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3 Link Questions, discussion and a brain dump

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On 26/11/2016 at 9:50 AM, Daan said:

As mentioned, those holes need tubing to take big loads. The main rails are only 2 mm thick.

I would completely support the front axle using the removable crossmember, like the qt 3 link system. Have you thought of a 1 link? That would solve a lot of problems.

 

Daan

2.5mm on a Richards! Coming forwards to the gearbox crossmember for all of it makes the links far too short for my liking  as it is the lowers will only be about the length of the original radius arms. 

I deliberately went away from 1-link idea so as to keep the adjustability later down the line. It would also incur problems later down the line as I'm building everything to be reversible at a later date if the trucks use changes. 

2 hours ago, Carloz said:

The construction you have drawn wants to turn around de bolts, so is completely dependent from the clamping force and not by a desired closed shape construction.. would not be my choice.

 

I understand you want to mount the link further backwards.

I would use in a way the original link mount hole to mount a sort of little subframe to and use the three M8 bolts for the gearbox mount to keep it in the right orientation.  So the horizontal strain will be taken by the original link mount.

So far I know the M8 holes are backed up inside by an anti-crush setup

That's what I've got (admittedly only on the one sketch), tying the the outside plate forwards to the original radius arm mount. Sorry for not making that clearer, I couldn't be bothered to draw it out each time! 

The other thing will be tying the extra crossmember forwards to the main gearbox crossmember too. 

That means the 3 bolt holes will only see small loads as most will be taken though the radius arm mounts and the gearbox crossmember. 

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On 27/11/2016 at 11:07 AM, Carloz said:

The construction you have drawn wants to turn around de bolts, so is completely dependent from the clamping force and not by a desired closed shape construction.. would not be my choice.

 

I understand you want to mount the link further backwards.

I would use in a way the original link mount hole to mount a sort of little subframe to and use the three M8 bolts for the gearbox mount to keep it in the right orientation.  So the horizontal strain will be taken by the original link mount.

So far I know the M8 holes are backed up inside by an anti-crush setup

He plans to brace back to the radius arm mount. should be a fairly strong setup really. so long as it's done right with an attention to the forces involved etc. 

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Ah, I missed that part. Got confused by the extra crossmember and bracing to the existing crossmember (both is not really necessary in my opinion). :-) 

Edited by Carloz

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The extra crossmember is there to support the two inner plates for the lower links. In turn that lends itself to being tied to the original crossmember for a couple of reasons.... first is it will reduce the chance of the plates being turned and it also makes a easy place for the bashplate to attach. As none of it is being welded to the chassis, the more the loads are spread about the better. 

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Made a bit of headway on the design last night, will post some pictures up soon.

I've also started running into space issues along side the gearbox :(. Its going to be snug there as I've only got about 4" between the chassis rail and side of the box.

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So this is where I'm up to at the moment with the design of the suspension mountings, I've still got a load more to do on the details but feel free to make any suggestions and comments. 

Some points worth noting:

  • All the joints in the model are a simplified 1.25" creeper joint, I'll be running one creeper and one rose joint on each link
  • 3mm S355 Weld washers on all bolt holes
  • 3mm S355 for all of the chassis parts
  • 4mm S355 for the axle top link bracket
  • I haven't drawn the axle mounts yet, they' are the next big stage
  • Haven't drawn the bits to tie into the old radius arm mounts yet
  • Current assembly weighs about 20Kg... but most of it is all thicker than the intended 3mm. Crossmember parts are all currently 6mm.
  • Weld Washers are on the inside of the joints to make it easier to fit the joints in place
  • Vertical blue surface through the middle is the centre line of the car
  • Green surface is ground level and the yellow/red/green Planes are the centre point of the front axle.
  • Blue joints are all in position in space even if they're not attached
  • Small Yellow surface is the side of the gearbox.

