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This instructable gives an overview of building two small cars from the ground up, both powered by electric bike motors.  The build includes  chassis, fibreglass body, steering and drive train.  The cars are designed for efficiency to extract the maximum performance from a 1hp motor and were used to compete in an electrathon competition.  It can be built for around $1500 including motor, controller and the latest lithium batteries and will go flat out around 50km/h for 1 hour before recharging.
Similar in size to a gokart, Roadbot 3 and Roadbot 4 have streamlined bodies, minimal frontal area and low rolling resistance tyres.  They are powered by brushless DC electric motors and a lithium battery packs.
They were built to compete in the Perth EV Challenge in Western Australia by the River Raiders team. 
 
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Step 1: Planning and Models

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After doing some drawings and measuring up the drivers, a scale foam body model is made from polystyrene foam and a full scale ergonomic study is made from plywood.  The shape of the sides shows how the vehicle profile will look and identifies a couple of places we can shave a bit off the cross sectional area.

This year we are using 20” wheels and are building 3 and 4 wheel cars.   The 20” rear wheel, down from 26” in previous years allows a more reclined driving position which reduces the frontal area.  The 20" wheels are also stronger for side loads than large bike wheels (note a bike does not apply side loads to a wheel when cornering) but have a slightly higher rolling resistance however at speeds over about 30km/h, reducing wind drag becomes more important than rolling resistance.

Step 2: Building The Body

The body is made in the following steps
   1.  Drawing up plans to determine the smallest aerodynamic package
   2.  Make a foam model 
   3.  Make a full size plug
   4.  Make a fibreglass mould from the plug
   5.  Make a fibreglass body in the mould


The Plug
It started off looking more like a flintstone’s car!  I found an old pine log in the paddock that was big enough to carve a plug for the body from and cut two large slabs, one each for the top and bottom car body.
Reasons for using a log are twofold, firstly cost - had an old log in the paddock so doesn’t cost anything other than the time and secondly the timber will give a stronger more rigid surface than foam to mould onto.  Timber can be formed easily with woodwork tools and can be finished easily to a good quality surface.  After the plug was completed it was sprayed with gloss varnish and given several coats of mould release wax and sprayed with a pva mould release film

Fibreglass Mould
The plug was cut longitudinally into 4 quarters.  See photos to clarify how the plug was cut.  This enabled the plug to sit flat on a melamine particle board which provides and smooth, flat surface for mould joins.  For the first quarter mould, a second smaller melamine board was used at right angles to the first board to create a second mould joint plane.
I won't go into any detail on fibreglass layup as there are other good instructables on fibreglass.  We used three layers of chopped strand mat with polyester resin for the mould.  In the corners the glass matting needs a gentle radius so we mixed wood fibre (sawdust from sanding) with some resin to smooth out any tight bends before laying up the glass matting.

After the mould has set (allow a few days to harden) bolting holes were drilled along the joints before removing from the plug.  The holes will be used to align and assemble the mould after the plug is removed.

Body
The mould was polished and wax, reassembled in two halves and the internal surfaces coated with mould release agent.  Don't rush or skimp on this step or the body will stick to the mould and be very hard to remove and may damage the mould.
After waxing and applying pva mould release, one layer of woven mat and one layer of chopped strand matt were layed up in the mould by hand.  A team of three people made it easier to complete including handling cloth, working quickly with resin before setting and wetting out the cloth and eliminating air bubbles in the fibreglass. Its a smelly, messy job but there are very few alternatives for a cheap, light, strong, curved body skin. 
After release, trim the flanges and cut a hole for the driver.  

Step 3: Steering

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The steering follows basic ackerman principals, that is the steering pivot points are in a line between the steering pivot (king pin) and the centre of the rear wheel.  This results in a different steering angle for each wheel - the outer wheel having a slightly large radius and smaller angle when turning than the inner wheel.  If there was no allowance for the different steering angles between the inner and outer wheels the car would still work OK but there would be tyre scrub when turning and would not be as efficient of fast through bends.

A model was made using ply and nails to represent steering joints to test the steering geometry before fabricating.

