Mounting Bars |
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Sarah
Welding Master Joined: Dec/03/2010 Location: columbia, sc Status: Offline Points: 109 |
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Posted: Jan/24/2011 at 2:31pm |
Debate in our team
Some think mounting shocks and a-arms to the 1in .035 wall would be fine. Others think it is too thin to mount stuff on.
input?
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University of South Carolina - Gamecock Baja 2011
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collinskl1
Baja Godfather Joined: Jan/21/2009 Location: Saginaw, MI Status: Offline Points: 1056 |
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It depends on the structure of the tubes... If the mount is at a node, sure it will be fine. If the span is super long, probably not. You could run a quick simulation to test it.
Also it depends on the car's weight, etc. for the loading. For reference, my team mounted our shocks on a 10ish inch span of 1.25 OD x .049 wall (car weight of ~480 measured at the RIT water weight) and never had any issues with deformation.
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Kyle Collins
Lipscomb University Alumni 2x Project Manager Nexteer Automotive Product Engineer, Electronic Power Steering ... and the 8th simple machine: a bigger hammer. |
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asims
Welding Master Joined: Apr/07/2009 Location: Tucson Status: Offline Points: 184 |
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Basically just to reinforce Kyle's point, we had a car a couple years ago that had the lower arms mounted to 1.25" x 0.065", but in the middle of an overly large span. The car weighed ~600 lbs. It worked fine for testing and competition, but we took it out for a demonstration at a local school and jumped it on concrete all day, landing sideways many times, and the tube ended up bending fairly significantly.
It was plenty strong for the conditions we usually see, but an entire day of adverse conditions showed the weakness of the design. So basically, mount near a node, and you could go pretty small. We now use arms mounted to 1" x 0.065" and we could probably still go smaller safely. |
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Andrew Sims
University of Arizona |
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blue2kss
Welding Master Joined: Dec/23/2008 Location: USF Status: Offline Points: 169 |
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This is where the engineering analysis comes in. Like others said, it should meet at a node. IMO shocks and A-arms should always meet at nodes because they transfer so much force into the stucture. Whether or not the tube will fail is up to you all to decide from either mechanics of solids or FEA. Your welding practices will also be a factor on the quality of the weld and joint design.
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Dustin Bride
University of South Florida SAE Alumni/Consultant Mechanical Engineer - Naval Surface Warfare Center, Marine Corps. Counter IED Development |
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RonGeorge
Welding Master Joined: Apr/17/2010 Location: Indiana Status: Offline Points: 286 |
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Something from our team. We build (or have built) our rollcage members forward of the firewall with one uniform tubing except for bracing members - 1.25 x 0.065". The way I see it, the a-arm mounts should be rock solid. Any significant deflections there and the purpose of building a suspension is defeated. So we'd rather get that advantage than saving the negligible 0.2 or 0.3 lbs/foot we can get with smaller tubing. Like someone said, the mounting of the shock to the frame member should ideally be at a node such that you put members in tension-compression rather than bending. For any kind of complicated analysis, I feel a Solidworks fatigue simulation is the way to go. |
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-Ron George
Systems Engineer (Cummins Turbo) |
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CLReedy21
Baja Godfather Joined: Nov/30/2008 Location: Marysville, OH Status: Offline Points: 736 |
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So, are you talking about the shock mounts on the frame and the a arms as a whole as two separate pieces. Or the shock mounts on just the A arm. Or the shock mounts on the frame and the a arms. As for the frame side we've mounted shocks to 1 x .035" tubing so it can be done, but it's totally dependent on the geometry and the unsupported length of the member in addition to the weight of the car and loading it sees. As for the shock mount on the A arm, you could very likely get away with a 1" x .035" cross member to mount the shock, but since those pieces are typically only 4-6" long I don't see any reason to risk it for what would amount to an ounce or so. We run .065" arms and .049" shock mounts. |
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-Chris Reedy
TTU Alumni Fourwheeler Drawer "Quick with the hammer, slow with the brain." |
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Sarah
Welding Master Joined: Dec/03/2010 Location: columbia, sc Status: Offline Points: 109 |
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sorry about the quick first post.. i was at school and i use the forum as a debate settler quite often (as i'm sure you guys have noticed).. you guys have more experience and screw ups then us lol
we were going to do the rear motor mount area in secondary member.. turns out we cant bend it so it'll be primary
drivetrain has just now decided they want to mount their shocks differently and wanted to add another bar as a mount point.. since we have so much secondary left they were just going to use it
as far as the front shocks and a-arms.. its either mounted to the primary and/or right around a node
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University of South Carolina - Gamecock Baja 2011
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smock
Milling Master Joined: Mar/24/2009 Location: Augusta, GA Status: Offline Points: 60 |
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My bad...
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Andrew Smock
Design Engineer John Deere Commercial Products Augusta, GA UA Baja Team Leader 2006-2009 UA SAE President 2010 www.uabaja.com |
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asims
Welding Master Joined: Apr/07/2009 Location: Tucson Status: Offline Points: 184 |
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In your defense it was either land sideways or mow down bunch of middle schoolers. Much easier to fix bent steel than broken bones. |
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Andrew Sims
University of Arizona |
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collinskl1
Baja Godfather Joined: Jan/21/2009 Location: Saginaw, MI Status: Offline Points: 1056 |
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those youngsters would heal in a few weeks!
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Kyle Collins
Lipscomb University Alumni 2x Project Manager Nexteer Automotive Product Engineer, Electronic Power Steering ... and the 8th simple machine: a bigger hammer. |
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