Category Archives: chassis

weight savings – trailing arms, or more T45 please vicar

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On each corner, I have two lower links, and one trailing arm. They all weigh the same, at 555g including the threaded ends.

I got to thinking – can I save weight by going to t45 or even mild steel. The answer is a strong yes, for little machining/fabrication effort.

The table below shows the comparison between what I have now, moving to mild steel and T45

trailing arm savings

 

 

The summary is I will save 1.5 kg. Not only that but half of that is unsprung mass as well. All of it is suspension mass, so whenever the wheel moves, it has to. This is a bonus. More T45, Vicar. NOW.

Height Adjustable Suspension – Part 1

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In the spirit of “if you’re going to change anything, change EVERYTHING”, I have almost finished the brackets for the height-adjustable suspension. As well as making the suspension height-adjustable, I’m junking the old wishbones for the following reasons:

  • I’m going to t45 oval tubing for extra strength
  • I’m going to spherical bearings rather than bushes (ugh – bushes)
  • I want to make the suspension height adjustable so I can lower it when I need to

 

IMG_2956 IMG_2962 IMG_2964The welding rod here shows the line of force that actually happens, and the angles it has to go through. Firstly nearest you is the angle through the bottom ball-joint. That’s quite severe. the second is at the chassis bracket where it will have the bracket under torsional force.

 

 

 

In order to get the bracket just where I needed it, and at 90 degrees to the line of force I made a simple jig – one hole to locate against the ball joint, and one there the bracket bolt goes through. The jig was machined to be a tight 90 degree fit against the bracket so it would always be perpendicular to the line of force.

 

And here it is up close. The wishbone will have a 3/8ths spherical bearing that slots into the bracket there, and then the bracket can be height adjusted by moving it up the slots.

The bracket is then reinforced at the back and welded to the chassis.

Shocker bottom brackets are finished – part deux

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So, Julian took a look at the brackets (from afar, through this site) and called “that’s a bit heavy looking”. I did a bit of thinking, and got the grinder out. The results are below:

 

IMG_2955I didn’t just chop into it. Oh no, I took some weights as well.

  • Original Weight: 380g
  • chopping 5mm from the outer face and changing the chamfered corner: 60g
  • polishing out the welds: 20g
  • chamfering the long edges: 10g.

 

 

 

So the end result is a reduction in weight of 24%. Worth the effort for a few minuets work. Now… to the personal diet.

Shocker bottom brackets are finished – part 1

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IMG_2952
here are the two brackets. Each is 6mm thick to give strong support to the bolt – it’s not rotating but being shoved backwards and forwards. If you don’t use a decent thickness of steel, the holes will oval in no time and the bracket will lose it’s precision and things will rattle about.

The shocker has a 1/2″ spherical bearing in there, and will be coming in at an angle of about 40 degrees from the vertical, hence providing some back gusseting support.

 

 

IMG_2953

Also, the back plate was 2mm going onto 6mm steel, so needed a little careful welding. I made a mistake on the first one (which you can see above on the right – the fillet is too big). I was running 95A which is good for getting a good puddle up on 6mm steel with a 1.6mm rod. I forgot to take it down to 85A when putting the gusset in (2mm corner fillet). however, I spotted my mistake and this side here is the result.

 

Tomorrow, I pick up some more argon and then these will go on the car.

 

I have my new wishbone receiving brackets

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Here they are. the gap between the bracket to receive the spherical bearing is 1/2″, and the width of the bolt is 7.9mm, and there’s a few spherical bearings that nicely fit in here. What bugs me isn’t the price of this (£56 per bracket) but the fact that they have been used. I wasn’t expecting to buy used when they’re advertised as new.
IMG_2804

These brackets are a great option to receive the wishbones and of course can be height adjustable.

 

That’s another kilo out of the weight

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cross-member

Do you see that yellow arrow? DO YOU SEE IT? Well, that plate has been cut out right up to the engine mount brackets. I’ve done the same on the other side. That’s knocked 1.2kg out of the weight. I’ll make a CF flat plate (with a core) and bond it on to the bottom of the chassis facing up over. I’ll get more strength and have a lots of weight out.

Welding up the holes

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I’m welding up every hole in the chassis. I need to do this for two reasons:

Firstly, when I have it sandblasted any holes will allow the grit to get into the chassis and add weight. Secondly most of what I’m going to be attaching to the chassis in future it will be bonded on not welded on. So I may as well add some strength back to the chassis and fill in the holes.

IMG_2312

 

Resin to cloth ratio by weight

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IMG_2088.JPGIMG_2087.JPGSo, here are the two sample pieces, as mentioned previously in this post. They’re rough and ready, and not pretty to look at. What’s more, I had an infusion issue so there’s more air in the part than I would want.

However, it’s worth looking at the following dry weight calculations:

Part Final Weight Dry Weight Diff % Resin
with Veil [1] 136 103 33 24.26%
No Veil 144 110 34 23.61%

So, the lesson is that the part absorbed about 24% resin, excluding that retained in the infusion mesh, pipework, etc. It is also very important to note that the 10mm core is cross-drilled every square inch with a 2mm hole and has resin channels scored in the underside to allow rising to flow over the other side of the core. this will have absorbed some resin as well, which won’t be there if a core isn’t used.

Next post, I’ll get these under the microscope and you can see what the bubbles look like. If I can find a text-book infusion part then I’ll compare against that to see what gets left behind when the job’s done properly.

[1]The veil part is an experiment I ran with a piece of polyester veil under the facing layer to see if it acted as an air-removal medium to make the facing layer more cosmetically pleasing. Due to me cocking up and getting air in the infusion, I have no idea if it would have worked. It certainly didn’t work for me as a backing layer (as advertised). it absorbed far too much resin, was a pig to wet out and didn’t easily go into corners, leaving bubbles behind the gel-coat which have to be repaired.

How much will my tub weigh?

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So, based on the sketch I made on the white board (below), I need to calculate just how heavy the tub will be. The main reason I need to calculate this is to be sure the 19kg I’ve taken out by chopping out all that steel and removing the ally panels isn’t then replaced by even more carbon.

 

 

IMG_1007.JPG

 

 

 

 

 

 

 

Method

I made a trial part, consisting of:

  • 4 * 600gsm carbon (2 above the core, 2 below)
  • 2 * 200gsm e-glass (1 above the core, one below)
  • 1 * 300 gsm aramid (on the bottom, facing the tarmac)
  • 1 * 300 gsm carbon (on the top, to look pretty)
  • 1 * 10mm thick closed cell foam for the core (in the middle)

The layup is symmetrical around the core, apart from the aramid on the bottom and the facing carbon on the top. I have discounted the weight of clear gel-coat applied to the finished part (assume 1kg at the end).

The part measured approximately 103mm * 204mm, and weighed 130g. This meant a unit weight of 0.006 g/mm2.

From this, I fed the dimensions of the panels above into my CAD package. Given a surface extruded to 1mm depth, it will tell me the mass of the panel, to a bazillion decimal places.

Conclusion

Part count Unit Weight Total Weight Running Total
Tunnel Side 2 2.37 4.74 4.74
Tunnel Top 1 1.16 1.16 5.9
Back 2 1.0375 2.075 7.975
Base 2 2.7 5.4 13.375

So, if I go for this, the new tub will weigh 6 kg less than the original steel work.

Assumptions

  • 10mm closed cell foam is used uniformly. This won’t be the case – the sides do not need a 10m core – I will probably go for a 3mm core.
  • the base, back and top of the tunnel need to be strong in bending load, the sides need to be strong in lateral load. As such, I can use a thinner (or even no core) for the sides. I think I will save 1kg there.