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Old 12-02-2009, 10:46 PM   #11 (permalink)
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Open Question

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Originally Posted by Winfield1990 View Post
Ahhh ok my bad , For the most part when I was including the "I know" remarks I was pretty much just wanting to say regardless of reasoning to just exclude those factors.

I wasnt really trying to saying that I knew about those issues my fault.

I was just wanting to keep it to the issues that I asked solely about the axle track and the single wheel drive. For the time being , then add whatever else needed to be addressed.
At this point, I could just add "whatever else" by quoting book chapters, but I see that a couple of the lads are trying to get you started. It is a fascinating study; I hope you enjoy it as much as I have.

The GM Sunraycer had 4 wheels and one wheel drive. When I asked Chet Kyle about that, he explained that it helped to provide the steering torque to counter the road camber, with the low thrust needed.

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Old 12-02-2009, 10:49 PM   #12 (permalink)
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At this point, I could just add "whatever else" by quoting book chapters, but I see that a couple of the lads are trying to get you started. It is a fascinating study; I hope you enjoy it as much as I have.

The GM Sunraycer had 4 wheels and one wheel drive. When I asked Chet Kyle about that, he explained that it helped to provide the steering torque to counter the road camber, with the low thrust needed.
Sauce? Specifically on the drive system employed? (Was it variable wheel drive, like not a dedicated wheel, or just, for instance, the left front wheel?)
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Old 12-02-2009, 10:50 PM   #13 (permalink)
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To add to this, if you narrow your front track you still need to consider ackermann geometry even if you leave wheelbase alone.

Or scrub tires, if you don't care. That's up to you.
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Old 12-02-2009, 11:07 PM   #14 (permalink)
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Ok, so with a reverse trike (2F1R), the two considerations for traction are the loss of the friction surface between one of the tires and the road. Assuming that you've widened the remaining rear tire to double it's original size, making up for the tire that's been removed (doesn't quite work that way, but bare with me here), it's less of an issue.

The next consideration is whether or not your front track width creates a right triangle or an isosceles triangle (google it). With an I-triangle, you're going to have more angular momentum on the rear tire going around a corner, but added stability in normal cornering situations (think rollover stability). With a R-triangle, you get rollover stability, but less normal cornering stability, and less angular moment on the rear wheel, thereby creating less chance of the rear taking the lead, so to speak.

Required speed becomes an issue here, if you're working with any kind of single rear wheel setup. For the absolute maximum compromise, you'll want to start with about 60/40 F/R weight distribution, which puts approx 30% between both front wheels, then adjust from there. There is no single setup that will give everyone the best results. Build it, learn to drive it, then adjust it to your liking/operating ability.
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Old 12-02-2009, 11:12 PM   #15 (permalink)
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well that clears it right up
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Old 12-02-2009, 11:15 PM   #16 (permalink)
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Well, it's not exactly a clear-cut answer... there isn't one for the question he asked. In fact, it's a rather progressive science that we're discussing here, to the extent that no single answer will cover all events, or even the majority of them, which is why I said what I said - build it, learn it, adjust it.

I'm going to resign to letting OP search out the answers he requires for anything further than I've posted, I don't want to be the reason he flips the thing and gets hurt or hurts someone else.
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Old 12-02-2009, 11:25 PM   #17 (permalink)
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But I don't even know what you were going on about especially with the triangles!
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Old 12-02-2009, 11:26 PM   #18 (permalink)
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"Sauce? Specifically on the drive system employed? (Was it variable wheel drive, like not a dedicated wheel, or just, for instance, the left front wheel?)"

At first, I thought it was just a bit too much KISS - one electric motor, on the ditch -side rear wheel. (They drive on the left, down under.)
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Old 12-02-2009, 11:35 PM   #19 (permalink)
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Quote:
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But I don't even know what you were going on about especially with the triangles!
I'm afraid I'd have to draw it out, but the shape of the triangle dictates the angle at which forces act on the tires, with a trike design. There are too many variables to discuss all scenarios, so the maximum is all I take into account.

With a Right triangle, the maximum turning force is located squarely on the front tire opposite the curve, provided the Cg is centered in the chassis. (I forgot to add that assumption, the Cg has to be located squarely between the three wheels on the plane parallel to the road's surface.)

At normal road speeds and conditions, some of this doesn't really apply.
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Old 12-08-2009, 04:11 PM   #20 (permalink)
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Nitpick time: A right triangle is any one that has one 90-degree angle. An isoceles triangle is any one that has two equal sides. (Equivalently, a triangle that has two equal angles in it.) There is exactly one that is both; it has a 90-degree corner and two 45-degree ones. For a trike, you would only consider isoceles triangles unless one front wheel is to be forward of the other.

That out of the way:

A general rule of thumb is when you widen the track at one end of the car, you get better lateral grip, and when you narrow it you get worse. This has to do with a lot of factors, but it holds pretty true in most cases. So a narrower rear end will tend to promote oversteer, which can be fun but can also be hazardous.

Going to a single rear wheel can make for exciting situations if you have a good amount of torque and drive anywhere that they paint the roads, or water gets on them, or other contaminants get on them. A friend found that out the hard way with his Corben Sparrow; on a rainy day he tried to turn and accelerate at a cross-walk. The rear tire spun pretty much instantly, throwing the car completely sideways. He said that it was just barely controllable and only because of his autoXing experience, and if the road had been any narrower he probably would have slid into a curb. Which can easily lead to a roll-over.

If there had been two drive wheels with a differential between them, only the low-traction wheel would have "lit up", and he would have pretty much just been sitting still, spinning one wheel.

All of this stuff can be mitigated to some extent by making various trade-offs. Some of it also won't be a factor under everyday driving conditions, but sometimes you hit extra-ordinary conditions.

There are enough things going on that experimentation is really the only way you will find how a given setup is going to drive.

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