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#Post#: 6819--------------------------------------------------
Re: Bédélia
By: Tinworm Date: May 14, 2022, 1:15 pm
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"Jacking effect is the moving away of the wheel from the centre
of the car in the road and this results due to the oversteering
and is a major handling defect. Jacking effect is the moving
away of the wheel from the centerline of the car in the road
surface."
Working on understanding that
#Post#: 6820--------------------------------------------------
Re: Bédélia
By: Tinworm Date: May 14, 2022, 1:48 pm
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Spent this afternoon welding. Very unattractive welds, but
penetration is sound.
#Post#: 6821--------------------------------------------------
Re: Bédélia
By: Jimr1999 Date: May 14, 2022, 2:11 pm
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[quote author=Tinworm link=topic=883.msg6819#msg6819
date=1652552137]
"Jacking effect is the moving away of the wheel from the centre
of the car in the road and this results due to the oversteering
and is a major handling defect. Jacking effect is the moving
away of the wheel from the centerline of the car in the road
surface."
Working on understanding that
[/quote]
This is how I read it,and it is something I will watch carefully
as it is evident in my Kart, ...
"Positive caster also creates a jacking effect when the wheels
are turned. The front inside wheel rises and the front outside
wheel falls. This creates a jacking effect putting more mass on
the rear outside wheel when cornering. This can create a
positive turn in effect as it helps to rotate the car on corner
entry. "
If I have too much, and I believe I have 4 degrees, it could
prove problematic in a three wheeler. I will be starting slowly
#Post#: 6822--------------------------------------------------
Re: Bédélia
By: StefanN Date: May 14, 2022, 5:45 pm
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Imagine the hypothetical extreme situation where the steering
pivot is angled so far back at the top that it’s at 45°. Now
steer right, by pulling the right hand end of the axle towards
you and left hand end away. The right hand end will push into
the ground lifting that side, and the left will drop as the
wheel is pushed away from the ground.
It’s a different mechanism for normal steering.
#Post#: 6823--------------------------------------------------
Re: Bédélia
By: Jimr1999 Date: May 15, 2022, 12:53 am
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[quote author=StefanN link=topic=883.msg6822#msg6822
date=1652568327]
Imagine the hypothetical extreme situation where the steering
pivot is angled so far back at the top that it’s at 45°. Now
steer right, by pulling the right hand end of the axle towards
you and left hand end away. The right hand end will push into
the ground lifting that side, and the left will drop as the
wheel is pushed away from the ground.
It’s a different mechanism for normal steering.
[/quote]
Absolutely agree Stefan, the effect is a lot smaller in a normal
steering set up but still present. Below are the measurements I
took of this effect on the three wheeler. I am using a 500mm
plumbob and the variation is lock to lock with an average full
lock steering angle of 27[sup]0[/sup]. Calculated out, full lock
throws me 0.75[sup]0[/sup] out of plumb to the outside of a turn
with a caster angle of 4[sup]0[/sup] - I hope that this is
insignificant with all the other dynamics of the chassis/ front
suspension but I intend to proceed with caution. I suspect this
will show up less on a four wheel car as the outside rear will
resist the twist.
Tinworm's centre pivot steering would exaggerate this effect.
#Post#: 6825--------------------------------------------------
Re: Bédélia
By: StefanN Date: May 15, 2022, 5:02 am
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These videos show how caster and to a lesser extent KPI create
vertical movement of wheels - hope they're helpful.
HTML https://youtu.be/QjPhJHj2KuA
HTML https://youtu.be/XU34K3vnLw0
#Post#: 6826--------------------------------------------------
Re: Bédélia
By: Tinworm Date: May 15, 2022, 5:19 am
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Funnily enough, I sort of got it instinctively. I don't really
fully see it intellectually, but I get that my inside wheel will
effectively push down, the more caster I have, and that the
other wheel will jump, and I worry that the car will sort of
trip itself up (or roll itself over into the corner?)! Maybe it
is just as well that the original is not castered?
I have designed the front end so that I can run it as originally
intended, then if and when it scares the bejeebers out of me, I
can switch to Ackerman.
It is interesting that in the early 1910s it was so successful
and that Mike Bullet etc have raced them in the last twenty
years, but someone suggested that its ability to hold a line was
probably due to its long wheelbase, which won't benefit me. And
of necessity, the fact that even shortened, it has a 5" longer
than standard wheelbase will also make cornering more difficult.
Looks like I shall have to be content to be lapped.
I appreciate that I have probably chosen a bit of an unfortunate
first build - possibly not one that even an experienced builder
should try -but it has bitten me.
Thanks Stefan and Jim
#Post#: 6829--------------------------------------------------
Re: Bédélia
By: StefanN Date: May 15, 2022, 5:55 am
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Successful Bélélia racing with central pivot steering? I'd like
to see that.
#Post#: 6830--------------------------------------------------
Re: Bédélia
By: Tinworm Date: May 15, 2022, 6:12 am
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[img][/img]
Read about racing somewhere.
The blue one is Mike Bullet at a VMCC event, I understand; and
the green, a French chap
I have made contact with the Bullet family, so can hopefully
find out more.
#Post#: 6831--------------------------------------------------
Re: Bédélia
By: Tinworm Date: May 15, 2022, 6:15 am
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Darn it, I just wobbled my bench and a wheel fell off and
buckled a spoke, which popped out of the rim. That is a
set-back. That's a hazard of working in a tight space :(
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