fail-proofing full hydro steering

[jesusgatos]

Just posted this over on pirate4x4, but I know there are a lot of people on here that know a lot about hydraulics too, and I'd appreciate any helpful input on this subject.

I know - it's not possible to fail-proof anything. But I'm building an offroad-oriented motorhome (M109 conversion) that I want to convert over to a full hydraulic steering setup, and I want to make it as safe as possible. This is a BIG truck (16,000lbs empty) and I'm going to be driving it on public roads. Plus, I'm going to be living in it full-time and, well, I don't want to crash my house.

The M35A2's all came with manual steering, and it's actually not as bad as I was expecting; at least when the truck is moving and the road is smooth/paved. But maneuvering in parking lots and steering through rough terrain is absolutely brutal. The M35A3's were outfitted with air-assisted power steering systems, and those air-assisted power steering systems were also retrofitted to some of the M35A2's. But I'm not at all interested in going that route. There is limited room to retrofit another (power) steering box, and no real way to run any type of crossover steering linkage. So here I am. I'm NOT asking whether or not I should run full-hydro steering on the street, so please don't turn this into another debate about whether or not full-hydro steering is legal/safe/etc. I'm comfortable with the idea of running full-hydro steering on the street - I'm only trying to figure out how to design and build the best/safest system for this application.

I've read through all the relevant threads that I could find, and I've read Billavista's tech articles. I know that all the components need to be carefully selected in order to create a balanced system, and let's just assume that the whole system will be regularly inspected and properly maintained. In some of the past discussions about running full-hydro steering on the street, we've talked about the back-up systems that they use in things like airplanes. I'd like to figure out whether it's possible/practical to design/build some kind of similar redundancy into this kind of steering system.

I'm most concerned about blowing pressure lines/hoses, as that's probably the type of failure that's most likely to result in a total loss of steering, right? I'm not too concerned about losing power/pressure, as that wouldn't be any worse than what I've got now (manual steering). But I guess the steering unit could fail somehow, or the ram/s could blow apart. Am I overlooking any other (realistic) types of potentially catastrophic failures that should be considered/addressed?

Having two completely separate/redundant hydraulic steering systems seems like one obvious solution, and that wouldn't be too difficult. But I'm wondering if I really need to double-up on EVERYTHING.

Is there any way to design/build a system that has two separate hydraulic circuits without using two pumps? I just don't have enough room to install a 2nd pump (at least not one that's engine-driven). I'm planning on using the stock 5-ton/LDS multifuel engine's power-steering pump. The specs on these pumps vary a little bit, but they're all positive-displacement type pumps, and they put out between 5-6gpm at 1000-1500psi (more info here). Could that be done with check-valves or something? Doesn't seem like that would be a problem.

What about the reservoir/s? Would it be a bad idea to use a common reservoir? I know that eventually a blown line would drain the system, but I'm going to have an extra-large reservoir (10-20 gallons) because I've also got a transfercase-mounted hydraulic PTO unit on this vehicle. I've got to use multiple reservoirs anyway due to space constraints, but I would like to be able to run all of the hydraulic fluid through the same filtration system if at all possible.

And what about the steering unit? I'm totally stumped here. No idea how to control two separate hydraulic systems with one steering unit. Is it just a matter of creative plumbing, or would I need a different type of steering unit? I definitely want to use something that's load-reactive, and I would like it to have a power-beyond port, but that's not essential.

After considering all the options (at least that I'm aware of), I think I'd like to use two cross-linked rams, mounted sort of like this:

But can I use unbalanced rams that aren't cross-linked?

I would consider using a single/balanced/centered ram, but I'm not thrilled about the side-loads. Especially on such a big heavy vehicle that's going to see a lot of street miles. Plus I like the fact that with two rams, I'd still have a backup if I lost one. More common and less expensive too (service/replacement).

Not sure how I'd use one (or more) of these, but I thought it was pretty cool:

 

[SixSpeed]

Let me know which state you'll be driving in, so we aren't there at the same time.

Why not hydro ASSIST?

 

[m16ty]

I know you said you didn't want to hear it but I can't resist.

Have you driven a full hydro steering at hwy speeds? I drove a rockcrawler that was full hydro down the road at about 30mph and that was all I wanted. It's just a very odd feeling at high speeds and is hard to keep straight. You can't beat it for off road but is a whole different animal at hwy speeds.

