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Would anyone mind lending me a hand.

5K views 8 replies 4 participants last post by  LSfan70s 
#1 ·
Could you guys help me with a project I am exploring. I would like to make a CAD model of a composite panel, monocoque chassis based upon the GTM. The same type of chassis that the DP1 http://www.dpcars.net/dp1v8/da.htm and Mosler MT900 http://www.mosler.co.uk/mosler/technology_road_bodywork_chassis.asp use.

I am toying with the idea as I have access on an hourly bassis to a panel cutting CNC. I use it frequently in complex case work in the custom homes I build. A blind dado’d cabinet case utilizes the exact same construction techniques as these aforementioned car chassis. My case work is done to a precision of +/- .003 and since these parts are self indexing and self squaring I can have $10/hr untrained labor assemble the most complex and demanding woodwork. In the case of the car chassis the tennons and mortises are epoxied together and heat cured.

The fact is I could likely produce a monocoques that is far more precise and more rigid then a tube frame for a more reasonable sum then one might think. I am under no illusion that there is any great demand for a new chassis for the GTM but it offers me a design starting point from which to explore with a ¼ scale model made of rigid foam panels as an analogue to the full scale thing. It may be that I can provide chassis for other low volume or start up kit makers. I am 90% sure I could produce a chassis for less then an unskilled person could hire out to have a tube frame built.

So if any one with a car would be so kind and indulge me with some dimensions.
Primarily I need the internal cage (as measured from the outside tube to outside tube). Rake of the windshield. Then I would need the vette fuel takes or I can just invent one. Then I can model the suspension. I can model one of my own or use the GTMs. From there I can work out rear sub frame and front box.

I realize that it may be a bit of work and not really practical for anyone here but any help would be appreciated.

As an example this is one I put together as a learning exercise to see what dimensions I really need. This is not based on anything just pulled some dimensions out of my *** and it is by no means complete just a sketch and I have not modeled the roll bars that span from the rear upper deck to the front upper deck. That provides the final bit of rigidity and makes it essentially a closed box made of I beams and closed boxes.



 
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#2 ·
VERY ENTERPRISING....

I was looking at dismantled Mosler today.....quite ordinary in many respects especially for $300k....this one was being retrofitted with a 1000hp engine package from Katech.

Rod Trenne, the guy that did the mosler chassis is a mate of mine...

Why not buy a GTM and use the body and sell the chassis on to someone ...that way you would have everything you need...??
 
#3 ·
Well this is more to see if I can put to use some of my resources and skills that are being under utilized in this current real-estate environment. My guess is that my market would be to low volume kit makers of GT40's or even someone wanting to do a 1 off show car. Once I program in the first body, changing it to different applications becomes a matter of hours. I could have a new chassis in code in about 4 hours and have it cut the same day. I could likely get it assembled for first cure in a total of 3 or 4 days. I just need a place to start dimension wise to produce the 1/4 scale mockup.

I really got the idea when we were making some really complex cabinets recently that were 10' tall. The whole unit was 16' wide and 10' tall and made of 64 pieces. The whole thing was out of square (as measured corner to corner) by less then a 1/32". The laser I use only goes to 32's and it was either 0 or 1/32 each time I shot it. You simple can't do that unless you assemble with cnc cut blind dado's. That got me thinking about how easy it would be to buy 1" nomex core panels form Teklam and cut them and assemble them to any thing I desire. In fact it is easier since composite panels are dimensionally more stable and less subject to atmospheric influences. Normally I have to account for the swell and shrink in the panels at the time of cutting.
 
#6 ·
Aren't there current problems with aluminum/ honeycomb panels delaminating?
I had not heard of that problem with the few cars that use this. These panels are most often used in aviation and again I had not heard of any FAA recalls for this.

Gt40- bodys are for sale in the $5-6K range.
I believe that is exactly the range I could produce this chassis for. Inventor says it weighs in at about 85lbs right now. My FEA shows the stress and flexure points but does not yield any empirical data. I will need a different program for that.
 
#5 · (Edited)
I have been using Teklam stuff as you know, I think you saw some at my shop when you were there...correct?

Teklam is good stuff...not inexpensive but good.

Once you start making the welded steel structure for the rear you may find the price jumps pretty quickly ...especially once you start needing different jigs to accomodate a new set up to maintain the same level of accuracy that the honeycomb allows......and may take more than the 3-4 days the cockpit section takes....

What about your suspension geometry changes when someone uses a shorter/longer wheelbase that your optimum design.?...just playing devils advocate here as I get asked these questions daily...as you can imagine..

Yes they do delam. quite easily as has been proven in wet conditions in offshore race boats...but for the correct applications they are great...many planes use this material for floor section/bulkheads etc but they do "life out" after being stressed..much like a carbon chassis does.
 
#7 · (Edited)
Once you start making the welded steel structure for the rear you may find the price jumps pretty quickly ...especially once you start needing different jigs to accomodate a new set up to maintain the same level of accuracy that the honeycomb allows......and may take more than the 3-4 days the cockpit section takes....

What about your suspension geometry changes when someone uses a shorter/longer wheelbase that your optimum design.?...just playing devils advocate here as I get asked these questions daily...as you can imagine..



The front box and mounting points are easy to alter. In a matter of minutes. Changes you make to it are then applied to the other parts of the assemble unless it causes a constraint problem, then you edit that part. But yes the rear really should be a welded structure to mount the motor and suspension and that can't be just pumped out.

Ultimately the beauty of this is it is not one size fits all. One could be given the cockpit dimensions and the suspension geometry. I need the upright KPI and rod end mounting points, control arm length, roll center. From there you could model the suspension and fill up the space in-between with the chassis.

Don't mistake this for some naive belief this is easy. Actually the chassis is the easy part to design. Establishing the harpoints, tolerances and motion conflicts, fitting all the STUFF in the samll area that is left and not getting sued. Now that is the hard part but you probably already new that. :) That is why I would never build my own car, much less 7 different ones.
 
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