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Rack and Pinion Steering

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Brad Wolfsburg Elder

3,764 posts · joined Aug 2002 ·

#182158
Well in my search to fit power assisted rack and pinion to my buggy I have learnt a lot about the subject. I did the reading and I bought the books... came up with my design and though all was pretty cool.

Then I found thsi picture of someone who has done it ......

Seems to me if thsi works then I have wasted many hours of my life ....

Brad
Why copy when you can own an original ?
Meyers Manx Australia

1303Steve Scirocco Rare

8,650 posts · joined Aug 2002 ·

#182166
Hi

That looks like a Camira rack.

1302Steve

Desert Moose Cut Cut Cut

2,098 posts · joined Mar 2004 ·

#182195
Not being rude but WTF. Go the bump steer

Brad Wolfsburg Elder

3,764 posts · joined Aug 2002 ·

#182212
Bump steer and I reckon the 30" tyres he has on the front will hit his rack ends.

It is teh best pic I could find of one actually setup.

Anyone got any better ones ? I an not putting my rack in this position but would like info from anyone out there who is running rack and pinion if possible.
Brad
Why copy when you can own an original ?
Meyers Manx Australia

Baja Wes V6 Baja Pioneer

3,119 posts · joined Aug 2002 ·

#182221
That set-up would have less bump steer than the original steering box. Having the tie-rods as long as possible is a good thing.

It looks like it was power steering but is bypassing to itself. LHD so not Camira.
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.

MikeM Buggy Head

1,429 posts · joined Aug 2003 ·

#182227
Baja Wes wrote:That set-up would have less bump steer than the original steering box. Having the tie-rods as long as possible is a good thing.
Hmmm, I won't say you are wrong, but I'm not sure I agree.

The suspension pivots at the torsion bars, for the steering to have no bump steer the steering should pivot at the same point. Ie. as close to the torsion bars as possible.

The setup pictured (and the one on the green buggy) both have steering that pivots further away from the torsion bars then the stock setup.

The best place to have the steering pivot would be right up the front at the torsion bars (where the adjusters get welded)

The rack used in the picture above, if moved right forward, would work well due to the long steering arms.

The rack and pinion shown on the webpage below would work well as it is mounted up on the torsion bars. This would make it better than the stock as it would totally eliminate bump steer.

http://www.chirco.com/projectbaja/baja_10.htm


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MikeM Buggy Head

1,429 posts · joined Aug 2003 ·

#182261


I've done up this diagram to try and give everyone a bit more of an understanding of steering geometry and to try to explain why the rack and pinion setup shown will give significant bump steer.

This is a difficult topic to get your head around so if I don't explain it in a suitable way let me know and I will try and elaborate.

There are two triangles on the picture (A & B). Triangle B shows the geometry of the suspension and I will explain it's relevance first. Triangle A shows the geometry of the rack and pinion setup.

Triangle B
The beetle torsion bar suspension pivots along the torsion tubes (blue line). The torsion arms (yellow line) are a solid and run on bushes in the torsion bar. Therefore their geometry to the blue line cannot change. The point where the torsion arms attach to the steering knuckle travels up and down in an arc at 90 degrees relative to the torsion tubes. So as the suspension goes up or down the point where the red and yellow line meet gets closer to and further away from the front of the car but it's distance from the torsion tube does not change (the torsion arm is a solid object). Now if you imagine the triangle (B) to be a solid object you could take the point where the yellow and red lines meet and spin it around and around the torsion bar and the length of all three sides of the triangle would remain the same. IE. in real life you can spin a torsion arm around and around the torsion tube when there is no steering knuckle or torsion bars in the torsion tube.

Triangle A
Triangle A shows the geometry of the rack and pinion steering in this car. The yellow line is again the torsion arm, the blue line is the static line or pivot line of the steering, and the red line represents the tie rod. The first sign that this setup is not geometrically correct is that the blue pivot line is nowhere near the same location as the pivot line of the front suspension (Blue line triangle B). As a wheel travels through it's movement the torsion arm (yellow line) will pivot on it's arc around the torsion tube. As it moves up and forward the distance between where is meets the steering knuckle (yellow meets red) and the centre of the rack (blue meets red) needs to increase. Since the tie rod is a static object and cannot increase, the steering is pulled inward and therefore the front of the tyre will move outward. Bump steer.

The best geometry for steering is to be exactly the same as the geometry of the suspension. The geometry of the suspension is triangle B, so we need to make the geometry of the steering as close as possible to triangle B to eliminate bump steer. This could be achieved by having a rack and pinion setup mounted right up on the front torsion tube with it's tie rods pivoting where the red and blue line meet on triangle B.

If the rack pictured was moved all the way forward, flipped end to end, mounted on the torsion tubes, and had the tie rod mounts attached to the back (instead of the front) it would work well. Looking at the rack, the centre section may well be free to rotate and could be rolled over so the tie rods attached to the back.

Hopefully I've explained that correctly.

[Edited on 4-6-2004 by MikeM]


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MikeM Buggy Head

1,429 posts · joined Aug 2003 ·

#182266
I sent the picture of the rack to my cousin who owns a power steering and transmission shop.

