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  #101  
Old 06-04-2010, 12:52 AM
Duncan Duncan is offline
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Default Re: Custom monocoque trike

On a more serious level I rode my two wheeled recumbent bike with a load of luggage on the rear carrier and it went into a horrible torsional resonance

Even if you don't have the twist from the tires if you are too flexible in torsion you can suffer!!
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  #102  
Old 06-04-2010, 06:15 AM
TomA TomA is offline
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Default Re: Custom monocoque trike

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Originally Posted by toddshotrods View Post
The best bet for the combined goals, as stated, it it to first invest in some really good software with FEA capabilities, and spend more time learing that software than actually trying to build. He could then model his ideas, run an analysis, and see what the results would be. Once he modeled the main monocoque chassis attaching a 200-400 pound pod to it, with different methods and seeing where the stress and resultant failures, would be relatively simple to do. Advanced engineering is a mouse click away in the 21st century.
I actually disagree. That's a huge investment in time and software with a very uncertain outcome or payback. The project is already cash-strapped. Its just too much to bite off and risks getting anything made at all.

Moreover, just because you can model something in 3D and render the surfaces and even convince yourself that you've done all the necessary math, it still has to be built, and the process of making anything in the flesh is going to be full of surprises. That's my experience, anyway.

TomA
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  #103  
Old 06-04-2010, 06:34 AM
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toddshotrods toddshotrods is offline
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Default Re: Custom monocoque trike

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Originally Posted by TomA View Post
I actually disagree. That's a huge investment in time and software with a very uncertain outcome or payback. The project is already cash-strapped. Its just too much to bite off and risks getting anything made at all.

Moreover, just because you can model something in 3D and render the surfaces and even convince yourself that you've done all the necessary math, it still has to be built, and the process of making anything in the flesh is going to be full of surprises. That's my experience, anyway.

TomA
I think you missed my point. That it's a huge investment in time and software, is kind of my point. The stated goals of the project are beyond the scope of the amatuer, backyard, builder. They are more suited to a university that is pursuing the project as an engineeirng challenge. In that case the software makes sense because the point is engineering, not the vehicle.

As stated, the goals make the project impractical and potentially unsafe. It would be far wiser to spend the money on software, and learn something than build something that can potentially hurt himself and possibly others.

I think you also underestimate the capability of modern software. Properly modeled, they're not just a bunch of pretty rendered surfaces. A real solid model is an exact representation of a real-world part, and the computer does the math. That's how modern vehicles (and practically everything else) are designed. The computer shows a pretty picture of your model with various colors indicating stress, heat, whatever you request. Behind that picture is more math than a human could possibly accomplish in the same amount of time.

Gotta love technology...
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  #104  
Old 06-04-2010, 07:19 AM
TomA TomA is offline
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Default Re: Custom monocoque trike

Todd, I get all of that. Being CAD illiterate doesn't make me ignorant...

There's still a big and tedious difference between the model and the part. Take one tiny example- the motor end bell mounts on your roadster. Theoretically, this is a simple translation of your design file to a CNC file to the finished part popping off the mill- but it hasn't worked out that way, and it is still a surprisingly tricky thing to get something made, even with full digital control. You have many hours in it, and years of experience.

I'm not beating up on you, you've got tremendous skills and your builds are stunning, but you're all the way at the digital end of the spectrum, and that actually isn't how most scratch-built vehicles are made. Passenger cars, tennis rackets, everything else for volume manufacture, yes, but generally not one-off cars with minimal budgets.

My point wasn't that the digital design phase wasn't valuable or even essential, which on this project we probably both agree it is. I was just pointing out that all that work is just a prelude to trying to build the rendered design, and that can be very, very hard, especially when the modeling creates shapes and structures without regard to fabrication realities.

At the end of the day, I guess Darxus has to decide whether he wants to build a trike, or embark on a self-taught CAD/CAM engineering program.

TomA
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  #105  
Old 06-04-2010, 08:01 AM
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Default Re: Custom monocoque trike

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Originally Posted by TomA View Post
Todd, I get all of that. Being CAD illiterate doesn't make me ignorant...

