A-arms are lame

Dylan

Well-Known Member
A-arms are OK but cant we do better??

What do we want our wheel to do and how do we want it to move?

At a given steer angle we only want one degree of freedom, up and down.

Let’s skin this cat another way!

Dylan
 

Bob_Sheaves

Well-Known Member
OK, accepting your challenge...LOL....

The single most important item in vehicle dynamics is control over the ground contact patch- all other things are secondary.

Agreed?

Best regards,

Bob Sheaves
 

Jimmy8

Well-Known Member
There is another way to do front suspension other than I beams, a arms or a 4 link if that is what you are getting at. We were going to apply it to my new Trophy Truck but decided against it. We may try it out on a pre runner before we do it on a competition vehicle, but there is another way. It hasnt ever been done before, and could revolutionize the sport. We have the idea, but I am not going to let it out in the open because we may do it in the future. Use you imagination.

Trophy Truck #15
Class 8 #8080
www.jimmybeaver.com
 

FABRICATOR

Well-Known Member
Ho hum...
Perhaps Bob, but there is the omnimissing parameter of application! Things like vehicle weight, speed requirements, terrain, and durability (just to name a few) will significantly affect overall design. Are we talking swell geometry on pavement, high speed over rough terrain, or what? Application defines what compromises are made to perfection.

<font color=orange>The best ideas are the ones that look obvious to the casual observer.</font color=orange>
 

Bob_Sheaves

Well-Known Member
Nope- reread what I said-GCP is THE SINGLE most important item-all else is lower priority, regardless of the application. In other words-you ain't going anywhere if you ain't got traction.

I was under the impression from Dylan's post that he wanted to have a discussion on designing a new suspension. This requires a starting point. If I am wrong, or ya'll don't wish my input-please tell me and I'll be quiet....LOL!


Bob
 

Dylan

Well-Known Member
Yes I agree!
But in off road conditions is the normal way we quantify the effectiveness of the contact patch (vertical to lateral load conversion, slip properties, ect.) really appropriate or should we model the tire after a farm plow disc that is displacing dirt?
On the “secondary” or maybe "primary" properties: how do we get the loads (however they are generated) at the contact patch back to the chassis with the reaction that we want throughout our ridiculous amount of travel. We have been using A-arms primarily but we never get the pivot points quite were they need to be.

??Eclipse lower “quasi” A-arm, Mercedes rear ??

Dylan
 

Bob_Sheaves

Well-Known Member
The next thing to define, now that we agree on the "ground set" boundary condition (for those not familiar- "ground set means the immovable element where traction force is applied), we need to define the starting point or "input set" boundary condition, i.e. the total mass of the vehicle. This is where you define the mass and center of gravity (obtained from a general packaging diagram with this info).

Combined with the GCP- this sets the limits of mass parameters. The input loading is applied to the CG (actually the polar moment, but we'll get into that in a bit) is reacted against the ground set through the GCP.

Best regards,

Bob

<P ID="edit"><FONT SIZE=-1>Edited by Bob_Sheaves on 04/09/02 11:47 AM (server time).</FONT></P>
 

FABRICATOR

Well-Known Member
Bob, my comments addressed a lack of specification from Dylan, and had nothing to do with your post. I don't think anyone here, especially myself, has anything but great respect for your experience and input.

As far as the "SINGLE" most important thing...it ain't going anywhere if it's broken either. It appears Dylan is talking about going fast off-road, but if it's not realistic it is of little use. My apologies if I only rebut some of your theories.

The extreme wheel travel needed, among other things, will dictate a lot about what must be used or cannot be used. The system must also put up with severe abuse. I must question dirt as an immovable element where traction force is applied. Seems that I don't agree with much today. I'll be quiet. (LOL)


<font color=orange>The best ideas are the ones that look obvious to the casual observer.</font color=orange>
 

Bob_Sheaves

Well-Known Member
ROFL!!! Guess we both misunderstood each other....LOL!!!

Anyway, I don't take offence so easy-you ought to know that....what I was intending was to introduce comments just like it was a real design project (I have started with less information before...LOL). Figgered that the mind excercise would be good for me. If no one objects-I'd like to use my software as the definition grows to show in 3D what the discussion is all about. Sound like a good excercise?

Btw- the dirt IS the GCP-one of the excercises will be to determine tractive effort applicable through varying coefficients of friction....

Best to you as always,

Bob
 

Mike_McCluskey

Well-Known Member
Bob, since your gonna use your software to illustrate whats discussed here why don't you guys take it one step further and create a whole new car. Get input from everybody and design the ultimate desert race car. Maybe some FABRICATOR might help get it built. The first car conceived online!

