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 Post subject: Swing Axle
PostPosted: Mon Feb 13, 2012 9:06 pm 
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I have an idea for a swing axle for my project ...... viewtopic.php?f=18&t=12997

The idea of a swing axle is nothing new and has been used on cars in varying degrees of success from Porsche, Mercedes(from 50's -70's), Allard, Mallock U2 and Lotus MK6 and Eleven just to name a few.....
I dropped the idea after reading how dangerous the suspension can be when the jacking effect happens
Then, I started to find articles that made me rethink my idea and how it might be achieved on a Reverse trike.........

THE IDEA:
Is to create a Zero Roll swing axle, by mounting the axle half's at or below the chassis and below the horizontal axis of the axle....... keeping the mathematical roll center just under the physical roll axis, rather than above it, Then attach a stiff anti-roll bar to level the chassis and then mount small coilover shocks on the underside of the axle to the chassis, helping to prevent positive camber.
This with a low roll center and 3 wheels, the line of action is almost horizontal (the hypotenuse of the triangle) so the vertical component is very small helping reduce the jacking effect ..... even creating negative camber and more grip.

It makes me think that a lightweight car running low pivot point swing-arm (or semi-trailing or leading) suspension and motorcycle tyres could develop a lot of grip while maintaining an ultra lightweight suspension, in turn giving a very low unsprung weight and low total vehicle mass. And the narrow wheels and tyres would also give far lower rotating inertia, improving acceleration and braking still further…
http://blog.autospeed.com/2007/07/24/sw ... -defended/

Here are a few more articles:
http://www.autospeed.com/cms/A_108852/article.html
http://www.jalopyjournal.com/forum/show ... &showall=1

Out of curiosity would this be considered a swing axle?
http://www.hyperracer.com/index.html

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 Post subject: Re: Swing Axle
PostPosted: Tue Feb 14, 2012 3:19 am 
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The 110 Alpine Renault would be the most successful (rear) swing axle car ever and it had simple droop limiters (simple leather straps in fact) so the axles went just below horizontal but not enough to jack.

Multiple Monte Carlo and World Championship rally wins on all surfaces and still a real threat in modern historic rallies against Porsche, Lancia Stratos etc. and stands as one of the great rally cars of all time.

http://en.wikipedia.org/wiki/Alpine_A110


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 Post subject: Re: Swing Axle
PostPosted: Tue Feb 14, 2012 11:52 am 
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I match your Alpine and raise you an Allard, :mrgreen:

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HUFFSTER:
Considering that the RC is based on the tire patch and the pivot point on a swing axle, the RC and pivot point would be chasing each other as you move the pivot point to raise the side loading. Eventually the pivot point is at ground level to maximize the affect you are after. That isn't going to leave a lot of room for a shock to be under the pivot point.

Also motorcycle tires are not designed to take serious side loads in cornering. Many motorcycle tires have a very narrow contact patch when vertical (something like less than 2" on my sons bike!).

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 Post subject: Re: Swing Axle
PostPosted: Tue Feb 14, 2012 3:27 pm 
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Yo, Rowdy-
Holy "Loud and Sideways" Batman! That Allard is cornering on about 1/3 of that skinny rt front!!! How the 'ell?!?!?

That front end looks like the "Independent Front Suspension" on Model A's that I've read about, where guys (the original Hot Rodders) would cut about 1/4 inch out of the front axle at the center, drill holes in the ends and bolt 'em to a plate they welded on, hanging down to axle level... Say it ain't so!?!?

Regardless, that driver has a "fo' real" set of cojones!

:cheers:
JDK

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 Post subject: Re: Swing Axle
PostPosted: Tue Feb 14, 2012 4:13 pm 
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Quote:
That front end looks like the "Independent Front Suspension" on Model A's that I've read about, where guys (the original Hot Rodders) would cut about 1/4 inch out of the front axle at the center, drill holes in the ends and bolt 'em to a plate they welded on, hanging down to axle level... Say it ain't so!?!?

JD, That's exactly what"s going on there. I don't think the Allard used a Model A axle, but something very similar. Some of the early Loti used a similar setup, the Mk 8 IIRC.

Huffster, Have you considered a twin I-beam type setup like the Ford trucks. Instead of the center of the frame, each axle half pivots off the opposite frame rail giving a longer swing arm, and lower R/C. Both of these factors should help reduce the jacking effect while maintaining the simplicity of the swing axle.

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 Post subject: Re: Swing Axle
PostPosted: Tue Feb 14, 2012 4:49 pm 
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GonzoRacer wrote:
Yo, Rowdy-
Holy "Loud and Sideways" Batman! That Allard is cornering on about 1/3 of that skinny rt front!!! How the 'ell?!?!?

Sh, it's not a motorcycle tire and it's filled with unobtainium! But can you imagine what would happen if one of the restrainers (or shocks?) running from the headlight to the axle were to break! :shock:

That front end looks like the "Independent Front Suspension" on Model A's that I've read about, where guys (the original Hot Rodders) would cut about 1/4 inch out of the front axle at the center, drill holes in the ends and bolt 'em to a plate they welded on, hanging down to axle level... Say it ain't so!?!?