Overview, but missing the upper link chassis bracket:

13F66659-18BC-49D0-8111-936F231FB977_zpstrrp8en6.PNG.bf42732e3971ff2db5d96d2e6528c3b6.PNG

 

Upper chassis Bracket in place

5A2FB287-2D99-4C90-9CD1-74E06CA75861_zpsknczjy22.PNG.38df790c1b0a73712e0282a0201721b2.PNG

 

Not much room around the upper chassis bracket. I need to measure but I'm hoping the bracket will end up along side a bit of space under the bellhousing so I can get the bolt in and out without dropping the crossmember.

AFF5EBE8-0969-40DC-9A5C-E4838DE3CDC8_zps7jy4h64s.PNG.2970d980b17b80041553a98afa075322.PNG

 

From the rear looking forward:

1B4EF419-2598-46C9-83A0-A464D2A59CA8_zpsfndpd6ky.PNG.00c5d9a142664d476d6a4ec66c5a7fb9.PNG

 

Above:

19329321-27FC-4782-B505-02524CDF574A_zpsncrl5kkq.PNG.92d63d381b1de4191cef75ecae3fc496.PNG

 

From the side:

CDBE737A-A6A0-4098-B134-CE5C27532E1C_zpswvlfpwhq.PNG.b6a6ca8ee34c6668bc9c5101fd764a58.PNG

 

 

 

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get rid of 3mm thickness on the crossmember plates.. remember, its only as strong as what its mounted to anyway. 3mm S355 is more than plenty. 

the box section used seems alright, what thickness is it? depending on loading and where mud can get easily, there should be a big scope for the removal of material within the box while still retaining strength. 

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On 1/6/2017 at 3:38 PM, discomikey said:

get rid of 3mm thickness on the crossmember plates.. remember, its only as strong as what its mounted to anyway. 3mm S355 is more than plenty. 

the box section used seems alright, what thickness is it? depending on loading and where mud can get easily, there should be a big scope for the removal of material within the box while still retaining strength. 

3mm wall box on the two crossmembers (S355), one 2x4" the other 1.5x4" to gain me some clearance under the transferbox/gearbox mounts for exhaust etc.

I've got the two different crossmember plates being laser cut shortly to test fit them and make sure the hole patterns are correct. I also need to make sure the inner plates of the lower link crossmember clears the seatbox mounting brackets.

Got another small update coming shortly... I've started the axle end of the lowers. Bolt on brackets that will pick up on the radius arm mounts and also track rod protection.

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Mk1 of the axle end of the lowers is at the top of these three:

AEE646BD-E6DB-4CF3-A4AA-E4A676D23BA7_zpsz96uxuyg.thumb.JPG.dafee3246c7de5d3d69e130cb055cd9b.JPG

That didn't fit due to the radius inbetween the two bolt holes. The middle plate is the chassis bracket for the lowers.... that also didn't fit as it clashed with the seatbox bracket. That's now been radiused further on the corner and the final item will only need the edge chamfering to clear the weld.

There's only so much you can do without a physical item to put in place....

D0E7EB0B-65D0-4C65-80D4-95852AD2D61F_zpsqonzqiyk.JPG.d101c351c6880d877a8057b0bff5bedf.JPG

2935EBFA-B640-429F-92E3-F2C34BC24CDA_zpsdqmggacs.JPG.704143672284e1bea50e48f732d1ebf4.JPG

CC4BE85F-A6A2-4CA1-BABA-5F50C6465767_zpsrfd1fxgg.JPG.e647b890c499818c72c40ed2804d0f49.JPG

Mk2 on the axle bracket was a muhc better fit, but still issues. Need another 5mm on the bolt hole pitch and some more space in the track rod hole.

565BC417-85DE-4006-9CA1-EF9E91DDB2FB_zpsuzee5fmg.JPG.821511310b534551266cfab0d54aafd2.JPG

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I should also explain the tack welds.... the sheet metal program the Laser chap uses managed to split the model down the mirror line when it was unfolded. Final ones will obviously be one piece.

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Time for an update here on the the suspension front! I'll copy this whole post into my build thread too so apologies to those who are following both! 

