Rear A-arm |
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Minesh
Bolt Sorter Joined: Jul/03/2013 Location: India Status: Offline Points: 7 |
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Posted: Jul/03/2013 at 6:42am |
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Guys i need your help regarding the Double wishbone suspension mounting in the rear. As we all know, in double wishbone the best suspension characteristics are obtained when the suspension is mounted on the lower A-arm. But, in our BAJA ATVs we are unable to do so in the rear due to the drive transmission shafts. Inspite of this many teams use the double wishbone type suspension with the suspension mounted on the upper A-arm. My query is does it really give a satisfactory result and what are it's disadvantages or advantages over lower A-arm wishbone mounting..?
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mp
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Pedro UFPBaja
Baja Godfather Joined: Mar/03/2010 Location: Brazil Status: Offline Points: 886 |
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Lowers the CG and allows the upper arm becomes extremely light, since it will only have to control camber. To the suspension geometry and constants makes no difference.
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Former Team Captain
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Pedro UFPBaja
Baja Godfather Joined: Mar/03/2010 Location: Brazil Status: Offline Points: 886 |
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It is NOT impossible to place the shocks in lower arm even though the drive shaft passing by
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Former Team Captain
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Minesh
Bolt Sorter Joined: Jul/03/2013 Location: India Status: Offline Points: 7 |
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ok ok. Thanx a lot.
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mp
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joey.m.gonzalez
Welding Master Joined: May/09/2013 Location: San Diego, CA Status: Offline Points: 132 |
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Hah, that last pic is our car from two years ago... that setup worked like crap but I blame the designer, lol
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ahmed
Milling Master Joined: Jul/05/2013 Location: Egypt Status: Offline Points: 70 |
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hello guys,
I've a little problem with understanding the REAR double wishbone mounting, in Race Car Vehicle Dynamics there is a form consisting of two A-arms and a toe link (or sometimes called track rod). what's the use of this link? can i ignore it especially i've see many rear double wishbone systems with only the A-arms and the shock absorber !! Thanks |
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Richie_Dagger
Baja Godfather Joined: Sep/25/2011 Location: Las Vegas, NV Status: Offline Points: 615 |
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It adjusts toe. And depending on how you design your suspension, you can get toe change throughout suspension travel.
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ahmed
Milling Master Joined: Jul/05/2013 Location: Egypt Status: Offline Points: 70 |
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so why i see teams using just 2 A-arms without this link ( like this in the picture below) , how can they adjust the toe angle. you know that much space is needed in the rear to mount the half axles.
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Soccerdan7
Organizer Joined: Sep/22/2010 Location: CA Status: Offline Points: 780 |
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That picture shows H arms, not A arms. A arms have a single outboard pivot. The upper and lower a arm pivots create a steer axis about which the wheel can turn (just like the front suspension). That is why you need a rear toe link. With H arms, they constrain any pivoting about a steer axis which means you can not independently set toe and you don't need that added link.
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Danny
Cornell (fall'07 - spring'12) Former Captain / MEng / that guy with all the carbon 10 races, 7 top ten's, 2 overall wins |
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ahmed
Milling Master Joined: Jul/05/2013 Location: Egypt Status: Offline Points: 70 |
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so what's the difference between H-arms and A-arms with twin outer ball joints like this in the image ? because in this type we need a fifth link too (the toe link) i think i need to understand the difference between the outer joint type in A-arms setup and H-arms setup ?!! |
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mikem
Milling Master Joined: Sep/11/2011 Status: Offline Points: 52 |
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An H-arm has a bushing for its outboard point. It thus constrains two additional degrees of freedom then a pure A-arm, which has a ball joint instead.
Think about the motion an a-arm would restrict vs an H-arm and it should make sense to you. Think about how the tire can move with the different constraints. |
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Mike M.
Team Captain 2011-2013 McGill Baja Racing 2009-2013 minibaja.mcgill.ca |
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ahmed
Milling Master Joined: Jul/05/2013 Location: Egypt Status: Offline Points: 70 |
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thanks Edited by ahmed - Aug/29/2013 at 3:33pm |
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ahmed
Milling Master Joined: Jul/05/2013 Location: Egypt Status: Offline Points: 70 |
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hello guys,
I'm designing the geometry of the REAR suspension, and i can't see the difference between using a normal A-arm and an A-arm with twin outer ball joints if somebody can help, please do. Thank you ^^ |
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zmpeck
Organizer Joined: Aug/29/2009 Status: Offline Points: 40 |
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What more of an answer do you are you looking for? You posted a picture that clearly describes the differences. Both will work, one uses less parts. If you're seeking to implement some anti/pro's or dynamic toe characteristics, you will have more freedom with the A-arm/toe link configuration. If you're just trying to make the suspension go up & down, i'd stick with the H-arm. Edited by zmpeck - Aug/29/2013 at 3:53pm |
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ahmed
Milling Master Joined: Jul/05/2013 Location: Egypt Status: Offline Points: 70 |
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i need to know the name of this rear suspension setup to search for its advantages,disadvantages, joints, installation ...