Have you looked at hyd assist? It basicly attaches and looks like an air assist but uses hyd instead of air. They are much better IMO than the air assist.

With all that being said, I don't know how you would have two seperate systems without having two of everything including hand pumps (steering wheels). I wouldn't be overly concerned about blowing hyd hoses if you used quality hoses and inspected them regularly. They do make valves that will lock the cylinder if a line blows or you loose pressure for some reason (cranes use them so the load won't fall if a hose gives out). I don't know if a locked steering would be any better than an out of control steering though?

 

[KsM715]

Full hydro steering is not legal as far as I know. Nor safe with a vehicle of that size that has been engineered (sp?) by a backyard mechanic. Not that I doubt your skills but people that design sytems like this spend many years and many dollars going to school to learn how to do it.

 

[Unforgiven]

How about two steering wheels, one manual & the other hydraulic. Put one of them on the passenger side. That way when the wife starts to back-seat-drive you can just let go of the wheel, fold your arms, and tell her to drive.

 

[rchalmers3]

Hey Sus Gato,

Man, you are really a creative sun of a gun, you know that? You think of some really interesting (and whacky) ideas!

Allow me to question? What are you trying to accomplish by going to fully hydro steering? What problems or situations are you anticipating? Most of your first post reads about the "HOW" and not the "WHY".

Info on the "WHY" may help us get a grasp on the possible solutions to offer.

Please don't read this as adversarial, I am interested in reading some new ideas as well.

Rick

 

[gimpyrobb]

A long long time ago, before I ever had a 6x6. I read an article about how a sagnaw power steering box was drilled and tapped to control a hydraulic ram. A few years after understanding what it was and how it worked, I saw an article about a guy that put an M37 or a WC on a shortened deuce chassis. He somehow installed that drilled and tapped power steering box setup in his deuce/dodge creation. I had an email or two from him but those emails and that web page have long been gone. I think I even spent a week looking for it again. I think that would be your best bet. Maybe I ought to look through my emails again. I think the brand "redneck ram" is based on this setup. Might want to look their page over.

 

[jesusgatos]

Yes, I've driven vehicles with full hydro steering. Some (most) of them are sketchy, but it's definitely possible to build a system that handles well (doesn't have any slop, has some road-feel, and returns to center). And yes, I'm familiar with hydro-assist, but I don't want to go that route on this vehicle. I've got my reasons, but I'd rather not even get into that. I've already decided to go with a full hydro steering system, and I would do that even if I wasn't able to make any improvements on the systems that are currently available. Full-hydro steering CAN be made safe. I'd just like to see if there's any way that I can make it safer. Personally, I'm far more concerned about the single-circuit brakes...

Full hydro is NOT illegal. We've had this discussion here before, and it's been beaten to death on pirate. I don't really want to get into this debate (about whether or not full hydro steering can be made safe), but I make my living designing and building things, including high-performance aftermarket products for off-road vehicles. I've designed and built several vehicles from scratch, and I'm confident in my abilities to design and build a safe steering system.

That's an interesting idea about having a ram that locks to center if there's a failure. Thanks, I'll look into that. If it ever came down to a total loss of steering, I'd rather be going straight than have the wheels turn to full-lock. At the very least, if the vehicle's going straight, I'd think you've got a better chance of slowing down without wrecking.

 

[rchalmers3]

GR,

Is the Red Neck Ram a fully hydro install or an add on "assist" system? I thought it was the later.

Rick

 

[gimpyrobb]

Yes, an add on assist. Since you have decided on full hydro, aren't alot of fork trucks full hydro? Might want to start there.

 

[rchalmers3]

I would surmise (not "know" 'cause I'm not an engineer) that a fully hydro system, in order to work properly at both crawl and highway speeds would be an engineering marvel.

In other words, the geometry of the steering and the power assist would be designed to work together to accomplish the traits that are desired over the entire driving envelope.

Simply adding full power to the existing deuce steering seems like a project headed for disappointment. I think you would want to reconstruct the steering rake, caster, SAI and tailor the power assist according to load and road speed.

You got game for that?

Rick

 

[jesusgatos]

Hey Sus Gato,

Man, you are really a creative sun of a gun, you know that? You think of some really interesting (and whacky) ideas!

