from the RH side to the left and cut and shut the normal LH one for the centre bit.This would use the LH steering box as a normal idler arm. Could still use the damper-just relocate the fixed end mount.Should eliminate the bump steer??????
MemberMikeM
Custom Title Time!
Buggy Head
*****


Avatar


Posts: 1429
Threads: 71
Registered: August 7th, 2003
Member Is Offline

Location: Brisbane North Side
Theme: UltimaBB Pro Blue ( Default )
Mood: :duh

posted on July 9th, 2004 at 04:05 PM


Quote:
Originally posted by nbturbo
Some one has probably come up with this already- what a
<snip>

Should eliminate the bump steer??????


When Wes first revealed that the short tie rod side had less bump steer than the long tie rod side I thought about doing this. I even started to track down gear. All you would need is a dead steering box to gut for the passenger side and a US (LHD) pitman arm which can be bought easily from the American after market. You then use the LHD pitman arm on the left idler box and you will reduce bump steer and not have a long tie rod to bend.

This got put on simmer until we had a definite answer about whether the Rack would work.

To be sure this would work we'd need to get Wes to remodel the stock setup and confirm there is minimal bump steer on the short tie rod side.




MemberBaja Wes
Bishop of Volkswagenism
V6 Baja Pioneer
******


Avatar


Posts: 3119
Threads: 94
Registered: August 26th, 2002
Member Is Offline

Location: Brisbane
Theme: UltimaBB Pro Blue ( Default )
Mood: Content

posted on July 9th, 2004 at 04:59 PM


Quote:
Originally posted by nbturbo
Some one has probably come up with this already- what about getting a steering box from a LHD Beetle,remove the input shaft and welch plug the holes-mount it up on the LH side of the beam,then fit a short track rod from the RH side to the left and cut and shut the normal LH one for the centre bit.This would use the LH steering box as a normal idler arm. Could still use the damper-just relocate the fixed end mount.Should eliminate the bump steer??????


You could, but I think it would be easier and cheaper to install rack and pinion which has heaps more benefits than just the elimination of bump steer.

If you spent alot of time you could probably adjust the original set-up for minimal bump steer. The problem that I see if that it's very difficult to get the original parts in exactly the right spot in order to get minimal bump steer. Things that can stuff up the stock steering geometry and give bump steer (with idler or not);

1 - Stock steering box rotation on the beam. This is not 100% accurately located. The underside claim is kinda doweled to the beam, but then long bolts attach the steering box. So if you tighten one bolt more than the other, the steering box can essentially end up in a range of different angles. The steering box should be dowelled, not the lower clamp.

2 - stock camber adjusters. These effectively change where the tie rod connection is relate to the top ball joint. The steering box cannot compensate for this, so the stock steering box location can only be exactly for one specific camber adjuster position.

There are other factors I will explain later.

The rack will be prone to the same probs, but can be factory set in a kit form to suit the camber adjusters at a specified orientation. The rack can also easily be shimmed and moved to eliminate bump steer if the owner wants to fine tune it that much.




Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... :)
www.taylorcycles.com.au - My DH MTB racing brothers shop.
Membernbturbo
Veteran Volks Folk
*****


