Electronic Steering 1

[Roktgr]

Considering an electric steering system for an off-road vehicle in lieu of a full hyrdo system. I have limited experience with this type of system. I did work on one a few years ago in which we used a linear actuator and rotary position sensor connected to the steering wheel. The system worked but due to weight the idea was scrapped.

I do have a few concerns about such a system though.
What rate of travel would be needed. While operated mostly off-road minor on-road travel would be required. Since it's for an off-road vehicle often the steering is used to push the vehicle off rocks, ect. Would it be safe to assume the power output to be close to half the vehicle weight or the whole vehicle weight? Is heat going to be an issue? From what I have found so far internal heat generated will cause the motor to slow down or even shut down. Whatelse should I be looking at.

Reasons for doing this is it's not been done that I know of. Less trouble then dealing with hydraulic lines, pumps, rams.
Many people are running full hydro with no reliability problems and I wouldn't see why and electric system would be any different.

 

[GregLocock]

If it is to be used on road then it needs to be road-legal. Nothing you can make would be road-legal.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Roktgr]

Sure it is, all depends on your vehicle laws per state. To be street legal in the state I live in all you need are headlight, brake lights, and a plate. Everything else can be completely custom.

 

[patprimmer]

Umm

Where do you live. I would like that info so I know to avoid it.

Any steering system that does not have a continuous mechanical link between steering wheel and road wheel is pretty scary.

All street legal power steering systems I have seen are power assist to a manual system, not independent total power systems controlled by an electronic controller. Drive by wire is OK for throttle, but I don't like the idea for steering or brakes.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Roktgr]

oh good night, I suppose the full hyrdo steering that many of these buggies are running on the road is just as dangerous. Also the new steer and brake by wire systems that are coming on new cars.

And here's a pic of what the rigs look like.

Street legal in 5 states and fully hydro steering.

 

[GregLocock]

OK.

Since you are the 'expert', here's the advice from a real engineer: don't do it.

typical speeds are 2 rev/s at the steering wheel
typical rack rates are 2.5 inches/rev
wedge forces will be around the axle weight.

If your insurance company ever gets involved, point the prosecutor here: Don't do it. If the other guy's insurance company ever gets involved: don't do it.

The pretty picture doesn't help. Don't do it.

PS my advice is not to do it.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

You still have not said where you are. That normally indicates the USA. I guess that makes it illegal in 45 states, in the USA, and probably all of Canada, all of the EEC, certainly all of Australia, New Zealand and Japan. I guess it might be OK in some of South America and Eastern Europe and most of Africa, and much of Asia.

That gives you and your cohorts plenty of room to play, and me plenty of room to avoid such devices.

I will be anxiously waiting on durability and reliability testing of steer and brake by wire devices compared to mechanical / hydraulic and dual circuit hydraulic. I will also be anxious to see how easily degraded systems can be identified by regular annual inspection before a catastrophic failure occurs.

In the meantime, I will do my best to avoid such models.



Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Tads3]

Pat,

While not disagreeing with you or Greg in this particular case, don't you believe that there can ever be a safe steer/brake by wire system? If so, do you fly on modern aircraft?! It's just that I can see some pretty big advantages to ditching the mechanical/hydraulic links.

Tom

 

[cibachrome]

May I remind you Gents that TRW systems have been around in publication since 2001. BMW Group are telling us that they have models ready for market with (ZF Computronic?) as soon as German law allows (2010?). The GM Sequel fuel cell crossover has a Visteon SBW system ready for production. Granted, these systems are not Steer by Hose (SBH) but completely electric systems, no mechanical connectivity.

 

[NormPeterson]

Tads - would you agree that there is a significant difference between air traffic and ground traffic? A few inches lateral separation between opposing ground traffic or between ground traffic and fixed obstacles while at speed is commonplace.

ciba - that sounds too much like another computer, with programming set by others that won't properly recognize things like increased tire grip or permit intentional operation above some arbitrary and administratively determined limit. A big resounding "NO THANKS!" from this direction.


Norm


Norm

 

[JsTyLz]

Norm,
Are you trying to tell me the response time of electronic systems are slower than that of the mechanical? less accurate? less precise? Does your vehicle have a carburetor?

 

[NormPeterson]

(1) Direct mechanical "feel" of what's happening down at the road - tactile feedback - will be non-existent. Synthesized feel is a poor substitute, and sensing what you're doing by steering wheel position alone is no substitute at all. While I do reasonably well at autocross (hardly ever hitting pylons or getting completely sideways), I can't keep an electronically simulated driving experience on the pavement to save myself.

