# Design and Build a electric car from scratch



## Duncan (Dec 8, 2008)

Hi
Have a look at this

http://www.autospeed.com/cms/A_112926/article.html

IMHO - hub motors are a waste of time - the issue is that torque is roughly proportional to weight
So to get enough torque you need gearing and one motor + reduction gearing and a diff is lighter than two hub motors capable of producing equivalent torque

If you use hub motors you may end up with something that wont go up a ramp or cross a kerb

This is my "scratch built car" 

http://www.diyelectriccar.com/forum...dubious-device-44370p15.html?highlight=duncan


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## mayhew (Jan 29, 2017)

If you are looking for aerodynamic efficiency stay away from F1 cars, they are designed to produce thousands of pounds of downforce at high speeds, not minimum drag. EVs have no problem producing downforce!


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## jasonpeace (Jan 29, 2017)

Thank you for your replys,

Duncan, looked at your build posts your car looks amazing 
You think hub motors aren't worth considering I saw this a few times across
other forums I'll have noticed the hub motors I could afford the speed ratings 
are usually very low (I'm guessing its because the motors are designed for torque to compensate for lack of gearing)

I might look into the cost of getting a old Quad bike rear diff and using that
should it be strong enough to handle the power (I'm guessing it should as hopefully my design wont weigh much more than a large quad)

Mayhew, At the moment I'm just doing sketches trying to find something thats both aerodynamic and feasible for me to build I understand F1 car have huge amounts of down force I would be looking at not having the huge wings they have just a slimline body might be closer to a 1960's f1 car at the current point ill post pics of possible designs when i manage to design 
something that Im happy with


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## piotrsko (Dec 9, 2007)

For design considerstions perhaps you should look at ecomodder aerodynamics as a suggestion


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## galderdi (Nov 17, 2015)

I have a similar delema with my next (second) EV project. I am aiming for sub 300KG with batteries and needed to solve the "diff" problem. I have opted to run a small gearbox from a front wheel drive car. In my case it is from an early VW golf/rabbit. But jsut because it is from a front wheel drive doesn't mean it must remain in the front. Plus if you are talking about a low weight vehicle the stress on the gearbox is greatly reduced. Plus it gives me the option of altering my gearing until I settle on the best ratio.

I will be running the ADC 8 inch FB1-4003 through the gearbox via sprocket and chain (hopefully 3 row but at least 2 row).


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## galderdi (Nov 17, 2015)

By the way I think your range targets are a little too optimistic. Even if you had access to F1 team resources I don't think you can achieve sub 400Kg with a 100Mile range. Unless you plan on only driving on flat road and no need to slow down and speed up again.

Typical battery requirements are something like 160Whrs per mile.

I think the batteries to give you 100 miles are going to weigh about 100-150Kg alone.

In my case I will be running 7KWh of Volt batteries weighing around 60KG. That only leaves me 240KG for the remainder of the car.


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## jasonpeace (Jan 29, 2017)

hello all I'm back sorry for the lack of reply's been busy,

got a tube chassis design sketched up no where near complete design
more sketch tbh but the longest tube on it is 900mm so call it a meter
and using

http://www.random-science-tools.com/physics/beams/tube.htm

25mm stainless tube at 1.5mm wall and 1 meter length comes out at 0.89kg
and there are 104 tubes in the design all under 1meter so the chassis weight should be well under 92.56kg leaving me approx 300kg for batteries, motors components and body shell 

I plan on having the batteries behind the driver (the only real space this car will have) 

space will be the biggest issue here i believe but it only needs to carry me and my lunch for work as that's the most i ever need and my girlfriends car can do all the long distance work and it doesn't matter how you look at it, its an improvement on my current transport my electric bicycle for 47 miles a day!

thats why i want 100 mile range so ive got double what i need so when the battery pack is aged and losing capacity it will still get me to work and back on 50%

i might need go the hub motor route just to save space right now 

one other thing ive got to design in is all the road legal requirements of the
dvla for here in the uk

ill try to attach the step file of the design if anyone wants to take a closer look if you want a different file type let me know

















View attachment tubecar.zip


I hope thats worked


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## Tomdb (Jan 28, 2013)

You might want to get it registered as a quad bike. Since the low weight and power.

Look at this for an example of an single seater kit car https://furorecars.co.uk/

Kit car builder forum, very helpful and loads of info. Thread on chassis weight http://www.locostbuilders.co.uk/viewthread.php?tid=147952


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## Duncan (Dec 8, 2008)

Hi Jason
That is an extremely heavy chassis - 100Kg for a single seater chassis like that!

The Caterham 7 chassis - which is a road legal two seater used to weigh 46lbs - 21Kg
But that was too light - my friend used to change her chassis every year as she cracked it on the track

My Device has a very heavy chassis and it is less than 100Kg
You are underestimating the weight of all of the other bits you need


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## jasonpeace (Jan 29, 2017)

Duncan, that weight was a deliberate over estimate based on the largest tube multiplied by the number of tubes.

i've just measured each tube and calculated the weight at 48kg

which leaves me 50kg for the rest of the running gear which is tight

my rough guess for weight at the start was 400kg total

100kg for chassis and running gear

150kg batteries (lead acid unfortunate as my funds wont stretch to anything better so that will be a later upgrade) 

75kg for motor and electronics

75kg for body and other bits ive forgotten 

hopefully ill be able to stick to something in that ballpark

tomdb, thanks for that info that was helpful now reading into
the test requirements for a heavy quadricycle looks like an easier way 
to getting it registered


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## galderdi (Nov 17, 2015)

It looks like you've done some good thinking there. You have a good plan to work from even if some of the details might change along the way.

If you already have lead acid lying around, great run with those as a stop gap. If not, don't do it!!! Purchasing lead acid is not a good idea, You are just introducing extra cost. You won't be happy with lead acid. If you can't afford lithium wait until you can.

I learned this the hard way. I have probably spent an extra $2000 on lead acid that is money down the drain.


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## piotrsko (Dec 9, 2007)

Same sort of comment: if you have FLA on hand, use em. The same cost for buying them new is a volt or leaf pack salvaged. 300 lbs of lead isnt that much battery capacity at 50 watts a us pound.


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