Triangulated 4 Link Joints?

[Anonymous]

I am trying to model a triangulated 4 link suspension setup and am having difficulties in setting up the joints.  I'm able to get the motion to work correctly until I add the upper bar (shown in the attached image in red)  I'm wondering if the joints think they are conflicting the bottom bar joints as they are not on the same axis?

If I model a regular parallel 4 bar suspension (both upper and lower bars run parallel with each other in side and top view) everything works correctly.

Is this possible and I'm just not setting up my joints correctly?  I don't necessarily have a model to share right now as I was using very basic shapes and components before spending the time creating the final parts.

  

[lichtzeichenanlage]

Would be nice if you could share your f3d file.

[Anonymous]

I will try to upload what I have this evening when I am finished with work.  I am new to this community as well as Fusion 360, so I'm not 100% certain how to share the file.  I'll see if I can figure it out when I am home with the file.  Thanks

[TrippyLighting]

This article explains how to share a file.

[davebYYPCU]

You have almost answered your own question, the bars work in parallel,

but I think you need pin slots or sliders, with ball joints, for triangulated moves.

I could be wrong....

[Anonymous]

@Anonymous

Hi, 

You will have to use either ball or cylindrical (the link translates and rotates about the same axis) joints.  Just look at the geometry and how the links move!  In a car (truck) you use bushings when mounting the links to the frame and axle.

The shorter upper bars change angle more rapidly than the longer lower bars, so there is an angle between their respective planes, which defines an instant center that gradually moves from infinity ahead of the car to somewhere in the middle of the car, as the rear drops.

I have not modeled a 4-Link suspension with Fusion360 as I rarely use this geometry for the type of cars we design.

However, if you can provide me (us) with your 3df file I am sure that one of us will be able to solve your problem.

I just don't have the time to model the suspension at this time, but I will be glad to help in any possible manner if you can provide the 3df file of your 4-link suspension.

Hope this will help and don't hesitate to ask for help.  I will be glad to help you.

Regards,

Isaac

[Anonymous]

Triangulated 4 Link Test Model

Okay thanks for the input and the offers to help find a solution.  Attached (Hopefully) is the rough mock up items I have currently.  I'm hoping to solve the joints / movements before I get too serious about creating the finished components.  Currently in this version I have revolve pivots on both lower bar ends, along with a revolve on the front upper bar end.  This leaves the upper rear bar end with no joint (as it constrains it and causes the issue)

Thanks for any further input or suggestions.  As I mentioned earlier, I'm fairly new to 360 and am just self taught as I go along.

[Anonymous]

@Anonymous

I just took a look at the file you uploaded.  I have not had the time to analyze it carefully but I noticed that you are using the wrong joint ends on your suspension rods.  I highly recommend using a high quality "Heim" joint. (unless you are using them but I can't tell in the drawing)

I have some questions?

What kind of vehicle are you building (off road .. rock climber .. etc)

Did you calculate the lengths of your links based on your wheel diameter or how did you calculate their length and angles?  It is important to know that due to the geometry.

Have you ever designed a T4L suspension before?

Did you perform a "PROJECTION" of Side View (of the links) to a Top view?

I assume you are a car builder and know what you are doing, right?

If I have time tonight I will work on it.  Otherwise, it might be tomorrow or Saturday.

I would like to know what kind of vehicle you are building.  

I love race cars!!!!!

I've added some drawings for your review.  You may know this stuff already!

 I know these drawings don't have anything to do with the joint question you asked but these may help you with the overall design.

Looking forward for your reply.

Isaac

[Anonymous]

This is just for a street car.  A custom 1949 Mercury on full air ride suspension to be exact.

I have built several vehicles with triangulated 4-link suspensions previous as well as a couple parallel 4 bar setups.  Personally for the type of vehicles I'm dealing with I typically prefer a triangulated 4-link so I don't have to incorporated a panhard bar.  Though each style of suspension design has pros and cons, running a panhard bar "pulls" the rear axle left to right through full suspension travel (air our to fully inflated)  This can cause issues with wheel / tire fit and spacing in relation to wheel opening and fender space.

