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Mid engine Ducati build (Exo-Duke)
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Author:  beast02 [ June 8, 2021, 10:16 pm ]
Post subject:  Re: Mid engine Ducati build (Exo-Duke)
Some pictures to support my last update. Things have progressed a little more from here but haven't taken snapshots and resized them yet.
Author:  Beelzeboss [ June 9, 2021, 12:29 am ]
Post subject:  Re: Mid engine Ducati build (Exo-Duke)
How thick are you planning on making those rear suspension plates? (The ones with all the holes in them)

As drawn I don't believe they'll be even close to strong or rigid enough unless they're so thick that it defeats the purpose of the holes. Have you considered making that piece from box section, similar to the front of a Locost? The lower suspension pickups are also placed mid-span on that member, which is not ideal, as the lower control arm feeds much more load into the chassis than the top one (ignoring the bellcrank at the same point). That point should definitely be triangulated.
Author:  rx7locost [ June 9, 2021, 8:49 am ]
Post subject:  Re: Mid engine Ducati build (Exo-Duke)
I don't usually have much to say about other's designs since I can't see inside your head to see your vision. I do see a few things, mostly related to reaching your goal of 800#. you have big steel where it isn't needed. the first is those big tubes running down the center of the car. Space frame cars don't need that extra weight IMO. You also have excess pieces that could be shortened and/or simply removed. Every oz must be considered in order to meet your goal. For some inspiration, I would recommend you take a look at some Formula Vee designs where the minimum weight is now 1025 pounds with driver.

Is this a street car or a track-only car? If a road car, most states have a rule that the chassis or any other part of the car cannot hit the ground if the car is resting on one rim. I see your lower chassis rails do not meet that requirement as drawn.

I see most all new posts and enjoy seeing others' visions move along. I look forward to seeing yours completed. :cheers:
Author:  beast02 [ June 9, 2021, 12:36 pm ]
Post subject:  Re: Mid engine Ducati build (Exo-Duke)
Thanks for the design feedback all! Much appreciated when you sit working in a tunnel!

For the weight i'm ok with 1000lbs and figure it is more realistic as safety and future iteration might require additional beef. I've toyed with the idea of fitting a Tesla model3 motor in the back and making an electric version (though this car was inspired by a Ducati at a stop light sounding so good). As designed right now there are 3 'box' sections that comprise the chassis, the outer sills which are more of a triangle and then the central tunnel which acts like the spine. I'm still in the editing phase, so some tubes may go or move including the 1/2" tubes giving the trellis look (like a Ducati).

Good input on the rear member. This is a concept i've drawn up, it's hard to see but about every 2 holes has a 1" dia tube along with there would be boxing in of the structure around the suspension points. I have yet to trade this with a simple welded tube structure. The pickups as depicted have doubler plates as well to increase thickness.

I'm not sure I understand the comment on the single rim touching the ground/chassis body can't touch ground.
Author:  rx7locost [ June 9, 2021, 2:11 pm ]
Post subject:  Re: Mid engine Ducati build (Exo-Duke)
Here is one reference from https://apps.leg.wa.gov/wac/default.asp ... 204-10-036.

4.6.h. A modified vehicle shall have sufficient ground clearance between the vehicle body chassis and steering components and the road surface on which the vehicle rests so that it will be able to be in motion on its four rims on a flat surface with no other parts of the vehicle touching that surface.

Other states have similar requirements. I seem to remember it was a requirement for resting on any one wheel rim with the other 3 on the tires. The above seems to indicate it is more stringent requiring all 4 corners on the rims. Whether you would have to meet this or not, depends on your state's requirements.
Author:  Beelzeboss [ June 9, 2021, 6:48 pm ]
Post subject:  Re: Mid engine Ducati build (Exo-Duke)
rx7locost wrote:
Here is one reference from https://apps.leg.wa.gov/wac/default.asp ... 204-10-036.

4.6.h. A modified vehicle shall have sufficient ground clearance between the vehicle body chassis and steering components and the road surface on which the vehicle rests so that it will be able to be in motion on its four rims on a flat surface with no other parts of the vehicle touching that surface.

Other states have similar requirements. I seem to remember it was a requirement for resting on any one wheel rim with the other 3 on the tires. The above seems to indicate it is more stringent requiring all 4 corners on the rims. Whether you would have to meet this or not, depends on your state's requirements.

The obvious dodge that springs to mind is to go through the inspection with 19" wheels and paper thin tyres, so it barely drops at all when a tyre is flat :lol:
Author:  beast02 [ June 14, 2021, 12:34 pm ]
Post subject:  Re: Mid engine Ducati build (Exo-Duke)
Beelzeboss - thanks for that reply, helped me understand the rule much better :roll: . After reading the law I still wasn't quite sure what was being stated.

I raised the ground clearance an Inch which brings it close but should work, as well as should make it more streetable.
Author:  beast02 [ June 30, 2021, 12:59 pm ]
Post subject:  Re: Mid engine Ducati build (Exo-Duke)
Now that I had the steel tube all modeled up and almost ready for ordering, I decided to try another design concept to see how it looks and what the resulting weight is. The new one is simpler with less tubing but larger diameter. It also does away with the .5" truss tubing on the first design which I always worried would be a pain to actually make and weld.

Old concept weight ~145lbs , 74 tubes excluding the 1/2", 119 with them
New Concept weight ~135lbs , 53 tubes

Not a significant weight savings, I could probably add some cross bracing in the floor which would bump up the New concept closer to 140.

Old Concept in color, new in grey. Note the rear suspension weldment needs updating and will likely change a bunch once I model up the diff carrier.
Author:  Miatav8,MstrASE,A&P,F [ July 1, 2021, 7:37 am ]
Post subject:  Re: Mid engine Ducati build (Exo-Duke)
I see Chuck mentioned regs but this isn’t going to be titled and registered for road use. Too many wheels for the drivetrain used and not a replica of a road legal vehicle but I have not checked regs in a while.

Assuming around 3:1 with a 530 chain to a diff, it doesn’t look like there is enough room in the render between the firewall and engine to clear the driven sprocket. You could eliminate the chain entirely by rotating the engine 90 degrees and coupling to a light duty, short pinion auto diff. The diff and engine would be mounted on the same frame to maintain alignment. This frame could then be isolated for vibration if needed.

Render is missing a left rear lca link for the reverse A-arm. I agree on not using ½ inch tube. Less rigid and moves around a lot when welding. Not even suitable for bicycles imho/e. If you want to go as light as possible, consider composite construction with glass over foam or use aluminum skinned coremat panels for structure.
Author:  beast02 [ July 2, 2021, 5:06 pm ]
Post subject:  Re: Mid engine Ducati build (Exo-Duke)
There should be enough space, what the renders weren't showing is the engine placement which has the front cylinder protruding into the cabin.
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