Just a thought. These are definitely some of the better discussions.
 

rdc

- users no longer part of the rdc family -
See Klaus, you are finally getting a car built for you! LOL

Bob I think 3D models of what you all are talking about is an exellant idea.. And if it were possible to build the RDC online unlimited car that would be awesome! I guess we better start taking donations...

Tony
<A target="_blank" HREF=http://www.y-not-productions.com>www.y-not-productions.com</A>
 

Bob_Sheaves

Well-Known Member
OK, guys...next is a list of information needed and assumptions for this "project". I will assume everyone will contribute to this?

In no particular order:

Assumptions:

1. Class car will run:

2. Number of passengers:

3. Maximum speed desired:

4. Gross vehicle weight: (this is a "wet" weight)

5. Number of drive wheels:

6. Fuel capacity desired:

7. Tire manufacturer:
a. Size:
b. Pressure:
c. SLR (Static Loaded Radius):
d. RPM (revolutions per mile):
e. Max section width:
f. Wheel profile and size desired (JJ, JK, or whatever profile):

8. Engine desired:
a. Weight Dry:
b. HP @ "X" rpm:
c. Torque @ "X" rpm:
d. Manufacturer:
e. Model:
f. Heat rejection (in BTU/minute):

9: Transmission desired (Automatic or manual trans)
a. Torque converter ratio (if used):
b. Number of ratios and numerical ratio for each:
c. Weight dry:
d. Manufacturer:
e. Model:
f. Heat rejection (in BTU/minute):

10. Final drive/ axle type (Salisbury, Hotchkiss, IFS. IRS, etc) desired:
a. Ratio of final drive desired:
b. Ratio of hub reduction, if used:

Suspension design is not specified, as this is the purpose of this discussion- to determine a "new" design that will fulfil the stated parameters. Now is the time to add any other desired design parameters also.....

Best regards,

Bob
 

Bob_Sheaves

Well-Known Member
To get you all familiar with thinking in 3D terms, I am attaching (I hope) a JPG image of the start model. In this image, the XYZ trihedron is your reference to what is up and down, left and right. In this image, "X" points towards the rear of the car along the centerline, "Y" points to the right side of the car, and "Z" points "up". In other words, you are viewing this from above the right rear corner of the car.....

The wheelbase shown of 3048mm (120 inches) and track width of 2032mm (80 inches) is simply for reference. The plane labled *PLN1 indicates the ground contact surface in the design position (you always start from a static, fixed plane when designing a vehicle). the other planes are referencing other information we will use later.

Bob
 

Attachments

Chris

Well-Known Member
No5: Four wheel drive!
 

DPpatrol

Well-Known Member
OK. Since nobody has actually proposed a new type of front suspension yet, I'll throw one out there. This design works to combine the long travel of an I beam suspension with double A arms ability to control the suspension camber curve. Each "upright" (see how my vocabulary is increasing) would be connect to two I beams creating a quaderalateral (excuse my spelling) and a radius arm to prevent rearward movement of the suspension. I attached a picture. The top diagram shows a truck with this type suspension while the bottom diagram shows just one wheel and its complimenting suspension. The dots and circles represent pivot points. The radius arms are not shown in the pics, but they are there, just in the background. So why won't this work? (since it probably won't)

jason
 

Attachments

tkr

Well-Known Member
where would you attach the radius arms? wouldn't they contact each other through the travel?

Matt Nelson
Team Kwik Racing
 

Bob_Sheaves

Well-Known Member
Good idea, but it's a little ahead of the game right now-Let's get the other parameters set first, then I will put up a packaging image so the suspension design can start....We have one vote for 4x4, any more comments on this or other information?

Bob
 

DPpatrol

Well-Known Member
The radius arms would be positioned behind the spindle just like normal radius arms. Actually I think their arc would be sweep more in just the verticle plane than with normal radius arms since the wheel will would have less camber change throughout the arc than with I beams, so they shouldn't contact. If you are talking about the beams contacting, you'd have to offest them just like normal I beams are offest.

jason
 

Dylan

Well-Known Member
Bob it must be nice to be retired, you can play on the Internet all day long.
What I was trying to provoke was a brain storm session on an alternative for A-arms. But if you want to design a whole new vehicle that’s even better, as long as it doesn’t have A-arms or beams ect.
The Mercedes rear 5 link design has been used in the rear of off road vehicle “in a very rudimentary form” quite a bit but what about the front ??
Checks out the eclipse reference that I mentioned.
Hell I don’t care, let’s get really outside the box. This is a seemingly stupid idea but what about each wheel on a huge linear slider or 6-foot tall struts or huge motorcycle forks at each corner. When all the cars were swing axle they said that IRS would never work and it didn’t succeed for a couple of years but eventually they got it dialed
Dylan
 
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