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Steering Stabiliser tech...?


Astro_Al
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Thanks guys, I'll check 'em out.

Is there no valving to consider? Whats the difference between models for different vehicles - just the dimensions and mounts???

Are they all the same inside, or do you need to consider vehicle weight / steering box ratio / tyre size etc etc - I guess no-one does, cos they just buy the one for their vehicle, but what if there isn't one for your vehicle...?

Cheers, Al.

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Al, if anyone can work it out, it'd be you! I'd say you need a damper which has peak dynamic damping at or around the natural frequency of a system. There is a force (from the castor angle) proportionate to speed(?) and an inertial effect from the gyroscopic motion of the tyres (given their size and 'steering' rotational inertia (steering inertia as viewed from above, not normal 'running' inertia viewed from the side). My instinct says the gyroscopic inertial effect will be a first order force (damping?) anyway since it isn't proportional to steered angle, but it's effectively a spring-mass system so you need a damper to kill the peak amplitudes. Simple really! :)

As an aside, I've found that a standard Defender doesn't seem to need a damper, only when there's some lift. I'd suggest that careful (read: experimental) design of the steering angles, especially castor angle, can obviate the need for damping at all.

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Agreed - most of the time they're really not necessary I think.

Its all very well fiddling around with my abacus, papyrus and long words, but in the end each company doesn't quote any kind of specs - just the 'vehicle' it is 'designed for' - which I'm starting to think is simply the dimensions :rolleyes: ... Its not exactly a tech minefield out there...

I think to be honest the critical situation is the shock loads from striking obstacles exacerbated by greater tyre diameter (moment arm). Those are the sharp thumb-rippers you want to damp out. In fact, wouldn't the gyroscopic effect of the spinning tyre serve to cancel out any shock side-loads? I think it'd help the damper keep things under control, you're effectively increasing the inertia of the steering system (about the hub pivots as viewed from above). Having said that - I'm never one to steer away from unnecessary over-zealous tech, so keep it coming! :D

I think I'll just find whatever is beefiest and the right size and throw it on... I bet you're impressed with my depth of analysis? :D

Certainly, the one on there at the mo is 40 years old and need to be removed and binned unceremoniously. Maybe I'll go all redneck and throw 3 or 4 chromed up dampers on there?!

Hmmmm... Al. :)

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greater tyre diameter (moment arm)

Nope. That'd be the scrub radius, and it's not (well, it's much less) dependent on tyre diameter.

wouldn't the gyroscopic effect of the spinning tyre serve to cancel out any shock side-loads

Yes, exactly - but unlike the castor angle which behaves like a rotational spring (force x displaced angle), the gyro load is a second order force (not first order as I wrote above) because it is proportional to the speed of steering input - effectively a damper itself. In theory, if you steer hard enough and fast enough with huge tyres there is a weight transfer across the steering axle. This is why scientific evidence shows portal axles make cars turn over and catch fire*.

Thing is, I reckon for a given road speed (arguable in any case because your top speed depends on tyres but you don't corner at top speed anyway) you'd have more rotational inertia with smaller tyres because the rotational speed term is second order and so will dominate. This actually proves, using science, that bigger tyres are better. I may write to my insurers and demand they reduce my premium. Did that sound clever? It did when I typed it.

This is all fascinating but unhelpful. Is there any way you can use the work-hardening properties of copper pipe to damp severe oscillations? Otherwise you're stuck with the Fandango-chrome ones.

* There's no actual evidence for this, but it is scientific fact.

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Anyone know how to spec a steering stabiliser? Do they come with different rates etc?

How do you decide what is appropriate? (apart from dimensions!).

Anyone recommend a make for something nice and beefy?

Ta, Al.

Just got off the phone to Rough Country ( ordering yet more +5" shocks :lol: ) and I asked them the question...

Their claim to fame is that they fitted the first evr hydraulic steering damper onto military jeeps over 50 years ago......

Stabilizers do have different valving but this is more by size of overall vehicle rather than different rates for the same car with bigger tyres and is far less critical than the damping rate of shock absorbers.....

ie. a Hummer has a different rate to a Jeep CJ, but a CJ uses the same stabilizer regardless of tyre size etc.

This leads to the addition of a second damper being standard practice rather than the fitting of a single bigger one.

Hope that helps

David

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I think to be honest the critical situation is the shock loads from striking obstacles exacerbated by greater tyre diameter (moment arm). Those are the sharp thumb-rippers you want to damp out.

Hmmmm... Al. :)

Al no amount of damping can hope to fix that, only a "over powered" system, or an "irevesable gearset" as a steering box would work.

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... but if the scrub radius was zero, it wouldn't happen? ie if you put on massive inset (negative offset) wheels, the steering would kick "the other" way, so there's a point in the middle where, if the rock hits the tyre head-on, no kickback. It makes sense in my head, but tonight it makes sense to me to withhold overtime from a four-strong workforce with a combined weight of 64 stone and a combined IQ of 12.

