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Post by joshuacbassett on Dec 15, 2011 22:12:45 GMT
Hello all,
Just talking through some ideas for a cartie with my brother. upon reading the cairngorm technical specs it says that glass, perspex i.e. materials that shatter plus any material that could harm driver or spectators in a crash.
What does this leave? We were thinking about fibreglass but that rule seems to rule out every material and anything 'could' injure someone.
Thanks
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Post by grahamk on Dec 15, 2011 22:27:47 GMT
I think this is referring to screens. I use PETG or Lexan
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Post by Scottish Cartie Association on Dec 15, 2011 22:47:10 GMT
Hello all, Just talking through some ideas for a cartie with my brother. upon reading the cairngorm technical specs it says that glass, perspex i.e. materials that shatter plus any material that could harm driver or spectators in a crash. What does this leave? We were thinking about fibreglass but that rule seems to rule out every material and anything 'could' injure someone. Thanks The "no glass, perspex" etc wording is common to most rules. Acceptable materials that have been used include; - corrugated plastic sheet (e.g. correx)
- plywood
- aluminium
- fibreglass
- carbon fibre
- duct tape
- newspaper and chicken wire
- canvas
This is by no means a complete list. Unacceptable materials include; - perpex
- glass
- depleted uranium
- barbed wire
- lego
- wasps
Again, this is by no means a complete list. Hope that helps.
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Post by brillo451 on Dec 15, 2011 23:56:09 GMT
Stephen Surely dead wasps would be a good material as this would give the nasty things a purpose in life... (well in their death) I am sure a wasp composite would also be very environmentally friendly material...LOL
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Post by Scottish Cartie Association on Dec 15, 2011 23:59:36 GMT
Dead wasps might be acceptable at the discretion of the scrutineer. Live wasps, however, are a definate fail.
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Post by leew on Dec 16, 2011 10:08:51 GMT
There goes my idea of building a cartie entirely from lego..... With some depleted uranium to bring it upto the weight limit.
Maybe mixing dead wasps with epoxy would yield a matirial even stronger than CFRP?
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Post by leew on Dec 16, 2011 10:12:33 GMT
Would steel sheet be Acceptable for a body? or would it be classed as ballast?
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Post by Scottish Cartie Association on Dec 16, 2011 10:23:43 GMT
Would steel sheet be Acceptable for a body? or would it be classed as ballast? As with any material, it would depend on whether you were trying it on or not. If it's relatively light gauge then it'll probably be OK. If it's thick enough to stop a round from a 30mm cannon, it probably isn't. It's impossible to formulate rules to cover every possibility, but the bottom line is this - if you know you're trying it on, then so do we. Just gonnae no dae that.
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Post by azuma on Dec 16, 2011 20:36:57 GMT
Lee we used a Sheet of galvanised steel for Naecost 1.4- 1.6. Cheaper and than ali, but will ding just the same. When covered with a vinyl can look good and need not be expensive. Naecost 2 went back to ali, for weight saving, but for durability, there are some good "plastic" materials out there, including HIPS (High impact polystyrene) and correx Or its GRP or CF excellent for flowing body shapes and durability as well. And for those that need it "Just gonnae no dae that" translates "divvint de it, man"
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Post by peasnbarley on Dec 16, 2011 21:25:35 GMT
I have been looking at various ways to make a 'safer crash resistant cart' using energy absorption dampers and crumple zones. I understand the Apache Strike helicopter design was based on the phonetic 'CREEP' C- Container = Solid protective cockpit R- Restraint = Pilot restraint via harness, helmet, seat, and floor mounting. E- Energy absorption = Ability of structures to attenuate crash forces. E- Environment (local) = variable factors P- Post crash factors = Risk of fuel fire, explosion etc.
The ability to attenuate crash forces in the Apache is done with the landing gear, floor structure and the seats. The Black Hawk and Apache rely heavily on the fixed landing gear and seats to provide the required attenuation of loads for the 12.8 m/s (42 ft/s) design pulse. The gear alone were designed to handle over half of the total occupant energy in a crash with the floor and the seats absorbing the rest. The result is that very few pilots have been killed in a vertical crash.