Avatar


Posts: 2170
Threads: 89
Registered: December 19th, 2002
Member Is Offline

Location: Whyalla Sth.Aust.
Theme: UltimaBB Powder

posted on July 10th, 2004 at 02:01 PM


Once you could locate a LHD steering box and pitman arm it would be a simple fit up-just measure and weld some new locating lugs.I am not quite sure what the reference to camber adjusting has to do with this because as you said that its a given no matter what steering you use-is even relevant to any new motor car if you alter from the factory specs.Small camber alteration from stock would have minimal effect on geometry and would be at its worst on full lock where a specific toe out on turns is required.Setting up the 2 steering boxes should be simple enough with straight edges and tape measures.From memory setting the correct steering box/Pitman arm inclination is as simple as making sure the steering shaft is located centrally in the outer tube.Years ago when we used to lower our Bugs by cutting the tubes and turning the locater, B4 we knew about castor shims,we found the way to moderately fix bump steer was to adjust the steering box on the torsion tube and have the steering shaft as high up in the outer tube just enough without rubbing. Just put a bit of strain on the rubber coupling but seemed to work OK. From my limited understanding of steering geometry it would appear that to fit a rack and pinion set up you would just need the steering rod fulcrums/pivots on the rack(in the centre/straight ahead position) to end up in exactly the same postion on the car as the original RH inner tie rod end that is attached to the Pitman arm and the LH inner that would be on the Pitman arm of the conversion with a LHD box as I have described,both in the straight ahead position. Volkswagen designed the the length of the Pitman arm in relation to the steering arms to be a set distance back from a centre line thru the torsion bar tubes or a centre line thru the King Pin/ Ball Joint pivots.Hope this makes some sense.
MemberVWCOOL
23 Windows of Awesome
********


No Avatar


Posts: 5158
Threads: 235
Registered: June 19th, 2003
Member Is Offline

Location: In the shed... Lake Macquarie NSW
Theme: UltimaBB Pro Blue ( Default )
Mood: happy to help

posted on July 10th, 2004 at 05:31 PM


I think its a Passat rack...



Pay your debts, CxxT
MemberFlintstones
Custom Title Time!
*****


Avatar


Posts: 1077
Threads: 69
Registered: August 27th, 2002
Member Is Offline

Location: Sydney
Theme: UltimaBB Psyche Blue

posted on July 10th, 2004 at 11:25 PM


Wes, Just wanted to find out if ride height made any difference to the positioning of the rack. Say I wanted to lower the car 2-3" would that programe of yours be able to calculate if there was any change?

VWCOOL, passat's have the racks in front of the spindle, where as beetles have the steering behind. If you fitted a passat rack on a beam front end, when you turn the steering right, the car would go left.....

cheers
MemberBaja Wes
Bishop of Volkswagenism
V6 Baja Pioneer
******


Avatar


Posts: 3119
Threads: 94
Registered: August 26th, 2002
Member Is Offline

Location: Brisbane
Theme: UltimaBB Pro Blue ( Default )
Mood: Content

posted on July 11th, 2004 at 11:01 AM


The problem with the 2 steering box idea is that you would have to get the design completed by the engineer and then approved. What I am saying is if your going to that much bother then why not just go to a rack and pinion design and get rid of the troublesome steering boxes that love to wear out and get flat spots in the center.

The comment on the camber adjusters is that moving them moves the best position for the inner tie rod ends forward and back. With a rack design, you can shim the rack forward and back to suit. With a steering box you can't do anything. Rotating the steering box around the beam mainly moves the inner tie rod ends up and down, which is not where the problem is.

The Excel sheet has a row (26) that calculated the length of the tie rods to have 0 toe at a given ride height. To change the ride height it's set at, simply change cell A26. set it to like -4 degrees for the upper torsion arm angle, or whatever angle you want. With a good rack design with no bump steer it won't matter where the normal ride height of the car is. But you can see with a set-up which is wrong it simply moves the bump steer curve around, and you still have the same amount of bump steer.

The Excel sheet can be used to look at the two steering box idea, or the stock setup, or a rack set-up. Simply change the coordinates of where the inner tie rod ends are.

From what I have measured so far, the stock set-up isn't right anyway, even for the short tie rod. I need to do some more accurate measurements though.




Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... :)
www.taylorcycles.com.au - My DH MTB racing brothers shop.
MemberBaja Wes
Bishop of Volkswagenism
V6 Baja Pioneer
******


Avatar


Posts: 3119
Threads: 94
Registered: August 26th, 2002
Member Is Offline

Location: Brisbane
Theme: UltimaBB Pro Blue ( Default )
Mood: Content

posted on July 11th, 2004 at 08:16 PM


Here's a 2nd draft of the Excel spreadsheet for calculating the bump steer.

You only really need to change the rack mounting position and see the effect. I also added a side on and top view of the front end, drawn as Excel charts. It does the job.

