# Diy Chassis



## Inframan (Jan 30, 2011)

How difficult would it be for someone skilled at welding to put a chassis like this SLC kit car? My plan would be to have an electric version of this type chassis where the front a rear suspension mounts to the front and rear battery box, the battery boxes are the chassis essentially with a column running down the center connecting the two (dog bone). Also where would be the ideal place for the motor? Below the rear battery box? I did some measurements and with a sixteen foot long chassis (same length as the model S) I can fit 100 kwh of LifePo4 cells.


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## rtz (Jul 3, 2013)

Chassis is the easy part. It's the fine trim details and finishing touches that are the hard part. A conversion or build is easy. Just a matter of parts acquisition. Spend money, install parts. Just start spending and you'll be done in no time.

What do you plan to do with it once it's built?


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## Inframan (Jan 30, 2011)

How can you say the chassis is the easy part? So much thought goes into them. Explain fine trim details. I've already done three conversions and a go kart none of the chassis past of present fit my needs this seems to be the only way to maximize the efficiency that I want. Would I have to have some sort of elaborate jib to construct something like this?


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## rtz (Jul 3, 2013)

What I meant was; taking a car from almost finished to complete.

Example of two cars in progress:

https://www.facebook.com/SmythPerfo...54477354119/10152361310804120/?type=1&theater 

Scroll way down to where this car is "mostly" finished:

http://thefactoryfiveforum.com/showthread.php?12203-SixStarCars-818S-Build-Thread/page2 

Getting to that point is the easy part. The final, final little details are the hardest part.


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## Duncan (Dec 8, 2008)

Hi Inframan
I agree with rtz getting the car to a rolling chassis looks like 90% of the way but is really 10% of the way
All of the little detail bits take forever!

Anyway - back to the chassis
Its not too difficult to make your own chassis - you only need fancy jigs if you are going to make a number of them
For a one off the easiest way is to start with a flat building surface
A sheet of MDF or chipboard
Screw some structure to the bottom to keep it flat
Then you can clamp your tubes to it - use spacers
All using the MDF as a base plane

Another good tip is to sit down in the evenings and make a scale model with balsa and cardboard

If you are like me you will end up making some things three times
First approximation
Cut and shut until it works
Make a nice part without the cut and shut lines

Also have a look at your "donor car(s)" - a lot of cars have the front or rear suspension mounted to a subframe
If you use these subframes your chassis becomes a lot easier and essential things like suspension arms and steering racks are located by the manufacturers subframes


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## Tomdb (Jan 28, 2013)

Best way to do this kind of thing is, get a kitcar body, and work from there. The body with its fittings is the hardest part, doors glass lights (all the nice things which gets it road legal).

But building a "central tub" with integrated battery compartment isn't to hard. Look at the way most modern supercars are made, bolt on front and rear aluminum/steel suspension hard points. How ever their tubs are carbon/composite you could fab one up of steel tubing, with easy removable battery boxes.

The motors/drivetrain could easily be inc operated into the bolt on structures for the suspension points front and rear.


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## Tesseract (Sep 27, 2008)

Duncan said:


> ....
> If you are like me you will end up making some things three times...


Huh... that's my experience with designing circuit boards as well. Weird. 

But just to stay on topic, it has been my observation - not my experience! - that the hard part with fabricating a chassis from scratch is the steering & suspension. Hence why so many kit cars rely on OEM assemblies/parts for those functions.

Making a car-sized box is otherwise not terribly difficult for a skilled welder (or one skilled in composites).


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## Inframan (Jan 30, 2011)

Tesseract are you talking about mounting the steering and suspension and getting all that straight? I find all the kit car bodies just not aerodynamic enough for what I'm trying to do that and they're not long enough to accommodate the batteries. What's a good candidate as far as price and easy mounting for the axles and suspensions/brake rotors? I definitely leaning more toward the aluminum square tubing of the SLC. Any tips for building a balsa wood scale model? You would have to show me some tutorial mocking up the real frame on some MDF.Right now I am just soley and hyper focused on the frame.
I really like the factory five car forum build is there somewhere documenting the whole thing?


