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Rear wheel steering


Fiddler
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Would like to ask members for their input on a future project I'm planning - to fit rear wheel steer to my modified/Class1 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 as they would if on the front. 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.

I should also say that I am hoping to power the hydraulics with an electrical pump pack - does any body have any experience of accumulators, i.e. so the hydraulic pump can build up the pressure and store it so the pump can cut in & out?

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

Cheers - Pete

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Thanks for your replies so far.

Could Dollythelw please reply again giving a link or contact details for POS steering people.

Have been talking to Neil about this - Which cAN BE viewde oh the AWDC website forum.

Have also been talking to Paul Leworthy @ venomprotruck.com - who's been telling me about a double ended ram he can supply for around £250 inc VAT

Would be very interested in more details of european systems

Cheers - Pete

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Does anyone know of a steering ram that has proximity sensors built in - and does anyone know the usual current draw on an average electrosolenoid valve - Cheers Pete

don,t know of rams with built in proxy switchs,i work with this type of gear all the time,you may or may not have seen the suzuki bodied rr chassis with rear steering in a recent t.o.r magazine,that had quite a simple but effective set up.to power it you could use a tail lift pump running continuously with a 2 way spool valve and a double acting ram mounted on the drag link,you could mount proxy swiches on a swivel which will show you when you are dead ahead,for hydraulic parts try harrier fluid power,they even have a ebay shop,very helpful and keen prices,if i can help any more just pm me,chris.

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What I've done (well, more or less, in a more complicated way), is use a handbrake cable to remote the movement of the ram to a nice sealed plastic box mounted somewhere dry(er).

In the box you have two micro-switches. When the steering is central, neither switch is on. When you steer one way or the other one or the other switch is on. When you want to centre the steering, you connect each micro-switch to the valve which moves the ram in the direction which would switch that switch off. Thus, if the steering is off centre, it will move such as to centre it.

It will over-shoot a bit and you will get some oscillation around the centre point which so long as your steering does not move too quickly will settle down. You need to position the switches close enough together to make the steering sufficiently central and far enough apart that it does no oscillate for ever - so it needs to be adjustable.

Instead of micro-switches you could use proximity sensors which are a lot more reliable and less sensitive to moisture - a better bet long term. Micro-switces are easier to understand - which is why I suggested them initially.

If you find you cannot stop it oscillating, you need to restrict the flow to reduce the speed of the ram.

Si

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Would like to ask members for their input on a future project I'm planning - to fit rear wheel steer to my modified/Class1 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 as they would if on the front. 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.

I should also say that I am hoping to power the hydraulics with an electrical pump pack - does any body have any experience of accumulators, i.e. so the hydraulic pump can build up the pressure and store it so the pump can cut in & out?

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

Cheers - Pete

most of the amarican 4WS monster trucks use a rocker switch on the gear leaver i dont know if thay has self centering but i would have thort one of them would have come up with the idea and got it right. but if not simonr' idea seem the simplest to get to work

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What I've done (well, more or less, in a more complicated way), is use a handbrake cable to remote the movement of the ram to a nice sealed plastic box mounted somewhere dry(er).

In the box you have two micro-switches. When the steering is central, neither switch is on. When you steer one way or the other one or the other switch is on. When you want to centre the steering, you connect each micro-switch to the valve which moves the ram in the direction which would switch that switch off. Thus, if the steering is off centre, it will move such as to centre it.

It will over-shoot a bit and you will get some oscillation around the centre point which so long as your steering does not move too quickly will settle down. You need to position the switches close enough together to make the steering sufficiently central and far enough apart that it does no oscillate for ever - so it needs to be adjustable.

Instead of micro-switches you could use proximity sensors which are a lot more reliable and less sensitive to moisture - a better bet long term. Micro-switces are easier to understand - which is why I suggested them initially.

If you find you cannot stop it oscillating, you need to restrict the flow to reduce the speed of the ram.

Si

This the kind of idea your talking about Si

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Yup - something like that!

The way I'm actually doing it is using a Range Rover axle position sensor to measure the actual position - and a PIC controller to provide the same functionality as the micro-switches / end stops. It also gives servo steering to follow another similar sensor on the front when required.

What sort of cable have you used? It looks much nicer than a hand-brake cable?

Si

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