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Learning how to build Lotus Seven replicas...together!
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PostPosted: Wed Sep 28, 2011 3:24 pm 
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Exactly as it states. If you have a really high RC, such that the chassis is 'hanging' from it, you could get the CG significantly below the RC. I think this would cause 'backwards' roll, the chassis would roll towards the inside of corner...

...so two wheels up front, one in back, would it lean like a bike? Or would you smash into a tree before finding out?

:cheers:

I haven't found much info on this idea, so it seems it is either very bad, or untested. Probably a bit of both.


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PostPosted: Wed Sep 28, 2011 5:26 pm 
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I'm pretty sure that I've seen some pedal powered recumbent trikes that worked that way although some quick googleFU didn't show what I was looking for. The Trailmate Funcycle ( http://www.trailmate.com/productFunCycle.cfm ) is sort of that way but, again, was not exactly like what I've seen before.

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PostPosted: Wed Sep 28, 2011 7:21 pm 
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I'm not aware of any tilting, road going vehicle with the cg below the rc.

On trikes and motorcycles where the entire vehicle leans, the rc is at ground level. Sport bikes typically have higher cgs which make it easier to lean back and forth.

On trikes where only part of the machine leans, such as GM's Lean machine, the roll center axis of the pivoting section is a line drawn between the tire at the contact patch and the pivot point, which is typically at axle height.

If only the passenger compartment pivots, the roll center of the passenger compartment is typically at axle height, below the passenger compartment cg.

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Growing various fruit trees, berry bushes, and wine grapes in zone 7b.


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PostPosted: Wed Sep 28, 2011 9:17 pm 
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All Formula 1 cars currently have their front RC above the CG.


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PostPosted: Thu Sep 29, 2011 7:22 am 
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There have been cars built with very high roll centers, that would bank into turns.

The roll center of a single-track vehicle is at ground level, despite what some motorcycle magazines say.

You'd have a sharply slanted roll axis. As long as a higher percentage of sprung weight was below the roll axis, it would bank.

The CG would have to be *very* low since the single-wheel roll center is fixed at ground level. Operator position and weight would be a major factor.

You could probably make it work with the operator laying nearly flat, but in that position who cares which way it leans?


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PostPosted: Thu Sep 29, 2011 7:46 am 
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I have often wondered about this too. Also then, in theory, if you could put the RC at the *same* height as the CG and keep it there, you would have zero body roll?


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PostPosted: Thu Sep 29, 2011 11:06 am 
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Tom17 wrote:
Also then, in theory, if you could put the RC at the *same* height as the CG and keep it there, you would have zero body roll?


Yes and no.

You actually have 2 roll centers, the theoretical one obviously everyone raves on about and the other one which is very real and is at the contact patch of your 2 outside tyre's (although not necessarily evenly distributed depending on variables).

Eventually if you have enough grip, your CG is high enough and/or your track is narrow, centrifugal force will eventually roll the CG over the tyre's contact patch, you will initially have roll as the inside lifts and gravity simply compresses the outside suspension (depending on spring rate of course) next step of course is the consummate body roll :wink:

A motorcycle's RC is roughly 1" off the ground due to tyre distortion but that's just semantics, contact patch is a good enough description.


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PostPosted: Thu Sep 29, 2011 11:22 am 
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cheapracer wrote:
next step of course is the consummate body roll :wink:

Like this? ;)
Attachment:
rollstart.jpg
rollstart.jpg [ 15.29 KiB | Viewed 1597 times ]

Admittedly, I did have a little 'apex help' in getting my CG sufficiently above my outside-wheel-RC...


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PostPosted: Thu Sep 29, 2011 12:25 pm 
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The point of tilting is to be able to easily shift the cg to the inside of the corner, allowing for a narrower track and reduced frontal area without tipping over in a corner.

The cg below the rc does just the opposite, but doesn't require input to stay upright when stopped, though I fail to see the point of such a system.

Along with a lower cg comes reduced ground clearance for tilting.

Cheapracer, I don't think Formula 1 cars tilt or have much suspension travel.

TRX, now that you mention it, I do recall having seen a really old racer that had bike tires and would tilt and also a newer German concept. We are talking about trikes and where the cg needs to be relative to the rc to tilt properly.

