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xLeadxSledx (Mechanical)
31 Dec 07 17:04
Does anyone know anything about the BMW or Carver tilt-steer three wheeler?

http://www.carver-worldwide.com/SubItem/SubItem.asp?S_ID=28&nc=1

http://www.leftlanenews.com/bmws-clever-concept-completed.html

There essentially the same setup.

This got me wondering about the old Mercedes Benz tilt-steer 3-wheeler

http://www.seriouswheels.com/cars/top-1997-Mercedes-Benz-F-300-Life-Jet-Concept.htm

They are 2 different setups with the carver actually in production.

Aside the function of the Carver tilting keeping the vehicle from flipping over like an old trike, it makes a good gimic. The Mercedes setup, however, actually "turns" like a motorcycle.

What I can't figure out is why this idea is not being worked on for a production model or even as a concept anymore.  Seems like the Carver idea is/has been worked on by many other companies, like BMW. (makes me a assume there is some worth in it)

Is there something wrong with the Mercedes concept I can't see?  Like the upward sloping roll axis?  The poor leverage ratio their tilt actuation has?

There is a lack of literature about the concept of tilt-steer 3 wheelers so I am looking for someone who has some experience with these concepts or is in the same position as me, scratching their heads.
Helpful Member!  GregLocock (Automotive)
31 Dec 07 17:46
It's a shame that it only 'has the cornering speed of a motorcycle' to quote the article. A car is faster round corners.

http://www.phillipislandcircuit.com.au/uploads/Lap%20Records_Bikes_March_2007.pdf

http://www.phillipislandcircuit.com.au/uploads/Cars%20-%20November-December%202007%20%20(2).pdf

Or if you prefer stock corvette or caterham super 7 vs any bike. Once you start rolling that contact patch you have a problem.

Why do you call them tilt steer?

The bodies tilt when you steer, but the steering action is primarily by adjusting the toe of the wheel, just like a normal car.

The primary disadvantage is weight and complexity in a safety related system.

The big problem is that there is no significant demand for complex motorcycles/lightweight cars in profitable markets, probably because the advantages are seen as small compared with the loss of flexibility, perceived and actual safety, weather, and cost of ownership. Remember what happened to BMW's scooter?

Cheers

Greg Locock

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xLeadxSledx (Mechanical)
31 Dec 07 18:12
All very good points.  I agree that a car will be faster than a bike around a corner.

In the end, the concept, either Carver like or Benz like, is a gimic.

From my point of view the positives of aerodynamic efficiency, reduced gas consumption, and ease of making it a hybrid or all electric vehicle are what attract me.  Not saying that the concept would be better than a car (maybe aerodynamically and weight wise tho).

The term "tilt-steer" was coined by someone else, not me.

The nature of the concept does force you to add complexity to the suspension and steering system so I also see the issue with that.  

In the Carver concept this would be a big issue (i.e. is the tilting mechanism fails, the car will not turn at all).  A take on the Benz concept, with the addition of steering on the front wheels at low speed in the urban environment, could result in a safe system even after loss of the "active tilting mechanism. Possibly solving that safety issue?

Greg, I know you are very knowledgeable about vehicles in general, much more than me.  Any comments on the Benz style vehicle?  The Carver?  I am just interested in what you have to say past the upfront safety issues.

GregLocock (Automotive)
31 Dec 07 18:34
My long standing bias is in favour of two wheels at the front, all other things being equal.

The Merc looks like a better solution in the dry, but it also has a wider track, so it is almost a full size car. In the wet I'd have thought that the tilting rear tire might be a bit of a handful, under acceleration in a corner. On the other hand at least you could brake in corners.

The Carver/BMW/VentureOne would seem to be likely to be rather unpleasant during brake-in-turn - very understeery. Good ESC might sort that out.

Take a look at the Aptera to see what you might be able to do with a non-tilting body and three wheels. For various reasons I think they are going to do a Siclair C5, but at least they have some of the basics sorted. Of course the VW 3 wheeler provides a more conventional solution.

Price for the Carver: $50000
guesstimate for the BMW from your link: $10000
Aptera:$27000
VentureOne: $20000

Well that's a pretty odd mix of prices.






Cheers

Greg Locock

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GregLocock (Automotive)
31 Dec 07 18:46
"very understeery"

or possibly very oversteery!

It all depends

Cheers

Greg Locock

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

GregLocock (Automotive)
31 Dec 07 21:37
This is my guess why they won't be especially popular in the forseeable future:

Until we segregate small fast vehicles from big fast cars, or get rid of the big fast cars, Sir Isaac says this is what's going to happen even if you have the best crash structure in the world

http://www.youtube.com/watch?v=02eghIfyHP0

Of course there are various head-in-the-clouds types who will explain that this is irrelevant. They probably drive their families around in SUVs.

Cheers

Greg Locock

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

xLeadxSledx (Mechanical)
1 Jan 08 22:09
Greg,

All great points, thanks for the feedback.  I was surprised that the smart car did so well in that crash.

These small cars and 3 wheelers would still be better than a motorcycle in a crash.

-adam

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