In reply to Apexcarver :
Very helpful,. thank you. So that's a 4 link with panhard? The "load paths" like you say to the pucks are convoluted, but that's just modifying leverage and distance ratios really, right? Just imagine a spring is what I'm telling myself.
I am interested in the puck or canister itself. If I understand correctly, you only get one puck per corner, which is obviously loaded in compression (bump). But what happens on rebound? Does the canister really just top out?
Yes, no resistance to rebound by the rubber. Actually the rear would top out axle housing to frame, not canister limited.
It really is just a pseudo primitive spring/shock. The interesting thing on mine is how far out the sides of the axle the connections are for roll resistance and how it allows tight packaging. Canister "spring rates" are far from linear though.
Think )1) where the 1 is the rubber for the insides of the canister
In reply to Robbie (Forum Supporter) :
I will take some more pics tonight but for the moment I had this one of the pull rod set up. The rear suspension uses 4 trailing arms; 2 each side, one above the axle carrier and one below. For lateral lateral location the Novakar used sliding pillar mounted on the center of the chassis.It obviously limits side to side movement but because the pillar is mounted on a pivot it allows the axle to rotate as the chassis rolls. I will take pictures of it. One other thing when the front of my car started to get hoppy it was down to worn friction dampers.
So here are the pictures of the rear suspension. First is the lateral locating device.
Next is the rear location links at their aft location
Do the canisters offer any damping via air intake/exhaust through orifices? I guess it'd probably just turn into another spring by the time the orifice produced much force...
Not effectively. Most dampning is via friction in rocker arms and just natural charastics of the rubber itself. One thing you have to remember, the cars normally weigh only 800lbs with driver. There was some stuff with loading the canisters with grease in the 80s, but was ruled against class rules if I recall correctly.
Robbie, I am trying to remember if you refreshed the rubbers. I'm not 100% on how challenge budgets work, but a sheet of the material is $90 from mcmaster and gives you enough to do several whole car sets. So if you buy the sheet and use say, 15% of it (or go percentages based on future sets that can be cut from it), I think you might get to rate that in the budget?
Fresh rubber pucks likely dampen better than old ones.
In reply to Robbie (Forum Supporter) :
The real problem is which corner of your favorite track will you set your car up for? Because for every other non identical corner it won't be maximized.
If you compromise a little you might increase cornering a little more in other corners and that is the slippery slope.
In that compromise, you select which ever corner you have the best chance of improving your position relative to your competition. I mean it's not going to suddenly improve your power. ( maybe more effectively put your power down). Or aerodynamics.
You might be able to improve the effectiveness of your brakes. Perhaps at the cost of some cornering speed.
Bottom line? You need adjustability in your suspension settings. You need to understand if you do this, this will be the result. You need a quick way to scale your car to see what you actually have.
In reply to frenchyd :
He's chasing a design problem, not a setup problem.
In reply to Tom1200 :
thanks! that center thing is an interesting take on a watts link...
Apexcarver said:Not effectively. Most dampning is via friction in rocker arms and just natural charastics of the rubber itself. One thing you have to remember, the cars normally weigh only 800lbs with driver. There was some stuff with loading the canisters with grease in the 80s, but was ruled against class rules if I recall correctly.
Robbie, I am trying to remember if you refreshed the rubbers. I'm not 100% on how challenge budgets work, but a sheet of the material is $90 from mcmaster and gives you enough to do several whole car sets. So if you buy the sheet and use say, 15% of it (or go percentages based on future sets that can be cut from it), I think you might get to rate that in the budget?
Fresh rubber pucks likely dampen better than old ones.
I did not refresh the rubbers, which was probably the single biggest impact thing I could have done but didnt before the challenge in October. I dont know why but I didn't really think about it or consider it. Maybe I did and then forgot. Oh well. Coulda woulda shoulda.
For challenge purposes the rubber is like any other homogenous material/supply. Like sheet metal or roll cage tubing, you're allowed to budget just what you use. So if I buy 100 ft of tube for $100 but only use 80 ft, it's $80 to the challenge budget. The refreshed rubber pucks would have been pretty cheap budget wise too.
My first plan was actually to refresh the pucks and reduce the body weight and see what happens (I think you may have even offered in my build thread that you have some extra puck rubber - I just haven't got to that yet). But I still think the rear 'design' I've got going on right now is creating lots of problems, mostly by encouraging things that shouldn't be springs to act as springs.
In reply to Jesse Ransom (FFS) :
There are friction discs that act as the dampers, they work surprisingly well.
In reply to Robbie (Forum Supporter) :
The sliding pillar allows the axle to move up and down, while at the same time it to swivel around the mounting axis. This way the rear tires are always planted vs the inside rear being pick up under cornering loads. It kind of behaves like a zero roll on a FV.
When I have the body off this weekend I'll get a better picture.
My car is the 3rd Novakar built, so obviously not state of the art, but it still works pretty damn well.
