kee
Posted a lot
Posts: 4,991
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Mar 30, 2009 15:22:01 GMT
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i'll be changing the suspension arm mounts aswell before someone points that out ;D cheers Slater, I'm a lot happier with that one, thanks to this forum and it's brainy occupants edit cos i can't spell, maybe I'm in the wrong game ;D
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Last Edit: Mar 30, 2009 15:22:24 GMT by kee
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Mar 30, 2009 15:49:07 GMT
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Just skimming this post at work so I'll have a proper look later, but golly gosh that's a heavy bit of work!! It looks a lot like an afterthought bracket on top of an afterthought which doesn't usually make for a neat design. I don't want to put you off here, so I'll have a go at helping more later, but for the moment I'd say it's very heavy, the springs feed into the middle of a tube at their top and there's a lot of metalwork going into the top of the bulkhead. Take heart, because at the end of any design you should evaluate it, and that'll get you marks. Part of your evaluation can say that for the benefits of double wishbone geometry, the weight and complexity have shot up compared to (for example) McPherson struts.
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filmidget
East Midlands
Mostly Lurking
Posts: 1,652
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Mar 30, 2009 16:24:25 GMT
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Still think you have got absolutely fundamental problems sticking with those wisbones. And those dampers look a bit short? What course is this for again? EDIT: Scratch that, just re-read the first post. Your in your final year
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Last Edit: Mar 30, 2009 16:26:14 GMT by filmidget
'79 MG Midget 1500 - Still patiently awaiting attention '02 Vauxhall Astra 1.8 Elegance(!) - Better than you might think '03 Mazda MX5 - All new and shiny looking (thanks to Antony at Rust Republic) '09 Renault Clio - Needs to go.
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Mar 30, 2009 18:20:56 GMT
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Are those rose-joints for the upright mounts? If so rose-joints arent designed to take bending loads as i understand it!
Also think of the practical elements of the design, can some of those tube joins actually be welded in the way you wish (i.e can you get the torch in the gap!).
Good luck with the project, i am in the same boat, but designing a hybrid drive unit for my project. Not long now!
Edd
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Shelby Daytona - Scratchbuild project.
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PhoenixCapri
West Midlands
Posts: 2,685
Club RR Member Number: 91
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Mar 30, 2009 18:31:00 GMT
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I would have to agree with filmidget here. The wishbones are very long and with such a narrow angle will have very poor lateral stiffness. And the coilover mounts look very weedy and very poorly supported, really could do with tying in more to all that strength in the main frame which itself doesn't look too bad. Also its normal to mount the coilover to the lower arm since it takes more of the bumb load and allows for a longer shock meaning you get much better travel and easier packaging - and more space for bracing. Its certainly improving but still some way to go before I'd trust it to cope with even a tiny curb strike! Have you read this book - Competition Car Suspension: Design, Construction, Tuning by Allan Staniforth, its very good an is an excellent introduction into suspension design, will certainly show you how to design some better wishbones! Good luck with it
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kee
Posted a lot
Posts: 4,991
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Mar 30, 2009 18:48:05 GMT
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wishbones need to be that size for clearance on the engine, otherwise they will be very short and pretty curse word. coilie mounts aren't finished yet and they can't go on the bottom arm cos ther is simply no room anywhere again because of the engine. i'm not very good at this because my course has entailed sod all of anything to do with spaceframes and proper suspension design, it's all such a massive learning curve and i haven't done much on this project this year which i am REALLY starting to regret. all the advice has been taken on board and trying to process this along with doing 3 other big assignments due in the same week, and bringing up a 10 month old, is getting to me and is affecting my work
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Mar 30, 2009 20:01:55 GMT
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Have you looked at the front suspension on an Alfa 156? double wishbone with a strut . Wishbones are short and the system is really easy to make adjustments too.
Keith
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retired with too many projects!
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Mar 30, 2009 20:41:25 GMT
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Back from work, I'll try and make it a bit more helpful Don't worry about not being taught about this stuff on your course, I wasn't either and still managed to learn a lot from doing what you're doing. Imagine how many hours of lectures you'd have to sit through to experience what you've done already ;D The wishbones look really flimsy. Have a look at normal car wishbones and see how big the section is. You could do a quick comparison of the second moment of area (bd^3 / 12) and see how the stiffness of your tubes compare with fabricated pressed steel ones. There's a lot of metal in your main spaceframe. It must weigh a ton, and when you're an engineer you've pretty much got to justify every bit of material, every welding operation, every nut and bolt. The other thing is that you want your car to be as light as possible to do the job. With this in mind, start from where the loads are - your suspension joints and the top of the springs. That's 10 nodes that you need to hold in place, and you need to attach the whole thing to the rest of the chassis. Any help?
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kee
Posted a lot
Posts: 4,991
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Mar 30, 2009 20:53:31 GMT
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the wishbones are drawn at 25mm OD, as of yet i haven't performed any FEA on them so will change them accordingly. The coilover mountings aren't finished yet, i don't really want them up there but I'm struggling for space. the frame is 38mm OD tube and the frame itself weighs in at 13.6Kg according to pro/e. sounds light but for a spaceframe is pretty heavy as far as i am aware. the furthest points on the frame in that pic are where it mounts to the rest of the car, there will be other points but not got round to that yet. thanks for replying
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stealthstylz
Club Retro Rides Member
Posts: 14,926
Club RR Member Number: 174
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Mar 30, 2009 20:59:18 GMT
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I don't get why having the coilovers mounted in the middle of a tube is a problem. Most drag cars run like that, and even with 350kg of big block and 3 foot wheelies they never bend.
