Is this correct?
Forces on acting on the spindle: Top ball joint - direction of force is inline with the arm, angling either forwards or backwards under brakes (x / y direction). There is no shear (z direction) other than MoI of the arm mass and suspension bushings and there is no rotational loading due to the ball joint. Lower ball joint - Forces here act in all directions (x / y / z). The entire weight of the corner of the car goes through this point, plus the majority of the cornering load. Steering arm - Forces are only towards and away the steering rack (y). There is no rotational loading other than the offset due to the pivot point of the rod end being offset from the arm. Hub bolts - Forces here are in tension and compression only. All shear loading should be taken by the press fit of the hub into the spindle. Caliper mounts - All forces here act axially around the centerline of the hub. The top caliper mount will be in compression under braking, whilst the bottom mount will be in tension. There needs to be enough sideways rigidity to stop any vibrations of the caliper. |
not quite. For loading I like the standard 2g braking, 3g cornering, 4-8g bump. That way it should have enough margin of safety to even work on a crazy non-dot aero machine, at least for a while.
Upper ball joint will see some of the cornering load I'd give it 800 lb pull and 300lb push, and it will see the braking load but its very strong in that direction compared to what its going to experience so I'd probably not even FEA it. lower ball joint will see a lot of the cornering load, give it 1.5k lb push and 800k lb pull, again for the braking. I'd give it 4k lb in the bump direction. steering arm will see the steering thrust forces, which if you've ever driven on 275 hoosiers with a manual rack you'll know they can be enough to make your wrist sore for a week. I cant even come up with a number here, just its more than you're expect. hub connection. Bolts should only ever be loaded in tension, just make sure your torque spec on them is high enough to ensure that. The mr2 hub itself shouldnt be press fit, it should be a slip fit into that hole for alignment only and should take the majority of its force in friction between the spindle and the hub, again make sure your torque spec produces a sufficient amount of clamping force to generate enough friction. you forgot the hardest stress to account for, and thats the brake mounts. Those fuckers are the hardest thing to make happy in the whole damn spindle when playing with the parts in fea. |
Originally Posted by Leafy
(Post 1359349)
steering arm will see the steering thrust forces, which if you've ever driven on 275 hoosiers with a manual rack you'll know they can be enough to make your wrist sore for a week. I cant even come up with a number here, just its more than you're expect.
Originally Posted by Leafy
(Post 1359349)
hub connection. Bolts should only ever be loaded in tension, just make sure your torque spec on them is high enough to ensure that. The mr2 hub itself shouldnt be press fit, it should be a slip fit into that hole for alignment only and should take the majority of its force in friction between the spindle and the hub, again make sure your torque spec produces a sufficient amount of clamping force to generate enough friction.
Originally Posted by Leafy
(Post 1359349)
you forgot the hardest stress to account for, and thats the brake mounts. Those fuckers are the hardest thing to make happy in the whole damn spindle when playing with the parts in fea.
|
Power steering...
|
Originally Posted by aidandj
(Post 1359355)
Power steering...
|
Don't forget the force when bouncing against a barrier.
Think of the light ones that "just" bend a steering arm or a control arm. Having the hub survive these incidents is a big plus. :o |
I'm slowly working on my design. Not sure if it's still the right direction or not but I may as well try it and see how it goes. I figure I'm just going to start machining stuff and see how it turns out. I always find it easier to judge weak points in a design when I have it my hand. I'll probably start with the billet UCA given it's easy to make first and I can run it on my existing hub.
https://cimg6.ibsrv.net/gimg/www.mia...dee3c91d09.jpg Here are a few key design features. 1. +3 degrees camber built into the spindle 2. MR2 hubs 3. Lightweight - approx 700 grams 4. Ducted 2.5" vent through hub to cool bearings and rotors (see below) 5. Spherical bearing for UCA connection 6. Billet UCA with 5/8 rod ends. Weight of the arm approx 550 grams 7. Rod end for steering arm 8. Solid mounts for radial caliper https://cimg9.ibsrv.net/gimg/www.mia...c7b4f338c0.jpg All up it looks a bit too light to me. I think I'm going to add a bit more meat by increasing the radius of the hub as well as the wall thickness of the inner and outer rings. I think the steering arm connection looks too large, so I might drop the height of that a bit. Questions: Should I include a small spindle drop or keep the factory hub location? Running the vent through the hub I think is a good idea. It should route air right past the bearing which will be nice to keep the temps down in the bearing itself. I might need to add a small shroud out to the rotor surface. Any issues with this? |
Keep up the good work!
Sub'd |
Love the work, thanks for sharing the journey!
|
What kind of wheel/rotor offset are we looking at here for these? Or, how much farther does the hub face protrude compared to stock?
|
Originally Posted by psyber_0ptix
(Post 1389121)
What kind of wheel/rotor offset are we looking at here for these? Or, how much farther does the hub face protrude compared to stock?
Placement is exactly the same as a stock hub. The MR2 hub is shorter by a small distance. From memory I think the outer surface of the spindle is around 5 - 10mm further out to make up for the shorter hub. I think if I wanted to run wider track I'd lengthen both the control arms rather than push the hub out further but that would mean making a billet LCA as well which is a whole stack harder. Machining the spindle will be fun. It will need to be made from a 75mm thick billet. I'm going to need to machine up a tool holder for my CNC machine to mount up a 10mm bit. I'll need the length. |
I'll get a new control arm scan done this weekend and send it over along with the upright scan I have. Sorry, that totally fell off my radar this past few weeks, been very busy with work.
|
.
|
Originally Posted by Art
(Post 1389694)
I think I mentioned this already and I don't mean to sound blunt but compare the size of the MR2 wheel bearing to the stock Miata if you have a chance. The Miata wheel bearing is too small for race cars evidenced as a known failure point. Moving the tie rod mount to help bump steer might also be cool in addition to adding negative camber which you mentioned.
The tie rod can be moved down by changing the spacer amount. If I make it so that the rod end center matches the stock position and then it can be packed downwards if required. |
Two offset thin section angular contact ceramic hybrid ball bearings, hollow titanium spindle, etc?
Joking, I know what that would cost. Nice looking piece so far, wish I could run it for my class. |
.
|
Abs mounting?
|
Originally Posted by aidandj
(Post 1389843)
Abs mounting?
10 hours on the CNC and out comes this. https://cimg2.ibsrv.net/gimg/www.mia...4da994e6a1.jpg Machined from 19.05 mm 6061 ally. Spherical goes in here with a bolted plate to stop it popping out. There is a small shoulder at the base of the hole. https://cimg3.ibsrv.net/gimg/www.mia...19fb5683f2.jpg It feels nice and light but still very rigid. I'm not sure if it needs more meat around the outside of the spherical. The holes might be a weak point. https://cimg7.ibsrv.net/gimg/www.mia...a8b832c030.jpg I still need to grab some 5/8" rod ends and a spherical before I can test fit it. |
Beautiful!
|
I forgot if this got asked - is that your personal CNC equipment or are you borrowing time on someone else's? Just because I'd *like* to step up to having the ability to do stuff but relatively few people do.
|
All times are GMT -4. The time now is 05:06 AM. |
© 2024 MH Sub I, LLC dba Internet Brands