Apexcarver said:In reply to frenchyd :
He's chasing a design problem, not a setup problem.
It is the same thing. If your tires aren't in the right spot what can you do to improve it? Caster, camber, toe, change tires, spring rate, shock rate, tire pressure, type of air, etc.
Morgan has a flexible chassis corrected by a stiff suspension. Some cars have stiff chassis and accordingly can use softer, more compliant suspension.
There is no one engineering solution to all corners. There is the compromise that yields the best solution for a given driver.
frenchyd said:Apexcarver said:In reply to frenchyd :
He's chasing a design problem, not a setup problem.
It is the same thing. If your tires aren't in the right spot what can you do to improve it? Caster, camber, toe, change tires, spring rate, shock rate, tire pressure, type of air, etc.
Morgan has a flexible chassis corrected by a stiff suspension. Some cars have stiff chassis and accordingly can use softer, more compliant suspension.
There is no one engineering solution to all corners. There is the compromise that yields the best solution for a given driver.
ok, so the car currently is lightning fast as long as the track is smooth as glass. If the corner has even a little bit of bump, the car goes airborne, and then keeps bouncing. When you are driving (and this is not an exaggeration) there was a left hand nearly 180 degree corner taken at about 40ish mph. First half was glassy. about 3/4 of the way through the corner, there was a bump which crossed the whole track, no where to drive around. So you're swinging around the corner, holding a pretty good line, have the ending corner gate in your sights and you are on track to nail it, when you hit the bump. We actually DNF'd (multiple different drivers at this same exact spot) a few different times because the car would bounce and go airborne straight outside the gate.
I'd like to trade a little bit of my glassy smooth performance for a shred of control in the 100 ft after a bump.
What should I do?
Cut weight, cut "unsprung" rear weight (rear suspension design), and either fresh pucks or motorcycle coilovers if the budget can take it.
If pucks are the path, I'll cut you a set. Just send me pics of what you have taken apart so I can verify it takes the same as my canisters.
Also look into friction discs if sticking with pucks while you redo the rear.
frenchyd said:Apexcarver said:In reply to frenchyd :
He's chasing a design problem, not a setup problem.
It is the same thing. If your tires aren't in the right spot what can you do to improve it? Caster, camber, toe, change tires, spring rate, shock rate, tire pressure, type of air, etc.
Morgan has a flexible chassis corrected by a stiff suspension. Some cars have stiff chassis and accordingly can use softer, more compliant suspension.
There is no one engineering solution to all corners. There is the compromise that yields the best solution for a given driver.
Generally I'd agree with that statement, however there is a literal design problem with the car as it sits right now. The entire back half of the frame is basically unsprung mass because the pivot point of the suspension isn't designed correctly. If I remember correctly the engine itself is part of that mass.
In reply to Robbie (Forum Supporter) :
Sounds to me like the car has 0 damping. So is it just the back that bounces??
The original F440s were completely rigid, then they went to a rear suspension where the whole back of the car moved up and down, those were marginally better. if it is that why I would considering updating the the rear to a more modern design.
If the car is like mine I would start looking for worn friction discs. Your description just sounds like a car with no damping at all.
In reply to Tom1200 :
It's hard to tell exactly what is bouncing. The whole thing feels like it is bouncing. But I do not have friction disks so 0 damping is how I would describe it for sure.
As if on cue, GRM is here to help me out. This video is one they took of the in car action, and this was the very first run. They let competitors go out on some untimed runs to try and clean up some of the water on the track. So Ian who was driving was probably only going 6 or 7 tenths. Run starts at about 3:40 and you can see the bounce I described earlier at about 4:02. If you were going any faster the bounce only got a lot worse. You can see some bouncing in the rest of the run too.
https://www.youtube.com/watch?v=xOajzWt6MCc&feature=emb_logo
In reply to Robbie (Forum Supporter) :
In my humble opinion you've added too much weight to a too light a chassis. Weigh the Datsun body compared to the original body. Then you lengthen the chassis. I see body flex and chassis flex.
In reply to Robbie (Forum Supporter) :
It's clear from the video at the 6 minute mark that you car is oscillating wildly. There is obviously no damping front or rear
On my car there are friction discs on on the upper A arms. By varying the torque setting on the bolt it varies the damping. Take a look at the first photo I posted you can see the discs behind the a!uminum plates, just below the brake line fitting.
If the discs are shot you are racing a car with blown shocks. You don't need to revamp the suspension you just need to get some kind of damping in the suspension.
frenchyd said:In reply to Robbie (Forum Supporter) :
In my humble opinion you've added too much weight to a too light a chassis. Weigh the Datsun body compared to the original body. Then you lengthen the chassis. I see body flex and chassis flex.
Believe it or not, he is in at 900 pounds... right in line with the SCCA rules for F500 with a bike motor. He does need to stiffen the body to frame connection. Going to a motorcycle coilovers will be a great place to start.
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