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## Duncan (Dec 8, 2008)

Hi Inframan

The first thing to do is to go and look at some cars - a vehicle dismantlers would be good

You are looking at front and rear subframes
Most cars these days have McPherson struts all round - not ideal, especially at the front
Look for cars with double wishbone (A-Arms) at the front

take measurements and prepare to buy assemblies if they look usable

You are looking for a front subframe that includes the rack mountings, the wishbone inner mounts, and the spring mounts

Balsa model - just buy a pack of balsa from your local model shop - decide on a scale 
about 1/10th and get cutting and gluing 
You will also need
rough models of the front and rear subframes, batteries, motor, yourself (model shops sell articulated human models - that might drive your scale)

You will make a number of models - much cheaper and easier than doing it in metal at full size

Start real rough and refine it - when you are ready go full size in metal

This is my car - not enough photos of the chassis build
http://www.diyelectriccar.com/forum...ns-dubious-device-44370.html?highlight=duncan

The build table 
Take an 8 x 4 sheet of MDF - get some nice straight 2 x 4 timber
Put the 2 x 4's on a flat concrete floor (4 inch up) - in an 8 X 4 rectangle
Screw the MDF to the 2 x 4's
Turn it over
screw a scrap piece of 8 x 4 MDF to the bottom

This makes a very rigid 8 x 4 surface - check that it is nice and flat
Sit it on something to bring it up to a nice working height

Use this to set your tubes on for welding - you can weld on the MDF its just a little smelly

Mark all of your reference lines on the MDF - centerline, where the tubes go
any measurements you don't want to lose.....

When you are finally finished the top sheet will look terrible - screw a new one over it if necessary

Aluminiun v Steel
I use mild steel - it is heavier for the same strength - but its forgiving - it tends to deform rather than break 
Your choice


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## Tomdb (Jan 28, 2013)

If you are serious about this project i would approuch some racers/car builders for help.

Check out this site, gold mine of information.
www.locostusa.com/forums/

Fixed link


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## Duncan (Dec 8, 2008)

Hi
I couldn't get Tomdb's link to work

http://www.locostusa.com/forums/

This one seems to


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## sergiu tofanel (Jan 13, 2014)

Inframan said:


> Tesseract are you talking about mounting the steering and suspension and getting all that straight? I find all the kit car bodies just not aerodynamic enough for what I'm trying to do that and they're not long enough to accommodate the batteries. What's a good candidate as far as price and easy mounting for the axles and suspensions/brake rotors? I definitely leaning more toward the aluminum square tubing of the SLC. Any tips for building a balsa wood scale model? You would have to show me some tutorial mocking up the real frame on some MDF.Right now I am just soley and hyper focused on the frame.
> I really like the factory five car forum build is there somewhere documenting the whole thing?


You are probably putting the cart before the horse. If you are concerned about aerodynamics, that should take precedence over the chassis. A good aerodynamic shape will place dimension and proportion constraints that you need to know BEFORE you design the chassis. Things like ground clearance, rear body taper and diffuser proportions become critical. 

I would not even bother with a chassis model at this point. Assuming you have a body shell, start building the chassis with your favorite CAD program. There are quite a few free software packages out there that will do the job. For engineering analysis purposes I really like the Linux based OpenFOAM package. It is capable of both aerodynamic simulations as well as structural analysis. 

Last but not least, aluminum welding requires serious skills. You may want to consider a chromoly frame instead. If it's good enough for NASCAR, it's probably good enough for a diy EV.


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## Yabert (Feb 7, 2010)

I also think that a good aerodynamic shape is more important than chassis.



sergiu tofanel said:


> You may want to consider a chromoly frame instead. If it's good enough for NASCAR, it's probably good enough for a diy EV.


Chromoly steel is only worth to save few pounds on a complete car frame.
IMHO, save a lot of money by using standard steel tube with thicker wall... or learn to weld aluminum!


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## Duncan (Dec 8, 2008)

Yabert said:


> Chromoly steel is only worth to save few pounds on a complete car frame.
> IMHO, save a lot of money by using standard steel tube with thicker wall... or learn to weld aluminum!


I would go for mild steel tubing
As well as cheaper it is much more forgiving 

Chromoly is good - 
If you know *exactly* what you are doing and have the facilities to heat treat the whole chassis once its complete

As far as aerodynamics is concerned - its no good having a wonderful design if you cant package the rolling bits

Also - once you get the shape about right the devil in aero is all of the details where things come together

A car with a "less good" shape and attention to all of the details like wheel wells, panel joints and mirrors will tank the car with the "better shape" and less attention to the edges


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## Inframan (Jan 30, 2011)

I only want to focus on the chassis because I have a particular size pack I want and I want to build the car around it. A friend of mine who is down for the project is an expert Al welder. I was thinking instead of drawing it in cad I would sculpt it out of clay and then scan it with an xbox kinect. Could I put a 3d scan into OpenFoam to analyze the aero data and how accurate is it when analyzing aerodynamics? Looks like I have some homework to do on that forum there


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## Tomdb (Jan 28, 2013)

@ topic starter,

Would you mind listing your desired specificiations for the completed car?
Weight, accel, range ect.

And the setup you have in mind?