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Turbo - yes I agree about scrub radius for head on impacts with the tyre, but I was kind of figuring (dubiously) these have a smaller influence than something striking the side of the tyre (i.e. sliding sideways or whatever) near the foremost/rearmost point. I suppose this is vaguely substantiated by the points that a. the tyre effectively ramps itself over obstacles encountered in the fore-aft plane, b. suspension comes into play when striking obstacles in the direction of motion (fore-aft plane again), and c. this is such a boring paragraph that no-ones reading this bit anyway.

The scrub radius is a much smaller moment arm than the tyre radius (for sideslip type impacts). Anyway, this is a small point.

Well, if the gyroscopic effect is acting as a damper, its best to hit all objects at as high a speed as possible! ;) - Unless you're running portals, in which case the universe will come to an end within 30 seconds of striking and object above 5 mph. Or so a wise ass man once told me.

Road speed is not a relevant factor in this discussion, since the vehicle in question is not yet capable of leaving the garage... <_<

Shut it, Fridge.

David - what are the max/min dimensions of those dampers? Can you get them in different lengths/mounting styles? Same question about your shocks (the longest ones).

Am I being dense here (yeah yeah...) - doesn't the addition of an extra damper actually REDUCE damping? (For a given damping coefficient in each damper). I can't remember and I sure can't be bothered to look it up, but dampers in series or parallel is analogous to resistors in series or parallel (which!) I think?

Dan - if you're right (and its highly likely that you are) - what exactly are we trying to damp out with these damn things. What you say makes sense to me, after all a damper is to remove energy from a vibrating system, not provide a restoring force against an input (that's your spring, not your damper), so they're just there to counteract shimmy at particular road speeds??? Or what?

Turbo - what you say about zero kickback makes sense so long as there is no lateral component of the impact force on the wheel, which is, accurately speaking very improbable (though it would almost always be quite small I guess, unless you're at full lock, but still drifting dead ahead into a tree trunk or something).

Oh Jeeez. Its only a frickin damper. Just buy five, chrome the carp out of them, and bolt both ends to the axle casing so they don't wear out whilst you drive along, like any self-respecting redneck. Job done (with appropriate neon underlighting, natch).

Al. Kinda wishing I'd never asked.

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Turbo - what you say about zero kickback makes sense so long as there is no lateral component of the impact force on the wheel, which is, accurately speaking very improbable (though it would almost always be quite small I guess, unless you're at full lock, but still drifting dead ahead into a tree trunk or something).

Not so - there can be plenty of lateral component as long as the direction of impact is through the kingpin axis, ie hitting a wheel-height rock with only one wheel, while on full lock, could bring the car to a stop without kicking the steering if the force acted directly through the kingpin axis. Of course, with zero scrub radius your steering would be very heavy at low speed, ie supermarket car parks etc. It depends on your projected use for the vehicle.

Lurching dangerously back towards reality, yes, the damper is there to mask shimmy amplitude that hasn't been designed out if the steering design was bashed out on a Friday afternoon by not properly moving the natural resonant frequency way out of the normal operating speed range. I really don't think you'll see a benefit with low speed thumb-breakers although it can't do any harm I guess.

Of course if you just plan to look at it then you could run wild offset, +2" headlights and dislocating CV joints without a problem.

Dampers are as capacitors: bigger in parallel and smaller in series.

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Yup agreed, but the force-through-the-kingpin case is a singularity really.

Hmmm. What scrub radius would make the steering light on a stationary vehicle... :ph34r:

Well, everything you say makes sense to me. I'm actually on about my Mog (so yes,reality ending portals are an issue, but at leastthe scrub radius is fixed...). I don't trust ancient factory spares that have sat on a shelf for 40 years (not shocks and dampers, anyway).

Apparently, there is a mode of vibration towards the higher end of the speed range, and so a damper is necessary - otherwise I'd just leave it off.

Cheers, Al.

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Am I missing something here - my only purpose for fitting a steering damper to the 109 way back when was to stop the wheel kicking round off-road as it resisted sharp movements, once you were moving it made naff all difference... now the PAS takes a lot of the kick out, however now I (once again) need to fit a damper because my caster is slightly below-par which makes it a bit skittish and a damper should help calm it down a tad.

All this gubbins about wheels and rocks and stuff, as I've experienced it when a wheel gets to a rock the tendency is for it to bump up against it and pull the wheel to that side. Here's the science bit as I see it: As the opposite wheel is still progressing along nicely, the action of the diff is such that the wheel going over an obstacle has to travel further (up, over, down) than it's opposite (which just has to go along) so if the wheels have a similar level of grip you'll end up turning in the direction of the obstacle. I can't back that up with pie-charts though...

Al, perhaps some trials in the field would help gather data - know anyone with a working truck? :ph34r:

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......know anyone with a working truck? :ph34r:

Fridge - now you are just being stupid..

Turbo - just to add a little grinding paste to the KY - adding more dampers surely throws up the potential issue of damping inballance (possibly leading to a sharp two stage fade characteristic) unless a pair of matched custom built and dyno'd dampers are sourced; I think the effects of this arrangement on such a high performance ornament such as Al's vehicle should be considered, the have been hundreds of thousands of cases where people have almost seen something described by a host of experts that might have well been fatal should it have actually happened, this is (as you rightly point out) a scientific fact backed up by 28% of statistics.

