Gyro
10-31-2011, 10:12 PM
Hey all,
I've been hard at work on packaging the steering subsystem for the past few weeks, and I've been running into some apparent problems with the steering column. I'm using a floor-mounted rear-steer setup, so the rack is relatively close to the front roll hoop (along the car's length).
Being that I don't have a lot of room, I've been researching various joints to make the steering column fit in the damn frame. What I keep coming up with is that the usual U-joint is only rated for about 35 degrees max (for the well-known Apex joints, anyway), and more importantly, that the max torque rating at that steep of an angle is almost useless.
I'm basing my standards here on having read Steve Fox's article for FS Germany, linked here (http://www.formulastudent.de/public-relations/fsg-news/news-details/article/steves-box-of-tricks/). Basically, he stipulates that the entire steering system be able to handle a 75-100 ft-lb torque input from the driver with no failure.
So I keep being told that the joints I'm considering are not going to be strong enough to get the job done (and I have included double U-joints in this group, to increase the max. operating angle), yet I also see designs that appear to use these same U-joints (or even joints that I would consider less suitable than those I have been looking at) at equal or greater angles than in my design, and apparently they work fine.
So my question is, where's the catch? Are the nominal ratings on these joints extremely conservative or based on high-speed applications, or do teams just use them beyond their rated capabilities, and trust that they'll be okay?
Or is there something else altogether that I'm missing?
As always, any input is greatly appreciated. All you guys out there are a big help to a first-time designer like me.
Cheers!
I've been hard at work on packaging the steering subsystem for the past few weeks, and I've been running into some apparent problems with the steering column. I'm using a floor-mounted rear-steer setup, so the rack is relatively close to the front roll hoop (along the car's length).
Being that I don't have a lot of room, I've been researching various joints to make the steering column fit in the damn frame. What I keep coming up with is that the usual U-joint is only rated for about 35 degrees max (for the well-known Apex joints, anyway), and more importantly, that the max torque rating at that steep of an angle is almost useless.
I'm basing my standards here on having read Steve Fox's article for FS Germany, linked here (http://www.formulastudent.de/public-relations/fsg-news/news-details/article/steves-box-of-tricks/). Basically, he stipulates that the entire steering system be able to handle a 75-100 ft-lb torque input from the driver with no failure.
So I keep being told that the joints I'm considering are not going to be strong enough to get the job done (and I have included double U-joints in this group, to increase the max. operating angle), yet I also see designs that appear to use these same U-joints (or even joints that I would consider less suitable than those I have been looking at) at equal or greater angles than in my design, and apparently they work fine.
So my question is, where's the catch? Are the nominal ratings on these joints extremely conservative or based on high-speed applications, or do teams just use them beyond their rated capabilities, and trust that they'll be okay?
Or is there something else altogether that I'm missing?
As always, any input is greatly appreciated. All you guys out there are a big help to a first-time designer like me.
Cheers!