There is a little "+" and "-" button for rotating the beam and watching it move. I am going to put an animate button on there but my computer keeps crashing when I try to write the macro (I'm on my old crappy computer at the moment). Anyway, have fun playing. :)

PS - it's a zip file this time to keep it under 50kB.

*File deleted - there is a new version further along this post*

[Edited on 13-7-2004 by Baja Wes]




Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... :)
www.taylorcycles.com.au - My DH MTB racing brothers shop.
MemberMikeM
Custom Title Time!
Buggy Head
*****


Avatar


Posts: 1429
Threads: 71
Registered: August 7th, 2003
Member Is Offline

Location: Brisbane North Side
Theme: UltimaBB Pro Blue ( Default )
Mood: :duh

posted on July 12th, 2004 at 12:30 AM


Measuring balljoints

Guessing ball middle to ball middle because the balls aren't spherical.

best guess 167mm

Error
Sorry, you must be a registered user in order to download attachments.




MemberMikeM
Custom Title Time!
Buggy Head
*****


Avatar


Posts: 1429
Threads: 71
Registered: August 7th, 2003
Member Is Offline

Location: Brisbane North Side
Theme: UltimaBB Pro Blue ( Default )
Mood: :duh

posted on July 12th, 2004 at 12:32 AM


Measuring balljoints

Ball bottom to ball top. Balls have a flat spot on the top which makes this difficult.

best guess 167mm

Error
Sorry, you must be a registered user in order to download attachments.




MemberBaja Wes
Bishop of Volkswagenism
V6 Baja Pioneer
******


Avatar


Posts: 3119
Threads: 94
Registered: August 26th, 2002
Member Is Offline

Location: Brisbane
Theme: UltimaBB Pro Blue ( Default )
Mood: Content

posted on July 12th, 2004 at 08:18 AM


Quote:
Originally posted by MikeM
Measuring balljoints

best guess 167mm


Thanks for measuring that for me. You can see in the excel sheet above your post I had it as 167mm too. So it's good that we agree, a nice check measurement :)

I'm actually suprised since I measured a fully assembled beam laying it flat on the shed floor and then using set squares and rulers and guessing where the center of the ball looked like it was :D




Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... :)
www.taylorcycles.com.au - My DH MTB racing brothers shop.
MemberBaja Wes
Bishop of Volkswagenism
V6 Baja Pioneer
******


Avatar


Posts: 3119
Threads: 94
Registered: August 26th, 2002
Member Is Offline

Location: Brisbane
Theme: UltimaBB Pro Blue ( Default )
Mood: Content

posted on July 13th, 2004 at 12:53 PM


here's another revision to the Excel sheet.

The last one had a small error when drawing the drivers wide wheel, it made it rotate the opposite way to the toe in, a + and a - sign in the wrong place. The bump steer calculation was still ok, but when it drew it as a stick diagram it wasn't quite right. fixed now.

I also put an animate button on the diagram page. I can't seem to make Excel animate it any faster, so it's a little slow.

[Edited on 19-7-2004 by Baja Wes]




Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... :)
www.taylorcycles.com.au - My DH MTB racing brothers shop.
MemberBaja Wes
Bishop of Volkswagenism
V6 Baja Pioneer
******


Avatar


Posts: 3119
Threads: 94
Registered: August 26th, 2002
Member Is Offline

Location: Brisbane
Theme: UltimaBB Pro Blue ( Default )
Mood: Content

posted on July 15th, 2004 at 01:37 PM


I received an email that has some questions that other people may find relevant....

Quote:
Hi Wes,

I've been playing with your rack and pinion spreadsheet but have a few questions.
1) I updated the info with my specifics - 205/50-16 tire size, plus inner tie-rod joint width of the Flaming river R&P unit (603.7mm). Niether of these is very far off of your original dimensions.

It looks like placement of the rack - both up and down and forward and back is extremely sensitive! Even slight movement really skews the bump-steer characteristics. Your original settings for rack position look to be about the best overall - I'm just wondering how one would implement them in a real-world installation. Seems like once your main attachment points are fabricated and installed - both front-back and up-down shimming/adjustments would be necessary to really get it dialed in, in small increments of movement. Especially when you're talking about dimensions of less than 0.1mm making a fairly large change!

