Outrigger construction

[Les Henson]

Question for those of you that know about stress points in metal, and that sort of thing. Step up Bish

I've been helping to build a Trakka the last week, and to avoid the IVA - the chassis has not been cut.

Because of the extended chassis length, the rear is a load bed - constructed out of EN10255 tubing, but not bent (this is to get a clean corner for the tailgate/rear lights). The connection to the main cage is by the usual fish mouth, but at the rear it's cut and shut - as is the tailgate itself, which will be held on with 3 x Defender rear door hinges. I had to therefore construct two outriggers to support the rear of the main cage (it would normally be the supplied rear crossmember on the cut chassis). There was a problem with suspension upper travel, which is why the outrigger is such an odd shape - I had to keep away from the wheel as much as possible. The chassis is saddled to some extent, as you can see in the picture with 6mm plate. The top and bottom of each outrigger is also 6mm plate, and the sides are 5mm plate (damned heavy things ). My concern is possible impact forces being concentrated to the corners of the outrigger profile and it may not therefore be as strong as it appears, which is why I used thick steel to compensate for that potential problem.

Pics -

What do 'we' think ?

Les.

[Bowie69]

Purely from a mechanical POV I'd be thinking about putting a tube brace diagonally (both in horizontal and vertical plane) from the outer part of the outrigger back to the chassis where is starts to kick up again -just past the fuel filler tube. I would hope that this would contain the obvious twisting forces from a front/rear roll over.

But then I am totally uneducated and what I said is just a guess from first principles, so Bish will be along to tell me off in a minute

Nice fab work as ever though Les, very nice

[landrover598]

I would have made the outrigger this shape personally

But i'm sure your design will be strong enough.

[missingsid]

I'm not and engineer but I agree with the previous comment.

But would add that the bit that would concern me is the 90deg angle in the middle as this surely mut be a weak spot??

Marc.

[Les Henson]

I think you're right David - your design looks stronger/better.

Les.

[Guest noggy]

I think you're right David - your design looks stronger/better.

Les.

Not only does it look stronger and better, it looks a damn lot easier to make and weld!!

[bishbosh]

Dave, thanks - you saved me messing around with paint!

Dave's design is what you want - you can easily retrofit the one you have Les if you feel the need. You don't want a 90 degree bend in tension - it will concentrate the stresses horribly. having said that, from the materials you have used I don't think you'll have a problem!

I also agree with the triangulation (suprise suprise ) of the outrigger either fore or aft.

[steve_d]

Hate to burst any bubbles but you have welded it to the chassis so have modified the chassis = IVA.

Steve

[Bowie69]

Hate to burst any bubbles but you have welded it to the chassis so have modified the chassis = IVA.

Steve

Tongue in cheek?

I certainly hope so....

[Bowie69]

I also agree with the triangulation (suprise suprise ) of the outrigger either fore or aft.

Fore would put it through the wheel, I think

[steve_d]

Tongue in cheek?

I certainly hope so....

Sadly no.

DVLA told me that even moving the engine mounts to put a different engine in constitutes a modification to the chassis.

Steve

[FKD]

Tongue in cheek?

I certainly hope so....

If its classed as light goods maybe, think the change over is in 2011? but if its a passenger carrying vehicle I dont know for sure any experts out there?

I ask because I'm chopping off the cr*ppy landy ones and grafting my own on, so whats the cut off point?

edit: %ugger you beat me too it but you have sort of answer my question...

[steve_d]

So as not to be branded a killjoy I will offer a positive comment.

I'm maybe not understanding the function of the outrigger. It seems to be just the mounting point for a brace running up to the back of the roll cage. If so then would it not be better to run those back and inboard so that both braces meet in the middle of the bed somewhere. The benefit is that they would then brace the cage from being pushed back along the length of the vehicle but also brace against the far more likely impact at upper corner of the windscreen which would be trying to push the cage both back and sideways.

For the bed itself if the frame was designed with full cross members these could sit on the chassis or the existing body mounts resulting in no modification to the chassis. The braces could then come down on the centre of one of the cross members.

Steve

[Bowie69]

Sadly no.

DVLA told me that even moving the engine mounts to put a different engine in constitutes a modification to the chassis.

Steve

Bish, time to book your IVA then, according to this.........?

I'd be astounded if this was the case, honestly I would.

[HoggyN]

Sadly no.

DVLA told me that even moving the engine mounts to put a different engine in constitutes a modification to the chassis.

And yet other people have been advised that replacing a standard 90 rear crossmember with a Devon type rear winch tray is ok

[steve_d]

.....And yet other people have been advised that replacing a standard 90 rear crossmember with a Devon type rear winch tray is ok

Very true and it basically comes down to the inspector at your local DVLA office.

