Brake Assisted Steering

[JWP]

Hmmmm, I see said the blind carpenter as he grabbed his hammer and saw! I think you are missing a bunch of things going on and are going to have to get rid of the mechanical concept and go electrical (micro sensors for example); too much monkey motion in the mechanical idea based on what I am now seeing. I don't think you want to put additional loads into the steering like that either. Also, I think you are not going to want that to be full time for several reasons like fuel economy for instance so you could easily shut it off if it were electrically based. think about how some of the cars can change their suspension on the fly from Grandpa/Grandma to Good-lord-Lucy, hang on to your depends!

I totally agree, electromechanical would be by far better, but that surely takes it out of my realm of affordability. Furthermore this goes into my pile of things to do when I hit the lottery so high that I can never work again and never run out of money, but I digress.

As for the suspension moving etc, I think this could be accounted for, but I had thought of that. I actually kinda took this idea from the early VWs that had cable operated brakes as did Model T's have mechanical brakes. Come to think of it the parking brakes are cable actuated and the suspension moves up and down.

The load on the steering could be a concern, and some calculations would need to be done to balance everything out but with some of the abuse that I know I've put my VW's through over the years, I would think some basic gusseting on the spindle steering arm would be sufficient. There is only one way to know for sure.

Do you see any advantages to a cable system over the lever system I described (and squiggled at) earlier?

Here is why I would do it the way I propose
Simplicity - to me it's more simple this way. I also realize I may not think like most people and to some this may seem more complex.
Adjustability - I feel the adjustment could be done in more fine increments
Hole in the front firewall - they are small and easy to make. If I am imagining yours right there would need to be a hole big enough for the lever to pass in and out of
Space limitations - The under fuel tank is a crowded area, I discovered this when exploring the idea of a pinto manual rack, which is now on the back burner for now.

From a functional stand point, your idea would work great. One thing I would explore to possibly improve your specific idea, I would consider connecting the end of the brake lever to the tie rod via a pair of heim joints. The inherent slop that exists may be enough such that when you slid the base back to disengage the system it wouldn't apply enough braking force to do much, but when you slide it forward then the heim joints are perpendicular to the lever and will actuate it. It could also be there is not enough slop and it wouldn't reduce the braking forces enough to make them not existent.

[spectre6000]

Ol'fogasaurus got me good about the up and down movement of the tie rods with the cycling of the suspension. I did not account for that at all. With that in the picture, I think the cable actuation is the better choice by far. Rigging cables sounds more complicated to me than a clamp on the tie rod, but the joints that would be required to allow and transmit movement in the X and Y axis and allow and restrict movement in the Z axis eliminates the simplicity advantage. The smaller hole requirements is also a bonus. If I'm going to try this out on my car and it doesn't work, it's much easier to plug a few tiny holes than to reweld a 6"X3" (or whatever) section of firewall (with two layers no less).

I think a combination of our two systems would probably serve best though. A single lever action setup seems to be far more simple and cost effective than two discrete lever setups. I need to squeeze my mind grapes a bit more to get my head around this setup to figure out how to vary amount and timing of actuation though...

As to electronics, I really can't see what would make them necessary. You don't need ABS for regular braking any more than you need D-Jet for fuel delivery. I'm sure having some electrons figuring out when to squeeze the clamps and when to let them go helps, but I can't see why a competent driver who knows how their car handles and how to handle it couldn't do better. If it's consistent and well adjusted, there shouldn't be any surprises to the driver.

[JWP]

I think the problem with a single unit is the need to push with just one cable and push pull. Moorse cables are the only i've seen that can push and I think their limits would be insufficient, but it could work.

[Ol'fogasaurus]

If you have ever driven rod or cable brakes you know why Dodge converted starting on some models in 1924 (if you are interested: http://www.carhistory4u.com/the-last-10 ... car/brakes). I it took others like Ford ('39 I think) and Chev ('37 I think) waited until ~10 years later to figure it out . Cable brakes are somewhat simple but the cable do stretch. Cable and likewise rod (rod brakes are also know as 'mechanical brakes' and use rods and clevises and I mean a lot of them per vehicle) systems to not account well for brake shoe wear well at all so they typically need to be adjusted (never adjusted cable brakes but I did help once or twice with rod brakes) frequently to work well (and I use the term 'well' lightly). Cable E-brakes show this especially if you forget to release them once or twice and have to re-adjust them. I also have seen the e-brake handle yarfed on so hard that it stretched or broke (comment deleted but it was funny... just not appropriate).