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## Inframan (Jan 30, 2011)

Well I can tell you the weight of the battery pack I'd like to use. I would like to use a 250 volt pack of calb 400's that's 78 cells weighing about 2500 lbs. I am shooting for a 100-140 watt hour per mile vehicle and I would like to get somewhere between 700-1000 miles range. I have a Netgain warp 9 but I am think about a dual motor ac system instead and since the battery box has to be the length of the vehicle I don't know where exactly to put the motor. If I put it under the box then it affects aerodynamics so I'll probably have to have a belly pan underneath the motor(s)


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## Frank (Dec 6, 2008)

Huh?? Sounds like you should do some basic layout work... Why do you need such range?


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## Inframan (Jan 30, 2011)

What basic layout work do you have in mind? Duh world record!


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## dcb (Dec 5, 2009)

Have you seen what dave cloud did with a metro? on a shoestring budget?

it is basically a glorified battery hauler:
http://www.treehugger.com/cars/dave-clouds-214-mpg-geo-metro-aka-the-dolphin.html

probably a couple thousand lbs there in used lead acid, and cheap series motors.

update the electrical bits and you are there. (skip the wide tires)


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## Frank (Dec 6, 2008)

What world record? Did I miss some discussion about trying for some distance or efficiency record?


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## Inframan (Jan 30, 2011)

http://www.treehugger.com/cars/elec...s-on-a-single-charge-breaks-world-record.html
and this shape wasn't even as good as the dolphin and it was only a 1 seater I'd like to do it with a two seater at highway speeds and with a lifePo4 pack but if I had a tesla pack which is almost the same kwh it would weigh half that I might even do 1200 miles to the charge hell I'd have the space for two tesla packs weighing in at the same weight as LifePo4. How many steps would be involved to turn a metro into a dolphin? Or could a from scratch vehicle be much more optimized as far as weight distribution, aerodynamics, steering components, and drivetrain that's better than the dolphins chain drive?


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## dcb (Dec 5, 2009)

Well you are only dollars away  $3k for a dolphin an a years worth of effort is pretty hard to beat (aka DIY). Any guesses what folks spent on team schluckspecht and equipment?


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## sergiu tofanel (Jan 13, 2014)

Inframan said:


> I only want to focus on the chassis because I have a particular size pack I want and I want to build the car around it. A friend of mine who is down for the project is an expert Al welder. I was thinking instead of drawing it in cad I would sculpt it out of clay and then scan it with an xbox kinect. Could I put a 3d scan into OpenFoam to analyze the aero data and how accurate is it when analyzing aerodynamics? Looks like I have some homework to do on that forum there


The OpenFoam utilities require both science and dark magic. The learning curve is steep, but worth the effort. I was able to run a few test cases and the results are promising. The simpleFoam solver, which runs incompressible turbulent flow simulations gives good results for well designed meshes. 

You mentioned that you hope to get <150Wh/mile consumption. I doubt you'll even get close to this number with a 3000+ lbs vehicle. Rolling and drivetrain resistance alone is almost 100Wh/mile. To get the consumption you are hoping for, you must keep the vehicle at less than 2000lbs.


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## Inframan (Jan 30, 2011)

My friend seems to think that we could get a dolphin like vehicle down to about 120 watt hours because the dolphin had it's issues like the tires not being low rolling resistance the motors not being the most efficient and had no regen and the there may have been alignment issues when it came to how he lengthened the frame because there was some sort of vibration as well as there being no front wheel skirts. The dolphin itself was at 150 watt hours per mile and it absolutely could have been better even at 3200 lbs. What is a good first step to learning openfoam?


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## sergiu tofanel (Jan 13, 2014)

Inframan said:


> My friend seems to think that we could get a dolphin like vehicle down to about 120 watt hours because the dolphin had it's issues like the tires not being low rolling resistance the motors not being the most efficient and had no regen and the there may have been alignment issues when it came to how he lengthened the frame because there was some sort of vibration as well as there being no front wheel skirts. The dolphin itself was at 150 watt hours per mile and it absolutely could have been better even at 3200 lbs. What is a good first step to learning openfoam?


A manual gearbox (no differential) has an efficiency between 92%-98%. Add a differential (for front wheel drive cars) and that efficiency drops to about 90%-95%. For the sake of this discussion, let's assume a gearbox efficiency of 93%. Also, let's assume a very generous motor+controller efficiency of 85%. Right off the bat, for every 100W of power being sucked out of the batteries, only 79 watts make it to the driveshafts. Compute for a power loss of 1% through the wheel bearings, and only 78W make it to the tires.

Now, let's further assume that the EV has efficient tires, with a Crr of about 0.7%. A 3000 lbs vehicle will use 1600*0.007*(3200/2.2)*9.8 joules per mile, or 44Whr per mile. 

The biggest power hog for cars is aerodynamic drag. At 60mph, a very sleek car with let's say a 18% drag coefficient and a frontal area of 2sqm will require 0.6*26^2*0.18*2*1600 joules per mile, or 64Whrs per mile.