The steering was made by welding a stub axel turned from 14mm rod onto a piece of 14mm steel tubing.  The inside diameter of the tubing was 10mm, neatly pivoting on a 10mm (3/8") bolt.  The stub axel pivoted in a U shaped bracket bent from 4mm steel bar and the back of the U bracket was welded to a 25mm (1") square hollow tube.  

Looking at the steering from the front, the steering pivot (king pin) is not vertical, an angle of about 10 degrees (king pin angle)  reduces steering scrub and makes the steering self centre, improving stability.  From the side the king pin is angled at about 5 degrees (caster angle).  Also the wheels are not completely vertical, they have a slight camber.  Camber is usually provided on road cars so the tyre sits flat and has more grip allowing for some roll when cornering.  In this case the reason for camber is very different.  We are not looking for grip, but a little bit of camber helps offset some of the side loading on the outer wheel when cornering, a bit like a bike leaning into a bend.  



There is no suspension here - its designed for a smooth track.  Creature comforts are not important, efficiency is the main goal.


Step 4: Chassis

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Here keeping it simple is best.  The weak points are probably the welds, so we keep these to a minimum.  This also help make it quicker to build.  Essentially the chassis comprises two 25mm (1") thin wall square hollow steel tubes, one each side of the driver with another for the axle at the front.  The three wheel car has a couple of tubes welded on like a horizontal rear fork.

The four wheel car is more complex.  It uses a small chain drive diff from a tricycle supplier.  It also has swing arm axles with rubber stoppers for suspension.  The suspension is not for comfort, but is required to keep all four wheels on the road.




Step 5: Drive Train

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The obvious source of motors for a small electric car are the bike kits that are cheaply and widely available.  They range from as low as 200w to over 1500w.  The motors usually come matched to a controller and a battery pack is used to suit the voltage and range required.

The  first choice to make is whether to use a hub motor or a chain drive.  A hub motor is simpler and more reliable, but cannot adjust the gearing and tends to be limited to about 40km/h maximum speed.  With a chain drive motor, the gearing can be adjusted and speeds can be alot higher for an aerodynamic body.

We used an 800w brushless dc motor and the lithium battery pack voltage and size was determined to suit the rules of the competition which limited the battery pack to 36volt 5kg maximum.

The use of standard bike components meant that chain sprockets and brake discs could be bolted direct to the wheels.

 

Step 6: Bringing it Together

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The bottom of the body rivets directly to the main chassis tubes and the top half of the body joins by pivoting at the front on a repurposed door hinge.  

Add paint, graphics, a windscreen to complete a simple electric car.


Step 7: Testing the Drive Train

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More Testing Footage

Step 8: Race Day

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Roadbot 3 (three wheeler) was noticeably faster than Roadbot 4 despite identical motor, controller and battery combinations.  The extra cornering grip and stability of an additional wheel could not make up for the additional drivetrain and aerodynamic losses of a 4 wheel vehicle.

Roadbot 3 was fastest on track setting a lap record and still had battery capacity at the end of the race.  Roadbot 4 was about third fastest on track and the battery pack and could not use its full speed if it was to make the full race distance because of the extra current draw from the motor.

After a botched pit stop (rules require two mandatory pit stops) where the next driver was missing, Roadbot 3 recovered ground to finish second overall.

Picture (l-r): Wayne, Rod and Jamie, the River Raiders Team

Acknowledgement:  EV Power supplied batteries and battery management for the cars.

2012 ITC Global Perth EV Challenge Official Event Video
http://youtu.be/i2-fg-HefL8

River Raiders Race Footage

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Congrats! nice job you did with this vehicles.
what diff are you using for the 4 wheeler? can you let me know where can i find one? been trying so hard to get one but i only find atv ones.
Greetings from Mexico
Leo G.

Ganhaar (author)  leo.gomez.5688472 months ago
Got the diff from Jeffrey Samagaga at www.samagaga.com
It was about $100 new including axels.
Ganhaar (author) 5 months ago

36V lithium (lithium ferrous phosphate chemistry). Batteries limited in the rules to 432Wh and 5 kg. We have tried a few different types of batteries such as pouch cells, but for this event we used 11 headway cells.

