Concept A
 

I've been toying with the idea for years, but I've decided that I now want to try and make my own EV. With the help of you guys, my friends in Bentley's Green power project and a few friends at Castle Creations. These are the targets I'm setting

1.carry 4 people+30kg load
2.Range = 100 miles+
3.Cruise speed 65mph+
4. has to acheive 80% ofpoint2 including extented times @ point3 whilst carrying 2 people

At the moment I haven't decided on layout, or construction but it would have to be simple design - most like to go open source once the bugs are sorted. The project is going to be a long one but My main aim is the car to be simple, modular to aid retrofitting upgrades and most importantly use existing technology to act as recycling.

Those are some fairly high goals you have there. You're going to need a heck of a battery pack to support 100+ miles. I'd probably start looking at small pickup trucks so it can carry the weight.

Standard issue question number one: How much you gonna spend on it?
You can do it if you want to pay 20k. I'd love to see a high-dollar build-up on this site as most of the others are el-cheapo (which is a good thing, too!)

clean sheet design :)

aiming to keep it light to loads down, hub motors to get rid of driveline losses....... even a 5th wheel regen braking - lots of randomness - lots of ideas that will probably not work. I think it was Edison who was asked how many failures did he have at making a working lightbulb. he answered - none. asked if this was incredibly lucky to get it right first time , he said 'no, I found thousands of successful way of making a non-working bulb and one way of making a working one' there alone is his genius (parapharsing hugely there!!)

@Matt, Haven't completely thought out Budget yet...... need to basic calcs first on what power/weight etc is needed:thumbup:

Spend some time on DIY Electric Car Forums Site Home EV Photo Album: Our Electric Cars on the Web and Domain Name For Sale - contact: info@nucom.com and you'll find lots of examples of people who have done exactly what you're looking at and they often talk about they issues and costs.

Are you looking to convert a car/truck, or design/build your own vehicle?

design my own;) obviously i may pillage certain components from other cars

How big are the people? If it was up to me I'd grab ~600-800lbs (30kWh) of LFPs, a pickup truck frame (~4500lb gross vehicle weight, but w/ no cab/bed/driveline it should weight in south of 1000lbs), and slap a compact car body on there, somewhere around 1500lb w/o the driveline/suspension. If you're thrifty and handy the body should be under $1000, but the pack would be ~$7,500-10,000, plus the motor/controller/etc, so maybe ~$10K-13K.

Having sliding battery racks connected to the frame would be neat imo and good for weight distribution, and instead of the rear axle, an old 4spd FWD transmission in the front or the back would save a couple hundred pounds compared to the stock axle/rwd trans/etc. All told I think you can get the curb weight near ~3500lbs, which should get you about 100 miles of range at 65+mph, provided you went with a LRR tire set and the alignment was as straight as possible.

Thinking about the tray idea and LRR tyres. I might get the drive train etc working in a small hatch to prove everythin out before making the final bespoke monocoque. final concept I want with cells but without passenger to be around 2000-2500 lbs with ultr simple interior and super low Cd

Your thinking is quite similar to mine, although I'm shooting to seat 6 and have an 80% DOD range in the 250 mile range. :D

WOW 250 range thats just nuts!!!!

250 miles is do-able, but...
 

" WOW 250 range thats just nuts!!!!"

Naaah. 250 is do-able. You just absolutely have to have a small truck to haul the money to buy the battery pack.

:eek:

Oh yeah, and a highly engineered strong/stiff/light frame. And an unbelievably low drag coefficient, and really small frontal area, and really low rolling resistance tires, and a really efficient drive train, and some other stuff I'm forgetting.

Can't wait to see it.

Don't forget, it's very easy to spend $30K or more and end up with a fine general motors or chrysler or ford product that gets 21 mpg or less. So spending 25K on a good battery pack in a slick design is not as crazy as it first sounds.

Plus, your home brew vehicle will not be designed so it's intentionally hard to work on, and wears out on purpose.

Please carry on.

troy

At current prices for LiFePo4, I'm estimating $17.5K. That of course is cell-only price, I'm sure the charger and balancing controller could drive it as high as $20K.

Aero? I'm borrowing heavily from the AeroCivic for my design. I'm going a step further and not having open wheel wells. The body will extend past the wheels far enough that I can turn the wheels 90º without having to deal with the wheel going beyond the body.

As for weight, the battery pack cells, without the miscellanea, will weigh just a touch over 1,100 lbs, which leaves me ~1,400 lbs to deal with everything else. I figure if I can reasonably use Titanium for the frame, and carbon-fiber for the shell, I should be golden. Plus no transmissions, no differentials, straight motor-on-wheel, no friction brakes, except a parking brake in the motors. I'm actually going as far as having the motors built INTO the rims, instead of having 2 separate pieces. No conventional steering system, all drive-by-wire with a light-cable backup.

Well, I can dream, can't I? :D

Just done my first batch of calcs - I feel quite dizzy. Using the most basic of sums I need 40Kw to accellerate my car to 65 then Iwill need 6Kw to keep it there. (factor of safety figured in there too! (i'm an engineer after all!)

I'm now trying to find a motor/cell/controller package that can give me a peak of 40Kw and a 215AH capacity (@72v)

Any suggestions?

Pics
 

first design idea -NOT TO SCALE

I like the concept you are going for here, i went for a little easier first time out doing this. Took the lotus 7 design and making that an EV.

The higher voltage you go, the lower the amps you will need to maintain that speed. So the lower discharge on your batteries. I have planned on 144V (12x12V), though may drop it back 120V (24x6V) to give better discharge.

Down the centre line is not a bad idea and allows you to drop the passenger sitting hight to really low (from that drawing) and so drop the hieght. Fromt drawings (lines wise) it looks like ur going for something like taller version of the birdcage; 2005 Pininfarina Maserati Birdcage Concept.

Good luck with the build! I am interested to see how i goes as my #2 ev build is going to be a closed body marathon runner. 7 is short blats only.

lokking into the 144 idea - seems a good idea - been thinking about 4 of these one at each corner (4x10=40 , genius :p) knocking back to just the rears in cruise. Also thinking of a variable pot system on the steering, the more angle the less power to the inside wheel - kind of an electric diff... (but i would have a 'lock button' rear power only, equal over volt power for drifting those 145 tyres on roundabouts...... I'm a child really!, but I have to appeal to the clarksons of the world)

I ran some guestimate numbers on those rims. Since they are rated for 1000rpm max, you're looking at about 95-100km/h with the 14 inch rim depending on the sidewall height of your tires. So you're a little short of your top speed requirement.

You also won't be able to hook them up to a junkyard knuckle (aka upright) - you'll be fabbing your own, which means you'll be fabbing your own suspension parts unless you're really clever and can make a knuckle that joins these hubs to an existing suspension.

Personally, i'd shy away from hub motors. There's not much lost in using a front motor and a rear motor with a diff at each end (or a double-shaft motor if you can find one that suits).

They are also only rated for 96V, but the mfg says they'll accomodate whatever... if you want to pay for it :)