Hydrosteer mechainical link ideas

[plasticbadger]

I'm currently working on the design for my next build (read - messing about with CAD as I don't have the time, space or money to do any real work) and I'm wondering about a system to give me full hydro steering with a mechanical link.

Without getting the can-o-worms out too much, it seems the actual text in C&U regs, IVA or MOT that says you must have a mechanical link is hard to find and none too clear, but to ensure my new truck can compete in the events I want to do it will need MOT so I'll be wanting a mechanical link.

The problem is though that the chassis layout lends itself to double triangulated four link front suspension without a panhard bar, so a convetional drag link would create bad bump steer. Hydro steer (with axle mounted double ended ram) would remove the bump steer and a few other packaging worries.

So my thought is fit some form of either-or steering where the drag link can be fitted for road or restricted event use, or removed to run full hydro when allowed -

Thought #1 would be to run an orbital valve with some form of drive-through, or gearing to the steering shaft that turns a normal steering box. In 'road' mode you'd fit the drag link and open a valve to recirculate the steering fluid through the orbital valve and ram. Thus you have normal power steering and the hydro ram acts as the tie bar. In 'competition mode' you remove the drag link and close the bypass valves to run normal full hydro.

Thought #2 would be to use a modified power steering box as the oribital valve (plumbed as you would for hydro assist), so that worked out correctly you can run normal power steering or hydro assist with the drag link fitted and full hydro with the drag link removed.

So, my questions are,

Is a full hydro / mechanical link hybrid possible, might my ideas work?

Does anybody have any other ideas?

What sizing issues might I have with pump, steering box and ram volumes and flow rates?

I think the Filthy Boy team are planning something full hydro / mechanical link on their next build, does anybody know what system that is?

Finally, the difficult one, how would event organisers and other competitors feel about a vehicle competing in an MOTed only event using full hydro steer, if it had an MOT?! After all, how many of the other competitors keep their vehicles in a completely MOTed standard - all working lights etc. My aim is not to have a sneeky advangtage, just a nicely packaged vehicle.

[simonr]

Is a full hydro / mechanical link hybrid possible, might my ideas work?

Yes and maybe.

Does anybody have any other ideas?

Never short of silly ideas!

I quite like the idea of a removable link.

An alternative would be a connection via flexible cables. There is already a precedent for this on vehicles - even chain based steering on plant.

The flexible cables, being flexible, could be left in place and only really provide steering force when the hydro fails.

What sizing issues might I have with pump, steering box and ram volumes and flow rates?

No idea - suck it and see! You could calculate the max steering speed you will get for a given pump, rpm and ram size and spec the pump based on that.

I think the Filthy Boy team are planning something full hydro / mechanical link on their next build, does anybody know what system that is?

Have you asked them directly?

Finally, the difficult one, how would event organisers and other competitors feel about a vehicle competing in an MOTed only event using full hydro steer, if it had an MOT?! After all, how many of the other competitors keep their vehicles in a completely MOTed standard - all working lights etc. My aim is not to have a sneeky advangtage, just a nicely packaged vehicle.

I guess, with the link in place, it is just a ram-assist vehicle which is OK. If they have an issue with the hydro - you run with the link in place?

You might be in trouble if it 'fell off' mid comp though!

Si

[sean f]

Without getting the can-o-worms out too much, it seems the actual text in C&U regs, IVA or MOT that says you must have a mechanical link is hard to find and none too clear, but to ensure my new truck can compete in the events I want to do it will need MOT so I'll be wanting a mechanical link.

One thing the IVA regs are quite clear about is the steering must be self centering, as far as i understand it in normal set up most hydro steer set ups don't do this. I am sure it can be sorted with a bit of thought but normally things like this are easier to try and engineer in from the start rather than modify later.

I do like the idea of a removable link, if it can be made to work it would be a nice clear way for the vehicle to be definately road legal for IVA / MOT and yet retain the advantages for off road use. Also for events which don't allow pure hydro steer it could be left in place although the suspension may need some sort of limiting to prevent damage if it is left in place.

[Daan]

I personally hate the idea of a removable link, why not invent a system that just works on and off road? The filthy boy project had a hydro assist system previously, but better engineered than most. I personally see no reason why hydro assist cant work, its just that they are usually built with mismatched components, hydro valves that cant cope, and pumps that havent got enough flow.

