Hi,
I've been teaching myself inventor over the past couple of months so I can design the rear suspension setup for my car.
I've got the IRS modelled with enough detail to show my engineer the concept, but I want the suspension to "work", ie each link will move as the suspension flexes.
I'm attaching the arms (blue, dark green, red and yellow) to the cradle (orange) using the joint command, and selecting "rotational". This works fine and the arms can swivel about a single axis as they should. But as soon as I attach the knuckle (lime green) to the other end of all the arms using the same type of joint (except the joint with the blue lower control arm, which is a ball joint), nothing will move.
I understand that in real life, each joint has a bit of "slop" in it, allowed by rubber bushings, which prevents the whole setup from binding.
To my uneducated mind, the solution would lie in one of 3 methods:
Convert all the joints to ball joints (I'd like to avoid this if possible)
Add some kind of flexible rubber bushing to all of the joints (probably not possible)
Get rid of the rotational joint constraints altogether and somehow mate all the parts to each other using work points, rather than a cylindrical bolt and eyelet, so that each arm has full range of movement in both the X and Y axes.
I hope this was more-or-less understandable. Any pointers would be much appreciated.
Thanks for your time,
Archie
Solved! Go to Solution.
Solved by CAG_DRAFT. Go to Solution.
Have you studied/researched bar-linkage design?
Are you aware of all possible 'Lock positions' in your design?
Are any of those lock positions within the normal operating range of motion?
Is it an acceptable design practice to have a lock position within the normal range of motion? (and rely on slop to break the locks...)
Edit:
upon actually looking at your picture I'm thinking that you will need to change joint types and set limits for the off-axis deflection somehow.
Generally the difference from "Street" to "Race" is bushing. "Street" suspensions use bushing to add compliance and absorb/dampen the road vibration. "Race" is a straight solid bearing arangement. You may want to suppress some joints/constraints and verify your basic geometry. If it's in a lock-up state it would sound like you have some geometry thats amiss.
Thanks for your replies and your patience CAG_DRAFT, I had a read in wikipedia and it did help.
Just thinking aloud here, but as my suspension is from a road-going car, the amount that this setup is designed to articulate is relatively small (compared to say an off-road vehicle), so to my uneducated mind, the amount of deflection would be extremely small, and only a tiny, but essential degree of freedom would be required of each joint. Surely this degree of freedom could be provided by a rubber bushing?
However, if what you say is right (it probably is) and the suspension is designed so each link pivots without any deflection, my methods of measuring the physical object (using rulers, protractors and calipers) are not accurate enough to reproduce an exact model that doesn't bind.
To get back to solving my problem, I will probably just have to accept that my available methods of reproducing the suspension geometry are only ever going to be "close enough" and use ball-joints to allow a degree of freedom so it wont lock up.
Any information you could give me on these mated work points with limit conditions would be useful. Would that mean I wouldn't have to physically model all those ball joints? I know how to create work points but I don't know how to mate them or add limit conditions.
Even if you could just point me to some tutorials, Id be grateful.
Thanks again.
HI I just started with inventor. I accidentally removed the origin history box tool bar usually on the left hand side of the work space. I cant find where to click so it goes back on the screen. I needed it to see the highlights. email me @ ecomunky@yahoo.com. not much spam please, but idc.
thank you.
...here.
The CADWhisperer YouTube Channel
Actually I think there is some suspensions that require bushing play to move around, my sideckicks suspension comes to mind, if you recreate it in a simple 2d sketch it locks up, I suspect all macpersons have that too.
Of course thats a ****ty car and also not a four-link suspension but still.
RM
SIDEKICK FRONT SUSPENSION: http://image.fourwheeler.com/f/33806431+w600+re0/131_1110_03%2Bsuzuki_roundup_sleeper_suzy%2Bfront_s...
See that the shock is completely fixed to both the chassis and the knuckle, and the a-arm at the bottom shouln´t be able to rotate (because rotating up would cause some sideway´s movement that the shock on top doesn´t allow.
The suspension that the OP posted has too many linkages, Is that the actual suspension or the modified one?