The test bracket I had cut for the upper link on the axle turned out to be completely the wrong radius on the top of the axle. This was expected to be a bit of trial and error to make it work as the axle case welds prevent the diameter being measured accurately. So the next test piece was produced, this time on the 3D printer! 

E2684562-FFA1-4204-8140-25E55884DC38_zps727lowvp.JPG.2bf38bbadc7f624a7d8beba3cb04ec54.JPG

This is better, but not quite right as you can see below:

39262070-EF22-4FE3-98E1-1446BB3AD76B_zpsl1tx6sak.JPG.6449349807064e3760df261781e065da.JPG

 

Whilst the printer has been in action it has also turned out a couple more test bits, this time for the gearbox crossmember:

7FACA33F-2492-48BC-84FB-34586A0CF7CB_zpse1sa5tgu.JPG.1983dc10d466b921bd6e0110d9a8890c.JPG

892D72CC-C9D6-4AB7-B1E3-91DC3339A551_zpsfny5eqgq.JPG.be493eb0b74fb2f6d9443322f3e0d97b.JPG

CE5C8BFB-2963-486D-AF7A-145A2638438A_zpsv0ffo9mi.JPG.1c5027c6f1532a1a20ee351efcc4c426.JPG

With the top link bracket sat on it, the positioning is looking great! 

CD692E86-4E1D-4A3E-A218-019039E920DA_zpsg6dhkchx.JPG.42fc0924a4bbd4dbfa955f89dcf0e31e.JPG

 

The next logical thing to print was a load of test radii to work out the axle radius:

CF5D3889-A2C4-4859-BDBB-C76510104CE7_zpsctn7z52b.JPG.3e263bbbbca4867d2b8c71dc3b3b9d9e.JPG

That has confirmed that the radius is 40mm on the top of the axle. So I've sent off the file for another test bracket.

Back to the lowers, I had another bracket cut after I'd adjusted the CAD... Much better! Fits on the Radius arm bolt holes and theres clearance around the track rod. Just waiting on another one to be able to check with a straight edge that the box section track rod guard is going to clear the diff.

7A24BDAE-91ED-4D84-AA3B-C1A0F8E3B456_zpsfnjdkpiz.JPG.f9e1d44cb919372999d8068f4b85e352.JPG

7991E4E5-95CF-43FC-A666-2546E3E09645_zpsihruzqxz.JPG.1e5342a93509e0d5efbfcc5dce2f9cd9.JPG

As always, I welcome any comments on the design! 

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Great to see some progress on this. I'd suggest a radius on the corners of the hole the track rod goes through and probably weld a bit of box section for the track rod to go through between the two plates that'll form the mount. You'll need to really beef up the link material for the lower link mounts I think as the lower mount on the axle will also see a substantial vertical component during braking which will be translated into an even more substantial horizontal component. I suggest making a mockup on your garage wall or door with a few straps of wood and screws and feel how it is. Your link geometry isn't too far from my own in concept and I had to tweak mine to avoid that large compressive force and allow the use of creeper joints at one end which have some compliance. The chassis ends of my 'links' are screwed to the garage door and the others are free to move relative to the door so I can lift the 'axle' up and down. Using a compliant material allows a very rapid assessment of the compressive forces in the links and could be a worthwhile exercise for you too. My pinion is rotating backwards towards full bump to increase my anti dive as the suspension compresses but more importantly to me to reduce it as it extends and hopefully climb steps on steep ground better. I used that triaged calculator too but found I had to add some real life to it as well to have any confidence in the results. Using a battery drill to move the link ends is way faster and more intuitive as well. I agree with DeRanged that the AD / AS numbers are just a tiny part of what's going on.

IMG_1257.jpg

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Jamie, thanks for the comments :). There's a bit more discussion in my build thread that isn't here about material thickness amongst other things so this lot should hopefully clear some things up!