On the lower section it states: "Table below calculates tie rod lengths, enter angle car normally sits at"
Where is this angle entered? Is this the overall chassis angle of attack or trailing arm angle?
Referring to trailing arm angle, I know you're working this up for an off-road application but I'm dealing with on-road, with most likely much less suspension travel - probably only around 130mm travel total. How can I plug this value into the spreadsheet, probably with a minimal top torsion arm angle (maybe about 4 degrees down?) as the normal static attitude of the upper arm? How does this affect the angle of the lower arm (or is this automatically compensating?)

Very neat work on the spreadsheet though - fun to play with!

Cheers,
Jeff


Hi,

A lot of this stuff has been covered on the http://www.aussieveedubbers.com  forum. I have attached the latest version of the spreadsheet so you can play with it.

Yes it is very sensitive to position of the rack. In order to address this you need to be able to shim it up and down. So yes you would trial fit it, then measure the bump steer. Using the excel sheet and comparing to the bump steer pattern you measured you should be able to accurately shim the rack to the correct position (by figuring out how far out, and in what direction it's out).

A center mount rack would be less prone to the problem. You would get half the error because your tie-rods would be twice as long (roughly speaking)

The funny thing is the stock steering box set-up suffers the same sensitivity to set-up accuracy. The stock short tierod will be very similar to a rack design. From my measurements so far, the stock tie rod end centers on the steering box appear to be located at;
drivers - 255, 36, 119
passengers - 215, 41, 104

You can plug those figures into the rack location in the excel sheet and see what the stock set-up is like. The problem the stock set-up has is that it is not adjustable or shimmable. Whereever it ends up is where is stays.

The angle the steering is set-up at is referring to the angle of the top trailing arm. -4degrees would be slightly up, +4 would be slightly down (lowering relatively speaking). You can see this just moves the bump steer curve left or right essentially.

If you don't want to use the full suspension travel then just ignore the upper and lower measurements. The big calculation table that is now grey in colour shows the upper trailing arm angle, and for each angle you can read across and read the "y" value which is essentially the suspension height in mm above or below a top arm angle or "0 degrees" (horizontal). And yes it calculates what the lower arm angle is for any upper arm angle.

Wes




Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... :)
www.taylorcycles.com.au - My DH MTB racing brothers shop.
MemberJenny
Officially Full-On Dubber
***


Avatar


Posts: 352
Threads: 20
Registered: June 26th, 2003
Member Is Offline

Location: Brisbane south
Theme: UltimaBB Pro Blue ( Default )
Mood: Is it Friday yet?

posted on October 21st, 2004 at 12:25 PM


This stuff is way over my head, but I'm curious to know how this all panned out.
MemberDoNkEy
A.k.a.: James
Wolfsburg Wizard
***


Avatar


Posts: 684
Threads: 69
Registered: July 1st, 2003
Member Is Offline

Location: Brisbane West Side
Theme: UltimaBB Pro Blue ( Default )

posted on October 21st, 2004 at 03:30 PM


here here...

i am intersted...does that mean the 75 pan i got sitting round..nicley restored will make a nice buggy????
MemberBrad
Wolfsburg Elder
*******


No Avatar


Posts: 3764
Threads: 332
Registered: August 24th, 2002
Member Is Offline

Location: SE QLD, Mt Nebo
Theme: UltimaBB Pro Blue ( Default )
Mood: Manx Buggy Building

posted on October 21st, 2004 at 07:01 PM


It is moving just fine .... :party



Brad
Why copy when you can own an original ?
Meyers Manx Australia
MemberBaja Wes
Bishop of Volkswagenism
V6 Baja Pioneer
******


Avatar


Posts: 3119
Threads: 94
Registered: August 26th, 2002
Member Is Offline

Location: Brisbane
Theme: UltimaBB Pro Blue ( Default )
Mood: Content

posted on March 4th, 2005 at 10:13 PM



just thought I'd reattach the rack spreadsheet for compulsive tinkerers. You will probably need Excel 2000 or later.