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Al, perhaps some trials in the field would help gather data...

Don't be rediculous Mr Freezer - I'll stick to me whiteboard where its warm and safe.

Am I missing something here...

Yes - you're starting to sound as confused as you look.

So you've fitted dampers to provide a resistive force against low speed impacts (at high speeds it made 'naff all difference'), and then also to counter 'skittishness' at high speeds...?

Your last paragraph states that a diff enables the two wheels to turn at different rates and then goes on to say that with similar levels of grip, the two wheels must travel the same path length... Your statement has more flaws than your truck has floors. :rolleyes:

Al. :D

P.S. There's no actual science in your 'science bit'... Its a small point, but, well, its not the first time you've heard that! ;)

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Yup agreed, but the tremor in the force is a singularity really.

polish the dilithium crystal.....inertial damping will be normalized again Al.....sorry mate couldn't resist :lol:

will be in touch about the g/box soon.

back on topic are you going to have power steering on the mog ? that will always help to damp kick back..as for high freq vibes :blink: (shimmy) just go for the biggest one that will cope with the travel on mog steering rods.

cheers

Steveb

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I've got no time to polish the damn crystals Steve - the flux capacitor is shot and I need to find some plutonium pronto...

Yes - I'm putting power steering in there - still not sure which method to go for though...

Bush - why?

Cheers, Al.

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Al - I didn't say it would make sense, but, having driven my vehicle off-road a little, I found it to be the case that hitting a big rock or tree stump even at 1mph gives a far bigger kick than running over, say, a 6" deep russian pothole at 60mph. Perhaps down to the momentum being carried by the wheel & tyre.

I also know that fitting a damper to the 109 back in the days before PAS greatly reduced the thumb-snapping moments whilst off-road, driving a club member's stock 88" at Minstead also confirmed to me just how horrible life is without PAS or a damper.

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Am I missing something here - my only purpose for fitting a steering damper to the 109 way back when was to stop the wheel kicking round off-road as it resisted sharp movements, once you were moving it made naff all difference... now the PAS takes a lot of the kick out, however now I (once again) need to fit a damper because my caster is slightly below-par which makes it a bit skittish and a damper should help calm it down a tad.

All this gubbins about wheels and rocks and stuff, as I've experienced it when a wheel gets to a rock the tendency is for it to bump up against it and pull the wheel to that side. Here's the science bit as I see it: As the opposite wheel is still progressing along nicely, the action of the diff is such that the wheel going over an obstacle has to travel further (up, over, down) than it's opposite (which just has to go along) so if the wheels have a similar level of grip you'll end up turning in the direction of the obstacle. I can't back that up with pie-charts though...

Al, perhaps some trials in the field would help gather data - know anyone with a working truck? :ph34r:

The pas does do a lot in damping it, So I dont think the damper makes such a big difference. The only people I have seen playing with this are the comp safari boys, running 2 dampers on the steering. Whether their purpose was to provide more damping or protect the steering box, I dont know.

My setup is slightly different than most, since my damper is on the trackrod rather than the draglink. It is similar to a rangerover, but the damper is above the draglink, rather than being at te same level. Reason for this is that the reaction forces and play in the system is the same for both wheels.

I use a genuine parts disco damper, which works very well with this setup, only remove the outer cover, otherwise it fills up with mud and you will be left with only one direction you can steer in (gues how I know!)

daan

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My setup is slightly different than most, since my damper is on the trackrod rather than the draglink. It is similar to a rangerover, but the damper is above the draglink, rather than being at te same level. Reason for this is that the reaction forces and play in the system is the same for both wheels.

Am I right in thinking this would also reduce the chance of bending the track rod, since the damper is likely to be exerting a force against one wheel or another from a mid-point rather than potentially down the drag link and then across the entire length of the track rod?

I guess the comp boys run doubles for a bit of both, I know snapped PAS box sector shafts are not uncommon, which was part of my reason for fitting the D2 box.

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A number of comp racers run two dampers, personally I found one was enough. It does take some of the high speed kick out but not enough to protect your thumb if you hook it around the steering wheel.

They do help mask problems in the steering on the road and likewise cause problems if they are slightly bent. I used to use Paddock ones and sling them at the first sign of trouble.

On the scrub radius, I was aiming for zero on my racer but a miscalculation meant I have a little. I believe zero radius makes the steering easier at slow speed as you are effectively not slewing the body ( for want of a more technical phrase).

I could reduce my scrub radius to zero with a shed load more work but I did read in a car handling article that it was advantageous to have some. It seems alot easier to agree with that opinion.

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Am I right in thinking this would also reduce the chance of bending the track rod, since the damper is likely to be exerting a force against one wheel or another from a mid-point rather than potentially down the drag link and then across the entire length of the track rod?

I doubt it. I have only ever managed to bend it by hitting something.

Daan

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