So assuming that the mechanical design of the car rivals VW's XL1, one needs (44+64)/.78, or 138 Whrs per mile. I put this number out there with great reservations, because I am not sure that the average diy-er can design and build such a vehicle on a average Joe's budget. Now, there are ways to cheat to give oneself some wiggle room: aerodynamic wheel covers for both front and rear, reduced weight (at approx 1500 lbs), and an unencumbered drivetrain (do away with the transmission altogether).

Regarding OpenFoam: it really helps to know a thing or two about aerodynamics (I happen to have one of those fancy rocket science degrees), and have a clue about C(++) programming and how compilers work. For starters, I would work my way through the example cases shown in the tutorials directory. There is a decent motorcycle example which eventually can be modified to run a car shape. It gives good results if one produces a decent mesh (look up the Courant number requirements). Last but not least, one needs a fast computer with at least 8GB of RAM running Linux (I prefer Ubuntu 12.04). Most case simulations take several hours to execute.


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## Inframan (Jan 30, 2011)

Your calculations are correct but I was thinking about avoiding the gearbox altogether anyway in fact the dolphin didn't have one either. As far as weight I was thinking the dolphin could have a weight reduction by having some of the bigger parts made out of carbon fiber that and if one were to go with a smaller more energy dense pack like something out of a model S it would significantly reduce the weight while having the same energy density. What are you using as your time constant for converting joules to watts? 2 square meters is like the area of a mercedes luxury vehicle a geo has I think a 1.4 square meter frontal area. This and all those reasons I mentioned before is the reason I think 100 watt hours per mile is possible.


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## sergiu tofanel (Jan 13, 2014)

1Whr = 1W * 3600s = 3600J

As far as weight reduction is concerned, carbon fiber is a budget buster. I happen to like the Lotus approach. The Elise (and the Tesla Roadster) have chassis made out of very thin aluminum sheet metal. The metal is so thin that is cannot even be welded. Instead, it's glued with epoxy. A full chassis weighs only 65Kg. There is a carbon fiber crash box in the front designed to take collision impacts. 

I am currently designing a Lotus style tub for a possible EV and I plan to use just pain old regular mild steel. The tub itself can be made of 2"x6", 2"x4" and 2"x2" square tubing with sheet metal reinforcements. It will not weigh 65kg, but I can definitely keep it under 250lbs, without suspension. 

As far as suspension is concerned, one must keep the (lower) control arms out of the airstream for the sake of aerodynamics. For this, one needs spindles where the wheel axle is closer to the lower ball joint than the upper. Right now I am exploring the possibility of using front suspension components from off-road four wheelers, like the Honda TRX. I am not sure yet if such a suspension is suitable for a car that weights 1500 lbs.


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## Inframan (Jan 30, 2011)

Hmm good thinking about the suspension. So your whole chassis is going to weigh 250 lbs? Why are you against using aluminum like the car I posted at the start of this post? I understand somewhat as to how you are putting together the chassis but what is your plan for the body? What do you think about covering the chassis with foam and then sanding it to shape and then laying fiberglass over it? Would it be possible to come the aerodynamic shape we're looking for using that method? What battery pack, motor, and controller are you looking at? Are you going for range, speed?


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## sergiu tofanel (Jan 13, 2014)

I have nothing against using aluminum for the chassis. However, at this point I am trying to keep costs down, so steel is the better bang for the buck. I'd rather spend the money on fancy batteries rather than aluminum and carbon fiber. 

The body will be fiberglass for now. I have a body shape that has yielded a Cd between 0.11 to 0.17 (fully enclosed front wheel fairings vs standard front wheel openings) in OpenFoam simulations. I am currently sectioning the body (delineate fenders, bumper, doors, etc) in OpenSCAD and subsequently generate the G-code to carve out the molds for the body panels (I have access to a 3D CNC router that is big enough for the job). 

The plan is to design the chassis from the body shell constraints and build a mockup. Then CNC cut the body panel molds and make fiberglass body panels. The windshield and all glass will be lexan for now. I have designed the windshield to have very little curvature.

As far as the drivetrain is concerned, I am currently cannibalizing a Bombardier Class E NEV. It only puts out 5HP continuous (25HP peak), but it can probably be pushed a bit more with proper cooling. It should be quite sufficient as a test platform, since the full vehicle will be roughly the size of a Smart car, at less weight.

So far I am still working on the main body components, while collaborating with someone else on the chassis/suspension. I hope to have a rolling chassis (full suspension, steering. brakes, etc + motor and driveline by the end of the year. Hopefully, I'll have most of the bodywork fabricated as well. It will be far from a complete car, but I may have a street worthy vehicle no later than next spring.


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