rear steer controls

[tomcat404]

Evening all,

I am now on with looking at how to control my rear steering axle and how to make it self centre.

Any ideas, experience or suggestions would be appreciated.

The axle is a spidertrax pro 60 axle with my portals on the end. The ram is all set up and fabricated onto the axle with the correct ackerman as per spidertrax.

I have the pump , but i need the valve block/ joystick and the self centre system.

thanks in advance,

nath

[Snagger]

I was wondering about how these things are set up when I saw a couple of 4-wheel steer vehicles on Youtube. I figures for self centring the rear axle would need to be orientated to have a strong positive castor angle so that if the rear steering unlocked at moderate speed, it'd naturally tend to the straight position. I thought that if I did it myself, I'd want the system to be mechanically locked and depressurised when the transfer box was in high range and active when in low range. Having a cable operated bypass valve in the rear hydraulic system and a solenoid operated folding lock on the axle to steering mechanism (fail safe so that the axle is locked when the solenoid is unpowered and unlocked only when the solenoid is energised). I had only considered having the steering act in the opposite direction to the front axle to tighten turns, rather than having the option of crabbing, by using a chain drive taken from the existing steering system to operate an input valve like that from a fork-lift. You could have a valve set (operated mechanically or by solenoids) to cross-connect the column operated command valve to the ram, selecting between conventional coupling to steer tightly and reversed coupling to crab.

Weta workshops (Peter Jackson's special effects company in NZ) made a 4 wheel steer replica of Halo's Warthog that drove at high speed and had both types of rear steer (despite the game vehicle having opposite direction steer for tight turns only, and no crabbing). They put it through its paces on a dirt race track and it looked pretty sturdy. It might be worth sending them an email enquiry.

1minute into this:

[elbekko]

I saw someone on Pirate do it a while back, it was a little black box that had a rod/cable going in from each swivel. Inside the box there were a couple microswitches to detect the steering angle, and with a touch of a button it used the microswitches to operate the hydraulic valves. When centered, none of the microswitches are engaged, and thus the ram stays there.

Probably very fiddly work to get it all dialled in, and not just spasm around uncontrollably, but I thought it was pretty fancy.

[Ex Member]

http://www.stazworks.com/old_rear_steer.htm

[Team Idris]

The Weta one looks identical in operation to the old JCB loadall with the 3 position switch. There's a magnet sensor on each axel at the centre point. In normal steer the rear axel is cut off.

For 4 wheel steer a valve relay isn't latched until the front axel is centred, at which point the relay 'latches' and engages a valve to connect front and rear rams in series. To exit 4x4x4 turning the switch to front steer only, the relay won't un-latch until the rear axel passes it's centre magnetic switch.

Same goes for 'crab', but the valve is thrown the other way so the rear rams direction/flow is reversed. The front and rear magnetic sensor switches just dictate when things can happen to keep alignment.

This is different to the mechanical Merlo, which lets you have all versions of steering, like 100% steer on the front while only having 50% on the back. They both still steer at the same speed and distance though, it's just that you can do 'odd' stuff with it, which I liked

Not that I've tested it, but when you go into series four wheel steer the hydraulic pressure is shared between the axels, so only half the force trying to exit ruts. I have the same problem when I have load on both hydraulic winches.

[tomcat404]

The Weta one looks identical in operation to the old JCB loadall with the 3 position switch. There's a magnet sensor on each axel at the centre point. In normal steer the rear axel is cut off.

For 4 wheel steer a valve relay isn't latched until the front axel is centred, at which point the relay 'latches' and engages a valve to connect front and rear rams in series. To exit 4x4x4 turning the switch to front steer only, the relay won't un-latch until the rear axel passes it's centre magnetic switch.

Same goes for 'crab', but the valve is thrown the other way so the rear rams direction/flow is reversed. The front and rear magnetic sensor switches just dictate when things can happen to keep alignment.

This is different to the mechanical Merlo, which lets you have all versions of steering, like 100% steer on the front while only having 50% on the back. They both still steer at the same speed and distance though, it's just that you can do 'odd' stuff with it, which I liked

Not that I've tested it, but when you go into series four wheel steer the hydraulic pressure is shared between the axels, so only half the force trying to exit ruts. I have the same problem when I have load on both hydraulic winches.

now that is an answer !! i will have alook to see if there is anything on the market that already exists that wont break the bank ( plus i can get hold of again if required)

As mentioned i already have the ram fitted, the pump and reservoir. I only need the control value block for manual use,,,, but i would ideally like the self centre

[sean f]

Doubt it would be possible to borrow any parts but I used to have a 4 wheel steer Honda Prelude for many years, worked great and except in very specific cases you never even noticed it in operation.

With small turns of the wheel the rear wheels turned the same way so the vehicle crabbed slightly, as you turned the steering more the rear steer centered and then finally reversed approaching full lock, this was all fully automatic and couldn't be turned on or off. The only issues I had with it was when I drove into a parking space tight to a wall once, by the time I got back some one had parked tight in front and behind me, turning the steering full lock to get out meant the rear of the car drove into the wall, noticed what was happening before it actualy hit but still took a while to get out using reduced lock.