Matt
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kee
Posted a lot
Posts: 4,991
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Mar 30, 2009 21:00:59 GMT
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it's just better to have the loads from the coilovers being spread elsewhere, will reduce metal fatigue somewhat and help with rigidity.
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Mar 30, 2009 21:14:08 GMT
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the wishbones are drawn at 25mm OD, as of yet I haven't performed any FEA on them so will change them accordingly. Don't get too hung up on FEA. What's the impact load you'll put in? What's the maximum load they can take? How many cycles for fatigue?? Sod all that, you want a rough idea before you go too far so just compare the stiffness of yours with a production car or racing car. Throw in the youngs modulus and you can get comparative strength and then see if you're miles out or close enough for the moment. The coilover mountings aren't finished yet, I don't really want them up there but I'm struggling for space. Sounds normal Write it all up in your report - the constraints you had. the frame is 38mm OD tube and the frame itself weighs in at 13.6Kg according to pro/e. sounds light but for a spaceframe is pretty heavy as far as I am aware. Dunno about the weight offhand but if you get that made (and that's why Engineers are there, to get things made and sell them for profit) it'll be at the welding station on the factory floor for an hour! Reduce the number of joins, the number of sections and the number of welds. I know it's a Uni project and not a real life thing at the moment, but demonstrating you've considered the bigger picture is a benefit. the furthest points on the frame in that pic are where it mounts to the rest of the car, there will be other points but not got round to that yet. All of them? What about the top bar at the front, that whole section isn't doing much is it? Stick at it, mate. This stuff doesn't get designed right in a day.
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Mar 30, 2009 21:19:03 GMT
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Most drag cars run like that, and even with 350kg of big block and 3 foot wheelies they never bend. I bet you a million pounds that they do bend The loads from the front suspension of a drag car are comparatively small, the fact that it's light means the springs can be soft and there's not too much force transmitted to the frame. Also bear in mind that a drag racer might do an impressive wheelie but it only does 20 or 30 before the chassis gets rebuilt. Cars that go around corners have much higher loads, and even a racing car sees a lot more of those loads, unless the driver is like me and would crash on the first corner every time ;D
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Seth
South East
MorrisOxford TriumphMirald HillmanMinx BorgwardIsabellaCombi
Posts: 15,538
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Mar 30, 2009 21:46:41 GMT
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I don't get why having the coilovers mounted in the middle of a tube is a problem. Most drag cars run like that, and even with 350kg of big block and 3 foot wheelies they never bend. Matt I shoudl imagine with regular hard "landings" a chassis like this would bend inwards. But then most pro-stock (which is what i googled to find this) type cars would run wheelies bars so would never be allowed to get much air and the front wheels would be pretty lightly loaded most of the time.
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Follow your dreams or you might as well be a vegetable.
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kee
Posted a lot
Posts: 4,991
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Mar 30, 2009 22:14:11 GMT
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well i think i have accidentaly solved my coilover problems, they are now on the bottom arms and nothing is hitting them ;D
i think it's because i moved the engine forward to line the driveshafts up with the hubs as they are in real life, and then subsequently forgot to check clearance on the suspension, silly curse word.
ONWARDS!
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Mar 31, 2009 12:24:57 GMT
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Looks better Have another think about where the spring units attach to the wishbones, you want them as close to the hub as possible. For now you've got a massive downwards force acting in the middle of the wishbone, and an upwards force at either end. That's gonna be a banana shaped wishbone shortly! I'd question whether you need the cross braces (in grey front and back and yellow underneath) It's a lot of extra metalwork and welding for probably not much gain. When you've got some time on FEA, try 4 scenarios: 1. As it is now 2. With the cross pieced removed completely 3. With some small sheetmetal stiffening triangles welded in the corners 4. With a flat sheetmetal piece welded across the whole opening. This is effectively another bulkhead and you might find it's almost as strong as #1 but for 20% of the cost. Also worth considering if you can simplify the spaceframe around the top spring supports?
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Mar 31, 2009 13:05:19 GMT
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its rly great to seethe development of this.are you at shef uni or hallam. I'm a first year mech eng student at shef uni and I've love to give you a hand with building this thing if i can. Was wondering with the previous designhow you were gonna get the engine in and out. I'm hoping to do something like this 4th year but i'll be doing alot of rwading in advance. gd luck sam
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'88 Toyota Supra Turbo
'88 Honda VFR 400 NC24
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kee
Posted a lot
Posts: 4,991
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Mar 31, 2009 14:26:50 GMT
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to have the coilover closer to the hub would mean it would have to be tiny, there just isn't enough clearance around the gearbox. i tried FEA last night and after 40 minutes of processing it decided it couldn't do it, and that was on just the wishbone itself, which is a bit of a curse word. i think for now i may just leave as is, see what my tutor says and then write about the other options i have in my report, i could go on doing this for weeks until the best method is found, and that would be to turn the engine around the other points you mentioned have been floating around my head, its strong now and although it would be a curse word to assemble, it's something else to talk about in my report. i'm not gonna get a decent design without experience as that is what these things generally come down to i have found. i really appreciate everybody's help on this, it's made my life a little easier recently and hopefully i can get going on the report and make it decent. Samwell, i'm at sheff hallam and can;t wait to leave, they are useless. i won't be building this, i plan to design a full spaceframe for the car once i have finished uni and also want to develop some performance suspension to replace the standard stuff.
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Mar 31, 2009 18:16:06 GMT
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Hey kee. If you save it as a parasolid, .x_t file, and e-mail it to me with some forces to apply and where you want it to be constrained, I will try running it through Unigraphics for you and see if I can get a result.
I don't have many (if any) translators so I cant open it using any other file unfortunately.
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Last Edit: Mar 31, 2009 18:17:10 GMT by PSmurfy
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