As you mentioned, the rough calculations start similar to the diagrams you attached and tweak from there to fit the specific vehicle and space constraints in the chassis and under the body / floor, etc.  Currently as I mentioned my "model" is rather generic as far as components and placement is concerned, as I'm hoping to be able to solve the suspension joint travel before I go too in depth modeling my finished components.  I will use this model to help "dial in" the location, angles, and placement of the bars, pivots, brackets, shocks, air bags, etc. before I fabricate the suspension components & geometry on the actual vehicle build.  Typically I just do this on paper or in my head, but I really am enjoying 3d modeling as a new "hobby" and if it helps this process it's a win win!

As far as the rod ends you.  That is the rod end style that I will be using (and have used in the past)  They urethane bushed on each end.  In the past I have purchased some tri-4 link kits (both direct fit and universal fit) from well known vendors in the streetrod / custom market and all have used this same rod end.  With that said, I certainly have used heim joints previously as well (for example on a radius rod setup)

[Anonymous]

Nice, I would like to see your 1949 Mercury when it's done!

I downloaded your 3fd file and I will try to work on it tomorrow or Saturday.

Hopefully I will have it fixed for you by then.

Don't know if you are aware but there is software for suspension design.  Performance Trends has several packages under $150.00  

I would recommend you take a look at their software.  http://performancetrends.com/SuspAnzr.htm

They have all kinds of software for car enthusiasts and designers at an affordable price.

Good luck and keep in touch.

Isaac

[Anonymous · Accepted solution]

Hi, I finally had some time to look at your assembly.

I made some minor changes and added a Motion Study for you to look at how the upper and lower bars are moving with respect to each other.

You will notice that there is a lateral movement that needs to be taken care of with the upper bar/bracket.

You should be able to do that by adding a Cylindrical Joint and Edit the joint limits so that it can slide. As you can see by the motion, your placement of the upper bracket on the axle might need to be moved because of the bar displacement. You will also have to add a Pin as you have on the other mounts.  It needs the pin to displace as it moves.

To enter the Motion Study, open the Motion Study folder, Right Click on MotionStudy-1 and click on EDIT, then just run it.

***In the car you will not have to add the pin for the upper bar as the bushing and bolt should take care of the flex/displacement (once your geometry is correct)

Should you have any questions feel free ask. I attached the file so you can work on it. Just download it to your computer, click on it and it will open in Fusion360. Hope this will guide you in the right direction.

Regards,

IK

[Anonymous]

I've taken a few minutes to download and view the motion study you added for the motion of the upper and lower bars.  Indeed viewing it in the study shows the movements that you explained.  From here I will tweak the upper bar and brackets to see if I can minimize the "roll" side to side as the axle moves through it's travel.  I will also look into trying to set up the upper rear joint as a cylinder in order to see if I can manipulate it into working.  I also agree with you that in the "real world" there is a bit more fudge factor with the urethane bushings and bolts that can take up some of these issues, however the goal is to design and locate the components and brackets to minimize it as much as possible.  I appreciate your input and help thus far.  Thanks

[Anonymous]

It is critical that you limit the lateral displacement of the upper bars as they are the ones that keep the axle from shifting laterally under loads.

Have you thought of using a spherical joint for your upper links?  They might do the job and work better for the uppers.  Although the urethane bushing ends that you are using usually work great for the 4 Link suspensions.  I use spherical joints regularly on racing cars.

                                                                                        This one is just a picture of a generic spherical joint. 

Please keep me posted as you advance with your design.  I would like to see it.  And please, don't forget to send me a picture of the car!

Good luck!

IK

[Anonymous]

I agree.  The visual representation of the motion study helps wrap one's head around the movements involved.  When I get time to change the upper bar / bracket location (just do it on my spare time / hobby...not work related) my head is telling me to lower the top axle brackets (to limit the lateral movement as the rear axle rolls forward or backwards) possibly moving the upper brackets forward a bit as well.  I'll see as I go, just in the design and thinking phase right now.  I also agree with you that a spherical rod end could be a good candidate for this as it may allow a little movement where needed.  However, I'd prefer to stay with the cushioned rod ends since this is for a street car (help eliminate bumps, jars, vibrations, etc. from different road conditions)  I agree that a race or off road vehicle where passenger comfort isn't as important the change to spherical rod ends would be a no brainer.  Thanks again

[dieselguy65]

just a mention, from my experience building suspension for street cars and jeeps.

the pinion angle is going to change drastically with this design. possibly beyond the operating limits of the u-joint.

depending just how much up and down motion you will have.

