Three-wheelers.... the way of the future?

Discussion in 'Polaris Slingshot vs The Competition' started by voyager, May 23, 2016.

  1. Tripod

    Tripod Well-Known Member

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    image.jpeg
     
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  2. Noah Katz

    Noah Katz Active Member

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    First, I'm going to backtrack on this staterment: "In fact power oversteer should be more controllable on a trike because there's no variation of roll stiffness; lateral weight transfer is purely a function of CG location, track, and cornering speed."

    Because of the low weight on the rear wheel and likely high power/weight ratio, a trike may be more prone to power oversteer.

    However it still has inherent understeer so all you need to do is lift off on the gas before the back end gets away from you.

    I like the idea of tilting vehicles because it's natural and feels cool, but does greatly increase complexity.

    Rather than an active system system with sensors and actuators I'd want it to work the same as a motorcycle, with lean controlled by countersteering (except at the lowest speeds).

    Not crazy about adding a 2nd rear wheel, even less so w/steering.

    First, it's now a car, and it defeats one of the big attractions of a trike - simplicity.
     
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  3. voyager

    voyager Member

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    Noah, I understand. The SS is meant as a fun vehicle with the idiosyncrasies of a three-wheel platform. What I meant, is that a three-wheel platform or semi three-wheel platform can signify so much more... including the fun factor, although not as much fun as the SS is offering.

    We have computers that do incredibly complex forecasts with regard to the weather, the global climate. There ought to be computer simulation programs IMO, in which you feed variables like wheel track, wheel base, wheel spacing, tire grip, CG, load, speed, G-force, corner radius, suspension setups...
     
    Last edited: May 29, 2016
  4. WI_Hedgehog

    WI_Hedgehog Winner of the "Most Factory Defects" award Staff Member Moderator

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    That's where engineering falls short of reality--they can't get the weather forecast right, and by me all they have to do is look West and see what is happening. They over-complicate everything, adjusting for all the variables, and still they get it wrong. Then after the fact they go back and issue a revised "forecast" documenting what happened and claim they've always issued "accurate forecasts, " which is why @Bob Runman went off on engineers in Bullet Speed Quad Kit I.R.S. Limited Slip Dif, Formula 1 inspired Push Rod/Rocker Suspension

    You don't want to "tilt it a little" when adding a complex system, you want it to tilt "the right amount," which is why tilting three wheelers are thin like a motorcycle. They certainly have advantages, and forum members including myself have looked into importing/buying/building/owning them. I was serious about buying one late last year for commuting until it was discovered there is no planned parts supply, so if it breaks kiss your $50k goodbye--and that price seems $35k over what the market is willing to pay.

    The shortcoming of the little vehicle I was looking at is it would have to avoid the freeway in rain or strong wind, and stay parked if it snows--still I'd have bought it if reliable and reasonably priced and parts would be available.

    Agreed three wheelers are unique compared to four. They have their own personality, and that's part of their charm.
     
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  5. voyager

    voyager Member

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    Yep, I guess you're right. If you have a wide-stance three-wheeler like the SS, you want it to corner like it does. If you want a tilting three-wheeler, make it narrow enough to ensure sufficient ground clearance. What are your thoughts on the slightly co-steering rear-wheels I mentioned in my previous post, never mind the complexity? Optionally assisted by the sort of active body control a couple of German automakers are experimenting with or even list as an option. It means that the interconnected dampers constantly adapt to the road situation, accelerating and decelerating, and steer input to control body pitch and roll. Some trains use it too (well, only for the body roll).

    [​IMG]
     
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  6. WI_Hedgehog

    WI_Hedgehog Winner of the "Most Factory Defects" award Staff Member Moderator

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    Awesome people here, the concept is interesting!

    78°F at the lakefront, sunny day, been thinking about this one for a while now. And if anyone develops an awesome new tilting vehicle, let me know! It seems just a matter of time before it happens. :)

    Concerning the steering of rear wheel let's ask what would be gained? Applying the German and Russian vehicle steering concepts has been of great benefit to larger vehicles. The Slingshot changes lanes easily, parallel parks in the tightest of spots, and the turning radius seems sufficient. On the Slingshot, it seems a solution in search of a problem.
     
