Image is very blurry:
Top (red) value = 1.451 E8
Bottom value (dark blue) = 1.449 E4
Image is very blurry:
Top (red) value = 1.451 E8
Bottom value (dark blue) = 1.449 E4
Joshua Byington
Boston University Racing
Josh,
Your calliper mounts look a little light on to me, and your toe base still appears to be very small, but apart from that it looks like a decent 'standard' billet upright.
Jay
UoW FSAE '07-'09
Thanks for the feedback Tromoly. Seems like the simplest solution.
Jay, I wish I could do FEA or just hand calcs for the caliper tabs in bending, due to the force from the caliper trying to center itself around the rotor. I have no for values for this, and feel I would be guessing if I came up with a value. The floating system should handle this, but we both know it will not absorb 100% of the axial motion of the rotor. One of the issues I have with thickening the caliper tabs (7.5mm current) is trying to fit a nut between the back side of that face and the rotor, + 2 threads showing..
Josh
Joshua Byington
Boston University Racing
We've had this solution for many years, it works well. Now I missed the "lid" in my quick picture-grab yesterday, but it solves both your points, stopping rotation and axial motion. It also conveniently held the CV-boot and the inner race of the bearing.
The current car has a slightly less elegant solution for the boot, but seems to work fine anyway.
Pontus Fyhr - Lund University Formula Engineering alumn/assistant FA
Fyhr,
How does your hub mount to your wheels? Is the left image missing a component (other than rotor)?
Are you running 61816 bearings?
Josh
Joshua Byington
Boston University Racing
The left one used inboard rotors, the wheels mount straight to the hub, see attached image. I don't recall the exact bearing number, but they are SKF deep groove ball bearings, you should of course do the free body diagrams and life-time calcs for your application and select the bearings from that. I snapped a picture of the hat I mentioned too.
Last edited by Fyhr; 11-05-2015 at 07:50 AM.
Pontus Fyhr - Lund University Formula Engineering alumn/assistant FA
Craig Kellermann
-Construction Science and Management (This is my Major)
-University Of Texas-San Antonio
-2011-present
" Charge It To The Game "
Josh,
Thank you. At last, something resembling engineering.
~o0o~
Now the bad news. Although you are approaching this the right way (ie. trying to analyse stresses, etc...), most of your analysis is wrong. Not unusual, because most other students make the same mistakes, or bigger (ie. education system down the tubes...).
[Mini-Rant] I never had the luxury of using "FEA". Back in my day we did all stress and deflection calcs by hand. Maybe because we had to do it all long-hand we made sure we made the right assumptions to begin with. No point spending ages on useless calculations. Anyway, it boggles my mind how BADLY done is most student FEA these days. So easy to get useful results, but instead just rubbish. What a waste... [Rant Over ]
In short, your FEA is quite useless. Do NOT believe any of it. But it also easy for you to get better results.
THE BIG MISTAKE -> You have made an initial assumption, possibly encouraged by your teachers or the FEA manual (?), that the upright should be FIXED at its bearing-mounting-surfaces. Why? And how will you estimate the DISTORTION of this reliability-critical bore surface, if right from the start you prevent it from moving!?
Any structural analysis is simply a case of putting "the structural body" inside a static Free-Body-Diagram. That is, it is a problem in the field of "Statics". There is no need for any "constraints" (which are useful in Kinematics), just "forces in equilibrium" acting on the body and squashing it from different directions. You cannot make any progress here until you clearly understand this point. You must know where the various external forces are coming from, and what are their magnitudes and directions. (This Analysis of Wishbones thread may help you, but it is quite long and not immediately necessary for your current problem.)
Nevertheless, it seems that FEA programs want you to give them constraints. So, what to do?
THE FIX -> Firstly, sack your teachers and ask for your money back!
Next, realize that an upright has 6 Degrees-of-Freedom of movement in 3-D space, so it ONLY needs 6 x linear constraints. Adding any more than the minimum number of constraints allows the constraints themselves to carry many of the loads, rather than the structure carrying the loads. Take this far enough and you won't even need an upright at all, because the artificial constraints (ie. inside the computer, not in the real world) do all the work! This is all too common in the design of FSAE spaceframes, and explains many of those abominations.
One way of doing the constraints is to realize that the upright sits between the forces acting from-road -> to-car-body, and the equilibrating forces acting from-body -> to-road. The second lot of these forces, namely those coming "from-body", reach the upright via the suspension links. Conveniently, you should be able to identify here six linear force Lines-of-Action acting "from-body" to the upright. These are [...drum-roll...] the six suspension tubes! Check: 2 x 2 tubes per wishbone + 1 x toe-link + 1 x spring-damper, or pull/push-rod (aaack!) = 6. Make these the six linear constraints.
Now try some realistic load patterns. Please try this one. To ease the description, I refer to your FEA screenshot at bottom page 4 and assume it is looking at the inside of right-rear upright, with front-of-car to left of image. Do a pure braking force analysis first (because easier to describe here), then only later try adding cornering forces.
The assembly of wheel+axle+upright+brake-disc+caliper has a single force acting on it through the wheelprint, with this wheelprint-force having a vertical upward component, say, Fz = 600 N, and a rearward longitudinal component Fx = 1000 N (just use round numbers for now). Further up the chain of equal-and-opposite force-pairs this wheelprint-force is transmitted to the upright ITSELF as three much larger forces.
1. An up-left force on upper-caliper-mount (pointing to ~10:30 o'clock in your image).
2. An up-right force on lower-caliper-mount (pointing to ~1:30 o'clock).
(Note: Forces 1 + 2 = Vertical upwards force on LoA through centre of caliper pads. It may be more realistic to include the caliper in your analysis, because it actually does constrain/reduce distortion of the upright.)
3. Distributed down-right forces on both bearing-mounting surfaces (distributed from ~3 to ~7 o'clock, but mostly around ~5 o'clock).
The 6 x suspension tubes provide the equilibrating forces. Hope this makes sense, else do the FBDs.
Lastly, and most usefully, get your magical FEA to draw a pretty picture of the DISTORTED upright when subject to these forces. You are mostly interested in the distortion of the bearing bores because that is what kills the bearings.
I would really like to see such a picture, especially of your original, thinner-walled, upright.
~o0o~
Also...
Webs inside your speed-holes will greatly stiffen the upright against above distortion. See Pontus' pics for such webs, and I think Goost also suggested this. Basically, leave a "floor" in the speed-hole.
Wider toe-base! The standard prior-art solution of bolting a channel section to the end of the upright that carries 2 x BJs is a reasonable way of reducing toe-slop that comes from BJ-slop. For a given amount of BJ-slop (= outer PLUS inner-BJs!), doubling toe-base = half toe-change.
I repeat Scotty's advice, page 1, "The insert you have in the model needs to be flipped around, and the pin used to keep it from rotating in the housing."
Z
Last edited by Z; 11-25-2015 at 06:31 PM. Reason: Spelling!
To properly apply forces to my bearing structure in FEA, which I agree is where it should be applied, should I really be distributing the face along the whole circumference and depth of the hole, or only along half the circumference, specifically the half in the direction of the force? The other half seems to just be..."there." Not sure if applying force tot he whole bearing bore would be a valid assumption. Thoughts?
Josh
Joshua Byington
Boston University Racing