Building an electric racing car

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.

Comments

[tezzachs]

nice to see a greenpower team using instructables, we were going to, but got engrosed in building and forgot the pictures! might do one for a goblin kit car at some point though

[rickharris]

Sadly an ex greenpower team, I retired and no one else would take it on. They gave the cars to another school that- as far as I know has yet to do anything with them.

[TheMadScientist]

these motors can by aquired at your local flea market/ resale shop for sure! old and new air compressors alike love these things, and they tend to be pretty massive... also, backup generators use these in reverse to generate electricity, which means that they can be taken out and used as an electric motor aswell. a third source would be the obvious washing machine/drier but they're a bit more difficult to get loose...

[rickharris]

Mmm these are purpose made for the job and are 24 volts.

You can get DC motors second hand but they are surprisingly rare these days. About the best source is Ebay and ex golf cart motors or up to 300 watts (claimed) electric scooters.

[rickharris]

Take care you are getting a DC motor of the required voltage and power rating there are a lot of toys (electric scooters for example) out there that use relativly small motors. Our motors are designed to operate on electric wheel chairs although there they have a step down gear box fitted. You need something in the order of 250 watts to be useful. BUT take care about using a generator to act as a motor. It will not be as effectent as a purpose built motor and could be and AC alternator which is useless. Car / lorry starter motors provide plenty of power BUT eat electricity - there is a drag car contest that uses them but after 200 yards the batteries are cooked. If you can find one perhaps a car DYNAMO will do at a push bit I wouldn't expect the range or power we get.

[The_Tom]

I got a motor from an old treadmill is says its a
2.5 hp at 130 VDC
17.2 AMPS
7090 RPM
25C
Class B
Thermal switch: 120 VAC MAX. 1800 VA MAX

Im kind of unsure as to what most of these mean lol and would it be a good candidate for a small go kart like yours?

[rickharris]

1. You need to get 130 volts to drive it - That's a LOT of battery!

2. Other than that it looks very useful.

Power is a function of Voltage and current so As you increase the voltage you can reduce the required current for a given power. This is why the F1 KERS systems use 300 volts + to power their system.

[omnibot]

I'd say so. RPM looks a little high but gearing it down should take care of that. 2.5hp is a good amount of power for a small buggy.

[The_Tom]

im guessing it meant 2.5hp at 130 dc volts?

[FrozenIce]

great instructable :) really liked it :) another thing about the breaks, wouldnt it be cool if u also put in some sort of wind break, like in the bugatti veyron?? it would look soo epic! just saying +5*

[rickharris]

Cool yes, but more weight to carry. When your racing the aim is to be as light as possible to make the battery go further.

thanks for the comment.

[tim127]

im trying to build an electric bike and the battary i want to use says its 10 ah and 24 volts how many amps is it and how well will it work with a 100 watt motor?

[rickharris]

A 10 Amper hour battery will in principle supply 10 amps for 1 hour - or 20 amps for 1/2 an hour or 5 amps for 2 hours - get the idea?

In actual fact it will fall somewhat short of this if you expect it to recharge and have much of a life.

Assuming the motor is 24 volt you may get 3/4 to 1 hour real running out of it. In principle the 100 watt motor will draw 4.amps to produce 100 watts at 24 volts.

100 watts is a little small for powering much other than a very light weight scooter. 200 - 250 would be better and not a lot more expensive.

in this car a 70 Ahr battery gave us about 2 hours running flat out - 30 Mph.

[tim127]

ok thank you, ill get a 250 watt moter and a better battary

[rickharris]

The steering mechanism is chosen for it' simplicity to manufacture and repair during the race. It has never let us down and works well under race conditions .

You have to understand the rules. The drive must be able to exit the car in under 6 seconds - a wheel gets in the way and to make it removable as in F1 is just too complicated. This isn't intended to be a raod car but has been built for a precise purpose.

As to having poor drivers in the UK I see in the current Formula 1 line up drivers from the UK - Australia, Germany Scandinavia in fact all over Europe and south America but No North American drivers have driven since 1993 and ever won the drivers championship.

Perhaps your driving experience is more suited for driving round simple oval circuits?
it's easy to be critical when you don't have the full picture!

[bmêttź]

Re: quick disconnect steering wheel.

A easy way to make a quick disconnect steering wheel is to use a socket wrench extension and a socket with a nut welded into it that is bolted to a steering wheel.

Use air socket wrench parts as they are better built for this purpose.

You can also use impact wrench extensions and the universal joints on them with small gas and electric motors if you have to mount a motor offset.

[benrice33]

Plus Britain has the greatest car show, or TV show in general for that matter, Top Gear

[fatboy106]

Great instructable, very helpful for when my team enters nxt year.

[rickharris]

If your entering next year a few tips:

Ensure you FULLY understand and comply with the rules.
Brakes are a BIG failure point - make sure the exceed the minimum demand.
When you race take spare tires and inner tube (You will get punctures)
Make a tool/parts list make sure you take them all.
Get to the race early so you can unpack, set up and get scrutinised.
Make sure every member of the team has a job to do and does it -
Practice packing and unpacking, changing batteries and drivers a LOT.Try to have more team members than the minimum or you will find some days not everyone turns up.
try to involve parents.