    Last edited: May 30, 2016
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  7. voyager

    voyager Member

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    We know what the wide-stance SS can do. The question (or rather my question) is how to have a narrow (semi) three-wheeler corner safely, without the need for an expensive tilting system, which would have it scrape the road surface anyway.
    Did some studying into four-wheel steering, more specific co-steering rear wheels, as opposed to counter-steering rear-wheels to reduce the turning circle at slow speeds (a three-wheeler don't need that).

    The magic words are vectoring and inertia. In most vehicles the vertical axis around which the vehicle turns (yaw) is located on the rear axle, causing the sort of inertia (resistance to turning) we're all familiar with. Easy to see that Slingshot's single rear-wheel functions as a pivot. With four-wheel steering turn-in is instant, causing the whole vehicle to change direction in a straight line... although I do think that the passengers themselves cause inertia to a certain extent. The downside is cutting corners, as corners by definition have a certain radius. That's usually taken care of by having the rear-wheels co-steer a fraction of the turn-in the front-wheels are displaying, to 'round' the bend.
    [​IMG]
     
    Last edited: May 31, 2016
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  8. Noah Katz

    Noah Katz Active Member

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    My responses following the *

    * seems to me that co-steering does the opposite; instead of going around the corner, you sidle right into it.

    Besides that the more co-steer, the less the vehicle turns; in the limit, 100% co-steer results in the vehicle not even changing the direction it's pointing
     
  9. voyager

    voyager Member

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    It's not about pointing the vehicle per se, but about changing direction to round the bend in a stable manner. No 4WS passenger vehicle does that by having the front and rear wheels point in the same direction. That would mean that it 'sides' into the corner, yes. If the rear-wheels turn in a fraction of what the front-wheels do (the new Porsche 911 uses a mere 3 degree), you are still able to round the corner. My picture exaggerates (perhaps). Although I do think that a narrow vehicle will have to use more turn-in on the rear-wheels to deal with the weight shift... what a wide-stance Porsche 911 doesn't need obviously.

    [​IMG]
     
    Last edited: Jun 6, 2016
  10. WI_Hedgehog

    WI_Hedgehog Winner of the "Most Factory Defects" award Staff Member Moderator

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    Independent of the conversation here, @WI_Squirrel discovered the Toyota i-Road,which is based on their i-Unit concept model. (sweet video she found)

    Revealed in 2013, the i-Road 1.25-passenger vehicle currently is under 3-feet wide, has about a 50-mile range and does about 35mph using a 2.7hp motor powered by a LiPo battery, which plugs into a standard wall outlet and charges in about 3 hours. As battery technology advances, so does the range and speed of the vehicle. In theory, the i-Road will cost $10,000, and was scheduled to be released mid-2016, but that's kind of like Polaris "2-week" delivery estimate, two weeks from tomorrow. Since the eighth test term is still underway, "release" and "mid-2016" seem a bit optimistic.

     
  11. James McKinney

    James McKinney Well-Known Member

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    @WI_Hedgehog dang all it needs is the mowing attachment then you can mow lawn and drive around. LOL
     
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  12. Blitzkrieg

    Blitzkrieg Well-Known Member

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    Toyota has done some interesting things with suspensions. My 2015 4Runner Trail Edition has KDSS (Kinetic Dynamic Suspension System).

    It makes an amazing difference on road and in off-road mode can fully uncouple the sway bars for articulation that would make most stock 4x4's frown. It is only an option on the Trail - not available on the SR5 or Limited.

    That being said - it's costly ($1800 option) and complex. Not complaining - I love it, but as the saying goes (slightly modified to fit my current statement) "Excellent suspension costs money, son. How complicated you want to get?".

    What I love the most about the SS is it's simple. And it works. Very well.

    I have a newly constructed decreasing radius highway entrance on-ramp very close to my house. The posted speed limit is 35 MPH. If you take it at 40 MPH in your average car it will may your butt pucker because its got negative slope as you approach the apex. It's designed to slow people down, not make a smooth entrance and exit.

    I took it at 60 MPH in the SS and the thing was begging for more. I am certain I could take that turn at 75 MPH in the SS which I would never even attempt in a regular vehicle.

    That, to me, is success in simplicity and execution of design. :)
     
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