Lightweight Front Hubs
#21
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.
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.
#22
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 ******* are the hardest thing to make happy in the whole damn spindle when playing with the parts in fea.
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 ******* are the hardest thing to make happy in the whole damn spindle when playing with the parts in fea.
#23
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.
The braking force isn't that massive given you have 4 of them working at once. I think the main thing here is to make the mounts rigid enough to stop the caliper moving around under load. I've found some references to high end spindles and the braking mounts aren't overly large, in fact some are on slim stalks. I figure as long as my mounts are larger and beefier than what is currently on the car I'm all good.
#27
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.
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
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?
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
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?
#31
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.
#34
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.
#38
The MR2 hubs have a speed sensor. I don't run ABS anyway.
10 hours on the CNC and out comes this.
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.
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.
I still need to grab some 5/8" rod ends and a spherical before I can test fit it.
10 hours on the CNC and out comes this.
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.
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.
I still need to grab some 5/8" rod ends and a spherical before I can test fit it.