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Post by jacksdad on Oct 20, 2016 21:57:40 GMT
Yep it's pretty rigid there is a 4mm polyurethane sheet clamped between the beams and the chassis clamps similar to the rigidity of the poly bushes that will soak up a bit of vibration I hope but it is very solid
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Post by jacksdad on Nov 10, 2016 12:34:09 GMT
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Post by jacksdad on Nov 15, 2016 20:20:36 GMT
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Post by jacksdad on Nov 16, 2016 18:25:39 GMT
I'm having a little crisis of confidence in my battery case mounts Now that i have made them up the front 2 cases feel really heavy at 60KG and i'm clamping half this weight to the steering rack : ' which i thought looked like a strong peice of steel tubing, does anyone know how thick the steel is as i haven't taken it apart, the clamps are close to the main rack support brackets with big m12 bolts so this seems ok i was planning to rest the case on some foam so some of the weight will transfer to the floor panel but would value other peoples feeling on this
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Post by pocketrocket on Nov 17, 2016 0:44:20 GMT
I'd be more concerned about the mounts, that are on the rack. They're 30-40mm?? offset from the centreline of the rack housing. So there will be a fair bit of leverage on the rack mounting bolts, mounts & chassis mounting plates
It may not be a problem, but it will be a hell of a way to find out if/when it is
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Post by jacksdad on Nov 17, 2016 12:59:03 GMT
Umm good point I will check the geometry could maybe make up a brace peice to counter that moment
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Post by jacksdad on Nov 17, 2016 17:20:36 GMT
So I have done an rough stress test on this bracket if we assume that each bracket supports at max half the weight ie 30 kg then using the limits set in some countries for max up and down G if 4G this then equates to 120 kg so I applied a direct weight of 100 kg (me) and then jumped up and down on the bracket with not a hint if movement so I reckon probably ok
I will try modelling the bracket in solid works as well
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jack
Junior
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Post by jack on Nov 17, 2016 23:00:42 GMT
Dad asked me to try modelling the rack bracket in solidworks to see if it is strong enough to hold the battery cases, i have not done this much before but this is what i did, i fixed the edge that is welded to the chassis and applied a downward force at 4G ie 4x the weight of half of the battery case or 1200N over the area of the contact of the rack to the bracket and this is what we got: So seems ok with stresses within the yield stress even at 4G and a FOS of 1.4 -i;m assuming i have set this up right if there are any experts please let me know what to do otherwise and dad did jump up and down on the bracket and it didn't bend and he has had a lot of pies!!
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jack
Junior
Posts: 76
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Post by jack on Nov 17, 2016 23:07:23 GMT
actually not sure i have the bracket quite right its welded along the front will correct and post back later
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jack
Junior
Posts: 76
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Post by jack on Nov 17, 2016 23:59:19 GMT
this is more like it: stronger than my previous (wrong shaped bracket) at 4G stresses well within yeild and FOS 2.4 at 4G
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Post by pocketrocket on Nov 18, 2016 1:02:50 GMT
My description might not have been very good. I was trying to describe the brackets that are on the actual rack, rather than the brackets on the chassis. On the rack, one mount is cast aluminium. That will probably be fine. But the one at the other end is a pressed up piece of metal, with a spot weld or 2 holding it onto the rack tube. This one was the one I was thinking might be a drama, if any.
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Post by mawdo81 on Nov 18, 2016 9:07:29 GMT
Apart from anything else, are you actually sure the bracket is effectively the corner of a hollow cube? I thought they were open L shapes? The lack of the additional plane will have a major impact on its weight bearing capacity.
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Post by jacksdad on Nov 21, 2016 11:57:07 GMT
Yep definitely looks like that ie the corner of a box, Pocket I understand now will try to model the bracket could be tricky as its an unusual shape i think its a continuous weld and the shape of the bracket holds the weight more than the weld anyway but will try to model it feels very solid with me jumping up and down on it though
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Post by pocketrocket on Nov 22, 2016 3:12:48 GMT
Just something else worth considering, regarding clamping to the steering rack;
I'm not sure what your plans are with the car, but if you're planning on doing any kind of motorsport (track day, hill climb, timed sprints etc), its certainly not uncommon for the car to have a collision with a crash barrier or another car etc. When this happens, its also not uncommon for the rack to get damaged. Should this occur, the possibility of damage to your batteries would be almost guaranteed. If they're expensive, I'd look at isolating them from the rack (not mounting to it). If they're relatively inexpensive, then this probably doesn't matter. Also, not know much about electrickery, in an impact, and the batteries bang together, can this cause fire??
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Post by jacksdad on Nov 22, 2016 9:16:28 GMT
Yes that is a good point, do you know what usually happens to the rack in this kind of crash ?? The batteries are supposed to be safe from penetration and not catch fire: shiftev.com/index.php/shop/batteries/battery-lithium-ion/1906-detail.htmlBut they are v expensive there is about £2K of batteries in the front compartment, I don't currently plan to do any racing. So i think i will stick with the current support system and get through testing then i might come up with a new steel support frame bolted to the chassis that holds the cases doesn't rely on the rack and offers some shielding from potential damage in a crash.
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