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Learning how to build Lotus Seven replicas...together!
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PostPosted: Tue Jun 28, 2011 12:34 am 
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Warpspeed wrote:
One further thought on beam axles and chassis design.
[snip]
Why does the main load bearing chassis structure have to extend way out beyond the axle centre lines ?
Why not have the chassis end at the suspension pickup points (within the wheelbase) and cantilever the beam axle(s) out beyond the chassis where vertical movement is completely unrestricted?

I would think primarily because we aren't trying to build a rock crawler. :)

The crazy hot rodders have been doing this for about a century at the front, it is about the only practical way to get the front of this type of vehicle down really low without losing suspension travel.

I think the general idea of a Locost is to have excellent handling not unrestricted suspension travel and therefore that feature isn't high on the list when designing the front end.

If you build a shortened chassis, it will not only probably weigh less, but it completely frees you of any suspension travel constraints regarding getting the steering linkages, drive shafts, or a beam axle, past or through the main chassis structure.

I don't think that the stock Locost IFS suspension has is a particular travel problem for the car's intended use.

The radiator is already mounted in front of the chassis and can't be moved back very much with most in-line engines). So the small amount of weight you save by cutting a few inches off the original frame will probably be added to re-enforce the front of the lengthened chassis to carry the spring loads.

The nose cone and bonnet would probably take a changed look and you may end with a Locost that looks like an old Riley race car with it's protruding front lower jaw (see picture below).

Unfortunately the Locost chassis is about as short as it can be if you build it by the book. And the wheelbase is still ~4" longer than the original Lotus 7. Using a suicide front end would increase the wheelbase even more. By moving the front axle further forward you will increase the rearward weight bias. Some of the cars that have the front/rear ratio mentioned are over 50% rear bias (especially so with a full tank of gas).


Behold, the classic "suicide" hot rod front end.

Behold ............. reverse Ackermann the way that one is set up. And the front axle and leading links, which are solidly mounted to the axle, become a gigantic sway bar. :(


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SPECIA~1_sml.JPG [ 13.41 KiB | Viewed 1402 times ]

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PostPosted: Tue Jun 28, 2011 12:49 am 
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cheapracer wrote:
olrowdy_01 wrote:
A beam axle maintains what ever camber you have built into the axle. It does not compensate for the tire deforming under side loads. That is the problem with the beam axle when pushed to the limit.

If it was so good then F1 cars would probably still be using them.

It most certainly does compensate for it via using caster. You turn the steering and you gain neg camber. The problem with a solid beam is that same "neg camber giving caster" also at the same applies the incorrect amount of camber to the inside tyre and while not as important does take away some of the beam's advantage.

Yep.

The way you reply with quotes to people is very confusing.
I sometimes do that to point out that the statement isn't backed up with any data etc. For instance, people might say, "it may" do this or that. I offhand think it "may" also NOT do that either. In the case of the "axles" is was because we were calling them axles but they sort of weren't in the true sense of the word.

That's probably more corn-fuze-ing than leaving the ""s off. :lol:

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PostPosted: Tue Jun 28, 2011 1:38 am 
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A few posts back you were whining about a beam axle not providing enough suspension travel when fitted to a standard Locost chassis.
Now you claim that Lo cost cars hardly need any suspension travel at all.

All you do is rubbish and criticize without adding anything new, innovative, or positive to the discussion at all.

The hot rod example in the above picture was only to show how a suspension may be extended beyond the ends of the chassis, to get around the often difficult problem of packaging and chassis clearance limitations.
And you start nit picking about Ackerman in the example, which is totally irrelevant to the discussion.

Sure, a shortie Locost chassis may look a bit unconventional without a body, but there is absolutely nothing preventing you from fitting a non structural nose cone (with radiator), or any type of front or rear extended bodywork you want, to improve aerodynamics or looks.

And if you are a bit clever, you can arrange all your suspension location, springs, and antiroll bars to be located within the wheelbase. A shortened chassis (with same wheelbase) is certainly not going to hurt either torsional rigidity or polar moment in yaw.

Thinking outside the conventional is what it is all about.
The late Colin Chapman was an absolute genius at shattering long held traditional ways of doing things.


