Tubular Wishbone Project

[bren_1.3 1]

have you thought about a spherical insert rather than a rose joint at the balljoint end?

[welshpug 1,658]

yeah I see what you mean, from what I remember of the 205 arms they didn't have the rear mount modified, shall have another look for the photo.

[Batfink 201]

[welshpug 1,658]

mmm KRS shiny bits lol.

 

 

Edited November 28, 2008 by welshpug

[mfield 20]

With your new design does the modeling software take into account that you've stretched the tube on the back wishbone ? I also think that you'll need a pretty decent tube bender to bend that angle , more than likely need to use more material and cut it down i.e. so it looks like a "V" shape to start with. Could always cut it to size, after the bend is put in the off cut could be used for the front length so no waste of material. I hate trying to describe stuff in wrighting

[Spiky 37]

you dont have locking nuts on your RJ's?

 

i still dont think you will have clearance with the ARB

 

what is the distance between the middle of the rear RJ hole to the outside edge, (where the aRB passes it)

 

and i will measure on my car to see if it will clear

[Spiky 37]

.

p.s. only trying to help, as it would be a shame for you to design a nice new product, but have a small design issue

Edited November 28, 2008 by Spiky

[Batfink 201]

With your new design does the modeling software take into account that you've stretched the tube on the back wishbone ? I also think that you'll need a pretty decent tube bender to bend that angle , more than likely need to use more material and cut it down i.e. so it looks like a "V" shape to start with. Could always cut it to size, after the bend is put in the off cut could be used for the front length so no waste of material. I hate trying to describe stuff in wrighting

 

I see where you are coming from. Why dont you just have a straight bit of pipe then just run the triangulation off that.... I'll draw it up and post a pic....

[Batfink 201]

 

something like this

it would be easy to adjust the design to give clearance for the ARB then too...

[Spiky 37]

but it wont, thats my point.

 

when you take into consiration the RJ's neck the locking nut, then the wishbone, your sticking out quite a bit

 

unless you use a smaller RJ (than the size used on compbrake one's)

 

i'm referring to this section of the wishbone

 

 

[Batfink 201]

ahh thats a better picture. Didnt know it fouled there too.

[Spiky 37]

ironically, the arms compbrake sent me were different to these and didn't fit,

 

i think they used a different RJ, which positioned the W/B further out, causing the issue

[welshpug 1,658]

[Spiky 37]

it's like playign top trumps lol

 

[Spiky 37]

oh and those WONT fit past a std ARB

[James_R 3]

"That is why the BMW 320si WTCC is fitted with huge brakes that can slow the car from 200kph to standstill in just 130 metres, pressing the driver into his safety belts with a force of 1.5g."

 

http://www.telegraph.co.uk/sport/2319536/F...ouring-Car.html

 

give you an idea of slicks and mega brakes and close to std road car aero, found aero cars (F1 and a like) can pull 2.5G or there about (depending on speed and how stuck to the track they are)

 

Good project Cam, keep it going.

 

As for lateral loading, I think 1.1G will be the max without aero on slicks and sus to boot, but worth over estimating that a little

 

As for shock loading, (impacts) as they are not purely vertical shocks (as the car is moving forward when it's shocked) so the vector will have some backward travel to it, if you take that M20 RJ's can be snapped by the rally cars from impacts and can be rated to about 54tonnes static loading, that's circa 60G (on a 900kgs car) that's if the pin hasn't failed first :s

[Miles 331 1 Cars]

I'm going to state the obious here, Why not move the pick up point's, Easy to do and you can stick them anywhere (Within reason()

[Cameron 16]

Ooo, a lot to catch up on!

 

With your new design does the modeling software take into account that you've stretched the tube on the back wishbone ? I also think that you'll need a pretty decent tube bender to bend that angle , more than likely need to use more material and cut it down i.e. so it looks like a "V" shape to start with. Could always cut it to size, after the bend is put in the off cut could be used for the front length so no waste of material. I hate trying to describe stuff in wrighting

 

No it doesn't, but the wishbone won't actually be like that. Catia seems to have some sort of glitch and about 80% of the time it refuses to model some tube geometries. So it was originally modelled with a kink and thats how it will be made, but when modelling this new one it refused so I had to put a very tight radius there instead. Really bloody annoying to be honest, but it shouldn't be far off in the analysis.

 

you dont have locking nuts on your RJ's?

 

Yeah I haven't modelled them but the finished product will have some. I see what you mean about that part of the wishbone, I'll have to check the dimensions later and see if it fits.

