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Electric Vehicle - A simple lightweight EV platform

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I've been looking forward to the arrival of electric car technology. Not just for the smooth quiet power, wide torque range, cheap running costs and minimal maintenance, but to design and build cars to take advantage of the simplicity and flexible packaging offered by electric technology. Some new knowledge and skills of battery and electric drive systems are required, but once you have an understanding of this, putting it all together is much simpler and quicker than using a petrol or diesel drivetrain. Why? The motors and controllers come ready to bolt on and plug together and all the sensors required are usually built into the motor.  Cooling systems, fuel storage and pump, gearbox, differential, exhaust system and complex wiring harness are not required. There are a few more components required to deal with high voltage electrical power, but other than this, it is really not much more complex than building a radio controlled electric car. With less complex mechanical systems to worry about, building your own car has become more achievable and more fun.
Electric car components have been available for a while now.  A friend converted his first electric car 10 years ago then changed it to lithium batteries 6 years ago. The technology is now becoming more readily available, costs are coming down and performance is increasing and this trend is set to continue.
Why build your own? Because you can and it is great fun to build a very light, simple car reasonably inexpensively.  It is a heap of fun to drive and has excellent performance because of the light weight.  Buggies, gokarts, grass roots racers and kit cars such as Lotus 7 clubman style car that is still going strong since the 60's have spurned their own industries.  Electric cars bring new opportunities for a fresh look at homegrown performance.
 
Concept and Design
This Instructable provides a summary of a basic layout for an EV platform that suits a wide range of applications and can be easily tuned with different size motors, batteries, gearing and size. It demonstrates a simple and compact system with a low centre of gravity that is strong, stiff and straightforward to build. The Instructable does not go into the design and fabrication of bodywork, I will leave this to others and your imagination. It is pretty easy to see that this rolling chassis is very flexible in the bodywork it could accommodate, but keeping the body light will maximise performance and range.
Key Design Parameters
When designing a new car platform from scratch, there are a lot of choices. A lot of thought and design effort has gone into keeping the design as simple, light weight and very easy to build - simpler than a Locost or clubman style car.
I will get straight to the point here and outline some of the key design features and why.
Drive - Rear wheel drive, one electric motor powers each rear wheel. Eliminates the need for a differential and CV joints.
Motors - AC Induction. Have good torque over wide speed range. Simple and robust with a motor controller for each motor. Mounted inboard.
Batteries - Large lithium cells. I used 45 Lithium cells for a total of 148V and 100Ah. This needs to be matched to the motors and controllers. This is a relatively small pack compared to production EV's vehicles but is ample for a car that is light and is not used for long range driving. Keeping the battery pack size down helps keep down the vehicle weight and cost. My large lithium cells are good for a peak current draw 3 to 5 times the rated hourly figure above (3C to 5C). Lithium polymer cells are available that have a higher energy density and will do much higher peak currents than this and they are commonly used in model cars and planes, but at present the large lithium cells are a lot more economical for larger packs and the 3C peak current is not a major limitation unless you need a high peak demand such as for drag racing.
Chassis - Folded aluminium box. The batteries are contained in the box which also handles all the vehicle loads. This is the key to a simple, light and very easy to construct car. It provides a high level of strength and stiffness from a very simple and light structure.
Suspension, Steering and Brakes - Double wishbones were used and they are the best choice for a number of reasons including lower height for maximum flexibility in body design, height adjustable again for flexibility in body styles and optimum handling performance. There are numerous vehicles that can be used to source suspension and steering components. I used parts from a Mazda MX5 (Miata) which has front and rear wishbone suspension and rear wheel drive so all the parts could be obtained one source. It also has 4 wheel disc brakes and a straightforward steering rack. Using mass produced parts helps streamline the project, keeps costs down and ensures that these important items are robust and reliable.
Gearbox - Nil. The electric motors have such a wide torque range that they will operate effectively with one fixed gear. I use a toothed drive belt at a ratio between 1:3 and 1:5 for smooth quiet and maintenance free transmission. A chain drive would also be ideal and would be lighter and cheaper but a little noisier.
Weight - The weight of the EV platform including motors and batteries is approx 500kg. Major components of the weight come from the batteries (150kg), wheels and suspension (140kg) and motors (118kg).
Vehicle Platform - A vehicle platform is basically rolling chassis with drivetrain installed. It is drivable and just needs some bodywork to complete the package. I avoid any body styling discussion in this Instructable and rather present a very flexible platform that will suit a range of body styles.
Driving the Car  -  With one gear and heaps of torque (300Nm from the twin motors) Driving is simple and effortless and the car rapidly gains speed and without a body the sensation of speed is greatly exaggerated.
 

 
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ToolboxGuy23 days ago

I think you meant "spurred" not "spurned" when talking about the spinoff companies...?

Think he means "spawned" (created/caused to be created)

aassad15 days ago

Would be cool to install a MultiSoundBomb on it :)

www.multisoundbomb.com

kweigant20 days ago

How would you like unlimited battery? I have the solution and it is 18 years old. Car factories watch out, I got even tesla beat on this.