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PostPosted: Tue Jun 28, 2011 11:09 am 
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Warpspeed wrote:
A few posts back you were whining about a beam axle not providing enough suspension travel when fitted to a standard Locost chassis.

I was illustrating that the DUAL BEAM axle idea you presented would not have any additional king pin length over the old Ford single tube axle with similar suspension travel that a IRS Locost already has.

Now you claim that Lo cost cars hardly need any suspension travel at all.

I did not claim that at all. I said, "I don't think that the stock Locost IFS suspension has a particular travel problem for the car's intended use." As we both know, a camber changing suspension NEEDs suspension travel to work.

All you do is rubbish and criticize without adding anything new, innovative, or positive to the discussion at all.

Baloney.

Actually I gave some numbers to your dual beam axle idea. Here's what I said,

"On a "book" chassis there is 11" between the front frame rails. If we allow 1" of clearance for the minimum clearance between the top and bottom of the axle(s) so they don't hit the chassis, that leaves 9" max from the top of the upper tube to the bottom of the lower tube as the maximum axle(s) separation dimension. Whatever you can take out of the 9" will be the bump/droop the axle(s) can move. If you want 2-1/2" up/down as the max suspension movement (5" total) you are back to about the length of the Ford kingpin (4"). :cry:

It just seems to be easier to use one tube and make the distance between the ball joints as large as you can to fit into the rims if that is the end result desired."

That certainly added a new dimension to the discussion. Otherwise why did you present the suicide front end? You could have presented YOUR data that a dual beam axle through the chassis proved my numbers wrong. Instead you presented another way to use a solid axle. And not even the dual beam one to boot (sort of like my VW inspired idea).

So my response must have presented something positive to the discussion.


The hot rod example in the above picture was only to show how a suspension may be extended beyond the ends of the chassis, to get around the often difficult problem of packaging and chassis clearance limitations.

And you start nit picking about Ackerman in the example, which is totally irrelevant to the discussion.
Having reversed Ackermann was a common problem on those show cars when the builders copied one another. I didn't want someone to copy your example too closely without considering another of it's bad points.

Besides, in responding to your example, I also pointed out that the wheel base would be extended, the weight transfer to the rear might be a problem. And by inference a person who has never built a car before would have to redesign a known to work IFS and chassis to a suicide front end.

Let's go back to the original poster's questions.
kf2qd wrote:
I know independent suspension is all sexy and all that but has anyone considered using a one piece front axle?

It would simplify the pieces involved in the suspension and in getting everything to align.

Some of the Locosts use a solid rear axle, why not a solid front axle?

I am thinking of a Locost as a daily drive and not as a perfoemance vehicle, something fun to drive back and forth to work. Reliability being the main idea.
One of his goals was to simplify the building of the car to drive on the street.

Do you really think a dual beam axle with all it's apparent problems with clearance etc would be the way to go? Would having him redesign the chassis to accommodate a suicide axle be something he would want to do?

You said, "Sure, a shortie Locost chassis may look a bit unconventional without a body, but there is absolutely nothing preventing you from fitting a non structural nose cone (with radiator), or any type of front or rear extended bodywork you want, to improve aerodynamics or looks."

The wheel base would increase, not become shorter. Improved aerodynamics ..... sort of like the picture below?

I'm not trying to criticize your suggestions out of hand, more that I think they aren't suitable to the goal kf2qd had in mind.


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DIXON_~1.JPG [ 16.68 KiB | Viewed 1384 times ]

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PostPosted: Tue Jun 28, 2011 7:42 pm 
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Why would the wheelbase of a Locost have to be extended ?

The front beam axle would be located wherever you wanted to locate it, it is the chassis length at the front that would be truncated to provide sufficient clearance for it.
In our types of cars, the front axle centreline is usually placed well ahead of the engine anyway.
The main load bearing chassis structure need extend no further forward than the upper spring mounting points, and the springs can be located behind the axle.

If you use a single tubular beam, it must be made fairly massive, especially with modern sticky tires to accept fairly high lateral suspension loadings without deflection or fatigue.
A tall slender twin beam truss would be lighter and much stiffer laterally.

I have never seen a single beam hot rod axle fitted with anything other than narrow based kingpins.

