Rear wheel/Four wheel steer

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Pete Broom
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Rear wheel/Four wheel steer

Post by Pete Broom » Thu Jul 24, 2008 12:26 am

Would like to ask members for their input on a future project I'm planning - to fit rear wheel steer to my Class 1 trials car.
The intended conversion will have a Defender front axle tube with the diff mounted in the opposite side so the steering arms on the hubs are facing to the rear. The axle on the rear is currently fitted with a pegged diff running with Ashcroft h/duty 4.11 crownwheel/pinion set, ARB locker and ashcroft shafts. I am expecting to run a full hydrostatic independant steering system with a joystick control and an electrohydraulic self centering system operated by simple on off button - hopefully mounted on the steering wheel spinner/knob. The theory being that once the obstacle has been negotiated full concentratin can be applied to diff locks or fiddle brakes whilst the steering hand centers the rear wheels without having to lean out and do it by eye.

That is my basic plan and I open it up to the forum to pick it to pieces - nicely please!

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Neil Whitford
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Re: Rear wheel/Four wheel steer

Post by Neil Whitford » Tue Jul 29, 2008 5:09 pm

Ahhh, rear steer - my favourite!!

I have outlined below the three differing systems I have used on various vehicles together with what I see to be the pros and cons of each. Any permutation of these should deliver the goods depending how much you want to spend or how much time you want to devote to the project.

Blitz - This used a Suzuki SJ front axle inverted and rotated with the diff and swivels re-rotated to drive the correct direction. A single acting ram was used mounted between the axle casing and the draglink. Hydraulic power was from a 12v hydraulic taillift pump activated by a microswitch on the mechanical valve body. Nice and simple, only three components required and because of the light weight of the vehicle was pretty quick. I devised a system which showed the relative position of the wheels on a series of LEDs on the dash.

Rock Rod - Being completely built from scratch there were no constraints on components used so the rear end was a mirror image of the front. Double ended hydraulic rams mounted onto the spaceframe with home made links to Shogun uprights. The valve body this time was electric so a simple joystick was required to operate it. Power came from the single power steering pump which supplied front and rear. The downside was that when either end was on full lock, the pump would bypass so there was no flow.
Proximity sensors were used on the rear ram to detect whether it was pointing left or right, this allowed a self centering circuit to be created which would automatically centre the wheels when the joystick was pushed forward. This system would be my preference but with a second power steering pump mounted so each circuit had its own.

Voltara - Basically a crossover between the two previous systems. Volvo portal axles with a double ended ram attached to each. 12v tipper pump which was too slow for the heavier axles and wheels. Same recentering function but this time controlled by a PLC rather than series of relays.

The re-centering circuit used on the Rock Rod uses only four Lucas relays along with the two proximity sensors. The same circuit has since been used on at least two other vehicles including the Mitsimog and is very reliable.

My ideal system would be - Double ended ram, engine driven power steering pump, 12v valve body and re-centering.

Hope that helps

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TeamUltimate
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Re: Rear wheel/Four wheel steer

Post by TeamUltimate » Tue Jul 29, 2008 5:47 pm

I've got a TD3 front axle casing already converted ready for rear steer with a over tube bar to fit 4 link suspension. Just needs the guts fitting. It's only in the way because I am now on Dana 60's so let me know if your interested.
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Pete Broom
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Re: Rear wheel/Four wheel steer

Post by Pete Broom » Tue Jul 29, 2008 8:12 pm

Thank you for replies

Neil - what is a PLC valve - probably obvious once you get into hydraulics.
I'm glad you suggested a 12v pump system as I was hoping to use one - no more space left on the front of my V8. I was also wondering if an accumulator of applicable size could be employed to keep a constant pressure. My thought stem from ABS braking systems where no servo exists - the accumulator maintains the pressure so the pump only needs to run periodically. Also with the pressure kept constant there would be no delay whilst the pump comes up to pressure. Where did your joystick come from? Any thoughts/hints on use - heat of the moment operating mistakes which could be reduced through design? What do you think of a centering button set into the steering wheel spiner?

