Building an Electric Racing Car

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Introduction: Building an Electric Racing Car

About: Retired technology teacher - 2 kids, I have an Hons deg in Design and Technology - 28 years as Computer systems engineer Trained as Electronics engineer in the Royal Air Force

A small team of school kids and myself have built and raced an electric racing car. This is how we did it.

Step 1: The Chassis

We built this car to enter a series of national races here in the Uk - Details can be found at http://www.greenpower.co.uk. To some degree this controlled how we built our car and what we used as the race series has rules that must be followed.

The chassis was a simple "Ladder" design made from 19mm aluminium square section tubing. This is easy to work and light as well as moderately low cost.

The various sections were joined with aluminium plates and pop rivets. We followed a Greenpower design as the basis for our car but made numerous changes along the way.

Step 2: The Steering

A simple lever steering system was chosen as i did not want the kids to have a "spear" pointed at their chest when they drove the car. As it turned out this was simple to get used to especially by drivers who have not yet driven cars and so have not preconceived ideas of how it should be.

The front wheels have a simple bent 2 mm mild steel king pin arrangement with a 19 mm bolt though for the king pin. With plenty of grease this works well. the steering rods have trackrod ends easily available from bearing suppliers to allow a certain amount of give in the system so no complicated alignment was required just set the wheels straight ahead.

We decided not to apply any toe in or wheel camber. the wheels are a 12.5 inch by 2.25 inch wheel chair wheel. Again, aluminium for lightness and ease of obtaining new tires.

Step 3: The Brakes

Although during a race the brakes are rarely used - the motor provides a lot of drag if you turn it off, they are necessary sometimes. We borrowed a bike disk brake set but found it very difficult to set up and easy to get out of alignment so will look to revert to a more simple system using a normal bike caliper brake over the winter closed season.

The brake levers are on the steering arms and operate the rear wheel brakes independently - this isn't a problem even at speed.

Step 4: The Motor and Drive System

The rules stipulate a 24 volt motor - the supplied motor is a wheel chair motor style without the attached slow speed gearbox. It operates at 20 amps at 2000 RPM.

With the gearing we have used it gives us a top speed at present of about 25 to 30 Mph - Not super fast but when your bum is only 2 inches from the ground!!

At a later date we will raise the gearing ratio slightly to up the top speed to 30 to 40 MPH provided we can do thig without over stressing the motor.

Cycle gears are also an option but may insert a complex system into something that needs reliability.

Step 5: The Motor Control/electrical System

This is VERY simple - just on and off. A 70 amp 24 volt automotive relay is switched by the red button on the steering lever and this in turn switches current through to the motor.

Although this system is very simple it is enough and reliable. Pulsing the switch on and off provided a crude speed control although for most of the race the motor is on if going in a straight line and off is the wheels are turned.

In line with the motor is a 70 amp thermal cut out to protect the motor from over current - I strongly recommend you fit this - the motor costs £100 new so protection seems advisable.

The motor runs at about 80 deg C in normal use but if stressed, e.g. pulling away from a slow spped too often, driving the motor when the wheels are turned, gearing up the drive too highly in the hope of attaining supersonic top speeds the motor temperature can ramp up alarmingly to the point of breakdown of the epoxy glue holding the windings in at about 200 deg C.

Some teams use water cooling as the motor is water proof, some like us use fins to provide air cooling.

Step 6: The Body

We wanted a racing car lookalike, a light body, and a gesture towards aerodynamics.

Our body is made from paper, laminated with wood glue this dries to almost wood stiffness with little weight. getting a good finish however has proved difficult and we will look at a thin fiber glass alternative.

The general shape works well but the top cover should be closer to the driver with a small aero screen and the rear should be rounded to provide a smooth exit path for the air flowing over the body.

Step 7: Batteries

These are standard lead acid car batteries. 2 per car one each side just in front of the rear wheels.
They sit on the chassis and are held down with a simple bar and threaded rod arrangement to allow ease of changing.

We are allowed 4 batteries in total and can get about 60 to 100 miles out of them at about 20 Mph.

In our initial race we did 67.5 miles at an average of 18 Mph but we changed drivers 6 times during the race. Our peak speed was 26.5 Mph.

Safety is paramount in any racing sport so full 4 point seat harness was fitted and a full face crash helmet worn at all times when racing.

That's the nutshell overview of our project there are many alternatives to our design some exotic some very simple. You pay your money and take your choice and have fun.

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    I get several queries a month on this project asking for more details, often asking how to make it go 60 - 100 MPH on 2 car batteries and how suitable is it for a college project.

    Well There are some serious issues here.

    Please people who are interested read the whole instructable AND follow the links for further information/

    Please research what others are doing. IF we could get 100 MPH from 2 car batteries and go 500 miles then Ford etc would be already doing that!