He said that the rack is very similar to the racks used on Camiras and some Audis. But obvisously Camiras and the Local market Audis have a RHD version.

The center section cannot be modified to mount the tie rods on the other side (back) as the center section on the Camira racks is cast alloy. What could potentially be done though is a piece of u chanel could be mounted over the center section to bolt onto the stock mount on the front but allow the tie rods to be bolted to the back. We'd have to confirm with a blue plate officer whether this would be acceptable.

This rack would be dead easy to mount on the front torsion tubes, it just depends whether we can come up with a way to mount the tie rods to the back and get it all approved.

Also my cousin mentioned that the shortest available standard rack (end mount not center) is actually a standard Commodore rack. These are around 20 inches long. Due to the number of varieties of commodores over the years the tie rods are available is many custom lengths so getting it the right overall length for the VW should be easy enough. I will look into this option a bit more as he has several commodore racks sitting in his workshop at the moment.

[Edited on 4-6-2004 by MikeM]


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Baja Wes V6 Baja Pioneer

3,119 posts · joined Aug 2002 ·

#182269
I never said it's good. Just probably better than stock.

Sure as it travels each wheel will toe out, be it will be even amounts.

The stock set-up weaves on big bumps cos the short tie rod and long tie rod are changing the toe different amounts on each side, causing it to make the car want to turn on big bumps.
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.

Desert Moose Cut Cut Cut

2,098 posts · joined Mar 2004 ·

#182270
If you have (and I know you will) a copy of Jeff Hiddard's book baja bugs and buggies, have a look at page 66. In a box on the left All about bump steer I use this when I set up a car with howe or wright racks and have on prob's. maybe It can help you to..

MikeM Buggy Head

1,429 posts · joined Aug 2003 ·

#182271
Baja Wes wrote:I never said it's good. Just probably better than stock.

Sure as it travels each wheel will toe out, be it will be even amounts.

The stock set-up weaves on big bumps cos the short tie rod and long tie rod are changing the toe different amounts on each side, causing it to make the car want to turn on big bumps.
I agree with that. The toe in and toe out change with this rack would be signifigantly more than stock, but at least it would be even side to side. So the bump steer would be less than stock, but the toe in toe out changes would be greater.

Unless of course one wheel was up and the other side was near neutral. Then one side would have more toe out than the other causing bump steer.

🙂

[Edited on 4-6-2004 by MikeM]


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Desert Moose Cut Cut Cut

2,098 posts · joined Mar 2004 ·

#182276
one more thing ????? while talking steering geometry. how do you guys go with the ackermans angle on your short wheel base Buggies

MikeM Buggy Head

1,429 posts · joined Aug 2003 ·

#182277
Desert Moose wrote:one more thing ????? while talking steering geometry. how do you guys go with the ackermans angle on your short wheel base Buggies
Hehe, yeah, they're not right. The tyres squel like mad when on a painted surface like a car park etc as they are not right. Not such and issue when offroad though.


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Desert Moose Cut Cut Cut

2,098 posts · joined Mar 2004 ·

#182282
something to look into if your making front stubs but

lexm Commited Dubber

57 posts · joined Apr 2004 ·

#182308
MikeM wrote:[
The best geometry for steering is to be exactly the same as the geometry of the suspension. The geometry of the suspension is triangle B, so we need to make the geometry of the steering as close as possible to triangle B to eliminate bump steer. This could be achieved by having a rack and pinion setup mounted right up on the front torsion tube with it's tie rods pivoting where the red and blue line meet on triangle B.

.

The best geometry for eliminating bump steer - YES.
The best geometry for steering -NO because the ackerman will be wrong.

The best compromise would probably put the inner ends of the tie rods about the same distance behind the front beam as standard, assuming the VW steering was optimum on the original and that the track and wheelbase was unaltered.

In the case of a shortened wheelbase, moving it back or forward could be used to correct the ackerman error (possibly at the expense of bump steer).

The bump steer characteristic would also be affected by any other changes to the front suspension such as raising or lowering.





[Edited on 4-6-2004 by lexm]

MikeM Buggy Head

1,429 posts · joined Aug 2003 ·

#182310
I see Bump steer as a much bigger issue than Ackerman. As long as the Ackerman angles are close to stock (which they would be with the rack mounted on the torsion tube or just behind) I don't think it would be a concern.

http://www.auto-ware.com/setup/ack_rac.htm

Here is a cool reference on car handling. Actually relates to RC model cars, but hey a Manx is just a big toy car 🙂

http://rctek.com/handling/index.html

This is pretty cool, gives some info on how Ackerman can be set.

http://rctek.com/handling/ackerman_steering_principle.html

This is actually a bit simplistic as it does not take into concern the arc travelled by the pitman arm or the steering knuckle.

Having now read a bit of info on Ackerman I believe that putting a rack and pinion on the humble VW may actually fix the Ackerman rather than make it worse. Is the Ackerman on a VW actually correct? It will be at one point, but probably not at all points due to the swing of the pitman and the issues with a short and long tie rod. At full lock I'd say a VW has incorrect Ackerman.