With the cable or mechanical style rods you have to account for length changes as you turn the front wheels and for the suspension to move up and down. If you are turning to the left, the left cable is going to get slack as the wheel turns (arc) and the right side cable is going to draw tighter (the spindles turn in an arc). If the suspension is going up and down the tight cable will have to accommodate both on a hard turn. How much am I going to have to account for: I don't know, that is what the laying of it out should do and you are going have to figure for worse case in each turning direction unless you can get things perfectly centered in-between the front wheels inside of the passenger compartment. You also might have to account for possible frame head deflection if the cables are going to be tight. I might be overstating the problem but I also think I could be understating it too. You have to think things out 3D (X, Y and Z dimensionally) before you get too far into this.

I think you are past basic noodling and have moved into the need for practical noodling: that is finding and solving noodling problems and weaknesses.

Lee

Addendum: I was trying to post and the two posts came up. Morse (style) cables do push and pull but they are problematic as I remember. Based on what I heard during the time I was into boats, they are notorious for locking up. Not what think you want to have with this design you are working on. They also have to be secured at reasonable distances and the diameter of bends they need is generous maybe to a fault.

[Ol'fogasaurus]

Compliment!

I must applaud you on the idea of a second set of calipers on the rear. I never have liked the idea of cutting into the brakes themselves which can, and has, lead to braking problems. I had a set of turning brakes go bad on me locking up the left rear wheel. I had to open the bleeding screw to relieve pressure so that I could limp back to camp in first gear w/o the use of brakes.

Putting the second set of calipers on the rear rotor, dedicated (mainly) to turning/cutting brakes, should give rise to differently made systems (you should be given credit if it already hasn't been done). Properly plumbed, it would allow the primary brakes to be basically stand alone and the turning brakes to be separate but redundant braking if plumbed into the master cylinder (dual circuit or tandem MCs) to support the other braking system. They could also be plumbed separately, either way is something I do not remember having seen or hearing of before. Usually whey go with multiple puck brakes. The would probably add some un-sprung weight but it might be worth it though. It sure opened up my thinking on the subject.

Lee

[spectre6000]

Ol'Fog, the cables are only to actuate the hydraulics from the tie rods.

JWP, no pushing involved. See scribbles:



Anchoring the cables on the levers to something threaded will allow some fine adjustment at that end; doing the same on the tie rod end of the cable will have similar effect. The longer the lever the lesser the effect of a turn on brake actuation and the lesser the additional steering input effort; the shorter the lever, the greater effect and the greater the additional steering input effort. It would probably be worthwhile to have the cylinder side of the lever be a reasonably long length to increase the amount of available adjustability, but I could be wrong there.

[JWP]

Ol'Fog, the cables are only to actuate the hydraulics from the tie rods.

JWP, no pushing involved. See scribbles:



Anchoring the cables on the levers to something threaded will allow some fine adjustment at that end; doing the same on the tie rod end of the cable will have similar effect. The longer the lever the lesser the effect of a turn on brake actuation and the lesser the additional steering input effort; the shorter the lever, the greater effect and the greater the additional steering input effort. It would probably be worthwhile to have the cylinder side of the lever be a reasonably long length to increase the amount of available adjustability, but I could be wrong there.

I thought you wanted to eliminate one of the cables. the only difference i see in mine and yours is that you added a pivot that i did not. However I was going to use the pivot that was included on your standard turning brake.

so mount this upside down on the bottom side of the trunk pan such that the levers are hanging down below the dash, forward of the shifter.

[Ol'fogasaurus]

I understand that, that why I said what I said. Have you ever driven with turning brakes (not trying to be a smart ass here); with short handles the leverage needed is not there so you have to pull very hard at times and the faster you go the more you have to pull. Weight is also penalty you are going to have to deal with.



This is my setup showing the short handles.

At slow speeds you still have to pull some (remember, you legs are much stronger than your arms and upper body are), at higher speeds I usually don't apply them or maybe pump them a bit if the front steering tires I am using are taking too long to change to the direction I want to head in. Also remember, there is only two spiders in most stock VW transaxles.

I just thought of it when I was thinking of the spider gears but with your design, when backing up and turning the brakes could also be applied and reverse is not that strong. If you have ever played with tired rezeppa (I am sure that this is miss-spelled) CV joints that were in some of the early military Jeeps (I had a '42 MB) when backing up with the wheels turning the Jeep they would slowly lock up and you could easily 'whang' (an onomatopoeia: http://en.wikipedia.org/wiki/Onomatopoeia) a transmission.

Lots to think about.

[Ol'fogasaurus]

Ol'Fog, the cables are only to actuate the hydraulics from the tie rods.