Allow me to question? What are you trying to accomplish by going to fully hydro steering? What problems or situations are you anticipating? Most of your first post reads about the "HOW" and not the "WHY".

Info on the "WHY" may help us get a grasp on the possible solutions to offer.

Please don't read this as adversarial, I am interested in reading some new ideas as well.

Rick

Thanks?

Ugh, the WHY. I guess that's only fair. Well, there are a lot of reasons. The first decision I had to make was to replace the stock steering box with... something. At the point where I'm trying to improve on anything, I like to explore the outer limits of what's possible, and then I usually scale things back to what's practical. I just like to make informed decisions, and that usually involves a ****-ton of research and a lot of time thinking about these kind of projects.

When it comes to steering, there are only so many options. I could have converted over to some type of power-steering box from another big truck. Several people have documented projects like that on here, and done really nice jobs with those conversions. But I hate the stock drag-link arrangement. It's really more a matter of geometry than power. And there's no room to convert to cross-over steering, which I would have otherwise considered. If I was able to make that work, then I would have gone with a hydro-assisted ram setup.

This vehicle is going to be an evolution, like most of my projects, and it will go through several build-stages. Right now, it's a relatively mild off-road vehicle (by my standards). But after I get through with the motorhome conversion, I'll turn my attention to off-road performance. And then the suspension will end up getting modified, and the stock draglink arrangement would be a major limitation / weak link. So I'm building with a vehicle that will need full hydro steering eventually, I want to improve on the stock steering system now, and I don't want to do this twice. That's more or less how I arrived at this decision (I've been around full-hydro steering systems on rock crawlers for a long time, and was already convinced that they could be made safe enough to drive on public roads).

A long long time ago, before I ever had a 6x6. I read an article about how a sagnaw power steering box was drilled and tapped to control a hydraulic ram. A few years after understanding what it was and how it worked, I saw an article about a guy that put an M37 or a WC on a shortened deuce chassis. He somehow installed that drilled and tapped power steering box setup in his deuce/dodge creation. I had an email or two from him but those emails and that web page have long been gone. I think I even spent a week looking for it again. I think that would be your best bet. Maybe I ought to look through my emails again. I think the brand "redneck ram" is based on this setup. Might want to look their page over.

Yeah, that's a hydro assist system Gimp. I've done that on other vehicles, and it works great. West Texas Offroad builds/sells the Redneck rams, and many other companies like AGR and Howe build/sell similar components/systems.

 

[jesusgatos]

I would surmise (not "know" 'cause I'm not an engineer) that a fully hydro system, in order to work properly at both crawl and highway speeds would be an engineering marvel.

In other words, the geometry of the steering and the power assist would be designed to work together to accomplish the traits that are desired over the entire driving envelope.

Simply adding full power to the existing deuce steering seems like a project headed for disappointment. I think you would want to reconstruct the steering rake, caster, SAI and tailor the power assist according to load and road speed.

You got game for that?

Rick

As far as I'm concerned, that's not even up for debate. Aside from the growing number of modified vehicles that have been converted using high-performance components purchased from companies like PSC Motorsports and Poly Performance (and some of those vehicles are very pleasant to drive, even at high speeds on & off-road), there lots of examples of production vehicles already out there driving on public roads that use full hydro steering, including the new unimogs, many large garbage trucks and other heavy equipment, some nissan sports cars (rear-steer), Chevy trucks with rear-steer, etc. The components needed to build a high-quality system already exist. I'm just trying to figure out if there's a way to design some additional safety into the system, and I don't know a whole lot about hydraulics, so I'm doing a bunch of research.

You're right about looking at everything related to the front suspension and steering as a whole though. I have, and I am. It's really not that complicated. With a straight-axle and leafsprings, there's just not a whole lot to it. I'm going to increase the caster (from stock to 6-8 degrees). That should help the steering return to center, and from what I understand, it's as simple as flipping the leafspring mounting pads around. I know what the kingpin inclination is, but there's no reason to change that. I only built my new wheels after figuring out what my scrub radius was going to be, and deciding that it was acceptable. All of the steering components will be sized with these things in mind, along with the weight of the vehicle, and desired handling characteristics. There is a LOT of published information out there about how to calculate these things. Not anything I'm going to pull out of my ass...