[ Edited on 5-7-2006 by Baja Wes ]




Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... :)
www.taylorcycles.com.au - My DH MTB racing brothers shop.
MemberBrad
Wolfsburg Elder
*******


No Avatar


Posts: 3764
Threads: 332
Registered: August 24th, 2002
Member Is Offline

Location: SE QLD, Mt Nebo
Theme: UltimaBB Pro Blue ( Default )
Mood: Manx Buggy Building

posted on March 5th, 2005 at 10:49 AM


it is still going ... finding the time to play with stuff is the hardest thing right now .... to many damn subaru engines to play with ... hehehe



Brad
Why copy when you can own an original ?
Meyers Manx Australia
Memberpete wood
A.k.a.: figure itout
23 Windows of Awesome
********


Avatar


Posts: 6828
Threads: 389
Registered: January 15th, 2004
Member Is Offline

Location: Nth Nth StMarys, Sydney
Theme: UltimaBB Pro White
Mood: upgrades = jackstands

posted on May 26th, 2005 at 03:00 PM


Anyone end up putting rack and pinion on something?

ANd if so, what rack did you use and do you have a pic?

I heard something about a charade rack on a buggy in VIC some time ago.




"stoopid is stronger than axles"
http://drivingnotpolishing.blogspot.com.au/ 
Membertassupervee
A.k.a.: Knob Jockey
Custom Title Time!
That really hurts doesnt it!
*****


Avatar


Posts: 1171
Threads: 25
Registered: September 21st, 2003
Member Is Offline

Location: Huon Valley SouthernTasmania
Theme: UltimaBB Psyche Blue
Mood: Moody!

posted on May 26th, 2005 at 08:49 PM


I ended up fitting a CB Performance steering rack to my race car
Tiny rack at a tiny price.

Simple to fit in a Vee.

Altho the bump steer characteristics are pretty ordinary when mounted directly inline with the stub axle pickup points, with the amount of travel I am using, and the positioning of the rack in relation to the balljoint heights, the amount of bump is pretty much academic.

L8tr
E




Im not a complete idiot, quite a few parts are missing....
MemberBaja Wes
Bishop of Volkswagenism
V6 Baja Pioneer
******


Avatar


Posts: 3119
Threads: 94
Registered: August 26th, 2002
Member Is Offline

Location: Brisbane
Theme: UltimaBB Pro Blue ( Default )
Mood: Content

posted on July 4th, 2006 at 08:50 PM



posting the spreadsheet again cos the last one has corrupted for some strange reason

[ Edited on 4-7-2006 by Baja Wes ]

Error
Sorry, you must be a registered user in order to download attachments.




Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... :)
www.taylorcycles.com.au - My DH MTB racing brothers shop.
MemberKimbo
Officially Full-On Dubber
***


Avatar


Posts: 207
Threads: 30
Registered: January 24th, 2005
Member Is Offline

Location: Adelaide
Theme: UltimaBB Pro Blue ( Default )
Mood: Is it beer O'Clock yet ?

posted on July 25th, 2006 at 03:10 PM



An absolutely terrific job Wes - and the timing couldn't have been more perfect as I'm in the process of replacing the cactus rack on the buggy with a new one which is centre load instead of end load and the front beams have been widened as well, so it's all highly relevent. However, I do have a couple of quick (and probably dumb) questions Wes:

1) "Spacing of the upper and lower torsion tubes" on the general measurements tab, I'm assuming that's the distance between the theoretical centre line of each tube ie where the arms pivot, as opposed to the actual gap between the tubes ?

2) If applying this to a K&L front end you'd presumably substitute the relative ball-joint "positions" for link pin positions - however, is there anything else in the depths of your calculations that need to be changed to handle K&L ?

Thanks ... Kimbo




MemberBaja Wes
Bishop of Volkswagenism
V6 Baja Pioneer
******


Avatar


Posts: 3119
Threads: 94
Registered: August 26th, 2002
Member Is Offline

Location: Brisbane
Theme: UltimaBB Pro Blue ( Default )
Mood: Content

posted on July 27th, 2006 at 09:32 AM



yes, spacing of the tubes is to the tube centerlines. Off the top of my head I think it's 120mm K&L and 150 BJ?