They made it sew. :roll:

Regardless, that driver has a "fo' real" set of cojones!

:cheers:
JDK
Probably made of Titanium. Maybe the team manager never showed him a picture of him cornering?

But here's a really cool looking driver doing some FWD three wheeling with a 500 cc Berkley.
Attachment:
File comment: I get 30% more tire mileage this way.
3 Wheeling w-Berkley 500a-sml.jpg
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Last edited by olrowdy_01 on Wed Feb 15, 2012 12:02 am, edited 1 time in total.

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 Post subject: Re: Swing Axle
PostPosted: Tue Feb 14, 2012 7:40 pm 
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The idea is for a Front Engine Rear Drive 3 wheeler and it'll have different handling characteristics than the 4 wheeled post WWII vehicles you fella's remember from your youth :wink:

By adding Modern shocks, anti-roll bars and better pickup points ..... I'm hoping it'll create a better handling beast than the Swing Axles of yore and give me the esthetic I'm looking for.......

Inherently Responsive Design

Designing to the three-wheeler's inherent characteristics can produce a high-performance machine that will out corner many four-wheelers. A well designed three-wheeler is likely to be one of the most responsive machines one will ever experience over a winding road. Superior responsiveness is primarily due to the three-wheeler's rapid yaw response time.
Yaw response time is the time it takes for a vehicle to reach steady-state cornering after a quick steering input. A softly sprung four-wheeler will have a yaw response time of about 0.30 seconds, and a four wheel sports car will respond in about half that time. A well designed three-wheeler can reach steady-state cornering in as little as 0.10 seconds, or about 33 percent quicker than a high-performance four wheel car.
Quick steering response has nothing to do with the number of wheels or how they are configured. It is a byproduct of reduced mass and low polar moment of inertia. A typical three-wheeler is lighter and has approximately 30 percent less polar moment than a comparable four wheel design.

Rollover Stability of Conventional Non-Tilting Three-Wheeler

A conventional, non-tilting three wheel car can equal the rollover resistance of a four wheel car, provided the location of the center-of-gravity (cg) is low and near the side-by-side wheels. Like a four wheel vehicle, a three-wheeler's margin of safety against rollover is determined by its L/H ratio, or the half-tread (L) in relation to the cg height (H). Unlike a four-wheeler, however, a three-wheeler's half-tread is determined by the relationship between the actual tread (distance between the side-by-side wheels) and the longitudinal location of the cg, which translates into an "effective" half-tread. The effective half-tread can be increased by placing the side-by-side wheels farther apart, by locating the cg closer to the side-by-side wheels, and to a lesser degree by increasing the wheelbase. Rollover resistance increases when the effective half-tread is increased and when the cg lowered, both of which increase the L/H ratio.
A simple way to model a three-wheeler's margin of safety against rollover is to construct a base cone using the cg height, its location along the wheelbase, and the effective half-tread of the vehicle. Maximum lateral g-loads are determined by the tire's friction coefficient. Projecting the maximum turn-force resultant toward the ground forms the base of the cone. A one-g load acting across the vehicle's cg, for example, would result in a 45 degree projection toward the ground plane. If the base of the cone falls outside the effective half-tread, the vehicle will overturn before it skids. If it falls inside the effective half-tread, the vehicle will skid before it overturns.
http://www.rqriley.com/3-wheel.htm
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Sprint Car Axle Bracket to attach shock to the axle to allow for quicker shock reaction and to attach Swedged radius rods

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Sprint Car Shock towers to attach shock to chassis, as well as head lights
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Where the axle meets the chassis I'll use these to adjust camber
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Last edited by HUFFSTER on Wed Feb 15, 2012 8:15 pm, edited 1 time in total.

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 Post subject: Re: Swing Axle
PostPosted: Tue Feb 14, 2012 9:43 pm 
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I don't think the reduction in unsprung weight will be worth the nasty camber curves.

IMO: stick with the solid axle.


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 Post subject: Re: Swing Axle
PostPosted: Tue Feb 14, 2012 11:58 pm 
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HUFFSTER wrote:
The idea is for a Front Engine Rear Drive 3 wheeler and it'll have different handling characteristics than the 4 wheeled post WWII vehicles you fella's remember from your youth :wink:

With a swing axle it should definitely have "different" handling. :roll:

By adding Modern shocks, anti-roll bars and better pickup points ..... I'm hoping it'll create a better handling beast than the Swing Axles of yore and give me the esthetic I'm looking for.......

A swing axle configuration (or just about any suspension) will work OK if you make the shocks and roll bar stiff enough. Shocks and roll bars were not unknown on three wheel vehicles old or new. In fact they are a basic requirement to give it stability. Mercedes used a low pickup point for their swing axle cars which reduced the jacking affect but didn't eliminate the basic cause of jacking. If you lower the axle pivot point you can increase the resistance to jacking but camber changes are still going to be uncontrolled as soon as the axle(s) pivot.

