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 Post subject: One Person BEC
PostPosted: Wed Feb 22, 2012 2:39 am 
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I have been lurking on and off for a long time now thanks to my room mate. :)
Thought it best to join and share gather ideas and get feed back. I am considering building a one person BEC using miata front and rear steering/brakes/uprights/rear end. and so forth. and a R1 Motor.. The car would be rear engine chain drive. Cockpit space is a factor i am a large guy very husky and 6ft 3in with size 12s..

Here is my basic "not to scale" chassis idea number one. feel free to share your ideas and corrections and concerns, I use the free google sketchup to give my ideas life. Feel free to give me some blunt honest thoughts..


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 Post subject: Re: One Person BEC
PostPosted: Wed Feb 22, 2012 4:34 am 
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The voice of reason
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Welcome and glad to have you.

You're doing well with Sketchup. It takes me a lot of work to line up my tubes etc.

TO go further I think it will help if you start adding real parts to your model. It looks like you're designing it a bit in a vacuum. So there are no motor mounts or suspension mounts and that's what a frame is for. There are pictures here of people who have made chain drive diffs and they have simple shapes - so that would be easy to model. You can get some things like a wooden model of a driver, uprights and halfshafts etc. from my models in my signature line.

Another fun thing is using a program like "Grape" to do the stress checking on your frame. We have threads here for that too.

Keep at it and ask some more questions.

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SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.


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 Post subject: Re: One Person BEC
PostPosted: Wed Feb 22, 2012 3:35 pm 
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Looks like a pretty good start (well triangulated, susp points would be near existing nodes, drivetrain and driver space is ample), but yeah, building around (even roughly decided) suspension points and engine/diff/driver models is much more efficient. I know dpcars has r1 block and a good editable driver model you could tweak to your dimensions, but I don't know much about importing to sketchup as SW is my medium of choice. :\

By the looks of it, you could slim the front and rear sections considerably (that pedal area is kinda awkward imo, and keeping the top tubes all even has little benefit aside from easier jigs/fixtures, both can be tapered to fit the driver and drivetrain, gain rigidity and drop a few lb), but as it's still essentially a blank slate this is relatively easy to play with as you go through suspension design and frame validation (FEA). The braces (longitudinal and X) over the cockpit don't seem to add to strength notably, and could be dropped altogether... though you could retain the X-brace between the roll hoop and front, but put raise the center of the X (so it's 4 tubes instead of 2 and points up a bit), which will give you a bit of extra knee/foot space. Your front roll hoop should ideally be one tube from the top of the cockpit, to the bottom frame rails on both sides with no 'breaks' in the line, though using multiple tubes is fine too, as long as it still looks like one hoop. You'd need to bring those 2 vertical tubes forward a bit, which I'd recommend anyway for comfort/space. Formula SAE is an excellent resource here for design and packaging ideas, there's a number of frame design papers packed with data and countless images to run through for ideas on packaging the parts neatly and creatively.

I'll just make a note that some of the miata parts are better replaced by scaled-down components suited to the role, but that's down to your budget and design. You'll have a tricky time trying to cram an OEM steering rack into that car without some major modification and potential bump steer problems, whereas a small rack would open your options considerably. The brakes will be overkill as well, but as they fit nicely, packaging is not an issue with miata uprights, and you know they'll work well enough, I don't see the harm. What are your plans/ideas for the suspension, and how are you mounting the diff?

There's an awful lot to consider in 1-seater frame design aside from maximum rigidity for minimum weight. Ergonomics/driver fit and comfort (egress rules/goals? these tend to be very snug and awkward, a cardboard/pvc mockup is a great idea), serviceability (does the engine/diff drop out, are there braces in its path that can be bolted in/out or adjusted to fit?), handling the torque from the drivetrain, as well as hanging all the important bits on it (shocks, diff, radiator) that may or may not contribute some load themselves. Of course, much of this can be guesstimated and sorted out on the shop floor with varying, but typically mediocre results, but IMO if 3 hours of CAD time can save me 1 hour of frustrating wheel-spinning during a build and produce a higher-quality result, I'll take it. Details and refinement (thought-out designs, not complexity) make all the difference in a car like this, I'd say you're off to a fine start thus far. :D


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 Post subject: Re: One Person BEC
PostPosted: Wed Feb 22, 2012 5:43 pm 
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Location: Zagreb, Croatia
hi... another singleseater build... cool.. :)

I am also building a single seater BEC.. but using bespoke suspension... I can share my chassis plans if it helps you..

v.

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build log: http://locostusa.com/forums/viewtopic.php?f=36&t=5899

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 Post subject: Re: One Person BEC
PostPosted: Thu Feb 23, 2012 3:41 am 
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Another +1 to designing towards a well defined set of constraints.

Ultimately the chassis is just a giant bracket that keeps the heavy stuff like engines away from the squishy bits, like us, and correctly locates the suspension pick-ups and has all the needed voids and brackets to hold every needed component. And it needs to be stiff enough not to become a spring in its own right. How it looks and its shape really do not matter much past meeting essential functional requirements.

If you can stop thinking of the chassis shape as the car's shape, you open up the ability minimize and optimize the actual chassis design and still have a more creative final body shape. Put the chassis where it needs to be and then drape the body to fit its own specific requirements.

