Instructables

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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CJSchecter962 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)  CJSchecter962 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
henryjimenez3 months ago

NIce design.. this are a big solution, im working in a small software for a electronic diferential over raspberry pi. Congratulations from Colombia.

Henry

Ganhaar (author) 4 months ago

Update on energy efficiency.

Measured energy consumption over normal driving on gravel roads and am achieving 0.74Ah/km or 106Wh/km

Squidyman5 months ago

so how much did this all cost?

Ganhaar (author)  Squidyman5 months 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.

wrsexton8 months ago

In researching further, I have a question about the bearings/mounts for the drive half shafts. Realize this car is together, but a photo would be useful. Also, type/brand of bearing you used and how its mounted might help me visualize this.

Ganhaar (author)  wrsexton8 months ago

I have added a sketch to step 2 showing a section at the rear pulleys and halfshafts. I don't have a photo and don't have any plans to pull it apart in the immediate future.

The inner bearings are mounted in a steel bearing holder with a flange and four bolts. A standard bearing face mount block would be ideal, but I had a lighter steel one that I recycled from a previous project. For the outer bearing block I machined this from recycled plastic to be larger without getting too heavy for spreading the loads into the thinner wall of the chassis box.

I think they were skf metric bearings, but any standard bearings are fine. The loads on these are not high, no side loading like the wheel bearings, they are just there to hold the shaft and tension the belt.

wrsexton Ganhaar8 months ago

I see. A pair of bearings for each half shaft. That makes perfect sense and is, no doubt, a very trouble free solution. Thanks for your response.

goldenshuttle8 months ago

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

dk_201310 months ago
Awesome work! Sorry for a bit stupid (newbee) question, but how do you think - is it possible to use instead of electric accumulators diving cylinders connected to electrogenerator to run these motors? I understand that direst air engine probably will provide more efficiency in converting energy of pressed air to car engine movement. But these equipment can decrease the cost of energy storage part for this kind of automobiles, provide all advantages of electric motors and can be used in something like publik transport applications (when vehicles moving on predifined routines and can be refilled with pressed air at end stops with compressing stations). And the all equipment is widely used (diving cylinders and compressors) and well tested.
Ganhaar (author)  dk_201310 months ago
Never built a compressed air car but I think you will find there are two major hurdles to overcome - volume of storage cylinder and heating / cooling when the air is compressed and released.
dk_2013 Ganhaar10 months ago
Yes, these are a lot of different pneumatic cars (serving pneumocars) which uses the energy of compressed air directly in pneumatic motors. Just interesting, is it possible to use hybrid scheme, but instead of internal combustion motor to use pneumatic motors like this - http://www.grainger.com/category/air-motors/pneumatic-motors/pneumatics/ecatalog/N-brn for example and standard diving cylinders. This will take more space for compressed air cylinders, but it will allow to increase speed of charging (with compressor stations) and decrease cost of energy storage devices, like batteries (by using instead of them cylinders). Ok, nevermind. Thanks for answer :) This is just my common suggestions.
sspence dk_20138 months ago

Compressed air invlolves a lot of friction, and is very lossy compared to batteries.

ANDY!9 months ago
That's one heck of a EV! Just wondering what sort of master cylinder you used for the brakes, vacuum assisted or manual. I'm working on an EV myself and have to work on modifying the brakes...
Ganhaar (author)  ANDY!9 months ago
I used the Miata vacuum assisted cylinder because I had a spare one off the car that I used for wheels and uprights. It has been working fine without the vacuum assist connected, probably because the car is much lighter (around ½ the weight) of the Miata, however they are a bit heavy and I have looked at fitting a vacuum pump which is available for around $200 suited to EV conversions. I haven't gone this way as the philosophy of the car is to keep it as simple and light weight as possible, so f I decide to go ahead with a brake upgrade it will involve removing the vacuum cylinder and increasing the mechanical leverage of the brake pedal or fitting a refurbished brake cylinder from an older car with unassisted brakes which will have a smaller diameter thus a larger hydraulic ratio.
If you are converting a car and the original car had boosted brakes then you probably have little choice but to fit a vacuum pump for compliance with vehicle licensing requirements.
Ganhaar (author)  ANDY!9 months ago
I used the Miata vacuum assisted cylinder because I had a spare one off the car that I used for wheels and uprights. It has been working fine without the vacuum assist connected, probably because the car is much lighter (around ½ the weight) of the Miata, however they are a bit heavy and I have looked at fitting a vacuum pump which is available for around $200 suited to EV conversions. I haven't gone this way as the philosophy of the car is to keep it as simple and light weight as possible, so f I decide to go ahead with a brake upgrade it will involve removing the vacuum cylinder and increasing the mechanical leverage of the brake pedal or fitting a refurbished brake cylinder from an older car with unassisted brakes which will have a smaller diameter thus a larger hydraulic ratio.
If you are converting a car and the original car had boosted brakes then you probably have little choice but to fit a vacuum pump for compliance with vehicle licensing requirements.
shonoe189 months ago
I'm 13... I'm going to try and tackle this project so by the time I'm able to drive..15-16... I was wondering what lightweight body I could put on top of the model? Any thoughts
Ganhaar (author)  shonoe189 months ago
I quite like the Porsche Spyder (e.g. Chamonix) or a Sylva J15. Both small and lightweight for a road body, although I am doing something more like a cross between a go-kart and ktm crossbow myself at the moment.
Kiteman11 months ago
What sort of range, speed & recharge time are you getting so far?
Ganhaar (author)  Kiteman11 months ago
It uses around 1% of the battery's charge per kilometre on unsealed farm roads and off road, so that equates to 100 km or 60 miles per charge.
For my application and testing, the range is a lot more than required around the farm and the pack was sized more to ensure safe peak current draw than range. The advantage is the extra pack capacity gives a mobile power source around the farm.