 

[Wrench Wench]

Cat Savior: Even after recovering my Pirate 4x4 account and logging in, when I click on those P4x4 links, I get 403s with a side order of 404. Is there anything you need to do to fix that, or is Pirate being a scallywag?

I've seen more hydraulics used at hydrostatic drive systems in motorcycles, usually diesel motorcycles, but there was one set of build vids on YouToob where the guy was setting up a hydraulic steering for the front swing-arm: http://www.youtube.com/watch?v=bnWZfiUORXg but he never finished it to the best of my knowledge. His last few videos have been of his kid (or grandkid, dunno).

Here's the most detail he gives on his hydraulic steering setup. Doubt it'll be found illuminating.
http://www.youtube.com/watch?v=ZHSXlemRbVo

 

[jesusgatos]

Cat Savior: Even after recovering my Pirate 4x4 account and logging in, when I click on those P4x4 links, I get 403s with a side order of 404. Is there anything you need to do to fix that, or is Pirate being a scallywag?

Links work for me?

 

[Jones]

One thing you'd need for sure is a proportioning valve (ROAD-OFF ROAD?) for control.
In my experience; the same thing that makes full hydraulic great for rock crawling (super responsive) makes it miserable for highway driving.
And it only gets worse when there's play in the steering wheel. By the time you've turned the wheel through the play far enough to bump the control valve and the truck has changed course (usually more than you intended), from there on any additional corrections end up as exponential oversteer.

If you're going to do it then find a lot of back roads and wide open spaces to practice in and get the feel of it before you venture out onto a public road.

Might save yourself some hassles by doing some reading in the vehicle code and a DOT manual. I too, think full hydraulic is illegal for road use because of the lack of "a direct mechanical link with the steering axle". If the system suffers a catastrophic failure, you'll end up still pointed the direction you were pointed when the hose, line, link, pump drive-belt broke-- and with no way of controlling things short of an emergency stop.

 

[Wrench Wench]

Jesusgatos: Even after I pulled up the Billavistas Tech Article, the images below 403 on me. *shrug*

I think a redundant system with steering wheel -> steering shaft -> hydraulic steering pumps -> hydraulic lines -> tandem ram -> tie rods qualifies as a direct, mechanical linkage. Replace the hydraulics with pneumatics and that would no longer be true, but the idea of hydraulics is the incompressibility of the fluid, hence direct, mechanical transfer of power.

 

[jesusgatos]

One thing you'd need for sure is a proportioning valve (ROAD-OFF ROAD?) for control.
In my experience; the same thing that makes full hydraulic great for rock crawling (super responsive) makes it miserable for highway driving.
And it only gets worse when there's play in the steering wheel. By the time you've turned the wheel through the play far enough to bump the control valve and the truck has changed course (usually more than you intended), from there on any additional corrections end up as exponential oversteer.

If you're going to do it then find a lot of back roads and wide open spaces to practice in and get the feel of it before you venture out onto a public road.

Might save yourself some hassles by doing some reading in the vehicle code and a DOT manual. I too, think full hydraulic is illegal for road use because of the lack of "a direct mechanical link with the steering axle". If the system suffers a catastrophic failure, you'll end up still pointed the direction you were pointed when the hose, line, link, pump drive-belt broke-- and with no way of controlling things short of an emergency stop.

No, you can get steering units with whatever kind of speed/power you want, and pick to suit your needs. I don't think there would be any need for any type of proportioning valve. If you've driven a vehicle with full hydro steering that felt like it needed something like that, I would guess that it wasn't set up right. There should be ZERO play in the steering wheel with a (good) full hydro system. Well, less than with any type of traditional steering linkage.

I've done the research (lots of it) and I would wager money that you can't find a state/federal statute that specifically prohibits full hydro steering systems. In states with mandatory inspections, or where there are rules governing custom-built vehicles, the rules all seem to be performance-based, and I don't have any doubts that my steering would pass that type of inspection.

 

[jesusgatos]

The whole "direct mechanical linkage" thing is bull****. I haven't been able to find anything about that anywhere. I'm not sure where that started, but nobody has been able to provide a source. There's just no such requirement.

 

[frodobaggins]

Links work for me?

P4x4 doesn't allow hotlinking. The links work for you because you have them cached.