Don't worry about getting the beam spacing right, it doesn't make a difference to the calculation.

I haven't measure the K&L front end, but I assume all the work points will be in the same place, as the K&L and BJ fronts use the same steering box, therefore must be the same geometry.

The only thing that will catch you out is using longer front arms.




Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... :)
www.taylorcycles.com.au - My DH MTB racing brothers shop.
MemberFakeDino
Learner Dubber
*


No Avatar


Posts: 3
Threads: 0
Registered: July 28th, 2006
Member Is Offline

Location: Pennsylvania, USA
Theme: UltimaBB Pro Blue ( Default )

posted on July 29th, 2006 at 10:44 AM



I was looking for a tool like this. I'm building a Kelmark from scratch using a Ford Contour 2.5 V6 and 5 speed in a mid-engine position. The front end is a modified Karmann Ghia disc BJ beam. I cut it, widened it by 4 inches, and welded in 4 adjusters.... I also shortened the torsion bars by 15 percent to make the suspension stiffer for the lighter body, and sports car handling. I will probably use a power steering rack (quicker ratio than manual racks) and just loop the pressure side port to the return port. You've done a great job on modeling the beam, while allowing adjustment parameters where I need them. I'll be able to fab a mount with the correct scale of shim available for nearly no bump. Thanks very much.

Gar
MemberFakeDino
Learner Dubber
*


No Avatar


Posts: 3
Threads: 0
Registered: July 28th, 2006
Member Is Offline

Location: Pennsylvania, USA
Theme: UltimaBB Pro Blue ( Default )

posted on August 15th, 2006 at 12:41 AM
Ackerman problem


I used the spreadsheet formula to locate the rack for minimum bump steer, but find that in doing so, I have an Ackerman problem. This is a result of the sharp angle that the tie rod makes between the end of the rack, and the tie rod end. If you look at the graphic you'll see this angle in the overhead view. The original Ackerman uses both the long pitman arm length, and the dual inner tie rod end slightly offset (dog bone) in combination with the angle of the steering arms on the spindles to properly control the inner wheel turning more sharply than the outer wheel. Following the design information for rack placement, you'll create anti-ackerman. Your wheels will toe in, rather than toe out as they should in a corner. Using a rack and pinion in place of the original design will mean accepting a compromise, either bump steer or Ackerman. I will be moving my rack further away from the torsion tube and will accept more bump steer. I'll post and let you know how the bump compares to the original with the Ackerman where it needs to be for low steed steering.
MemberBaja Wes
Bishop of Volkswagenism
V6 Baja Pioneer
******


Avatar


Posts: 3119
Threads: 94
Registered: August 26th, 2002
Member Is Offline

Location: Brisbane
Theme: UltimaBB Pro Blue ( Default )
Mood: Content

posted on August 15th, 2006 at 08:55 AM



I never got around to calculating the Ackerman for the VW. It's more complicated than it first looks.

Basically we decided (being interested in offroaders) that the bump steer was more important than the ackerman. You feel the bump steer when trying to travel straight. This is a problem when trying to go fast on a bumpy road.

If the ackerman is out then it just changes the oversteer / understeer tendancies a little. This has a much more managable impact. And when you corner all the weight is on the outside turning wheel so what the inner wheel does doesn't matter that much.

Drive a manx buggy and you will see having completely stuffed up ackerman (because the wheelbase got shortened 14.5") doesn't have that bad of an impact. It is a lot less noticeable then when the bump steer is bad.

The rack set-up prototype that we came up with has centre mounted tie rod ends on the rack. This prevents the really tight angle you get with the end mounted tie rods (on the rack).




Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... :)
www.taylorcycles.com.au - My DH MTB racing brothers shop.
 Pages:  1  2  3  4  5  6


  Go To Top


Powered by GaiaBB, © 2011 The GaiaBB Group


[ Queries: 40 ] [ PHP: 33.9% - SQL: 66.1% ]
#Duration:Query:
1.0.00040007SELECT * FROM ubb_settings
2.0.00032401SELECT moderator FROM ubb_forums WHERE moderator != ''
3.0.00029111SELECT DISTINCT uid FROM ubb_members WHERE username = 'BUGBOY'
4.0.00017905SELECT DISTINCT uid FROM ubb_members WHERE username = 'MickH'
5.0.00014997SELECT DISTINCT uid FROM ubb_members WHERE username = 'barls'
6.0.00015283SELECT DISTINCT uid FROM ubb_members WHERE username = 'vanderaj'
7.0.00014496SELECT DISTINCT uid FROM ubb_members WHERE username = 'Cam'
8.0.00023484SELECT DISTINCT uid FROM ubb_members WHERE username = 'vw54'
9.0.00014496SELECT DISTINCT uid FROM ubb_members WHERE username = 'SuperOwen'
10.0.00015903SELECT DISTINCT uid FROM ubb_members WHERE username = 'helbus'
11.0.00014591SELECT DISTINCT uid FROM ubb_members WHERE username = '65busser'
12.0.00012994SELECT DISTINCT uid FROM ubb_members WHERE username = 'Baja Wes'
13.0.00014091SELECT DISTINCT uid FROM ubb_members WHERE username = 'Dasdubber'
14.0.00020385SELECT DISTINCT uid FROM ubb_members WHERE username = 'MISS VDUB'
15.0.00079894SELECT LENGTH(robot_string) AS strlen, robot_string, robot_fullname FROM ubb_robots ORDER BY strlen DESC
16.0.00038600SELECT f.fid, f.theme FROM ubb_forums f, ubb_threads t WHERE f.fid = t.fid AND t.tid = '23861'
17.0.00047207DELETE FROM ubb_whosonline WHERE ip = '18.204.227.34' && (username = 'xguest123' OR username = 'xrobot123' OR username = 'Anonymous') OR time < '1621246428'
18.0.00038195INSERT INTO ubb_whosonline (username, ip, time, location, invisible, robotname) VALUES ('xguest123', '18.204.227.34', LPAD('1621247028', '15', '0'), '/viewtopic.php?tid=23861&page=4', '0', '')
19.0.00024819DELETE FROM ubb_guestcount WHERE ((ipaddress = '18.204.227.34') OR (onlinetime < '1621160628'))
20.0.00011396DELETE FROM ubb_robotcount WHERE ((ipaddress = '18.204.227.34') OR (onlinetime < '1621160628'))
21.0.00010395INSERT INTO ubb_guestcount (ipaddress, onlinetime) VALUES ('18.204.227.34', '1621247028')
22.0.00026989SELECT * FROM ubb_themes WHERE themeid = '1'
23.0.00017309SELECT * FROM ubb_pluglinks ORDER BY displayorder ASC
24.0.00018501SELECT id FROM ubb_banned WHERE ((ip1 = '18' OR ip1 = '-1') AND (ip2 = '204' OR ip2 = '-1') AND (ip3 = '227' OR ip3 = '-1') AND (ip4 = '34' OR ip4 = '-1')) AND NOT (ip1 = '-1' AND ip2 = '-1' AND ip3 = '-1' AND ip4 = '-1')
25.0.00062490SELECT fid, type, name, fup, status, private, userlist, password FROM ubb_forums WHERE private != '5' AND private != '3' AND private != '2' AND userlist = '' AND password = '' AND status = 'on' ORDER BY displayorder
26.0.00026107SELECT themeid, name FROM ubb_themes