Tom17, keeping the rc at the cg (not easy) would prevent roll up to the roll over point, but having the rc high to meet the cg also causes poor camber gain and jacking.

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My reverse commuter trike build log: viewtopic.php?t=11384
Fitting glass and weatherstripping: viewtopic.php?f=23&t=6451
Growing various fruit trees, berry bushes, and wine grapes in zone 7b.


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PostPosted: Thu Sep 29, 2011 1:42 pm 
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Miatav8,MstrASE,A&P,F wrote:
Cheapracer, I don't think Formula 1 cars tilt or have much suspension travel.


Indeed they don't. They have a minor "stagecoach" effect to offset chassis roll to help keep the car's chassis low and level for the all important ground effects.


Miatav8,MstrASE,A&P,F wrote:
having the rc high to meet the cg also causes poor camber gain and jacking.


Entirely dependent on suspension type/design.


Miatav8,MstrASE,A&P,F wrote:
TRX, now that you mention it, I do recall having seen a really old racer that had bike tires and would tilt and also a newer German concept. We are talking about trikes and where the cg needs to be relative to the rc to tilt properly.


Google - Piaggio MP3, Quadro 4 Scooter, Brudelli 645L, 4-wheel 4MC, Harley Davidson leaning trike patent and "Google Patents" for tilting vehicles/motorcycles/cars for others.


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 Post subject: Rol Center on a bike...
PostPosted: Thu Sep 29, 2011 1:57 pm 
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Roll center on a motorcycle - are you sure it is the tire patch? when I have been riding hard and playing the bike rolls about a point somewhere off the ground, depending on how hard I am rolling it.


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PostPosted: Thu Sep 29, 2011 3:47 pm 
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Cheapracer, I found your responses to be very strange.

You bring up a formula 1 car in a topic about tilting trikes.

You have referred to leaning trikes that have the rc lower than the cg as having just the opposite.

You've indicated that there are no compromises to roll center location.

Is this correct?

K2fd, I get it :lol:

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My reverse commuter trike build log: viewtopic.php?t=11384
Fitting glass and weatherstripping: viewtopic.php?f=23&t=6451
Growing various fruit trees, berry bushes, and wine grapes in zone 7b.


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PostPosted: Thu Sep 29, 2011 5:26 pm 
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Formula 1 car suspension was brought up earlier.

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PostPosted: Fri Sep 30, 2011 1:35 am 
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Miatav8,MstrASE,A&P,F wrote:
Cheapracer, I found your responses to be very strange.



Fits right in with my character. :wink:

But I could have read the title better, not that it's that clear nor was my head at the time to be honest.


Miatav8,MstrASE,A&P,F wrote:
C

You've indicated that there are no compromises to roll center location.


I did? I thought I made it clear that RC's (plural) was quite a dynamic thing.


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PostPosted: Fri Sep 30, 2011 2:18 am 
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IA599 wrote:
Exactly as it states. If you have a really high RC, such that the chassis is 'hanging' from it, you could get the CG significantly below the RC. I think this would cause 'backwards' roll, the chassis would roll towards the inside of corner...

...so two wheels up front, one in back, would it lean like a bike? Or would you smash into a tree before finding out?



Ok, I got it now, sorry for my waywardness.

I now see what you mean, you don't mean a titling trike you mean a trike that "stagecoaches".

Stagecoache's with luggage on the roof and the driver sitting so high have a very high CG so to combat this the manufacturers have the coach suspension pivots (RC) as high as practical to stop them falling over and keep the coach level for passengers comfort. When a coach only has people and no luggage the coach's CG is below the coaches RC so the lower part of the coach actually swings out and the top tilts inwards but this is false economics, the CG is still being forced outwards not inwards (or down) so yes it may tilt but no gain.

There's an older suspension system on the net that actually has the front control arms crossing over each other (the lower BJ goes to the top pivot and vise versa) that prevents body roll and I have often toyed with the idea of that being ideal for a zero roll reverse trike especially to keep the rear tyre perpendicular - if I remember it's name .....


Ok found it, "Link-X" by Todd Wagner ...

http://www.youtube.com/watch?v=qvnqKZrYXZE

http://www.google.com/search?hl=en&neww ... 0l0l0ll0l0

http://www.google.com/search?tbm=pts&tb ... ch+Patents


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