mx5cartalk.com

Hi all,

Well I have ha d my 89 Eunos now for around 5 months and while I have loved the driving experience, it has come the time to start the modifications.

My garage thread will be up in the next few weeks (waiting for stuff to get back from powder coaters, etc) but in the mean time I thought I would throw up some of the things I have been working on.
I have been working closely with a good mate of mine who is getting his fabricating business of the ground - 'ATS' (Austin Technical Services). He originally comes from an engineering background as well as being a car nut so he has great insight into fabricating components to meet the required job.

Recently we have been working on tow hooks (among other goodies ) and have came up with something that not only looks the part but performs excellently as well as being lighter then the standard OEM brackets (this was also the case in mild steel mock ups, however many other materials can be used which will further add to this weight reduction).

Front:


He was then able to do a Finite Element Analysis (FEA) on the tow hook to test the load strength that this design would allow

This diagram shows a fixed static load on the tow hook with the full weight of a MX-5 Na, as you can see there is only mild deforming of the tow hook with this load force. This level of force would NOT be seen from any standard rescue on a circuit.



Rear:


Again showing a fixed static load on the tow hook of the full weight of a MX-5 Na


So at the moment we are looking into whether there would interest in such a product, before sending mine off to be cut.
Material at this stage is a mild steel (but again can customize to fit need) will come powder coated RED (other colours can be chosen however may incur additional fee)
The price of the product at this stage would be:
- $38 Front
- $42 Rear
or the pair for $70
Plus postage - located Brisbane South

All products would come with a Material Certificate, a FEA Report and a isometric Auto-cad drawing.

An EOI can be done here through PM or posting.

Thanks guys,

Benn

sorry mods if this was in the wrong section

already available from many manufacturers

Whilst you are correct project.r we could say the same for any product and with your logic there would be but one shop where every product is sold... So while i agree and understand there are probably many many different places that sell a product similar to this one, i still found the need to make one that would meet ALL of my needs (lightweight, strong, looks good and available for a reasonable cost) therefore there must be a gap in the market where a product such as this would sit.

Benn

One suggestion for the tow hooks, to be CAMS compliant they must be able to accept a 40mm OD cylinderical test object (40mm OD pipe). So make sure the hole for the front hook is a minimum of 40mm diameter, I would recommend 45mm diameter

A lot of the guys here that would be looking for tow hooks do track days so you might as well make them compliant to the organisers' requirements.

thanks for that Matt, I had not noticed the error in size for the front hook, Rear is 60 so will be fine.

Will pass on changes

Benn

Have you considered lateral loading of the tow hook for when the tow strap can't pull in the same plane as the tow hook? This is when the tow vehicle can't be perfectly aligned with the bogged vehicle. This situation is quite common and I've seen many a tow hook fold up into rear valances and front bumpers. Also, forces associated with retrieving bogged vehicles can exceed 1g.

Regards,
Danny

Lol. What danny said about the 1G thing.

More like 3 G.. or 5.

Dann

Don't disagree with your points, but at the end of day you can't design for every situation. This product is design to do one thing well (i.e. be lightweight and sufficient to recover the vehicle in 90% of situiations i.e. gravel sandtraps etc).

Both tow points will handle fairly significant lateral loading, the front in particular will handle loads in pretty much any direction.

A key point to note is that the "FEA" utilised 9800N of loading and neither recovery point failed.

The following website ( http://www.webtec.co.uk/tech/equations/ ... of_rolling )
shows a table of forces to add per 100kg of car weight. I.e. if car sitting on concrete it would require 15N x (900/100) or 135N to move the car.

So say put the car in worst case scenario deep mud, it would take 1342N to move the car.. This tow hooks are rated to 9000N+.

In any case, either tow point would support that increase in mass/force.

In the case of a rescue being over 1G look at it like this:

3 G is 3000kg x 9.81m/s

thats i.e. 29340N of force.

To achiece that level of force you would need a 3 tonne vehicle travelling at 35 km/h trying to recover an mx-5 and coming to a dead stop...assuming that 100% of the force of the vehicle would be absorbed by the tow point and the car did not move an inch.
So highly unlikely...

Anyway guys I hope this answers some questions, happy to answer any other quires.

Ben

Benn wrote:Both tow points will handle fairly significant lateral loading, the front in particular will handle loads in pretty much any direction.

Hi Ben, the x-x section modulus and the y-y section modulus of each of those tow points are significantly different. Has FEA been conducted for the tow points with an out of plane force?

Benn wrote:A key point to note is that the "FEA" utilised 9800N of loading and neither recovery point failed.

The following website ( http://www.webtec.co.uk/tech/equations/ ... of_rolling )
shows a table of forces to add per 100kg of car weight. I.e. if car sitting on concrete it would require 15N x (900/100) or 135N to move the car.

This is true when the towing force is purely in the direction that the wheels will/can roll in. However, as soon as the towing force is not collinear with the direction the vehicle can roll in you have a force component that is trying to drag the vehicle sideways. For instance, if the towing force is angled at say 30 degrees from the centreline of the vehicle, the lateral component is then half of the towing force. In my personal opinion it would not be unforseeable for a tow strap to be utilised at this angle.

Here's some more applicable information on tow/retrieval points from an industry expert: http://www.arb.com.au/getting-started/ask-arb/recovery/Recovery_points.php

Lastly and more importantly than all of the above, I strongly recommend that whoever is the designer/manufacturer of these tow/retrieval points have Public and Products Liability insurance to ensure that they are not fully exposed to potential Darwin Award nominees.

I hope this information helps.

Regards,
Danny

Pistols at dawn?

I agree with Danny on the public liability insurance and would raise a professional indemnity as your work has a design component and while we are at it is the IP being used yours or could you be infringing a copyright or patent.

Maybe you could target the looks department and not for actual use? Yes there are lots of similar products like yours out there, but what makes your so different for people to buy? Cost is one thing, desired use is another and few people would even think (or care) about the safety aspect.

Have your designer do the modelling on side forces and post the data? Warning people before they purchase it that the pull angle must not exceed XYZ deg. Offer free tow stickers with them. Also possibly not mix a 'I just purchased a MX5' and 'modding soon' with a by the way I'm also selling this product. Separate the thread and put the tow hook in the for sale.

Hey just my opinions...