There's still a big and tedious difference between the model and the part. Take one tiny example- the motor end bell mounts on your roadster. Theoretically, this is a simple translation of your design file to a CNC file to the finished part popping off the mill- but it hasn't worked out that way, and it is still a surprisingly tricky thing to get something made, even with full digital control. You have many hours in it, and years of experience.

I'm not beating up on you, you've got tremendous skills and your builds are stunning, but you're all the way at the digital end of the spectrum, and that actually isn't how most scratch-built vehicles are made. Passenger cars, tennis rackets, everything else for volume manufacture, yes, but generally not one-off cars with minimal budgets.

My point wasn't that the digital design phase wasn't valuable or even essential, which on this project we probably both agree it is. I was just pointing out that all that work is just a prelude to trying to build the rendered design, and that can be very, very hard, especially when the modeling creates shapes and structures without regard to fabrication realities.

At the end of the day, I guess Darxus has to decide whether he wants to build a trike, or embark on a self-taught CAD/CAM engineering program.

TomA
I think we're probably in near total agreement, just expressing it from different perspectives. I certainly didn't mean to infer that you are in any way ignorant - even with CAD. Your experience and wisdom are self-evident in your posts. I just didn't know if you were aware of how much modern software is capable of - on an everyday computer. My interest was more in keeping him safe. I suggested the software more as a means of safety (considering the technical issues he's proposing) than a cure-all solution.

I have more experience working with my hands in fabrication than I do behind the computer screen, so I understand your points and agree 100%. Your points on translating digital design into real-life parts are also well-taken. Eric, my CNC machinist, has a PhD in engineering, and a shop full of awesome equipment, and we still had a few issues in the process. One that note: the rear mount is officially out of the clamps and in my hands now. You haven't seen anything yet! That was one of my less-complicated designs.

My original (and real) suggestion was really to build a more conventional EV first, and work on this one in the background. The point of the software is it would take time to master, and then time to accurately model, and then time to implement. Along the way Darxus would learn a LOT about design and engineering, and hopefully build something safe when he finally gets around to this monocoque concept. The software isn't a cure-all, but it would do the same thing we have been doing - tell him when he's about to get himself into trouble.

Honestly Darxus, I think you should find an old motorcycle, convert it to a reverse trike EV, and have fun building your first aluminum body shell. You will learn a lot about fabrication, a lot about EVs and reverse trikes, and have a much better foundation to start on for the monocoque. It may even be possible to design so that the components from the motorcycle-based trike can be used on the monocoque later.
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  #106  
Old 06-04-2010, 12:09 PM
Darxus Darxus is offline
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Default Re: Custom monocoque trike

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Originally Posted by Duncan View Post
Use the driver as a structural member!!

I like it!!
Oh believe me, I've considered it. Although more in the crouching position. Thanks.
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  #107  
Old 06-04-2010, 12:31 PM
Darxus Darxus is offline
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Default Re: Custom monocoque trike

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Originally Posted by TomA View Post
At the end of the day, I guess Darxus has to decide whether he wants to build a trike, or embark on a self-taught CAD/CAM engineering program.
I don't feel a need to decided. Wandering in either direction is fine with me.

I guess it was too vaguely implied that along with dropping the rear seat I also expect to drop the monocoque.


Quote:
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...torsional resonance...
Good term, thanks.
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  #108  
Old 06-04-2010, 10:53 PM
Darxus Darxus is offline
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  #109  
Old 06-06-2010, 07:48 PM
Darxus Darxus is offline
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Default Re: Custom monocoque trike

Frame.


Body. Nurbs surfaces are fun.
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  #110  
Old 06-06-2010, 08:37 PM
Darxus Darxus is offline
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Default Crouching

If you're interested in driving in a crouching position, I recommend looking into formula 1 sidecars. I guess they were once motorcycles with sidecars used for racing. Now they vaguely resemble that layout. One of the amusing things is the passenger, the monkey. They climb all over the back of the thing to optimally balance weight in turns. You know that trunk monkey commercial? That's where they got the term. People talking about making a mechanical monkey to put in the trunk of their car.
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