Instructables
Picture of 1HP Electric Car
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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

Picture of 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.

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.

CAHNTX3 months ago
Ganhaar,
My apologies if you'very answered this one...what was the aprox. diameter of pine log used for the plug?
Ganhaar (author)  CAHNTX3 months ago
Only a guess as I didn't record measurements - probably 600 to 800mm diameter or between 2ft and 3ft.

Regards
Wayne
-DOUG-5 months 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-5 months 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
shonoe189 months ago
I don't know if you answered this... But approximately how fast does it go?
Ganhaar (author) 9 months 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!
matthieutje6511 months ago
ever thought about making the shell in Carbonfiber? I could give you some advice if you want to! cool project btw ;)
Ganhaar (author)  matthieutje6511 months 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.
pocdragon Ganhaar10 months ago
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)  pocdragon10 months 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)  pocdragon10 months 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.
wrsexton11 months 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)  wrsexton11 months ago
Samagaga from China. As well as looking good, the big spokes seem fine for cornering loads, so far haven't had any failures.
Stuart21 Ganhaar11 months ago
Taiwan. Has been known as 'Free China', tho.
Bverysharp11 months ago
Amazing design and construction. Job well done!
Stuart2111 months 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)  Stuart2111 months 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.
Stuart21 Ganhaar11 months ago
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?
SANDBOX111 months ago
GREAT WORK!!! And congrats on the race. Where did you get your parts?
Ganhaar (author)  SANDBOX111 months ago
The major components were batteries and battery management EV-Power and the motor was a Cyclone Motor bike kit.
SANDBOX1 Ganhaar11 months ago
Ok thanks. I am looking to build a 4 wheeled pedal car and was curious about a good parts supply.
bennelson11 months 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!
Hoffermagic11 months ago
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."
astral_mage11 months ago
now add flexible solar panels to your car. uill have some passive recharging as well.
chrwei astral_mage11 months ago
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.
falexandre111 months ago
fixe
andrea biffi11 months ago
impressive project!!
ubiquity11 months ago
cool!
mbernstein311 months ago
Fantastic! Thanks for taking the time to share this.
dndr11 months ago
Awesome instructable... impressive
mikeasaurus11 months ago
It's fun to read about the differences between the 3 and 4-wheeled versions. Looks like a lot of fun!
Ganhaar (author)  mikeasaurus11 months ago
A point I should have made about the three wheelers was that the stability was also great. If pushed to the limit the rear wheel will slide before it shows any signs of rolling or instability.