Driver6920 days ago



I'm still looking for some one to come up with a electric handycap van for my wife.

Wow...that is really cool. I've always wanted to have an electric car. There's nothing more satisfying than driving right past the petrol station...and the minimum maintenance is a super plus. I live in southern California...and don't have access to a place where I could build an electric vehicle. But I can dream...right? Nice car guys.

ramses25 days ago

In the update on step 6, do you mean 0.74kWh/km?

Because if you mean 0.74Wh/km, your range is >20,000km.

Also, have you noticed any handling issues arising from your lack of a differential?

It probably handles great... or it may also act as if it was operating on a straight axle... if you had a seperate controller for each engine and added two potentiometers (one for left cut and one for right cut) into the stearing system feeding from the accelorator pedal split between each controller you could have turn controlled acceloration... like turn the wheel right and the right wheels motor cuts back to maintain traction while the left wheel maintains 100% corasponding to the accelorator and visa versa for a left turn. It would also help the action of cornering and could be applied to braking as well... you don't want the motors to drag the wheels too much into a corner especially on a wet surface.
Generally motor drag can be controlled in the form of proportional regenerative braking (Ganhaar, care to comment on regen?).

You also bring up the concept of traction control. Does this vehicle have any kind of traction control?
Ganhaar (author)  ramses24 days ago
Also with regards to the diff query it is a good question and there was a debate about this issue on the Australian Electric Vehicle forum (AEVA) about this very issue before I built the car and a few people though it would create issues but in practice it works perfectly and the characteristics of the motors are such that the motor with less torque rotates faster, thus they self regulate perfectly and no issues. Even if the throttles are not set evenly they balance themselves fine.
ramses Ganhaar24 days ago
I actually missed where you said you had 2 motors; as long as you are contrilling them separately (which you are), that does provide a differential effect.

That said, have you considered differentially controlling the motors to give you torque vectoring?
Ganhaar (author)  ramses23 days ago

Definitely, but I was going to try this first on the gokart where it is a bit safer if I get th e algorithms wrong. I'm currently using two throttles that are mechanically linked (potentiometer type, 0-5V output to motor controller) and I can't see why you couldn't put an Arduino in series with a single throttle to reproduce the throttle outputs. You wouldn't even need fancy sensors, just a speed sensor for each motor and if the differential speed went over a certain level you would cut back the voltage on the throttle for that motor. It should work just the same with four motors.

I had some discussions on this with AEVA Forum members but they recommended not to use an Arduino and much better to use the CAN BUS which most production cars use and is also built into the motor controller but that was where they lost me.

Ganhaar (author)  ramses25 days ago
Well spotted it should be 0.74Ah/km.

I did an update about a year ago and measured energy consumption over normal driving on gravel roads and am achieving 0.74Ah/km or 106Wh/km
steve00024 days ago

Hey mate, I have seen this before.


  • 45 x CALB CA100FI cells with CM090 cell modules and BCU-PEV-45C
  • Dual GLE IM15 AC induction motors, 150V 300A 6000rpm each
  • Belt driven rear wheels
  • vehicle weight < 500kg
Ganhaar (author)  steve00023 days ago

Where abouts? Do you have a name or a link or somehow I can follow this up, I would be interested to see other similar projects and what sort of performance they are achieving.

rramos124 days ago

We should use these to conserve our fuel reserve. I will make one in the future.

What if the engine took moisture from the atmosphere and then extracted the hydrogen from the water? And also how do you know how much hydrogen it needs to run... You say 'it would take x amount of air' but to calculate that you'd need to know the consumption rate of hydrogen. Ive seen what appear to be genuine examples of powerful engines running on pure h2o, assuming they're real, and the hydrogen is the fuel, one can imagine some super efficient condensermajiggy that can collect atmospheric moisture and keep you running. I gueeeeess if I had to top it off with a gallon of Poland Spring before I left the house, that'd be ok lol. Anything that runs on any kind of fuel has the potential to run out of that fuel so it can't be 'perpetual', but the idea of an engine equipped with a system to 'gather' it's own fuel is interesting. I think I read somewhere that one of the electric cars out there uses the friction created by braking to recharge the electric battery. If you could do that efficiently enough, you could have a self charging electric car that basically fueled itself. Probably gives oil stockholders nightmares!

This is a great post indeed. You probably want to try this book which shows you how to make your car run forever without recharging the battery. It really works:

http://www.ivantic.net/Energija/fuelless_engine_50-350hp.pdf

If you are working against the principles of the Law of conservation of energe ,then you will definately end up wasting your time,energy and money.

I believe there is a motor in existence that runs on hydrogen, and refuels from hydrogen present in the atmosphere. My dad and I debated whether or not that falls into the category of perpetual motion, but regardless, mechanical failure aside, it could 'run forever' without the user physically refueling. It does require fuel, but it auto-refuels- sort of like if your gas car could draw petrol from the ground while you drive!
Ganhaar (author)  SirCooksalot24 days ago

The amount of hydrogen in the atmosphere is about 0.00005% so you would need 2,000,000 litres (or gallons) of air to extract one litre (or gallon) of hydrogen. It you were using 10 litres per hour and and your extraction efficiency was 50%, you would need to process 40,000,000 litres of air per hour or 11,000 litres per second.