The hot rod guys are mostly interested in "the look" rather than high force vehicle dynamics, hence all the sacrilege often committed with Ackerman, radius arm geometry, bump steer, and unsprung weight.
I am a hot rodder myself, and what I see all around me is pretty disturbing, which is why I come here.

Light gauge hollow tubing in straight tension/compression is the way to build any serious suspension.

If an experimental front beam axle design is your thing, a light gauge hollow tube structure is still the way to go, however you do it, especially as it would all be unsprung weight.

But beware of really short king pins, they are an instrument of the devil.


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PostPosted: Tue Jun 28, 2011 8:58 pm 
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olrowdy_01 wrote:
... I didn't want someone to copy your example too closely without considering another of it's bad points...

I used to do that, thinking that I was being helpful; all it did was piss people off because I was raining on their parade - misguided or wrong didn't seem to matter. Now I just read and don't get sucked into pointless flamefests. The idea came to light after I had to add two people here to the "not friends" filter; it was a sign to spend more time elsewhere. To "not care" is kind of sad, but it's a good way to avoid high blood pressure. You may come to the same conclusion, too.

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PostPosted: Tue Jun 28, 2011 11:01 pm 
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Warpspeed wrote:
Why would the wheelbase of a Locost have to be extended ?

Why do I have to do your homework?
PLEASE, look in the "book" and figure out if you could keep the wheelbase the same. I gave it a quick look and here's some more non-relevant information.

To keep the same wheel base with a suicide front end you will have to move the radiator somewhere else because right now it is in -front- of the front axle line. If you decide to move it behind the axle line that would mean you would reduce the clearance between the front of the engine and the radiator by at least 6" (to get the radiator TO the front axle) + the thickness of the radiator and perhaps a shroud + the thickness of the dual axle + some clearance for the nose cone to fit between the radiator and the axle(s). The nose cone would look pretty much like the picture of the Riley that I posted.

The minor problem is that the engine is in the way when all that stuff is moved back! Many of the Locosts I've seen have the electric fan mounted -behind- the radiator. If you move the fan to the front of the radiator you have to make the new nose cone longer than if the fan was behind the radiator. Which now means that you have to move everything further to the rear. It's sort of like the self eating watermelon.


The front beam axle would be located wherever you wanted to locate it,

But right now we are discussing leaving it exactly where the IFS center line is.

it is the chassis length at the front that would be truncated to provide sufficient clearance for it.
In our types of cars, the front axle centreline is usually placed well ahead of the engine anyway.

Yeah but now you need to move everything (the radiator being the largest thing) that was in FRONT of the axle line to behind the axle line. Many cars also have an oil cooler and the radiator header tank in front of the engine somewhere.

The main load bearing chassis structure need extend no further forward than the upper spring mounting points, and the springs can be located behind the axle.

In that case you should have a cross tube running between the top of the coil over shocks. Only thing is the engine or maybe some of the stuff that has been moved back is in the way.

If you use a single tubular beam, it must be made fairly massive, especially with modern sticky tires to accept fairly high lateral suspension loadings without deflection or fatigue.

Please read what the original poster wants to use the car for. No sticky tires, no high loads, just a fun car to drive around.

A tall slender twin beam truss would be lighter and much stiffer laterally.

And to put it bluntly, it would look like s**t sticking out in front of the car with the triangulation! I would hazard a guess that the length of tubes required for the twin axles plus triangulation plus leading links would be more than the tube length used for the IFS "A" arms.

All that stuff sure isn't going to reduce the aerodynamic drag compared to the small diameter IFS tubes being used now either.


I have never seen a single beam hot rod axle fitted with anything other than narrow based kingpins.

So make them longer and stop whining about narrow based kingpins already! :roll:

Jeez, you've got the guy redesigning the front suspension, redesigning the chassis, moving the radiator back, using a non-standard nose cone and you're worrying about two ~6" lengths of steel that go into two 4" lengths of steel tube plus he has to come up with a spindle that uses kingpins.

A Locost only has 500 to 650 pounds of weight on the front axle. The wear of even short kingpins is NOT going to be the same as a hot rod with a 400 to 700 pound engine alone.