Model tests I have undertaken seem to show that high speed roll over and nose over end crashes result in less cart body damage than do head on impacts mitigated with energy absorbent dampers. (However wheel damage in end over end and roll crashes is usually total)
The only reason I can come up with that less damage occurs in rolls and end on ends is the kinetic energy is being dissipated in momentary peaks rather than one short sharp impact. In other words the time is extended for energy dissipation. The wheels and suspension units bleed off considerable kinetic energy as does each momentary ground contact with various parts of the cart. Very unscientific tests on models I accept but there must be something there worth exploring further.
The Ginger Sheep crash is a good example where there were several contact peaks which resulted in only moderate damage and a driver walking away.
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Post by azuma on Dec 16, 2011 23:04:51 GMT
PnB - you are onto something there. Ideally bits on the outside of the carts should dissipate some of the energy in any form of accident i.e. deformable body parts, wheels etc should take some of the brunt of the energy before getting to the chassis and driver. BUT these bits should not pose a significant risk to the driver in the event they do hit something first. As far as I am aware none of us have the funds to build and crash carts to see the aftermath of accidents, but a little commonsense/guidance when building can go along way towards safety. There have only been a few serious injuries I know of in recent years, Roys accident at CSE2009, (carts are now significantly better) and Colin CSE2010, (again improved safety), but bad luck on that day. Most drivers have seen these and tried to improve their carts, which can only be a good thing. There have been a number of signifcant crashes over the years which have not done as much damage to drivers. Stephen Heape at CSE, King Peter at Catterline, Me on a number of occasions, likewise Iain and then the master of the wrecks Richard Stockdale. Good design, luck , or the type of crash, I don't know, but we walked away (ish) and lived to race another day. Carts are only going to get better, especially if we look at the ones which have survived and we build to at least aim to achieve similar standard. One thing CSE has helped to do. is to raise the bar on safety and most of us are trying to meet or go beyond the minimum. Which if CSE had not been here carts, would/may not have evolved as they have and accidents, at other events, may have been greater. I think what I'm trying to say, is the same as PnB, build your safety cell strong and use the outside bits to save you and don't sacrifice yourself to save outside the bits on your cart, they are expendable - drivers aren't.
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Post by peasnbarley on Dec 17, 2011 20:45:20 GMT
Hi Azuma the problem I found was the restraints imposed by build criteria in regard to providing sufficient crumple zone structures. Because of this I looked at hydraulic ram type dampers but in all the tests I conducted they only provided significant positive results in simulated speeds of 10 - 40mph. Speeds in excess of this consistently indicated the dampers were inhibiting bounce which resulted in damper mounting point failure and greater body damage to the cart. A longer piston stroke would possibly alleviated this but there is no room within the build criteria. I was prompted to post in direct response to lee's question on using steel sheet because in my opinion there is a valid reason to use steel sheet if it is there as part of the pilot's protective cockpit. I just didn't realise how very vulnerable the pilot is when sitting on a thin aluminum sheet floor.
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Post by azuma on Dec 17, 2011 22:58:18 GMT
One of the reasons we use a galvanised sheet floor, it can add to the rigidity of the main tub even if rivited. Also, if it does add any weight, its going to be low down. It is also going to protect the man bits from the tarmac more than thin ali, but thicker ali will be just as good, but a damn sight more expensive. Hadn't thought of using damped bumpers, but it is a feasible idea. Might just stick with expendable external parts though, we don't have masses of free weight to play with. Anyway PnB are you sticking with your current cart or building new?
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Post by kingkay on Dec 17, 2011 23:27:59 GMT
"expendable external parts "
legs yeah?
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Post by azuma on Dec 18, 2011 0:49:27 GMT
would make for a shorter cart
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Post by peasnbarley on Dec 18, 2011 10:52:13 GMT
Quite right Kingkay with three years hindsight my cart design and many others seem to consider legs as 'expendable parts.' I now 'know' the suspension units are the most likely parts to fail after the wheels and they are in close contact with my knees. In a unlucky rollover the floor directly below my arse is the most exposed, least braced area on the cart. Having done my little tests I don't think I would have the bottle to drive her again before some serious modifications and it is probably easier to start a new build.