Wayne

rajaram234955 months ago

Kindly give the battery spec please..

please I need more informations about this car

Ganhaar (author)  vipinbatheriyil6 months ago

Happy to answer specific questions,

Ganhaar (author)  vipinbatheriyil6 months ago

Happy to answer specific questions,

please I need more informations about this car

please I need more informations about this car

please I need more informations about this car

FXSTi6 months ago

Thank you for making this instructable. Very entertaining and thought provoking.

matsciteacher9 months ago

I am the advisor for an after school Electrathon Racing Club in Olympia, WA. This year we are aspiring to upgrade our older cars and build one or two new vehicles. We had been researching body kits for which we could build frames, steering, suspension, braking systems, and drivetrains for. We have the ability and equipment for doing welding and some metal fabrication, but no saws, fiber glass choppers, etc. which would be crucial for building a body such as yours from scratch. Plus, I can only commit to so much time in the afternoons and evenings and still remain married to my wife of 41 years! Would you be interested in building and selling us one or two of your car bodies, since you have already invested the time and expertise into building a mold? It would be an opportunity for you to generate more funds for your projects. By the way, thank you for the information about Samagaga. They are very helpful. We are getting ready to order several sets of wheels, hubs, axles, and misc. from them. I had never seen their wheels before stumbling across your page here on Instructables. We love the design of your Roadbot 3! Thank you for all of your information.

CAHNTX1 year ago
Ganhaar,
My apologies if you'very answered this one...what was the aprox. diameter of pine log used for the plug?
Ganhaar (author)  CAHNTX1 year ago
Only a guess as I didn't record measurements - probably 600 to 800mm diameter or between 2ft and 3ft.

Regards
Wayne
-DOUG-1 year ago

How do you source these parts? I don't see your sprocket hub from the 4 wheeler, the wheels. How do you find these things to work with.

Ganhaar (author)  -DOUG-1 year ago
We found these components online and ordered them from a supplier in China, Samagaga. I think the components are made primarily for pedal tricycles.
I focused on the 3 wheeler for the drivetrain in the instructable as it was more efficient, simpler and cheaper than the 4 wheeler.
The 4 wheeler had a diff, CV joints and drive shafts and pivoting swing arms. The rear drive sprocket attaches directly to the diff of the 4 wheeler and the CV joints were all part of the diff and driveshaft components supplied by Samagaga. I would not recommend taking this approach for a four wheeler due to the added mechanical complexity.
If you were going for a simple rear wheel drive arrangement for a 4 wheeler and a solid axel was not suitable, then I would recommend either twin electric motors independently driving each rear wheel (as I have done on the EV platform, my other EV instruct able) or for a cheap, low power arrangement where traction is not an issue, drive only one of the rear wheels and let the other freewheel.
Regards
Wayne
shonoe181 year ago
I don't know if you answered this... But approximately how fast does it go?
Ganhaar (author) 1 year ago
With 4 times the power performance would be impressive and you should be able to comfortably go more than 60mph which would be scary in a car using bicycle components.
Where were you getting the motors from to get a pair of 2hp motors for $40? Sounds like a great price.
Teamtestbot has some good advice in his instructables about using RC motors for scooters and how much you need to derate the quoted power for this sort of application so you don't end up with smoke and tears.
If you are looking for more specific details on any of the details about the car Im happy to try and help, let me know what sort of info you are chasing.


