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Date: 08 May 2005 13:08:07
From: leavoa@gmail.com
Subject: Centerpoint steering
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Hello,
I have started reading http://www.eland.org.uk/steer_intro.html and I
have a question regarding this:
>Also, if just one of the front wheels is braked, or the two front
wheels are
>braked unevenly, the forces should again all pass through the kingpin
axes and
>not affect the steering.
How is this possible?
The wheel can turn around the kingpin , and it's axel is not exactly on
the kingpin, so any force on the wheel axle (which would be created by
breaking) would turn the wheel and affect the steering.
right?
-Leav
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Date: 09 May 2005 11:10:13
From: LoGo USA
Subject: Re: Centerpoint steering
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Leav wrote:
>[A tadpole's front] axle is not exactly on the kingpin, so any
>force on the wheel axle (which would be created by braking) would
>turn the wheel and affect the steering.
To which Jeff (very astutely IMHO) replied:
>... the kingpin's axis should intersect the ground on the same
>line as the centerline of the tire. This will prevent the tire
>from being steered right or left by off-center braking...
But having been officially notified now in another thread that:
>... experts are welcome here too provided they do not go on and
>on at too great a length.
Perhaps, I too (a modest non-expert) can expand a bit:
It may help to think of braking force applied to the hub carrier
assembly (kingpin) at the tire's contact patch. If a line through
the rotational axis of the kingpin hits the center of that patch,
almost no matter what kind of other parts are in the assembly or
their 'internal' geometry, then the braking force will ultimately
have almost no 'lever arm' to cause the kingpin to turn and steer
the trike.
FWIW: There's a bit of highly technical design and jargon in the
science (and art) of steering with a two-wheeled 'axle', most of
which is of almost no relevance to most tadpole riders. E.g.,
the tire's contact patch is really usually slightly behind the
kingpin's ground reference point, (which most folks think of as
'trail') to enhance high speed stability.
Most newer tadpole designs also have the tread contact patch
located just inboard of the kingpin's ground reference point, so
that single-sided braking actually applies a small intentional
force toward rotating the kingpin away from the braking side.
For example, if you apply only the right side brake, this force
would try to steer the trike to the left. But braking on one
wheel to the right of the trike's center of gravity also creates
a couple (or moment) on the trike as a whole ('body' or mass)
that tries to make it turn to the right. If this steering design
(called ABC for Asymmetrical Brake Compensation on the LoGo
trikes) is done well, the end result will be that the two forces
almost exactly balance, and the trike shows almost no tendency
to pull to the side, even under very heavy one-sided braking.
The design tradeoffs for ABC are relatively trivial, and most
trikeys who've ridden a tadpole with this design love its added
safety and convenience.
Regards,
Wayne
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Date: 08 May 2005 14:29:53
From: Jeff Wills
Subject: Re: Centerpoint steering
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leavoa@gmail.com wrote:
> Hello,
>
> I have started reading http://www.eland.org.uk/steer_intro.html and I
> have a question regarding this:
>
> >Also, if just one of the front wheels is braked, or the two front
> wheels are
> >braked unevenly, the forces should again all pass through the
kingpin
> axes and
> >not affect the steering.
>
> How is this possible?
>
> The wheel can turn around the kingpin , and it's axel is not exactly
on
> the kingpin, so any force on the wheel axle (which would be created
by
> breaking) would turn the wheel and affect the steering.
>
> right?
>
> -Leav
No, the kingpin's axis is not vertical. It is angled so that the bottom
of the kingpin is farther out than the top. In order to design
zero-scrub-radius steering (which is what you're describing and *not*
centerpoint steering), the kingpin's axis should intersect the ground
on the same line as the centerline of the tire. This will prevent the
tire from being steered right or left by off-center braking (not
"breaking") forces.
Jeff
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Date: 07 Jun 2005 18:35:00
From: 25hz
Subject: Re: Centerpoint steering
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From what I've read, zero-scrub IS center point steering. The contact patch
and king in axis intersect at the same point, and produce zero scrub.
Positive and negative scrub radius are not "center point steering" however,
and while I've heard that positive scrub radius is called asymmetrical
braking compensating (or something like that) I haven't heard of another
term for negative scrub radius.
> No, the kingpin's axis is not vertical. It is angled so that the bottom
> of the kingpin is farther out than the top. In order to design
> zero-scrub-radius steering (which is what you're describing and *not*
> centerpoint steering), the kingpin's axis should intersect the ground
> on the same line as the centerline of the tire. This will prevent the
> tire from being steered right or left by off-center braking (not
> "breaking") forces.
>
> Jeff
>
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