If I get enthusiastic I will look into this more. There must be some equations relating to this somewhere.

[Edited on 4-6-2004 by MikeM]


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ducky Believer in Buggyism

1,238 posts · joined Aug 2003 ·

#182390
love this stuff
Baby Loves to Mumbo

Brad Wolfsburg Elder

3,764 posts · joined Aug 2002 ·

#182966
mmm looks like some people have gone and gotten some big words........ hehe

If all goes to plan I should have a Power assisted R & P on a ball joint front end in the next few weeks. Just sorting out exactly what the engineer wants before he will approve it.

The above does make for very interesting reading though... so where are all your pics of setups though ??
Brad
Why copy when you can own an original ?
Meyers Manx Australia

seagull Compulsive Aussie Vee Dubber

4,979 posts · joined Dec 2003 ·

#183149
the center mount race rack no good Brad .I know where there is two of them .Not power but very good $$ :alien
Looking for that special lady : PM me for coffee & cake

Desert Moose Cut Cut Cut

2,098 posts · joined Mar 2004 ·

#183272
Buggy Brad wrote:so where are all your pics of setups though ??
G'day Brad
No pic's now but I will have some for ya soon. I use a S.O.R.E rack, non power (like a wright rack) which is center mounted and a power steering servo out of a forklift up near the S/wheel. the pump runs off the crank with a small pulley and a type III bolt. the pump came from Kartek in the U.S. with the mount for Type 1 motor (3 nuts on the alt stand and one case stud)

Desert Moose Cut Cut Cut

2,098 posts · joined Mar 2004 ·

#183276
This is the pump its not the best pic but I will replace it later with a better one and also one of the rack and servo..

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MikeM Buggy Head

1,429 posts · joined Aug 2003 ·

#183370
Buggy Brad wrote:😎
Ahh, the ever mysterious Brad.

Well when you get it approved can you give us a brief run down on what the engineer required to get it past? I am interested in running a Rack and Pinion in the SubaManx so I'm curious as to the engineers requirements.

Mike.



[Edited on 7-6-2004 by MikeM]


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Secoh Fahrvergnugen

926 posts · joined Sep 2002 ·

#183462
FWIW that first picture IS using the same rack setup as Camira. Remember Camira is an Opel and was sold all round the world as the GM "J" car, so you can do the same setup here using the camira rack. JD and JE were available with power steering.
If it aint broke,
Make it go faster!!

Desert Moose Cut Cut Cut

2,098 posts · joined Mar 2004 ·

#183545
Hey Mike, I know where you got that photo you posted...... lol

the Wright place

Jenny Officially Full-On Dubber

352 posts · joined Jun 2003 ·

#193018
A fellow Eureka owner has used a R & P out of a Hyundai not sure on how legal it is but I'll see if I can get pics.

There was an old 1980's vintage article on R & P steering for VW based kit cars. Go to the Nova site here

http://www.nova-international.net/home.htm

then on the left bar click ‘data’ when the page loads, scroll down the Right hand side and click ‘The chassis’ then when that loads scroll down to "an alternative steering system to the VW"

Baja Wes V6 Baja Pioneer

3,119 posts · joined Aug 2002 ·

#193233
Jenny wrote:http://www.nova-international.net/home.htm

then on the left bar click ‘data’ when the page loads, scroll down the Right hand side and click ‘The chassis’ then when that loads scroll down to "an alternative steering system to the VW"
I just looked at that. That guy has no idea what he is doing, and his set-up sucks. Problem is he is thinking 2D, not 3D. The susp arms actually swing in an arc out of the page of his pic. macpherson strut susp design doesn't work on torsion bars.

I've been running some calcs for Brad. I have found the stock set-up can get nearly no bump steer at all if set-up absolutely precisely accurately perfect. The problem is this is very unlikely to occur in the real world. error's in exact steering box angle, eccentric camber adjustments and other things eventually lead to the stock set-up being prone to bump steer.
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.

Desert Moose Cut Cut Cut

2,098 posts · joined Mar 2004 ·

#193310
Hey Brad I don't know if this will help you but a long time ago when I was fitting racks I made a toe beam. What’s this you ask, it one step up from a tape measure...lol. I got a 25mm piece of Polly pipe 6" short of the inside of both front tyres (about 1100mm long) then a 12” bit of broom stick and a 24mm spring that was about 10” long. Drill a hole in the stick 2” away from the end and put a bolt though it. But the broom stick in the pipe with the spring between the bolt and the pipe. On the broom stick at about 5” and up to 7” mark it off in millimeters this is where you read your toe change. Take you torsion bars out and use a jack to lift and lower the front of the car to check the bump steer. With the rack tacked you can move the rack up, down, back or forward to get the right bump steer before you weld it. This cool backyard tool can be used as a bodgie wheel aligner as well. When the car is back together but it at the front of the wheels then roll the car forward till the toe beam is at the same height at the back this will give you your total toe reading e.g. the difference between the to reading. Bodgie but it works. (I use a laser aligner now to setup but it takes longer).

Moose
:thumb