Team Ultimate - The TD5 axle sounds tempting - what have you done to make it suitable for rear wheel steer - ie turned around/over or is the diff re-orientated - front to back?

Cheers - Pete

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TeamUltimate
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Re: Rear wheel/Four wheel steer

Post by TeamUltimate » Tue Jul 29, 2008 9:02 pm

The crown wheel cover has been flipped so that the diff runs the right rotation, the knuckles have been flipped and switched so the hubs will run forward with the correct camber, then i have welded a tube over the top with brackets to fit top links in a four link W set up. I could get a picture if you like.
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Re: Rear wheel/Four wheel steer

Post by Pete Broom » Tue Jul 29, 2008 11:10 pm

TheTD5 axle - how have you re-orientated the knuckles/swivels - have you turned the flanges or re-drilled them?

Cheers - Pete

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Re: Rear wheel/Four wheel steer

Post by Pete Broom » Tue Jul 29, 2008 11:14 pm

Forgot to say yes please to the photos - Cheers - Pete

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Neil Whitford
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Re: Rear wheel/Four wheel steer

Post by Neil Whitford » Wed Jul 30, 2008 7:31 pm

The PLC is a Programmable Logic Controller I happened to have laying around from the Traction Control system I designed for the Rock Rod. The re-centering circuit consists of only 4 cheap Lucas relays whereas the PLC costs around £120. Just dabbling really!

The accumulator makes sense - similar system to the Citroen suspension units. Rob Tunnah has used them on the hydraulic suspension on the Mitsimog so he may be worth talking to.

The joystick is just a cheapy 4 way thing from an industrial machine. Probably available new from RS . I think you are right about getting the wheels back to straight as quickly as poss so you can concentrate on what is coming next not getting the rear straight. It made a huge difference to my efficiency of operation. On the Voltara I has a trick gear stick knob from the states with four buttons on it. I set these up for left, right and straight ahead so didn't need to take my hand off the gear stick. The spinner as you suggested would achieve the same

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Re: Rear wheel/Four wheel steer

Post by hirobosuddo » Sun Aug 10, 2014 4:07 pm

Neil
I am having problems with rear wheel steering on Mitsimog at the moment and was wondering if you were able to send me a wiring diagram??
As you have mentioned in your post it has 4 relays to provide the logic for the rear wheel steering centralization system, and the joy stick to provide direction as you are fully aware. The wiring is in pretty bad shape and will need to be redone but before I started this I wanted more information can you help please??
The switches on the joystick seem to be the weak link in the system as the quality of them are pretty poor to be honest producing a high resistance even from new, could you recommend something a bit more reliable a PCB or micro switches etc.
Thanks for your help in advance

I have been steadily going through here getting it back to being fully reliable once again but this is the last part of the process before I can compete once again

Here is Mitsimog with here new Trepadors on ready for KOV until this happened with the steering. It centres but will only turn to the left intermittently.

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Re: Rear wheel/Four wheel steer

Post by hirobosuddo » Mon Aug 11, 2014 11:30 pm

Neil
I am having problems with rear wheel steering on Mitsimog at the moment and was wondering if you were able to send me a wiring diagram??
As you have mentioned in your post it has 4 relays to provide the logic for the rear wheel steering centralization system, and the joy stick to provide direction as you are fully aware. The wiring is in pretty bad shape and will need to be redone but before I started this I wanted more information can you help please??
The switches on the joystick seem to be the weak link in the system as the quality of them are pretty poor to be honest producing a high resistance even from new, could you recommend something a bit more reliable a PCB or micro switches etc.
Thanks for your help in advance

I have been steadily going through here getting it back to being fully reliable once again but this is the last part of the process before I can compete once again

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Neil Whitford
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Re: Rear wheel/Four wheel steer

Post by Neil Whitford » Wed Aug 13, 2014 11:57 am

Hi

If you drop me an email at najw99@gmail.com I will send you a copy of the wiring diagram so you can rewire it. It shouldn't take long even from scratch.

As far as recommending a joystick I would suggest you look at industrial component suppliers like RS. I only ever used secondhand parts off industrial sweepers and the like.

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