For off road I think full manual control would be needed to get the best from it and as others have said some form of manual lock out would seem sensible whether electronic or just a drop pin pulled out before competion depends on how confident you can be in electronics, I generally lean towards, keep it simple and it is less likely to break!.

[Snagger]

Having the series ram pressure drop in 4ws may not be a bad thing - while it may make manoeuvring at crawling speeds heavy, it will at least reduce the chance of over-input and roll-over at speeds over 10mph (the Manby mud run youtube video shows how easy it is for 4ws to roll a vehicle on level ground at little more than walking speed).

It seems that most users of 4ws use a separate tiller or joystick for the rear axle rams, rather than an input from the front steering. I was under the impression that the WETA 'Hog used inputs from the front through a electronic module to control the rams so that the rear wheels will turn by the same amount as the front but in either the same or opposite direction, with 2ws as a third mode. Tillers or sticks give you the option of varying the amount as well as direction of rear wheel steer relative to the front, which has its merits. The down side is having to take a hand off the wheel to operate the tiller and having to learn a skill of operating two inputs simultaneously, which will e hard and a little risky at first. The upside is a simpler system with much more control and flexibility.

If you want to have the rear controlled by the steering wheel but want the dual active modes, then a cross-over valve in the feeds to the ram to reverse the connections should work. The problem then is that you need an interlock to allow this mode change only when the steering is at neutral otherwise the datums for each axle will drift out. As for a safety system for 2ws use (on road or if the rear system fails), I'd be looking at a hefty lug with a tapered hole and a locking arm with matching tapered pin, with a strong spring on the arm holding the pin into the hole, with a solenoid holding the pin clear when the 4ws is in use - a failure to the 4ws electrical system would thus allow the pin to drop into the luhg and lock the rear steering straight ahead. By tapering the pin, you won't need to worry about wear and will have a positive mechanical lock with no play.

[elbekko]

The down side is having to take a hand off the wheel to operate the tiller and having to learn a skill of operating two inputs simultaneously, which will e hard and a little risky at first.

I don't think that's really a problem, rear steer isn't usually something you use when at speed, but when crawling to get a tighter turn. So very rarely at the same time as your main steering IMO.

And for this use, I don't think you'd want anything but a joystick, tying it into the main steering removes so many options you'd otherwise have to get out of a rut etc.

[tomcat404]

For simplicity i don't want to tie the rear steering in with the front steering at all. Separate systems completely as i've seen many have issues with the same pump and flows etc.

I am just looking for a joystick control valve for flow direction and some form of control for the self centre.

[zim]

You need some proximity sensors or little micro switches controlled by whatever means possible ..... Then it's a few relays and some funky wiring

I'm not sure how Rob and Barry set theirs up, but I came ip with a drawing where you click once on a button. Let go the button and it self centres - rather than having to hold it ghe entire time until centre. It also had a cancel feature by which if you pressed right or left. It would cancel the centering

G

[Nigelw]

I was thinking on the centering with the joy stick and instantly thought of Volvo loaders, the L180E I used to drive used some kind of sensors and when adjusted to your routine work heights you pulled the lever back into a detent and it kicked out at the magic point same for lowering, it allowed you to drop the arms and concentrate on steering and it would kick out at a given height off the ground, for you app this woul be center, if I remember rightly there were magnets involved, but worth looking at as well.

[Team Idris]

I see I got the wrong end of the idea. Not self centring 4x4 steering, but an on-command return-to-centre ram

That's 'logic' territory

How; When you send the ram left it sends a signal to the valves go-left solenoid and latches an independent left-relay, who's only job is to hold the 'logic' that you "last went left".

When you press the centring-button, this latched relay sends the go-right signal to valve until it reaches the centring proximity switch, which cancels the action (by breaking the trigger wire on the left logic relay).

Going right is the same stuff but using a latching RH relay.

Your parts list is; Joystick (winch switch), a centring button, proximity switch on the axel, 12volt solenoid valve, two relays with a wire that goes from input to coil input so they latch, some back-feed diodes (otherwise you turn left and it keeps going left because the left-latch-relay back-feeds).

Which explains the 'black box' you can buy, as it will have all this logic built in

[Team Idris]

I should also mention that there will be a hand operated spool valve available from somewhere, which has a detent to hold it fully left or fully right until a valve on the side of the ram is tripped. (as per JCB 3CX mid 1990's). I can't think of the right description to put into google

[zim]

You need at least 2 prox sensors. It then knows if it's on the left or right stroke. Centre is between the 2 prox sensors.

[Team Idris]

Nice one Zim, I see where you are coming from

In which case you are doing it like the Trumph CNC press at work, with two bars fastened to the moving thing. It has two proximity switches which are staggered, so the front bar actuates one and the 'further back' bar trips the other.

If it is steering any version of left, the left sensor is on. If it is steering any distance/angle of right, the right the right sensor is on. If neither is on, they must be in the gap between the two bars.

So is it;

The 'centring button' sends power to both position/proximity switches, which have there outputs connected to the hydraulic solenoid ? And maybe back-feed diodes in the lines if they are hall effect? (just to be safe).

I guess ideally hall effect sensors, but those industrial switches with the roller on the end would do (on google as limit-switch).