Make an R/C version first as proof of concept. I highly doubt it will work, but no harm trying.

I'm pretty sure that if this worked, it would be breaking one of the fundamental laws of nature, the Law of Conservation of Energy.

Suffice to say, I'm skeptical.

According to Stephen Hawking, all you need to beat conservation of energy is a Big Bang. Should be simple enough.

I am 100% positive that the Fueless Motor you describe is bogus. No it does not work because devices which power themselves would fall into the category of Perpetual Motion and as a previous poster said, it would contradict the Law of Conservation of Energy.

ryadia25 days ago

Way back when... I built a car from the ground up, intended for production from what was a rolling chassis of a medium size family car altered to take advantage of a "Tradesman's market'. It was based around a 6 cyl rear wheel drive vehicle.

It was originally supposed to have an Aluminum body... That's where I came into it but by the t5ime they engaged me, they already had wooden molds made to create the body in Fiberglass.

Quite apart from the lack of consideration for weight, the body - complete with luxury leather interior and hand made steel engine cover/radiator surround, the body was surprisingly light at just over 450 Kg.

I think with today's stretch forming technology (forming aluminum to complex shapes) it would be entirely possible to build an aluminum body for this vehicle amazing vehicle using vertical hinged doors that would weigh very little. Even in sedan configuration.

The future of transportation propulsion is most decidedly is either Steam or Electricity. Because of the reduced dangers of using electricity, recycled steam may remain locked away in the Australian Patent office.

Building a EV is only armchair dreaming for me now but I still have all the knowledge of how to build a lightweight, good looking body ready for production. Maybe I was born 50 years too soon!

Ganhaar (author)  ryadia25 days ago
I saw an article on a steam car built in south australia maybe 20 years ago - a small sports car with a small piston engine directly driving the rear axel, no gear box. A small flash boiler reduced the safety problems of a steam vessel.
More recently I have been thinking about how modern computer controls could be used to simplify and increase performance and efficiency, but I think getting away from burning a fuel which will improve air quality and less noise and complexity makes EV's the best power source to pursue.
tyscof26 days ago

Total price?

Ganhaar (author)  tyscof25 days ago
about $15k. Major costs are batteries $150 x 45 100Ah cells = $6750 and motors (with controllers) are about $3000 each.

Wheels, hubs, brakes, steering was only $500 because I bought a damaged car for $1500 and sold off engine, gearbox and computer for $1000.

Chassis was about $400 in materials including pressing the aluminium box.
CJSchecter9611 months ago

very cool Itd be cool to make one of these someday. would it be possible to have energy recovery where like, you have a motor on the front wheels but not being driven, so when you accelerate and the axle spins the motor produces electricity and puts it back into the battery? or a wind turbine-esque turbo?

Ganhaar (author)  CJSchecter9611 months ago
A generator creates drag when generating power. Try shorting out the three thick wires on a brushless motor and you will see how much drag that can be created. The extra drag created will be slightly more than the power generated as these things are not 100% efficient. Similar result with a wind turbine although it will generate energy from the wind. Sorry no free energy. Better idea is to connect your car to solar panels or a wind turbine when it is parked in the garage to recharge the batteries.
regards
Wayne

Use solar panels or a wind turbine on the front of it. That way, it doesnt add drag to the wheels.

Wish it was that easy. Solar panel on the roof may generate 150 Watts max. Trunk and hood, maybe 300 - 400 watts? Running the motors will be much higher. There are solar car races out there. Those cars look nothing like a typical car and would never make it in regular traffic.

Wind turbine would cause a lot of drag, something the motors would need to overcome. Perhaps a huge tail wind?

Solar panels on the car - not enough surface area to make much difference. Wind turbine on the front - adds wind drag. Although there are races with cars that only run on their own solar panels, these are amazingly small and light vehicles that don't go very fast. Best thing to do is charge it in the garage - trying to make a perpetual motion machine that generates its own power isn't going to get you anywhere. If you want cheap power, put the solar panels on your garage.

I think there's some electric cars that have a solar roof, so it gains as much energy from the sun as possible, since the whole car is basically one big solar panel.

Not that you'd be able to implement that on an electric car you made in your garage for fun for less than a million dollars.

I was thinking more along the lines of range boosting.

Make it happen! I would first start with RC cars. You make an RC car run 'forever' you will have a hit on your hands with just that toy!

loki201225 days ago

Great information!

fstedie26 days ago

You would not be able to license it for road use in the US though, you'd have to make it a 3-wheeler

Ganhaar (author)  fstedie26 days ago
From what I have seen i agree it would be easier to license as a three wheeler, but it doesn't make a lot of sense that it is easier to license a less stable, i.e. less safe vehicle.
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