Speed is ridiculous for farm tracks and haven't explored the upper end of the speed range, this will have to wait for track time. On the tree lined farm tracks I wouldn't go more than 100km/h or 60mph. Estimated top speed is around 160km/h or 100mph but dependent on the aerodynamics of the body as the car good low end torque geared for a top speed of 200km/h (1:3 motor to drive ratio, 6000 rpm motor speed) although it will not be able to reach speeds this high without a low drag, streamlined body.

The recharge time is about 5 minutes per 1% of charge or 8 hours for recharge from fully discharged using a 10amp 240 volt single phase battery charger. The charge rate is not linear and as the battery approaches fully charged, the charge rate drops off.
espdp2 Ganhaar10 months ago
I love this project. Over the top, and yet I'm tempted to think "I could totally do that!" Fantastic documentation as well.

What about length of driving time? Assuming you are just doing "normal driving" (I know, impossible...), how many HOURS of driving around the farm roads before it really has to be recharged? Thank you.
Ganhaar (author)  espdp210 months ago
Driving around the farm is very much short drives and stopping and starting frequently and doing jobs along the way, so a bit difficult to say. Would be guessing about 1.5 hours of continuous driving.
Kiteman Ganhaar11 months ago
Awesome, thanks.
wrsexton11 months ago
Perhaps I missed this somewhere, but with two motors, I assume you use two controllers? If so, how are the linked to a single throttle? Or is your controller one controller operating both motors?
Ganhaar (author)  wrsexton11 months ago
two throttles bolted together to operate as one feeding two motor controllers is the current solution because my electronic skills are very basic. An electronic throttle splitter would be more elegant and I am hoping to find someone who can help point me to a circuit diagram or supplier.

wrsexton Ganhaar11 months ago
I guess Google really is my friend. Once I read your description of what to look for, a search for two motor controller gave me this thread: http://www.diyelectriccar.com/forums/showthread.php/two-alltrax-controllers-single-throttle-84495.html. You'll probably have to cut and paste it as I don't think hyperlinks work in these comments. It references the attached diagram. Thank you for inspiring me to learn!
DWG-ONE-THROT-TWO-AXES.jpg
To put in a hyperlink use the rich editor.
lelelevi11 months ago
Roughly how much did this total project cost you in USD if you don't mind?
Ganhaar (author)  lelelevi11 months ago
About $15k AUD for a fully driveable rolling chassis, which is similar to USD but I think you would be able to source parts cheaper in the US. When considering costs of an EV keep in mind that your running costs are a lot lower but capital is higher. Also we are talking recent technology, early stage of mass production, all new drive train and battery components so costs are very reasonable.
roofuskit Ganhaar11 months ago
Any chance you could break down at least the major component costs? I'm sure the batteries were the bulk of it, but it'd be interesting to see.
Ganhaar (author)  roofuskit11 months ago
Major costs are batteries $150 x 45 100Ah cells and motors (with controllers) are about $3000 each.


Ganhaar (author) 11 months ago
Video now uploaded on youtube at http://youtu.be/2miI3-AONnc
evilmunkey11 months ago
great job. im currently working on electric bikes and trikes (see my instructable) i have gone from bike to trike and car is next. you should find an old VW shell to put on it. they are light and easy to unbolt from the VW drivetrain pan.

keep up the great work.
MrNathann11 months ago
Cannot wait to see some action videos, great job. Would also love to see some amp draw reading as it's being used and both motors.
Also, have you noticed any temperature issues with the batteries?
Again, great job.
joseph45111 months ago
Good job.
sikopasha11 months ago
Great instructable... thanks for sharing.
Voted and followed... :)
DIY939311 months ago
I voted for you! You so deserve this! I love the fact that it is electric!

I love cars, classics preferably but I love seeing these types of posts.

Thanks so much for sharing your craftiness and knowledge.

TheGreatS11 months ago
How is this not in any contests? I would totally vote for it if it was in something. It's just so amazing.
Ganhaar (author)  TheGreatS11 months ago
Its waiting to be approved for workshop contest which seems to be the most applicable at present.
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