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cujdubs
Welding Master Joined: Sep/25/2012 Location: Potsdam Status: Offline Points: 116 |
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That is a H-Arm. You notice that the upright has no ability to rotate about the king pin axis and there are no toe links.
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John Hannum
Clarkson University Steering Leader |
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ahmed
Milling Master Joined: Jul/05/2013 Location: Egypt Status: Offline Points: 70 |
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do you know a suspension software to model this setup and simulate it , i need to check how camber,caster,toe, kingpin, ... change with wheel travel?
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Red_Beard
Organizer Joined: May/14/2009 Location: Bellingham, WA Status: Offline Points: 269 |
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Solidworks |
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SDSM&T 09-10 Team Lead
2nd & 9th Baja West Project Engineer Matrix Service - Bellingham, WA |
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ahmed
Milling Master Joined: Jul/05/2013 Location: Egypt Status: Offline Points: 70 |
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but this suspension mechanism is only kinematic if your chassis attachment points are perfectly parallel and your upright axis are also perfectly aligned.
Any angular error particularly with pivot joints all-round will cause the suspension to lock-up under bump/rebound travel as it is over constrained. don't you think so ? |
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zglazer
Baja Godfather Joined: May/27/2012 Location: Metro Detroit Status: Offline Points: 593 |
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You can account for that with a good jigging setup and by using spherical joints or rod ends at some of the pivot points to allow for misalignment.
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Zack Glazer
McGill Baja Racing Alumnus 2009-2013 http://baja.mcgilleus.ca/ 2012-2013 Drivetrain Designer |
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cujdubs
Welding Master Joined: Sep/25/2012 Location: Potsdam Status: Offline Points: 116 |
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Some teams and some production vehicles use hard rubber or something similar for the bushing material so that there is alittle give to compensate for things not being perfect.
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John Hannum
Clarkson University Steering Leader |
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ahmed
Milling Master Joined: Jul/05/2013 Location: Egypt Status: Offline Points: 70 |
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so what's the advantage of this setup over using a H-arm and single upper link, why would someone take the risk of having his suspension locked up especially that i think the setup below provides a similar behavior like the two H-arms and can replace it, am i right ?
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Soccerdan7
Organizer Joined: Sep/22/2010 Location: CA Status: Offline Points: 780 |
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A setup with 2 H arms is better at reacting moments from the wheel loads and makes it easier to mount the shock to the upper link. The picture you attached with the single upper link is essentially the same anyway since the pivots are bushings, and those bushings will probably wear out quickly.
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Danny
Cornell (fall'07 - spring'12) Former Captain / MEng / that guy with all the carbon 10 races, 7 top ten's, 2 overall wins |
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ahmed
Milling Master Joined: Jul/05/2013 Location: Egypt Status: Offline Points: 70 |
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i thinks it's much better to mount the shock on the lower arm !, i guess i will have the bushings problem in both setups :( |
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OffTrac
Bolt Sorter Joined: Aug/27/2013 Location: Cleveland, OH Status: Offline Points: 15 |
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If you're looking for software to simulate a geometry you've already got drawn out, Lotus is useful. But to be honest, it's just to validate a design and show it's characteristics throughout the range of motion...you have to have the majority of the things you listed above (king pin, caster, etc changing with wheel rate) to get a good simulation output.
Least that's what I've found it useful for - It's definitely not a "my top arm is X and bottom is Y, I want Z caster and...." and it spits out a finished geometry you can cut and weld together. It's a lot of work. But it's worth it in the end.
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Jacob Rhodes
BBB Motorsports CWRU Baja Captain '12 '13 "If it can get a tire on it, it'll go over it" |
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ahmed
Milling Master Joined: Jul/05/2013 Location: Egypt Status: Offline Points: 70 |
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Does anybody know the advantages of the H-arm & single upper link suspension rather than the few number of links and the easy packaging ?
I'm puzzled to use this setup or use a three link suspension like this in Polaris rzr |
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jeiB
Baja Godfather Joined: Jul/17/2009 Location: Montreal Status: Offline Points: 604 |
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Its the same difference.
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Jeremie B.
McGill Baja Racing 2009-2011 Captain minibaja.mcgill.ca |
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