The hot rod guys are mostly interested in "the look" rather than high force vehicle dynamics, hence all the sacrilege often committed with Ackerman, radius arm geometry, bump steer, and unsprung weight.

Yet you are still recommending the use of "the look" axle on a Locost?

I am a hot rodder myself, and what I see all around me is pretty disturbing, which is why I come here.

Light gauge hollow tubing in straight tension/compression is the way to build any serious suspension.

The stock Locost suspension already does that.

If an experimental front beam axle design is your thing, a light gauge hollow tube structure is still the way to go, however you do it, especially as it would all be unsprung weight.

But beware of really short king pins, they are an instrument of the devil.
Make them longer grasshopper. :)

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PostPosted: Tue Jun 28, 2011 11:20 pm 
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Golly, I never realized that the radiator and front numberplate were so heavy they needed the full strength of the main chassis to support them.


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PostPosted: Tue Jun 28, 2011 11:21 pm 
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KB58 wrote:
olrowdy_01 wrote:
... I didn't want someone to copy your example too closely without considering another of it's bad points...

I used to do that, thinking that I was being helpful; all it did was piss people off because I was raining on their parade - misguided or wrong didn't seem to matter.

So it seems.

Now I just read and don't get sucked into pointless flame fests.

I'm wondering why someone would continue to discuss something with a person who acts like this, "All you do is rubbish and criticize without adding anything new, innovative, or positive to the discussion at all." :lol:

The idea came to light after I had to add two people here to the "not friends" filter; it was a sign to spend more time elsewhere. To "not care" is kind of sad, but it's a good way to avoid high blood pressure. You may come to the same conclusion, too.
I usually just "unsubscribe" when I've had enough.

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PostPosted: Tue Jun 28, 2011 11:24 pm 
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olrowdy_01 wrote:
Quote:
I usually just "unsubscribe" when I've had enough.


Very good advice Rowdy.


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PostPosted: Wed Jun 29, 2011 1:49 am 
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Warpspeed wrote:

Why does the main load bearing chassis structure have to extend way out beyond the axle centre lines ?
Why not have the chassis end at the suspension pickup points (within the wheelbase) and cantilever the beam axle(s) out beyond the chassis where vertical movement is completely unrestricted?


Well mine isn't a Locost but both my rear beam is outside of the chassis and it does make for a smaller main chassis.

If you look at your hot rod front end my rear is the same in principle but has a rotary pivot in the middle of the DeDion tube(s) to allow roll freely whereas the hot rod doesn't without twisting the beam or the longitudal links.


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PostPosted: Thu Jul 28, 2011 9:02 am 
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olrowdy_01 wrote:
The main problem I see is the position of the axle itself in relation to the lower frame rails.


Here's how Colin Chapman dealt with it:

Attachment:
Beau.HazelGrinsR500.jpg
Beau.HazelGrinsR500.jpg [ 46.4 KiB | Viewed 1296 times ]


It's a Lotus Mark 3, from 1951.

Not real pretty, though.


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PostPosted: Thu Jul 28, 2011 10:19 am 
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olrowdy_01 wrote:
... I usually just "unsubscribe" when I've had enough.

Ha, I've never subscribed to any thread. As a result, when reviewing the lastest "View new posts", I'll run across inflammatory threads I'd forgotten about and think, "Oh, yeah, this thread..."

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PostPosted: Thu Jul 28, 2011 10:36 am 
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Quote:
Here's how Colin Chapman dealt with it:

Attachment:
Beau.HazelGrinsR500.jpg


It's a Lotus Mark 3, from 1951.

Not real pretty, though.

[/quote]

Cute!!

I had a bugeye Baja Bug once. .. great car as a daily driver, got awesome mileage with minor engine mods even with crappy aero and sounded like a Cessna going down the highway. of course it ran out of oomph ~80 mph. ..
But I wonder, could it get around headlight restrictions as a reproduction?

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PostPosted: Wed Aug 03, 2011 4:11 pm 
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From what i've read/come to believe, the Lotus Mark 3 had swing axle front suspension. Chunky took a solid front axle and cut it in half. They used this type of front end on all Lotus' up to the Lotus 12 Formula 2 car, which had somewhat proper IFS.


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