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Post by Organgrinder on Dec 20, 2011 11:11:21 GMT
I have been looking at ways to give protection in the event of a head-on impact, which as PnB has already suggested is likely to be much more dangerous than a roll-over in the sort of carts we are all running at the moment. I agree about stiffening the floor area, as this will result in a stronger "survival cell".
I have had a look at the crash cushions that are fitted to the rear of motorway maintenance trucks. These units are designed to stop a car from 70mph in about 1.5 metres, protecting the workers in the truck, while minimising injuries to the occupants. Pretty impressive performance.
The crash cushions appear to be a simple aluminium honeycomb, contained in an aluminium shell. Probably very similar to the materials that used to be used in formula race cars.
The main problem we have with protection in frontal impacts is that we have very little space in front of the driver's feet to install any meaningful crumple zone, while complying with rules that restrict overall length to no more than 2.5 metres. Realistically, for most of us, this only leaves about 500mm in front of the driver's feet to play with. However, that space could be better used and I am experimenting with using empty coke cans encapsulated in builder's foam to make a sacrificial collapsible nose section, that could also be readily shaped with nice compound curves. Skinning this with grp and separating it from the footwell with a bulkhead would (I think) give a cheap and reasonably effective crumple zone that would protect the driver's feet and the chassis of the cart.
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Post by Scottish Cartie Association on Dec 20, 2011 13:09:35 GMT
This is not entirely without precedent, as Greenpower have included a requirement for energy absorbing materials in their 2012 spec' It's worth checking out their build spec and technical handbook ( www.greenpower.co.uk/node/187 and www.greenpower.co.uk/node/188 respectively), as there are some very useful tips in there which are directly applicable to cartie racing. The ironic thing is that I almost included something similar in the draft spec' for CSEx2012 as well, but didn't in the end becuase of the anticipated howls of complaint . I think it's important to remember that we want to keep the technical requirements as low as possible to make it easy for people to get involved. It probably also worth mentioning that making carties better at crashing is probably less important than making them less likely to crash in the first place. Many carties and drivers are operating at, and sometimes comfortably beyond, their limits in terms of handling. What works at 40mph might not necessarily be so good at 60+mph, and the margins for error are extremely small. Steering, stability and brakes would be the areas I'd be concentrating on, and I'd want them absolutley spot on before I started thinking about crumple zones.
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Post by Organgrinder on Dec 20, 2011 14:40:20 GMT
Stephen's point about prioritising active safety over crash protection is well made. However, we are all amateurs and for most of us the only way to find out whether a cartie handles predictably and in a benign manner at 60+ mph is to run it at those speeds, thus risking a crash and serious injuries to establish whether our theoretical improvements work in practice. I remember (and still bear the scars from) a testing crash I experienced before racing at Belchford in the good old days before we shortened the track and introduced chicanes to keep speeds in check - believe me, crashing at 55mph into a ditch at the side of the road without seat belts and a roll cage was not funny! From that point on I became much more interested in passive safety and to be fair we have seen huge advances in the last few years. CSEx may be seen by some as driving this process, but many of their recent rule changes have already been pioneered by other organisers. They have also brought in good, cheap and simple innovations that have improved the chances of walking away from big crashes. Adding protection at the design and construction stage is bound to be easier than doing a retro-fit job with a broken arm!
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Post by peasnbarley on Dec 21, 2011 10:33:48 GMT
organgrinder: Please keep us posted as to how the Coke can experiment turns out as that one was on my try out list. I think you should be careful as to the ratio of cans to foam filler because the foam will provide great rigidity to the wall structure of the cans, or transversely partially collapse the wall of the can. I agree with Stephen thoughts it's better to prevent an accident than to plan for one but even with good handling characteristics shit happens. I believed my cart was well up the list of 'safe good handling carts' but now have serious concerns that with hindsight I could have done a lot better. I don't want to start any arguments but if the problem of providing sufficient front and rear crumple zones is space within the build criteria would that not be a reason to look at increasing the allowed length of carties some time in the future? To be fair the existing length criteria would provide just about sufficient space at the front end if the driver's position was more upright but that stuffs up the aerodynamics so I am off down to the S.T.F.U.C Club for a Morgan's Spice and wish you all a Merry Christmas and a Happy and successful event filled New Year. ;D
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