I say just do a better job than what most others do and it should work fine. After all, the comp safari boys were having similar problems to us, but they now have solutions with a mechanical link that work.

daan

[plasticbadger]

An alternative would be a connection via flexible cables. There is already a precedent for this on vehicles - even chain based steering on plant.The flexible cables, being flexible, could be left in place and only really provide steering force when the hydro fails.

I quite like that idea, you could use a dual cable setup from a boat steering unit to act as a pull-pull with one cable acting on each knuckle. It would have a lot of packaging advantages too as the main problem is the lack of chassis in front of the axle to mount a steering box on. The quadrant on the steering column could even be disengaged when 'mechanical' steering is not required.

One thing the IVA regs are quite clear about is the steering must be self centering, as far as i understand it in normal set up most hydro steer set ups don't do this. I am sure it can be sorted with a bit of thought but normally things like this are easier to try and engineer in from the start rather than modify later.

I've only really got hydraulic steering experience from boats, but in theory the components could be engineered to provide self centring due to castor the same as a conventional steering setup.

I personally hate the idea of a removable link, why not invent a system that just works on and off road? The filthy boy project had a hydro assist system previously, but better engineered than most. I personally see no reason why hydro assist cant work, its just that they are usually built with mismatched components, hydro valves that cant cope, and pumps that havent got enough flow.I say just do a better job than what most others do and it should work fine. After all, the comp safari boys were having similar problems to us, but they now have solutions with a mechanical link that work.daan

The two problems with my current design is that the axle wont move side to side under bump and therefore a conventional drag link will cause bump steer. The other is that there is a lack of chassis ahead of the axle on which to mount a steering box. A longditudinal drag link from a steering box mounted in the footwell area combined with hydro assist could be made to work.

[nicks90]

ok, completely off the wall idea - but what about mounting the steering box on the axle itself? Then use a mechanical link from the steering wheel to the steering box. Obviously there would need to be a slip joint and a couple of small uj's in there to accomodate any length changes due to the axle moving up and down.

hydraulic pipes would hang down in the same way they would for the ram on teh axle anyway - in fact you could piggy back the steering box and hydro ram off the same 2 pipes so they work in conjunction, the steering box acting as the orbital valve possibly?

[simonr]

ok, completely off the wall idea - but what about mounting the steering box on the axle itself? Then use a mechanical link from the steering wheel to the steering box. Obviously there would need to be a slip joint and a couple of small uj's in there to accomodate any length changes due to the axle moving up and down.

Not too bad an idea either. Difficult to make the linkage to the steering wheel robust, but not impossible.

You could even just use a steering rack from something big like a RRS. They are capable of producing a lot of steering force - and have a solenoid valve operated bypass to increase the steering 'stiffness' when traveling fast.

Tell you what - you could gear up the steering at the wheel, and down at the box to make the steering shaft high speed, low torque. That could potentially lend itself to using a 'speedo' type cable to transmit the drive?

Si

[Night Train]

The only problem I can see with mounting the steering box on the axle would be bump steer caused by the rotation of the axle when one wheel lifts and the other drops. That small rotational angle would cause the steering box to steer towards the raised wheel.

The amount of 'steer' would depend on the size of the bump and the ratio of the steering box.

[landroversforever]

You could have a smaller, PTO sized (or even smaller) prop shaft?

[plasticbadger]

I'm still thinking more about the cable idea. A boat system could be used inline on the column with the hydraulic orbital valve, thoughts?

[simonr]

I'm still thinking more about the cable idea. A boat system could be used inline on the column with the hydraulic orbital valve, thoughts?

That looks perfect!

What about using two of the spools pictured, linked with cables to a steering box on the axle? It would reduce the force required in the cables.

Si

[Timmy511]

im not fully up on hydro steer or how it all works but.....

why not run a standard steering set up, rig a chain and sproket on the end of the steering column / on the steering linkage going to the pas box, then drive the orbital valve by a chain, then you adjust the gear ratios with different size sprokets to match the speed of the standard steering box for the speed of the ram. then it would still have all the mechincal link and be full hydro assist using a ram from a forklift or simliar mounted to the axle.

[SOA 93]

I think one of the main questions to ask regarding full hydro is is it going to see a lot of road work?

If it is to be trailered everywhere and the only road work it's going to see is between sections on a challenge event then there's nothing wrong what your describing.