[Anonymous]

That is a very valid point and one I am aware of.  Typically in a custom or street rod on full air ride you have 3 "ride settings"

1.  Ride Height (where you are doing 95% of your driving of the vehicle)  This is the height where you set all the optimum geometry for the vehicle.  Drivetrain angles (carb if equipped), front and rear suspension (also at this position is where you set for a wheel alignment as well) and pinion and u-joint angles as you've mentioned.

2.  Air Out:  Where you park or show the vehicle at.  Not driveable at this height for numerous reasons.  Frame may be on the ground, front wheel camber angle changes very drastically, wheel to  front fender clearance is typically gone as far as turning radius is concerned.

or

Minimum Air:  Deflating the bags to get a very low drive height, yet leaving some ground clearance for possibly idling around a car show, etc.

3.  Full Air:  You have the option to raise from ride height in the event of needing clearance to go over a speed bump, driveway angle or dip, loading onto a trailer, etc.

Those are the 3 settings you have pre programed into the ride height sensors and can certainly fine tune from each height if necessary.

Each vehicle and it's purpose determines how much full travel is wanted.  On this particular vehicle I'm aiming for a ride height (driving height) of 5" - 5.5" at the front of the rocker panel and 4"-4.5" at the rear rocker panel.  Thus giving me those same values for height drop.  Full air should be about 2"-3" higher than ride height.

I certainly appreciate all of the comments, input and concerns regarding suspension setup.  This is certainly not my first project build, however it is my first time that I wanted to give a shot at doing some of the design work in the 3D world.  Doing that ultimately stumped me when I couldn't visually get the Tri 4-link to animate the joints properly, this the reason I came here seeking advice.  Also as I mentioned, the current 3D model does not represent any real world geometry or components, but instead some basic components drawn and set in place in order to figure out the animation & joints needed to have the tri 4-link move through it's travel limits.

I was finally able to get the upper link joint working as per the suggestions above!  I added a "pin" as he mentioned and added a "ball" joint to the upper axle bracket.  Then I added a "slider" joint on the upper rear bar rod end to the pin.  This is a "work around" as I know in real life with the urethane rod end bushings, there is more flex & play in the joints than the computer "allows"

Thanks

[jafarsydi]

Would be nice if you could share your f3d file please ?!

fusion

[jafarsydi]

Would be nice if you could share your f3d file please ?!

fusion

[Anonymous]

http://a360.co/2gRRHJ7

Okay no problem, here is the latest file.  Beware, that it's very messy and unorganized currently in the browser side of it.  When I am in testing and figuring mode I throw all concept of organization out the window!ha  Later when I get the testing sorted out I'll go back and re-do everything nice and organized so it's much easier to make sense of.

Late last night I also set up a very basic joint and front frame stub in order to help the movement of the chassis.  Again that represents nothing in the real world, but instead its just for testing purposes now.

[Anonymous]

Dane,

It is nice to see how you are advancing. 

I just downloaded your file to take a look at it.

Please keep in touch.

AWESOME WORK!!!!!!

Regards,

IK

[Anonymous]

Triangulated 4-Link Test 3

I was able to put some more time into this design this evening.  As Isaac had mentioned previously, there is a lateral movement / misalignment between the upper bar rod end and the corresponding mounting bracket on the axle housing.  I estimate there was about 3/8" lateral deflection at the peak of suspension travel.  I didn't eliminate this movement 100% yet, and really with the urethane bushed rod ends I don't need to, but I do want to eliminate it as much as possible (plus it's the challenge of solving it that's half the enjoyment)

My findings this evening:  If I rotate the upper bar along it's length a couple degrees (currently at 2 deg.) along with the mounting brackets & pivot points on the frame and axle housing, the lateral movement is almost cut in half or better.

Attached is the latest version.  (Click on the axle housing and raise and lower the suspension through it's travel limits)