  • Radius on the track rod hole: Not really much point doing that, if you see the next point.
  • There is going to be a 100x60x3mm Box running from outside-to-outside through all four radius arm brackets, and be fully welded to each of them. So not a lot of point radiusing the corners of the holes as they'd have to be tiny to let the box section in and then they're just going to get melted! 
  • Materials, everything is going to be S355 so stronger than your normal mild steel.
  • Thickness - these haven't been decided yet, but with the cost of the laser cut stuff its not worth my time knocking up prototype brackets. So where others might use a cardboard bracket or a rough steel one, I've had them cut. So at the moment they're only I think 3mm or 4mm. They're most likely to end up at either 5 or 6mm.
  • Radius arm brackets are going to be fully boxed in ~3mm S355, with weld 'washers' on the insides being one piece blending back into the track rod protection box section.
  • As I want it all bolt-on, and to work with an unmodified chassis, I'm a bit forced as to where the links go so all I'm really able to work with is the AD by adjusting the chassis end of the upper link.

Think I need to post another up date with some pictures.

Working on a few bits at the moment:

  • Track rod box section clearance with the diff.... or lack of. I think its going to have to be notched to clear and plated back in. I just need to make sure there is enough space for the track rod to pass through the guard to make removal easier.
  • Got the track rod box section mocked up with some string.
  • Main thing at the moment is to work on the narrowing of the upper link axle bracket. I've got 115mm between the side of the chassis and the side of the sump. And the bolt at the moment is the same!

Once the upper link axle mount is sorted I'll tack it in position and pull the axle out to sort the rest on the bench. I'll probably check the suspension link to chassis clearance first actually, with some mock up steel links.

 

Has anyone run a track rod guard where you needed to take the TRE off to remove it? was it a real pain in the arse? :unsure:

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Here's the most up to date CAD assembly.... this is missing things which I've not bothered designing until the major parts of the design are finished, bits like the radius arm mount braces and the boxing in of the radius arm axle brackets. I also need to change the size of the Track rod box section to 100x60 to take the trackrod through it.

 

Capture2_zps7osejfch.PNG.542ecf662af516ac207f0dae6b9bad8f.PNG

 

Capture_zps3rvgqqqc.PNG.2606fa5276018e357c11c1cce05a4009.PNG

 

 

5992e5768c81d_Capture3_zpsnyecbkvr(1).PNG.32d983eaba974eb51598e8faeafd7e25.PNG

 

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Great CAD work Ross. Everything looks good and solid, only thing that is really still a big questionmark is how the handling will be, but only time can answer that one! Is there someway you can fit a couple of longditutional bolts on that crossmember holding the upper link arm to the front? I'm afraid it would wiggle loose over time? Relying only on the clampingforce between the chassis and crossmember

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Thanks Soren :) 

As you say, only time will tell how it handles. It might drive like a bag of sh!t who knows! I've tried to make the 3-link calc numbers around where they should be, but obviously limited when it comes to link placement on a standard chassis.

Not sure where I would be able to add them, other than to say I'm probably going to be linking the two crossmembers together, either with some kind of skid plate and frame or just a bolt in frame. Thankfully the line of the arm in place (doesn't look like it in the above pictures though) is in between the upper and lower bolts for the crossmember so there should be little rotational forces on it. If I was building this onto a non-galv chassis I'd weld a bit of bar in front and behind that crossmember.

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Could you put a bend on the bottom of the side plates to snug up against the bottom of the chassis instead? Would certainly stop it rotating, of course you'd have to get it pretty accurate :) 

To be honest though, I doubt it would be an issue, if you work out the clamping forces of 4 * M12 bolts then you will be way off the charts of being 'fixed'.

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Easiest option there would be to weld something on each end that overlaps the chassis a bit, perhaps part of the skid plate. Not sure what the clamping force would be for 4 M12s, but its going to be pretty high! 

 

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can you cycle it out on cad? I think the lower links so far back on the rear axle could have a bad result when you get a big hit on a wheel.

the axle might rotate around the upper axle pivot and the lower links go past dead centre and move upwards.