I posted on a previous Hydro thread about the valve available from Rakeway. Clicky

Bill VS also posted in another hydro thread about the fact that LR steering box has no power a few degree's either side of straight ahead.

Also elsewhere, it has been noted that self centering is a product of caster settings.

I think Will Warne also suggested a system using a manual box. Which is the direction I want to take.

Rakeway's Ridgeback racer uses one of there steering valves but with a rack for sensitivity and the ram for power.

I asked Neil (Rakeway) a while back whether this would work with a manual LR box, he was convinced it would, in fact such a system had been fitted by him to his old Tomcat before he sold it, however it had not been tested and was removed prior to the sale.

[plasticbadger]

SOA 93, there's some interesting ideas. I'm going to do some more research and some sketches to think about the options so far.

It is likely that the truck will see very little road use, I only really want it to be road legal to comply with competition rules, such as UK challenges and European events like TAT and Dresden-Breslau. That said, if it ends up being usable on the road then I'll probably drive it to local playdays and to the supermarket .

At the moment the plan is to use the steering pump and possibly the box from a Chevrolet K5 Blazer, for which you get a completely matched hydro assist kit from PSC including modified box, uprated pump, ram and hoses for around $1000. So that's an option, but mounting the box infront of the axle is still looking difficult, as well as the preferred link arrangment.

[will_warne]

Hello mate, I'm not on my computer so I'll keep it brief - collar me when I next turn up to a club meet. The basic issue with full hydro and a mechanical linkage comes down to simple geometry: one part is trying to move in a linear motion and the other half in an arc. This means the system will fight itself. Not good. You have correctly identified the issue with triangulated 4 link and hydro assist - have you thought about untriangulated 4 link with a panhard? Also, why were you planning an approach angle much more than 90 degrees? You really don't want the winch fairlead too far behind the front of the tyre.

OK, hydro assist. Most of the issues with the majority of setups seem to stem from people wanting to keep LR steering boxes. These cannot handle the flow and pressure needed to make a successful system. Get the right valve and hook it up to a suitable manual steering box and you are away - fast, reliable, powerful and light steering.

As for self centering - add enough caster and any setup will self centre. You may need to clock the swivels but anyone planning on re-engineering their steering system should think about all aspects of the system before they begin...

[yella 90]

i really wouldnt trust the rotary helm unit of a marine cable

it just isnt man enough even rated upto 250hp

the better option would be the old style fletcher rack and pinion.

much stronger

but much bigger

dan

[plasticbadger]

Hello mate, I'm not on my computer so I'll keep it brief - collar me when I next turn up to a club meet. The basic issue with full hydro and a mechanical linkage comes down to simple geometry: one part is trying to move in a linear motion and the other half in an arc. This means the system will fight itself. Not good. You have correctly identified the issue with triangulated 4 link and hydro assist - have you thought about untriangulated 4 link with a panhard? Also, why were you planning an approach angle much more than 90 degrees? You really don't want the winch fairlead too far behind the front of the tyre.

OK, hydro assist. Most of the issues with the majority of setups seem to stem from people wanting to keep LR steering boxes. These cannot handle the flow and pressure needed to make a successful system. Get the right valve and hook it up to a suitable manual steering box and you are away - fast, reliable, powerful and light steering.

As for self centering - add enough caster and any setup will self centre. You may need to clock the swivels but anyone planning on re-engineering their steering system should think about all aspects of the system before they begin...

Thanks Will, I have thought about a 'normal' 4 link (and 3 link as per my last build) and panhard, the main 2 issues being that I'm trying to keep the frame narrow up front which make mounting the panhard and steering box difficult, but not impossible. The other issue is that I'm using portals, but want to keep the truck low which makes a conventional 4 link hard to package under the cab and engine. I think after looking at it that the compromisses can be worked to simplify the steering, but I'll have to re-run the 4 link numbers.

Like I mentioned I'll probably be running the steerng pump from a Blazer, so matching up a purpose made hydro assist is easy, if expensive. Though a full-hydro setup is probably more money anyway!

The axles are being narrowed and the offsets changed, so clocking the caster will be an easy addition.

Dan, I did think that the marine cable steering would be a bit flimsy, but the aim would be just to 'tick the box' with a mechanical link which would work when moving on a flat surface, but would be very little use any time else.