[Snip]
Designing to the three-wheeler's inherent characteristics can produce a high-performance machine that will out corner many four-wheelers .................
[Snip]
A conventional, non-tilting three wheel car can equal the rollover resistance of a four wheel car, provided the location of the center-of-gravity (cg) is low and near the side-by-side wheels.
[Snip]
http://www.rqriley.com/3-wheel.htm

Yes but did Riley ever consider using a swing axle? I don't remember reading about it if he did.

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IMG_0913.JPG
Are these pictures of what you have built? By making the swing axles short as shown, the camber change will be more pronounced for the same change in pivot up/down movement as compared to a longer axle.

To visualize things like this I just use extreme dimensions. i.e. imagine that an axle is is supported by a tire on one end and the pivot point on the other end which moves 1" vertically up/down. What angular change of the axle would occur if it is 2" long vs 2 feet long? Obviously the shorter axle has more angular (camber) change and scrub to boot.

As we know, good cornering is helped by having the camber change in a controlled manner to keep the tire footprint correct as cornering speed builds up (roll sets in etc). Assuming there is no bounce/droop, a stiffly sprung and/or heavy duty roll bar swing axle setup is somewhat similar to a solid axle in that one setting can't automatically adjust to suit changing cornering conditions. But unfortunately uncontrolled camber changes from pot holes etc will occur.

Lowering the axles pivot point(s) and making the axles as long as possible (crossing over to the opposite side of the chassis etc) will help. BUT eventually the requirement to have ground clearance will still induce jacking affect. Crossing the axles to the far side will cause camber to go positive on the outside tire when cornering at high speeds. This is due to the body rolling and lifting the side towards the inside of the turn more than the other side of the car. (See Allard picture.)

Add in that any up/down movement of the mounting point of the axles (assuming the pivot points don't drag on the ground) will affect the camber that might not be what is desired at that time since it is haphazard and unpredictable (unless you know where all the pot holes are).

If the jacking doesn't get you, camber change might. Combine the two ..... ? This will be an interesting experiment.

Pros and cons,
http://en.wikipedia.org/wiki/Swing_axle

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 Post subject: Re: Swing Axle
PostPosted: Wed Feb 15, 2012 8:10 pm 
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IA599 wrote:
This will be an interesting experiment.


It sure will......... if not, I'll have a attachment point for a lower control arm :wink:

Thanks for your input and have a good one

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 Post subject: Re: Swing Axle
PostPosted: Wed Feb 15, 2012 10:10 pm 
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HUFFSTER wrote:
IA599 wrote:
This will be an interesting experiment.


It sure will......... if not, I'll have a attachment point for a lower control arm :wink:

Thanks for your input and have a good one


I guess I could have explained my opinion more. It looks like your solid axle & swing axle designs share common mounts for the trailing arms and shock mounting points. The major difference is only three mounts, two for the swing axles, and one for the lateral locating link (panhard bar er whatever). You could combine one mount into both functions. So you could have a chassis that would function as both, and you have a straight axle, so it would be easier to start there and see how it handles before cutting it up.

Also, swing axle with the shocks outboard like that...minus whale use macstruts and have a much greater choice of donor parts and improved camber control.


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 Post subject: Re: Swing Axle
PostPosted: Wed Feb 15, 2012 10:49 pm 
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Oh, and I'm biased. I like the solid axle, and I want to see how well it works.


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 Post subject: Re: Swing Axle
PostPosted: Thu Feb 16, 2012 12:11 am 
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IA599 wrote:
Oh, and I'm biased. I like the solid axle, and I want to see how well it works.
I'd certainly use a solid axle before a swing axle. Actually I'd use -any- axle before a swing axle.

HUFFSTER: I forgot to mention in my long monolog but by having a short axle lengths with the pivots somewhat lower than the wheel center line,(as your pictures show) vs longer axles you might very well create a higher RC compared to having the axles meet below the differential center. By holding a straight edge on your front view picture the RC would appear to be at the top edge of the straight axle. Considering that the RC of the rear wheel is at ground level the trike will tend to understeer.

When I said Riley didn't mention swing axles I meant in conjunction with a three wheeler. But it is interesting what he does say about swing axles in general at http://www.rqriley.com/suspensn.htm

"The Swing Axle
[snip]
Swing-axles produce large changes in camber and tread during bounce, and the design can become unstable in turns due to the "jacking" effect. Setting the wheels at a negative camber can reduce the tendency to jack. However, too much negative camber can also produce a vehicle with a vague, mushy feel of directional instability. Slings under the axles or zee brackets can be designed to limit downward travel and thereby avoid wheel tuck-under. A correctly designed swing axle suspension works reasonably well, but its undesirable characteristics can never be fully overcome."
_________________________________________________________________________

But cheer up, no matter which axle you go with it can't be as bad as this picture. :lol:

"I've GOT to take this car in for an alignment!" :shock:
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 Post subject: Re: Swing Axle
PostPosted: Fri Feb 17, 2012 5:00 pm 
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It might not be long before you see production cars with negative camber running around
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http://www.multimatic.com/news/release.php?release=43

Thanks to Bill Milliken's MX-1

Image

So, I'm all smile's :D

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 Post subject: Re: Swing Axle
PostPosted: Sat Feb 18, 2012 5:41 pm 
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This is a more better way of doing it,

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