    Lastly please attend to the points below.

    1. This is a BIG task - I also made an electric car fro my collage degree and it took me almost a year of very long hours and hard work  to do  - make sure you can finish the task.

    2. You will not get 50 - 60 MPH and a reasonable distance on a couple of  car batteries. THINK - if this were possible then commercial manufacturers would be doing it.

    3. You must do some in depth research there is a LOT of information on the web, this is only a starting place. You must look to see what others have done and how they did it or you are bound to fail. As a teacher of design  I am worried that you don't have enough grasp of the essential issues to complete the task.

    4. At best you will probably get about 30 or 40 MPH on the flat for about 2 hours from 2 car batteries - so a range of about 60 miles.

    5. The most energy dense electrical power supply at present that is easily available is Lithium ion batteries like in mobile phones BUT these are going to cost you a LOT. commercial cars combine a HUGE power pack with a higher voltage motor to get a better power to current rate.

    6. Our motor was 250 watts and if you rad all of the instructable and follow the links you will see runs at about 2000 RPM and was geared to give 35 MPH at the wheels - I leave it to you to work out what the gearing has to be as it depends on the wheels you use.

    7. Our car cost us about £1500 to build say $3000 so it isn't a cheap project to do well.

    8. Your better bet would be to develop a part of such a system and show how it is integrate into the whole vehicle.

    9. For a commercial day to day car you will need to look at Pulse width modulation speed control. This will give good control without wasting energy, Energy recovery on braking (KERS system). A suitable material and construction for a VERY light weight body/chassis. A suitable source of mechanical running gear. Some way to steer and some way to stop the vehicle.

    10. As I said at the start It is a long and complex engineering problem, it can be done - we did it, but you MUST ensure you have the time and skills to complete the task.

    Good luck

    hi sir!!!!!!! we are doing project on solar vehicle..for college.so, we are having a BLDC motor of 1500 RPM & 60 AmH. we have a battery limit upto 48V. All that we needed is the requirements of connections and your suggestions..

    Sir iam goin to participate in e baja ,electrical drive train,so how should i srtart with ,and give a effecient ,doing my research as well,but if you through some light it would be helpful

    1 reply

    PLEASE read the entire instructable, then read my post above this. I have NO IDEA what your aiming to do, how fas,t how powerful, how far you want to travel or how much you might spend.

    What I can tell you is to go fast, far or for a long time will COST a lot.

    Engineering wise, build a light vehicle, Build it strong enough, Your choice of motor, battery and control system will govern the rest and much of that is down to how much you can spend.

    Look at what other people have done in the same area and follow their lead. If there are rules follow them.

    From what I can see googling E baja your going to need a lot of money.

    How did you get the gear box off? Didn't the shaft have a worm gear?

    1 reply

    The gears are keyed to the shaft. Removing a link from the chain allows you to remove the gears if you need to.

    Sir .... We started a solar car project .. We are actually participating in ESVC 2016 ... The electrical specifications are given as
    Max voltage and power of motor are 48v and 2kw ....... Max voltage and power of battery are 48v and 4kwh ...our car weighs about 210kgs with driver.... Sir can you please suggest me what specifications should we choose in order to get the best maximum speed

    1 reply

    Very Very light,

    Get a good electrician to advise you

    Study what others have done building solar cars, then study and analyze it again, they have MUCH more experience in this particular field then i do.

    Build early and test test test - improve on the basis of your tests.

    Excellent article. We are just starting out with Greenpower so your post is just what we needed with exactly the right balance of technical detail and down to earth common sense. I have asked all our team members to read it for homework. Thank you.

    1 reply

    What are the dimension's of the motor?

    1 reply

    Physical?

    Around 12 inches end to end and 9 inches diameter. they are specially made for the racing contest so everyone has the same.

    250 watts continious power but run at 500 watts with cooling fins.

    Hi.. I'm curious about dimensions as well... But just the perimeter for now... What's the width and length of the frame?

    1 reply

    Actual dimensions aren't important - You need to fit the driver in.

    Ours was 8 feet long and about 33 inches wide. (2.4 m long and about 1 m wide)

    hi im building a go kart that has 100 amps and a 24 volt motor how many mph will that go??

    1 reply

    Sorry I took a long time to reply. the robot has stopped sending out email notifications.

    Its difficult to predict - Much depends on how much it all weighs, what your gearing it to do and how well it has been made.

    Ours was designed to suite an endurance race so speed was offset against battery life.

    you may have to try it to fond out.

    Not allowed under the race rules and if you go on the road would be illegal.

    It is enormous fun Shame adults can't join. Not us we suffered punctures in both finals we entered.