He/she has the power to decide if the mods you are proposing or have carried out will require a test. If the inspector has engineering skills and decides that your mods do not present a hazard then they can be agreed. If the inspector does not have those skills then they may have to require a test carried out by an engineer.

As you can see there are both technical and procedural anomalies across DVLA and before you start conducting a survey of where is best to go you can only deal with the DVLA office for your area.

Steve

[HoggyN]

As you can see there are both technical and procedural anomalies across DVLA and before you start conducting a survey of where is best to go you can only deal with the DVLA office for your area.

I must admit that I abandoned a rush to build a bobtail before the end of the SVA because there was no way I could build it fast and build it properly. I've accepted the fact that an IVA and a Q plate are unavoidable, so now I've got plans for something a bit more ambitious.

I just wish that they would stop moving the goalposts, don't they know how long these things take to build?

[steve_d]

I must admit that I abandoned a rush to build a bobtail before the end of the SVA because there was no way I could build it fast and build it properly. I've accepted the fact that an IVA and a Q plate are unavoidable, so now I've got plans for something a bit more ambitious.

I just wish that they would stop moving the goalposts, don't they know how long these things take to build?

There would have been no category under SVA that you could present a bobtail for test (ask Bish how he knows).

Under IVA they have re-written one line in the amateur build category which now makes it possible.

If you are planning a build then the IVA manual has to be your bedtime reading from now on so that your design takes you towards a pass.

Steve

[Les Henson]

Nige - you win a lollypop.

Les.

[HoggyN]

There would have been no category under SVA that you could present a bobtail for test (ask Bish how he knows).

I'd actually sorted that before I started. They agreed that I could go in the amateur built category as I was starting from the ground up (I got it in writing). That was the good part, the bad part was that starting from the ground up meant it took too long to meet the SVA cut off.

[Daan]

I cant believe people are so afraid, and get themselves into all this trouble, when the test is such a minor thing. If you dont pass that, the car shouldn't be anywere near a road.

Daan

[V8 Freak]

Firstly, I want to thank Les for a fantastic job so far... And maybe more to come.... Better get a bigger wallet Les....

(Or just take my bank card... I'll give you the PIN details ! )

Secondly to thank all who have contributed so far in the thread.. Enlightening, if not slightly worrying....

So... Can I try and clear up what I understand from this thread please....

I can see the simpler lines of the "painted" outrigger / cage mount would be stronger.

Assume it was changed, did one of the posts recommened a further brace from the re-shaped outrigger / roll cage brace back to the chassis further back as it rises back up again, to add an additional element of rearward rigidity ?

And.. As it was welded to the chassis, like the majority of roll cage mounts I've seen, does this mean there are hundreds of trucks out there illegally needing IVA and the MOT stations are ignoring this fact ?

I'd like to understand the reality of this situation.....

Lots in here... Mmm.. Welded cage mounts

The whole idea was to try and avoid IVA by not cutting the darned chassis !!

Lets thrash this one through.. I want to MOT this baby in June !

Neil

[steve_d]

........... did one of the posts recommend a further brace from the re-shaped outrigger / roll cage brace back to the chassis further back as it rises back up again, to add an additional element of rearward rigidity ?

I suggested that if the brace had been taken from the top of the cage down to the centre of the bed then the outrigger would not have been required.

And.. As it was welded to the chassis, like the majority of roll cage mounts I've seen, does this mean there are hundreds of trucks out there illegally needing IVA and the MOT stations are ignoring this fact ?

DVLA has stated any modification to the chassis = IVA but others will tell you that they have been known to deviate from that ruling. I was told even moving an engine mount was a chassis mod.

This type of change does not fit any of the MOT inspection criteria. They will only be inspecting that the chassis in that area is sound and is not cracked or rusty.

The whole idea was to try and avoid IVA by not cutting the darned chassis !!

If the cage had been fabricated as a separate structure a beam could be run right across at the height of the outrigger. Supports, with a 'shoe' at the base, could then have been welded under the beam to sit on the chassis without being welded to it.

Steve

[HoggyN]

I cant believe people are so afraid, and get themselves into all this trouble, when the test is such a minor thing. If you dont pass that, the car shouldn't be anywere near a road.

In my case it was mainly financial. The IVA test is a LOT of money. I don't care about the argument that it takes two blokes eight hours to do the test, the bottom line is a bill for nearly 500 quid.

[steve_d]

I cant believe people are so afraid, and get themselves into all this trouble, when the test is such a minor thing. If you dont pass that, the car shouldn't be anywere near a road.

Daan

I agree the test is nothing to fear but until now, with the introduction of IVA, it has not been possible to take the test for most of the modified vehicles that frequent our fraternity.

Steve