Daan

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Afraid not Daan, I've only modelled the joints as a solid lump for a visual so they haven't got any moving parts.

Are you thinking the lowers might go over centre and lock out?

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Ross, regardless if they are solid models or not, on Catia its pretty simple to get it moving as it would in real life. 

if you want to throw me the model ill happily constrain it and set the pivots for you.

 

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Any progress on this?
What Daan was saying was more eloquently put than me but we're saying exactly the same thing.

Rather than model it in cad which would be difficult to achieve real world compressive forces and deflections, make a mockup with easily found materials. I have a similar setup with the lowers mounted very far back behind the axle centreline. As the links come close to over centring, the compressive forces will be massive and destructive. You really need to make sure these are ironed out.

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Not made much progress lately... been busy with work mainly but I have been thinking about lots of elements of the design. 

I did manage to eventually track down some S355 100x60x3mm box that I want for the track rod guard/radius arm bracket brace... annoyingly though I only need about 950mm, but had to order a 7.5m length!

Have you got any pictures of your setup Jamie?

As for a mock-up... As people probably know by now, I just get stuff laser cut, the small cost here and there for the odd bracket or plate makes it not worth making stuff by hand! So all the bits get cut and trial fit as I go along. This means I will eventually have pretty much the complete setup to be able to tack together and cycle.

My main focus at the moment is changing the size of the trackrod guard from the 80x60x3 in the models so far, to 100x60x3 that I need to be able to get the trackrod through. due to diff space constraints, I'll be loosing only about 5mm forwards and 15mm to the rear of the slot so this will push the lower links back a touch further. I will be able to 'reduce' the 15mm by loosing some of the space I've currently got between the track rod guard and the major radius of the creeper joint.

Next thing after that will be notching the side of the sump to clear the bolt head of the upper link so I can keep that bracket full width. I decided that rather than narrowing the bracket and loosing material thickness or washers that I was better off keeping it full width.

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Update time again :)

Its progress is getting frustrating at the moment, didn't even step foot in the workshop over the christmas break!

Bought myself a new tool for the fabrication of the infill in the sump, its a little pressbrake for the vice and produces a lovely bend.
IMG_1418.thumb.JPG.32e7ce6f1a5e06b0c2177a3fa118a2d1.JPG

Bit of measuring, jiggery pokery and I had this:
IMG_1422.thumb.JPG.4a73f2aa607639a7434cb4727a04c2d6.JPG

Looking good, and fits well:
IMG_1424.thumb.JPG.bf6227d43c42f557c2579581a1cdc616.JPG

Stopped taking pictures here for a bit as I was doing lots of toing and froing but I ended up scrapping that bit and starting again. By the time I'd notched it to fit around the oil pump it was a mess so I started afresh. 

So with a new bit made I taped it into position and cycled the suspension.
file-1.thumb.jpeg.501f367709758f2da6097d27168ffdad.jpeg
file1-1.thumb.jpeg.679c0b120f3e5eba46049e052321c3ed.jpeg

As the bolt passes the chassis on the chassis side of the bracket it is at it's closest due to the arc of the panhard. At this point I've got 10mm to the chassis:
file3-1.thumb.jpeg.759eef8bde2f940648c282a3f88e38d5.jpeg

As it then passes the (new) edge of the sump I've also got 10mm clearance:
file4-1.thumb.jpeg.2a46ff3489f558cc7a3a3d0aa68d9a3d.jpeg

Then with the axle up against the chassis I've got another 10mm to the new infill piece which slopes towards the drivers side due to the arc in the axle movement. Not as much space as I'd like but equally not  a bad result given the starting point.

So the next port of call before finishing the hole in the sump is to build a complete working mockup of the suspension that I can cycle fully. I need to check how much the bracket moves fore-aft before I commit to welding the sump up completely. So I'm just tracking down some CDS for the links at the moment and box section for the crossmember while I wait for the laser parts. Its all just being done in some nice thick mild steel before I start looking at loosing some weight from the system. Will have to wait and see how that pans out.

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