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 Post subject: Re: One Person BEC
PostPosted: Thu Feb 23, 2012 8:32 am 
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Where are you BigDan? I am building the same configuration for AMod autocross. I am in eastern connecticut. You are more than welcome to visit...


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 Post subject: Re: One Person BEC
PostPosted: Thu Feb 23, 2012 12:34 pm 
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The voice of reason
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Hi Sean, glad you're still at it. How about some pictures or a build log one of these days?

BigDan, you should probably add forward braces on your roll hoop. Going from the where the rear braces go to the dash area. They are required in some organizations for formula cars. They help lowering yourself into the car anyway...

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SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
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 Post subject: Re: One Person BEC
PostPosted: Thu Feb 23, 2012 1:04 pm 
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I would tweak the dash hoop some more. There is no bracing below it and there are several tubes at about the same angle going to it. I don't think its providing much stiffness - it looks like a lot of metal for little gain.

+1 on Marcus's suggestion. Cockpit areas are tough to make stuff since one side has to be open to accommodate a passenger. I had one frame where I added two forward braces and it almost doubled the stiffness. It seemed like a pretty darn good tradeoff.

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 Post subject: Re: One Person BEC
PostPosted: Thu Feb 23, 2012 3:59 pm 
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Location: Zagreb, Croatia
the triangular stiffeners on the sides of my frame increased the frame stiffness about 4x... :)

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Building a single seater middy BEC with GSXR 1000 power :)
build log: http://locostusa.com/forums/viewtopic.php?f=36&t=5899

day job: http://smg.photobucket.com/albums/v723/turbolimac/portfolio/


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 Post subject: Re: One Person BEC
PostPosted: Thu Feb 23, 2012 5:08 pm 
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Thank you all for the wonderful ideas. I am going to give them some thought and then do a redrawing of the chassis this weekend incorporating your suggestions.
As for a defined set of constraints, I don't have a lot yet as i am still planning but I plan to use what I have or can get a hold of around here, such as.
R1 Motor
Miata 1.8L lsd diff modified for chain drive
Miata front and rear uprights and brakes
914 steering rack. or?
Front suspension will be inboard ( I found some drawings awhile back I plan to modify for my use. )
Have not give the rear much thought yet
Forward angle of chassis cockpit area will house dual small radiators ( one each side).
Engine bay will have bolt in bottom bracing to allow motor removal
Non complex but strong chassis shape to help with chassis Jigs and body construction ( I plane to use sheets for the body much like the locost does )
For end goal I am going for a Street legal toy to also use for autocross. Most of my inspiration comes from the Marengo 2 hill climb car.
None of this is as of yet set in stone, I am always up for improvement and changes, This is just what i have bouncing around in my head at the moment..

Sean in CT
I am in WA towards the Spokane area close to the Idaho line. but i would love to see your build feel free to send some details / photos my way.

kikiturbo
Glad to see other single seat builders around I will have to check out your build log. I would love to get a set of your chassis plans to look over for ideas / inspiration.
I can open most formats including solidworks and Autocad.


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 Post subject: Re: One Person BEC
PostPosted: Fri Feb 24, 2012 4:09 am 
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Joined: Sun Jul 22, 2007 10:58 pm
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Location: Zagreb, Croatia
yeah, check my build log, I also have removable brace under the engine, although you can also make the roll hoop braces removable, and then pull the engine from above...

I'll upload my chassis plans and send you a link..

cheers
v.

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Building a single seater middy BEC with GSXR 1000 power :)
build log: http://locostusa.com/forums/viewtopic.php?f=36&t=5899

day job: http://smg.photobucket.com/albums/v723/turbolimac/portfolio/


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 Post subject: Re: One Person BEC
PostPosted: Fri Feb 24, 2012 7:19 am 
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It will not be possible to do this with every tube intersection, but in your redesign, try to imagine your chassis as a collection of tetrahedrons connected at the corners. The closer you can get to this ideal, the more rigid the chassis should be.

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 Post subject: Re: One Person BEC
PostPosted: Thu Mar 22, 2012 7:00 pm 
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BigDan wrote:
Forward angle of chassis cockpit area will house dual small radiators ( one each side).

For end goal I am going for a Street legal toy to also use for autocross.


Why have the radiators way up front fighting for space? You could hang a single factory-sized unit off either side of the cockpit, or one smaller one per side, though IMO I don't think the engine would need 2 in any case, and you're having to compromise significantly for footwell and suspension packaging, besides having to run (hot) coolant lines along the entire car.

While I'm parade-pissing :lol: I think you'd be up against an absolute brick wall trying to get a car like that street-legal. Not that any one element may be illegal, but you'll need to fit a body, lights, potentially bumpers, fenders, and depending on laws where you live, any number (0-inf) of rules to comply with meant for normal cars, and be hard-pressed to find an inspector who would ok a tiny, short-wheelbase, bike engined, open wheeled single seater that wraps around the driver like a glove as he sits an inch off the ground, staring at everyone's tires. It's possible (anything is with enough money and stubbornness), but the amount of effort and fighting that's likely to take could be much better spent driving it as a strictly track/auto-x car, IMO.

That said, it is your design, whatever works best for you or looks good to you is what goes in, I'm just trying to flesh out what you're getting into a little more.


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