 

Those yellow wishbones look pretty good. I see it seems to be the norm with having rose joints with grease nipples.. the ones I was going to use have a PTFE lining so they're maintenance free but they aren't cheap!

 

I think a compromise has to be drawn between making an absolutely bombproof set of wishbones but compromising weight and making a still very strong set that will be far lighter as well as cheaper. A large impact will most likely damage most / all of the suspension parts so its pretty pointless trying to make them ridiculously strong.

 

I'm going to state the obious here, Why not move the pick up point's, Easy to do and you can stick them anywhere (Within reason()

 

Well, I could but that would reduce the likelihood of being able to sell them once they're proven. I would like them to be easily bolted on the same way the standard ones were.

[DanteICE 72]

Oh really? To be honest I don't know. At first I thought they were cast but when I examined them they seemed to have some tell-tale forge marks so I thought I'd be cautious and assume they were. I tried to search for some info but couldn't find anything other than something saying the 106 rallye had forged wishbones. I thought that if they had bothered to forge wishbones for that then they may well have done it for the GTI.

 

Does anyone know weather they are forged or not?

 

That's interesting about the cast wishbones breaking like that. Does it happen quite often in rallying then?

 

I showed my 309 gti wishbones to my dad (metaligist, maybe spelt wrong) and he said straight away, 'closed die forging', he said you can tell that by the edges being ground down and the holes will have been milled out after.

 

Hope that helps with your strength tests.

 

Geoff

Edited November 28, 2008 by DanteICE

[Cameron 16]

Cool, good to get some confirmation. Cheers!

[Miles 331 1 Cars]

There is that I know but on my 306 I have a re-located front ARB with different pick up point's and different hub's, It wasn't cheap but it works out a very good set up,

Think of what a S/H subframe cost's and the time and Material needed is not allot, and just do them on a exchange basis,

 

On a off topic don;t forget about your insurance if your going into production

[Cameron 16]

Yeah I will look into weather I'd need insurance or weather a decent disclaimer will be ok. But that's a long way off at the moment. It would be really good to change the pick-up points, I actually have a spare subframe now (once I pick the new one up) as I had to mangle one of the suspension mounts to get a seized bolt out of the old wishbones. I think I might look into something like that for my final year project. A subframe with revised pickups, geometry and wishbones would be a cool (but expensive) product.

 

Ah, I see what you mean now. If the subframes are modified to order and come with the wishbones? Would drive up the cost a bit though!

Edited November 28, 2008 by Cameron

[davemar 16]

I haven't read all this thread, but great to see to proper engineering going on, with pretty pictures too! Just a thought with the lateral forces. While many "impact" type forces from bumps and potholes are vertical, so don't really affect the wishbone so much; there are some impact lateral forces I can think of. Those speed bumps that you can straddle if your wheelbase is wide enough can exert some lateral forces I reckon. Most car's suspension isn't really designed to deal with the wheels being forced apart like this, so it might be worth baring in mind. There's also a road near me with potholes so bad on a corner, that if you go round it at more than about 10 mph, it can throw the car sideways. I reckon it caused one of my wishbone bolts to loosen. It'll be good if you could somehow sense the forces going on in real situations like this, which you could then put into your simulation.

[Sandy 191]

There is that I know but on my 306 I have a re-located front ARB with different pick up point's and different hub's, It wasn't cheap but it works out a very good set up,

Think of what a S/H subframe cost's and the time and Material needed is not allot, and just do them on a exchange basis,

 

On a off topic don;t forget about your insurance if your going into production

 

Colin Satchell already does this.

[Cameron 16]

Found out a bit of handy information today, I'd expected the rose joints to be made from forged mild steel but it turns out they are actually forged from 4140, which means they have a huuuugely high yield strength of between 1 and 1.2GPa! So that helps things a lot, since normal steel ones would have to be around 25mm to get the strength of an 18mm one. So with that in mind I can stick with a max of 20mm outer and 16mm inner joints.

 

I tried a design where the ARB bolts to the wishbone too, and it seems to cope very well. I don't have the exact spring rate for the ARB which makes things difficult but with a rough calculation assuming standard weight, 1.3G cornering and 60% front weight distribution I got a force of around 430kg - upped to 500 for the simulation.

 

 

The peak stress is very low considering the high loads - 750kg cornering + 500kg at ARB. Which is a good thing!

 

Then a simulation under braking:

 

 

The peak load is a little higher and located in the rose joint but its well within the strength of the material.

 

I also went out and checked the clearances between the mounting points and the ARB, and there is very little space! So another re-design is in order.

I think it might be worthwhile making a simplified model with the mounting points and ARB so I can simply add the wishbone and then check for clearance throughout the suspension travel.