[fatboy106]

Thanks, it's nice to hear pointers from someone with hands on experience (the greenpower lot didn't help much).

[rickharris]

We got to the final twice - call it coincidence but we got punctures both times from drawing pins? How freaky is that!!!

Our down fall was that it took so long to change the tire that put us out of the running.

Build simple and reliable, you will outlast may of the fancy, even corporate entries who have spent BIG money on their vehicle.

Find somewhere to let your drivers practice driving. This can be really difficult as wide open spaced are few and far between.

Remember every year you need to bring in new members. We used to keep the car in the school foyer as an advert - It not only impressed pupils but Ofsted as well.

try hard to get a range of staff interested so your not short of adults when you need to race. i was lucky that out groundsman was interested and almost always available.

[Billgun]

Over in the UK you people keep the kids so uninformed about cars that they don't even know they are supposed to have steering wheels? wow thats so sad. I was driving MY one-ton around my house and down a old road by the age of 9 years old Let kids drive cars around thats what teaches them Because when you put a kid in the driver seat for the first time at the age of 16 they are going to be REAL terrible drivers thats probably why the UK has a reputation of bad drivers

[soccer man]

Cool car I'll try to build it. :) P.S how much money did you spend on that?

[rickharris]

The basic car cost around £250 as it is with the aluminium body - Then on top of that the motor was also £250 the battery set (4 x 12 volt 75 Ahr) cost £120. A lot depends on what you have and can scrounge for nothing. If I were to do this again and not for racing where the aim was as light as possible I would probably use plywood as a building material.

[teslafan100]

cool :)

[iminthebathroom]

The wheel chair motors you have used can be found SOMETIMES cheaply at medical supply centers. Most suppliers of powered wheelchairs that also do repairs have very odd contracts with suppliers. Most of the time if there is an electrical/mechanical erros with the chair, the standard rule is to A. either give the new person a new chair, or B. replace a very large portion of the wheelchair completely. Now the odd part is, that the parts that have been removed or even the whole chair are ordered to be scrapped. This is for insurance reasons on there behalf. Now most of these places will actually strip the motors and sometimes the speed and controller units, all though the latter is not often kept. The motors and the like are then used for people who's warranties have expired, or for people just wanting the motors for there kids to make go-karts or the what not. Remember to be kind when talking to these people, explain what you are doing and if they can't help you right now, ask them to keep your number.

[oscarthompson]

Heres The pictures of the electric Go-Kart I am making.
I have decided to split the current through 2 relays as I couldnt find any 40A relays. I am using 2, 350w 24v 19A 2550rpm motors geared down so they have suffient torque.

I am using light wieght alluminuim for the frame

Thanks

Oscar

[rickharris]

Looks good. You might find you will need to move your switch closer to your thumb but you will find out when you drive it.

How about brakes? Stopping is more important than going!!!

Have you modified an existing kart or built from scratch. Getting steering right is very tricky.

[robert]

i cant do that at all

[rickharris]

Can't do what exactly?

[oscarthompson]

I was thinking of that when I made the whole although my thumb just reaches it the push button. The brakes are not disk brakes but the same as the ones on bikes, just modified. I have build this from scratch from an old swing set

The steering is still needing to be perfected.. The spindles and the steering column work fine its just i need to find sutiable push rods and joiners. I used m6 bolts (the long ones you can cut to size) but it keeped locking up.

Thanks

Oscar

[rickharris]

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

[knuckel]

 This is a amazing instructional, I was just about to make my own electric vehicle!

[rickharris]

Your welcome - good luck. It's a big undertaking but lots of fun.

[oscarthompson]

hello.

I would like to know what gear ratio you are using? And does gearing the motor down increase the torque. eg. a 300w motor geared down so 1 revalution of the wheel is 5 revalutions of the motor, would mean the torque is equivelant to 1.5kw motor?

thanks
oscar

[rickharris]

14:1 geared down. The motor runs most efficiently at 2000RPM and draws about 20 amps. yes gearing down increases torque.

[oscarthompson]

Do you have any diagrams/schematics for you elctrical system?

Thanks

[rickharris]

The attached image shows the wiring. this is very simple. The 2 batteries are wired in series to give 24 volts. A key lock isolating switch prevents accidental operation of the car when not wanted and a way to isolate the batteries in case of emergency (they do happen)

The breaker protects against excess current - initially we set it to 75 amps but later changed it for a 100 amp breaker - That is a LOT of amps. -

The motor is controlled by a simple on off push button - this quite enough for the type of racing was were doing anything more complicated adds weight and gives a higher failure chance.

It is IMPORTANT you use correctly rated automotive wire for this as the motor can and does draw around 75 to 90 amps on occasion. A car battery is quite capable of melting insulation and wire and starting a fire so safety MUST be a first concern.

[oscarthompson]

Thank you Very much.
I have two motors and each one draws about 19amps. I am also using a automotive relay to switch the power on and off. I know the the gauge of wire for the motor connections have to be thick but for switching it on, does it have to be thick?

My gauge of wire is that type out UK (united kingdom) extension leads, I dont know how to measure it ?

Oscar

[rickharris]

If your 2 motors are wired in series they will need 2 x the voltage.  If wired in parallel  then 2 x the current.

Are they driving the same wheel? if not will they run at the same speed?