(2) I am adamantly opposed to the introduction of yet another electronic nanny that could (and probably would) be programmed to leave excessive margins against a 100% assembly-line OE car and some unflattering assumptions as to driver skill. I want the road wheels to steer in a reasonably linear relationship with my inputs under all conditions, not in accordance with some map of speed, amount of and/or rate of steering wheel input, etc., that was decided by somebody else. See #1.

Carbs? None of the running ones do any more. I have retrofitted an aftermarket EFI to the car that was carbureted as delivered. Mechanical throttle control only, of course (I almost never use the cruise control on either of the other cars that have feature anyway).

I'm not against the use of computers in support roles. But don't let them filter any of my control inputs. Those are my intentions of the moment, and they vary over a wide enough range (and for no apparent reason as far as any computer could possiby determine) that reliably second-guessing them would be highly unlikely. That I won't buy a car with an automatic transmission is at least in part for this reason.

[/rant]


Norm

 

[Tads3]

Norm,

I enjoy driving a decent car down a good road as much as the next man when I'm feeling good and the weather's nice but 99% of driving now (certainly here in the congested South East of the UK) is a highly mundane and dull experience. I submit that we already live wth with cars that modify the driver's inputs to such a large extent (ABS, ETC, EBD, brake force assistance, variable rate power steering etc etc etc.) that most driver's wouldn't even notice the difference in a steer/brake by wire car.

If you need a seat of the pants drive there'll always be Caterhams/Lotuses in the UK and whatever the American equivalent is! In short I think your opinion represents a vanishingly small minority (albeit it probably a highly skilled one). I also used to dislike automatics until I started working with them; in the off-highway market they let me do things I just can't do with a manual box and I now loathe the occasions I hit a traffic jam when I'm in a car where I have to change gear!

In terms of my analogy with air transport I was really referring to failure rates and the associated safety concerns: I don't see why an electronic system is necessarily less safe than a mechanical link.

 

[Roktgr]

Quote "In terms of my analogy with air transport I was really referring to failure rates and the associated safety concerns: I don't see why an electronic system is necessarily less safe than a mechanical link."

I am wondering this as well. In my mind it's not any different then a full hyrdo or mech. steering system.

As for the road feel, yes there would not be any but I don't think it's needed per say offroad. The front tires you can see and if you have rear steering you as the driver learn were the tires are moving and how it's going to respond.

I'm not the expert as some suggested above it's just most people only are familiar with paved road driving, the application this would be used for is very foreign and most just don't understand. I enjoy reading the responses so continue on.

 

[JsTyLz]

With electronic steering they could map the road feel if one wanted to, much in the same way a stylus follows the high and low peaks of a record groove. I have worked with electronic steering feedback, and the strong centering feel I love is augmented with the use of steering assist. I guess I am in the new school and love what oppurtunities there will exist when electronic systems replace or enhance purely mechanical. I am on the other hand still skeptical of the purely electronic.

 

[ssn596]

Could you control steering electrically YES
Could it be done safely YES
Could it be done safely on American roads like those I drive YES -- IF there is driver override. How is this electric rig going to detect pederstrians stepping in front, imminent collisions, who knows how many different scenarios, etc etc.
Comparing to airplanes a bit
first off the control systems have several systems of redundancy.
Second a lot of research and development has gone into this.
Third the pilot is not needed most of the time - the computer flies the plane and yes it could land it. BUT the pilot is there to handle the unexpected and to override the computer as needed.

Dan Bentler

 

[NormPeterson]

Regarding reliability in terms of downstream consequences, I can't think of any mechanical steering system failure short of a fractured and completely separated steering column or pitman arm that would be analogous to the loss of alternator or dead battery/engine off scenarios for an all-electric arrangement. Batteries discharge, alternators die, and drive belts loosen and/or break on a rather more frequent basis than the aforementioned mechanical steering failures occur.

I realize that this is still a road driving oriented comment, but unless an all-electric-steered vehicle is always trailered to the off-road venues it still needs to have failure consequences that are at least comparable to that of existing mechanical systems. Other traffic has to rely on known assumptions regarding directional control under observable conditions, and a faulty electrical system in such a vehicle does not fit within this. Off-road, where there is generally greater risk to begin with and greater awareness of a wider range of risks is likely a different story.


Norm