Designing the Satchell Link

[MonzaRacer]

Ok I understand the design, But as for a person who actually drove a simialr set up dont forget that while you design the"most perfect" set up dont forget(talking as an alignment tech) dont forget that while the link designs are very close you still have to dial in alignment specs to get the most benefit from it.
I asked a friend who had a simiar set up on a Sunbeam Tiger (after rebuild it was readended) and he spent 3 weeks on a 4 wheel alignment machine then back to track/road for driving tests. He had some great twisties around his house and was doing late night bonzai runs to test it.
while he thought he had a bad set up he found it really came out better than he thought after he figured out that it required different specs side to side to deal with his 347 in Windsor engine over the 289 that came "factory".
Good luck and after I get his extension program(puts me under blanket license) for advance suspension design (very similar to what Ford/GM/Chryco used to use for designing) if we tried to buy it it would take 3 servers and about 80k to purchase but his company bought the older set up from GM design group and let him add users for help on thier designs (they are actually using it to design some suspension systems for boat engine mounting but system was used to hundreds of inputs so the 20 or so they have is not exactly taxing it too hard)i hope my computer will work ok as its not very fast(new dual core/dual processor AMD Raid 5 setup coming in spring woohoo) oh well goodluck and If it models out for me Ill repost for you,
Lee

[boodlefoof]

As for setting it up for a particular car, I guess it depends on what you want the car to do. I have made all of my mounting points fully adjustable about 2-3'' vertically. I plan on starting my baseline with the upper arms parallel to the ground and the lower arms set up for 100% anti-squat. If I remember right that gives me an RCH around 10''. I can lower the RCH down a bit at the expense of anti-squat. That might work out well since this will be a light car with short wheelbase (92'') and a pretty even weight distribution. Then I will tune with an adjustable sway bar.

[911industries]

Im getting ready to set up a satchell link on my 61 falcon this weekend. Ive read everything I can get my hands on to try and fully understand this suspension design. I was wondering if any of you could help me with the important things to watch for.

What Ive got so far is long links(around 20"), 45 degree angle on lower links. Shoot for 100% anti squat.

My questions are what is and ideal and an acceptable RCH? What about roll understeer? Where do I want that?

[boodlefoof]

911industries, welcome to the board!

Before you start welding, you may want to download the free 10 day trial of Suspension Analyzer from Performance Trends and map out your design.

Depending on the relative length of your links, roll understeer may be a bit high. Also, the measurement of understeer is dynamic (changing with roll). At ride height, I designed mine to have zero understeer, but it gains a little (I forget how many degrees now) understeer per degree of roll.

Acceptable RCH is also debatable. Lower RCH usually involves lower AS. Since there are so many factors at play, I set up my mounting points such that I have a lot of adjustability to move RCH from about 8'' on the low end to 11.5'' on the high end. AS goes down as RCH gets lower.

If you haven't seen it already, go over to corner-carvers.com. There is a long thread regarding the Satchell link. Search the suspension forum and you will find it.

Good luck!

[911industries]

Thanks for the help. Where can I get or download the suspension analyzer?

[boodlefoof]

http://www.performancetrends.com/download.htm#sa

[jerome]

how does one make suspension mounts fully adjustable with a range of heights. i know the jaguar on corner carvers has it too. is it just a elongated hole that you put a bolt through? it doesnt seem you could generate enough clamping force to suspend a car like that.

Jerome

[boodlefoof]

Jerome,

Yes, you can elongate the bolt holes to gain the adjustability. Nearly all of the forces acting upon the rod-ends is going to be forward/backward forces. Since the holes are elongated in the upward/downward direction, it shouldn't be much of an issue.

If it does turn out to be a problem, one could use washers with an offset hole (much like in the C5/C6 suspension). It is difficult to describe how this works, but if you get a chance to take a look at the Corvette suspension it will make sense.

[911industries]

Ive figured out where everything is sitting on my car and I plugged in where I want my links. I cant figure out what to look at to find my roll understeer. Also when I roll the car in the view mode it says I have convergence but doesnt say anything about fixing it.

my specs right now are x,y,z

ulf 30,15,22
ula 30,15.5,0
llf 2.5,11,16
lla 18.5,10,0

with 26" tires

If you can help me with figuring this out it would be great.

[boodlefoof]

To find the understeer, take the tangent of the upper arm angle (vertically from front to rear).

What kind of output figures is your design giving you? You really want to pay attention not only to the static figures, but the change in figures in bump and roll. I found using the graph feature very useful to compare setups.

[911industries]

I cant believe its been two years since I posted. I got my car on the road a few months ago. I had no sway bars at first and the fender skirts on my falcon made the tires rub bad. I did a quick fix with a bronco sway bar I had laying around which works but isnt right.

After thinking that my design was flawed for awhile I've realized that the satchell link has great possibilities and I cant wait to start fine tuning.

Im just wanting to thank you guys for your help and to let you know that its because of you that I went through with this suspension.

[terryr]

Neat. I'd like to do a Satchell Link one day. Will mufflers and tailpipes fit in there?

[911industries]

Yeah, exhaust was easy because I put the mufflers behind the axle. Those are old pics. I'll post some new ones soon. I found out the hard way that the crossmember needs to be braced. I broke it in two and tore up my floor. My problem I havent figured out yet is body roll. For some reason I thought a low roll center meant less body roll, I think its the opposite. This thing feels like a lifted truck when I yank on the wheel.