27.0.00107312SELECT name, template FROM ubb_templates WHERE name IN ('functions_bbcode', 'functions_bbcodeinsert', 'functions_smilieinsert_smilie', 'functions_smilieinsert', 'viewtopic_reply', 'viewtopic_quickreply', 'viewtopic', 'viewtopic_invalid', 'viewtopic_modoptions', 'viewtopic_newpoll', 'viewtopic_newtopic', 'viewtopic_poll_options_view', 'viewtopic_poll_options', 'viewtopic_poll_submitbutton', 'viewtopic_poll', 'viewtopic_post', 'viewtopic_post_email', 'viewtopic_post_site', 'viewtopic_post_icq', 'viewtopic_post_aim', 'viewtopic_post_msn', 'viewtopic_post_yahoo', 'viewtopic_post_search', 'viewtopic_post_profile', 'viewtopic_post_pm', 'viewtopic_post_ip', 'viewtopic_post_repquote', 'viewtopic_post_report', 'viewtopic_post_edit', 'viewtopic_post_delete', 'viewtopic_post_attachmentimage', 'viewtopic_post_attachment', 'viewtopic_post_attach_noborder', 'viewtopic_post_attimg_noborder', 'viewtopic_post_sig', 'viewtopic_post_nosig', 'viewtopic_printable', 'viewtopic_printable_row', 'viewtopic_multipage', 'viewtopic_post_attachment_none', 'viewforum_rules', 'viewtopic_post_blog', 'viewtopic_post_rpg', 'viewforum_mpn_info', 'viewtopic_next_prev_links', 'viewtopic_captcha', 'css', 'error', 'footer', 'footer_querynum', 'footer_load', 'footer_phpsql', 'footer_totaltime', 'header', 'message', 'meta_tags', 'shadow', 'shadow2')
28.0.00061107SELECT t.tid, t.fid, t.subject, t.views, t.replies, t.closed, t.topped, l.uid as lp_uid, l.username as lp_user, l.dateline as lp_dateline, l.pid as lp_pid FROM ubb_threads t LEFT JOIN ubb_lastposts l ON l.tid = t.tid WHERE t.tid = '23861'
29.0.00031996SELECT * FROM ubb_forums WHERE fid='57' AND status='on'
30.0.00018311SELECT code, url FROM ubb_smilies WHERE type = 'smiley'
31.0.00010204SELECT find, replace1 FROM ubb_words
32.0.00026703SELECT id, title, posts, stars, allowavatars, avatarrank FROM ubb_ranks
33.0.00034189UPDATE ubb_threads SET views = views+1 WHERE tid = '23861' LIMIT 1
34.0.00098395SELECT COUNT(pid) FROM ubb_posts WHERE tid = '23861'
35.0.01303506SELECT t.tid as t_tid FROM ubb_threads t LEFT JOIN ubb_threads o ON o.tid = 23861 LEFT JOIN ubb_lastposts l ON l.tid = t.tid LEFT JOIN ubb_lastposts x ON x.tid = o.tid WHERE l.dateline < x.dateline AND t.fid = '57' ORDER BY l.dateline DESC LIMIT 1
36.0.01203680SELECT t.tid as t_tid FROM ubb_threads t LEFT JOIN ubb_threads o ON o.tid = 23861 LEFT JOIN ubb_lastposts l ON l.tid = t.tid LEFT JOIN ubb_lastposts x ON x.tid = o.tid WHERE l.dateline > x.dateline AND t.fid = '57' ORDER BY l.dateline ASC LIMIT 1
37.0.00045013SELECT vote_id FROM ubb_vote_desc WHERE topic_id = '23861'
38.0.00090694SELECT pid FROM ubb_posts WHERE tid = '23861' ORDER BY pid LIMIT 90, 30
39.0.00377083SELECT * FROM ubb_attachments WHERE pid IN('200197', '200657', '200786', '200881', '200984', '200995', '201016', '201251', '201294', '201411', '201470', '201611', '201746', '201747', '201770', '202430', '203382', '249864', '249953', '250092', '311044', '311229', '362675', '362859', '507931', '515269', '515936', '516640', '522620', '522669')
40.0.00301695SELECT p.*, m.*,w.time FROM ubb_posts p LEFT JOIN ubb_members m ON m.username = p.author LEFT JOIN ubb_whosonline w ON p.author = w.username WHERE p.fid = '57' AND p.tid = '23861' ORDER BY p.pid ASC LIMIT 90, 30