JWP, no pushing involved. See scribbles:



Anchoring the cables on the levers to something threaded will allow some fine adjustment at that end; doing the same on the tie rod end of the cable will have similar effect. The longer the lever the lesser the effect of a turn on brake actuation and the lesser the additional steering input effort; the shorter the lever, the greater effect and the greater the additional steering input effort. It would probably be worthwhile to have the cylinder side of the lever be a reasonably long length to increase the amount of available adjustability, but I could be wrong there.

I thought you wanted to eliminate one of the cables. the only difference i see in mine and yours is that you added a pivot that i did not. However I was going to use the pivot that was included on your standard turning brake.

so mount this upside down on the bottom side of the trunk pan such that the levers are hanging down below the dash, forward of the shifter.

Think about having to add residual pressure valves for two reasons, one: your turning brakes are going to be above your master cylinder and you can get bleed back into the reservoir. The second is tied to the first as the turning brakes are sitting at an angle which could exacerbate the situation. I don't know this for sure but it needs to be thought out thoroughly.

[spectre6000]

I've not driven with cutting brakes, no. Leverage can be built in pretty easily though. Low speeds in reverse may present a problem. I doubt the Porsche system is active in parking lots. A means of disabling the system will likely be necessary.

Think about having to add residual pressure valves for two reasons, one: your turning brakes are going to be above your master cylinder and you can get bleed back into the reservoir. The second is tied to the first as the turning brakes are sitting at an angle which could exacerbate the situation. I don't know this for sure but it needs to be thought out thoroughly.

They're not connected. Two discrete systems. The only way they're even related is that they share a rear rotor and the lines will run parallel to each other.

[JWP]

You have a vaild point. I don't think we had reached that point of the discussion until now. In which case you would then need to explore MC bore and stroke options.
The drift guys use a single master cylinder to lock up their rear brakes and operate them by hand, rapidly and repetitively. While not illustrated I did mention in an earlier post that I would want some sort of way to disconnect this for the "parking lot" maneuvers ie reverse, tight turns, this is where electronics would shine because you could flip a switch must like modern day traction control to disable and enable the system. But for me that would be so far out of my budget I wouldn't even try. In fact I really think if I were going to do this, I'd just set up a steering brake with a single lever steering brake like in my rail, but i would probably only use this in AutoX.

[JWP]

I've not driven with cutting brakes, no. Leverage can be built in pretty easily though. Low speeds in reverse may present a problem. I doubt the Porsche system is active in parking lots. A means of disabling the system will likely be necessary.

It's not it uses speed sensors to activate. If we are talking about the same car it also has 4 wheel steering. At low speeds it steers opposite of the front tires to help tighter turns be tighter, and at higher speeds it steers the rear with the front tires to maintain stability.

[JWP]

Ol'Fog, the cables are only to actuate the hydraulics from the tie rods.

JWP, no pushing involved. See scribbles:



Anchoring the cables on the levers to something threaded will allow some fine adjustment at that end; doing the same on the tie rod end of the cable will have similar effect. The longer the lever the lesser the effect of a turn on brake actuation and the lesser the additional steering input effort; the shorter the lever, the greater effect and the greater the additional steering input effort. It would probably be worthwhile to have the cylinder side of the lever be a reasonably long length to increase the amount of available adjustability, but I could be wrong there.

I thought you wanted to eliminate one of the cables. the only difference i see in mine and yours is that you added a pivot that i did not. However I was going to use the pivot that was included on your standard turning brake.

so mount this upside down on the bottom side of the trunk pan such that the levers are hanging down below the dash, forward of the shifter.

Think about having to add residual pressure valves for two reasons, one: your turning brakes are going to be above your master cylinder and you can get bleed back into the reservoir. The second is tied to the first as the turning brakes are sitting at an angle which could exacerbate the situation. I don't know this for sure but it needs to be thought out thoroughly.

agreed, i would run a dedicated line from the mc resivoir, maybe T off the supply to the rear circuit.

[spectre6000]

JWP, for some reason we're all having issues communicating these ideas. I didn't realize that's how you had it set up in your head. It makes a lot more sense that way, and the off the shelf parts require a lot less modification. One change I would make would be to flip it 180° and mount it on the tunnel. Mounted on the underdash would almost assuredly require some reinforcement and make it less of a bolt-on/bolt-off proposition. Like so.

EDIT: Note the dedicated reservoir exclusive to the system for above concerns.


As for disabling, a means of quickly disconnecting the system shouldn't be too hard to figure out. If leverage proves an issue, there are simple means of amplifying leverage as well.

[JWP]

I thought about putting it on the tunnel and that would require less bracketry, reinforcement, etc. I wanted it on the trunk pan just to keep it off the floor and out of the way of my feet, it may fit just fine as you have shown.