[Norm Peterson]

Yeah, exhaust was easy because I put the mufflers behind the axle. Those are old pics. I'll post some new ones soon. I found out the hard way that the crossmember needs to be braced. I broke it in two and tore up my floor.

After you design the geometry to suit your purposes (and probably tweak it a bit so it'll fit), you still have to make everything strong enough to resist the loads (which can get pretty big).

My problem I havent figured out yet is body roll. For some reason I thought a low roll center meant less body roll, I think its the opposite. This thing feels like a lifted truck when I yank on the wheel.

All else equal, low roll centers do mean you'll get more roll than you would with high roll centers.

Having a low roll center means that the car's mass (simplistically, up there at the CG) has greater leverage against the suspension than it would if the roll center was higher. So you either live with more roll - or choose stiffer springs and sta-bars to limit roll elastically.


Norm

[911industries]

I thought I had some pics of the new braces but apparently I was in a hurry. Ill get some this weekend, I hope I will be able to work on my car. In the books I was reading they never metioned the differences is low and high roll centers. They kept on talking about how you determine where it is and I guess I naturally thought that lower was better. Ooops.

In some way a low roll center would be better because you can use your sway bar to tune it better. If you have a high roll center and very little body roll then minor changes will make a big difference. If your body rolls like a boat then you dont have to be so accurate. Thats just my justification so I dont have to say that I really screwed up.

These pics are just before Kool april nites. Me and my coworker drove down there and back. Around 800 miles round trip. If you look on the left weld on the top of the tunnel you can see the gap from the break.
The second shot is my buddy Jeremiah helping with the interior. Last is me just getting a good hump on with one fine car.

[Norm Peterson]

In some way a low roll center would be better because you can use your sway bar to tune it better. If you have a high roll center and very little body roll then minor changes will make a big difference.

That's pretty much the way it works. Springs and bars (and shocks) can only tune the handling based on the amount of roll that occurs. With a high RC and not much roll, it takes much greater changes in the spring and bar stiffnesses to achieve a given handling change. When the suspension gets really stiff, you start losing a lot more of your tuning efforts to chassis flex unless you go back and stiffen that, too (not as easy as you might think, BTW). Never mind what happens to the ride.


Norm

[iou1choke]

911,
It appears that you are using a heim type joint on one end and solid bushing on the other (?). May I ask what type of bushings you decided to use?
I also notice you have the heims on the forward bar mounts. I was under the impression that they should normally be used on the axle end of the bars. Was wondering if you had a particular reason for this orientation?
Also curious if you determined which directional forces seemed to have the most effect on the damages to your x-member? How did your rod ends hold up?
What do you think of your roll steer characteristics? Does it respond how you thought it would from a design standpoint?

Nice to see a satchell link. I, coincidentally, am in the middle stages of fabbing and installing this link set up in my vehicle.

[Rhino]

Small world. I'm in the planning stages of a Satchell myself. It's nice to see others trying it as well. Up until last week I hadn't found many online real-world tests. I'd be interested in seeing the issues with the crossmember as well.

[Norm Peterson]

I found out the hard way that the crossmember needs to be braced. I broke it in two and tore up my floor.

I think the crossmember needs at minimum some fore/aft bracing at each of those LCA chassis side pickups, and the other ends need to be tied off to something more substantial than just being bolted to the middle of some sheetmetal. Not having this bracing means that the longitudinal components of the LCA forces are being resisted by the crossmember in torsion.

The inside "corners" of the existing crossmember at the top of the tunnel should probably be filled in with a plate formed to a radius, as sharp corners = fatigue "hot spots".

I'd also consider adding some lateral bracing from the LCA brackets if you can fit it underneath. Or some sort of transverse structure above the floor and solidly welded to it from the tunnel to the sills if you can't (given the roll bar, I don't see the back seat area ever being occupied). Any bending loads that you can get off the crossmember where it goes up and over the tunnel can only help things.


Norm

[911industries]

Sorry for the delay guys. My car kinda took dump and life stepped in to say my time needs to be spent on other projects. The car problem is burning coolant which took out the O2 sensor which the computer didnt like. Basically I need to tear out the engine to see if its the heads or head gaskets.

Anyways back to the subject.

-Heims and bushings. I cant remember where I got the bushings but if you like certain size tube and call up energy suspension with some numbers Im pretty sure they can find a bushing that will work. I put the heims on the body side so they will see less road debris and last longer. I dont think that putting them on the axle would make them work any better. The axle and links roll the same no matter where they are restricted from. The roll restriction is the bushings.

-crossmember destruction. I've talked to some guru's about that and basically it was do to the POWER. Ha, ha, ha. After looking at all the aspects of the failure the desire for the axle to roll under hard launches makes the most sense. When you launch the lower arms which are those want to push forward and thats exactly what they did.

I had room to put a 45 degree tube above my exhaust from the LCA to a roll cage crossmember. That seems to have done the trick but I havent had much rough testing lately.

-Roll steer. Because I dont have a rear swaybar and a bad front swaybar its hard to tell. The thing I can say is that this car is scary at 140! Why you ask? It has more to go and it feels like Im going 60. Another fun fact. Bad hood hinges and high speeds will actually make your hood lift up and really make pucker.

Even though I roll like a boat the car still takes the line I choose. I was playing with an Audi R8(I think) and he never pulled me even in 30 mile curves with 80 on my speedo.

-Crossmember construction. I also added some diamond shaped plates over my weld points. Those ar supposed to help distribute the load away from the weak point just outside of the main weld. Thats the thing with a weld is; it is strong and so is the tube but the weak point is th hot spot created in between the two.