Hi, awesome job on this project! I've been thinking about doing the same thing for some time now. I have a background in radio control, and I was looking at using a pair of these motors, one for each of the front wheels. this would give 3kw of power, or around 4hp. all for $40 for the two motors combined. I'm planning to run them off 6 cell li-po battery (roughly 23 volts). any advice would be greatly appreciated!
Hi, awesome job on this project! I've been thinking about doing the same thing for some time now. I have a background in radio control, and I was looking at using a pair of these motors, one for each of the front wheels. this would give 3kw of power, or around 4hp. all for $40 for the two motors combined. I'm planning to run them off 6 cell li-po battery (roughly 23 volts). any advice would be greatly appreciated!
ever thought about making the shell in Carbonfiber? I could give you some advice if you want to! cool project btw ;)
Ganhaar (author)  matthieutje651 year ago
Didn't do carbonfibre to keep costs down and from previous experience is simpler to do polyester resin with glass cloth by hand. I am interested in potential for using natural fibres.
the body looks like a box for roof racks
they are aerodynamic ridged and are cheap second hand
i bet you could make a EV car for alot less $$ then 1500 bucks!

awesome build i prefer the 3 wheeler myself!
maybe because your using a differential between the two rear wheels
one wheel drive on the 4 wheeler would same weight and might help your initail rolling resistance on the drivetrain.
<3
Ganhaar (author)  pocdragon1 year ago
also good suggestion with driving one wheel only on the four wheeler. It would be a good experiment to determine if there is a problem with drag in the diff or the rear axle bearing assembly.
Ganhaar (author)  pocdragon1 year ago
Sure you could build it cheaper, but $1500 is not expensive for a custom build with brushless electric motor, regen, lithium batteries and new wheels.

The body is very thin glass fibre and fits like a cocoon, maybe you could find a roof rack box that is just the right size and that would save a lot of work building moulds and fibreglass.
wrsexton1 year ago
Despite my best efforts at blowing up the photos, I can't decipher what brand of wheels you used. Haven't seen them over here. What are they?
Ganhaar (author)  wrsexton1 year ago
Samagaga from China. As well as looking good, the big spokes seem fine for cornering loads, so far haven't had any failures.
Taiwan. Has been known as 'Free China', tho.
Bverysharp1 year ago
Amazing design and construction. Job well done!
Stuart211 year ago
Hi Gan, great work.

I am surprised that you get such a difference between 3 wheels & 4 wheels - how is your steering alignment? Suggest removing 1 front wheel & running (if it will balance) check amp draw wheel on, & wheel off. If significant diff, try adjusting toe in to min amp draw.

My guess is ~ extra 5% for 4 wheels - not more than 10%?
Ganhaar (author)  Stuart211 year ago
We have a turnbuckle on one of the steering linkages and can adjust toe in / toe out on the fly while monitoring current draw so that shouldn't be an issue.
The four wheeler is a lot heavier by the time you add up the weight of the chassis, suspension, diff, driveshafts, rear arms and extra wheel. This along with the extra bearings and aerodynamic drag all add up to a few percent which is along the lines of your guess but makes a big difference in a race with a very limited amount of power.
I also suspect that bearing alignment was not perfect and adds extra drag.
You have also highlighted a great point with testing. With an electric car the amp draw from the motor is a very simple, accurate and consistent method of testing drag and efficiency and is great for testing modifications.
How much does each (3 wheel & 4 wheel) weigh? Are other factors the same?
i.e how much is the extra driven wheels weight penalty?
SANDBOX11 year ago
GREAT WORK!!! And congrats on the race. Where did you get your parts?
Ganhaar (author)  SANDBOX11 year ago
The major components were batteries and battery management EV-Power and the motor was a Cyclone Motor bike kit.
Ok thanks. I am looking to build a 4 wheeled pedal car and was curious about a good parts supply.
bennelson1 year ago
Well done! Great job on a purpose-built vehicle. I tested an "Electrathon" three-wheeled vehicle at the local high-school a while back. I intentionally TRIED flipping it. I was amazed at the stability! These are fun vehicles!
How big is the motor? kW?
im gonna quote from the project:
"We used an 800w brushless dc motor and the lithium battery pack voltage and size was determined to suit the rules of the competition which limited the battery pack to 36volt 5kg maximum."
now add flexible solar panels to your car. uill have some passive recharging as well.
except at current flexible solar efficiencies you'd get an unnoticeable range extension from such a small area on such a fast vehicle. it's more useful to but solar panels on the garage and charge it there.

the solar-race vehicles are more than 10 times the surface area as this racer and are not very fast at all. they are really quite impressive for completely different reasons.
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