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. 

Step 1: Planning and Models

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.
Very impressive!
<p>Hey Ganhaar,</p><p>Firstly, thank you so much for this instructable, it does a REALLY good job. So, I'm starting an electrathon team this year, and I just have a couple questions.</p><p>I'd like some more info on the race you competed in, specifically, length of time that the cars had to drive for, were there any hills on the track.</p><p>On the subject of batteries, I have to use SLA batteries, but I would like to know the specs of your batteries, and the voltage of your system. I would also like to know amperage draw of the motor in your system, if you know that off the top of your head.</p><p>Finally, I would like to know your thought process when you determined your angles for steering (camber, caster, and kingpin). I would also like to know how exactly you built your steering to align with your Ackermann angle. I understand the principle, but I want to know how you determined your measurements.</p><p>Thank you in advance!</p><p>-Bryce Karlins</p><p>Peachtree Ridge HS Electrathon</p>
<p>Thanks so much for putting this on instructables. We are just attempting to put our first electric race car together and need all the help we can get. Cheers!</p>
<p>Thats great, good luck and let me know how you go.</p>
<p>What is the name of the motor you used?</p><p>Thanks in advance!</p>
The motors came from Cylone Motor in Taiwan
<p>Congrats! nice job you did with this vehicles.<br>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.<br>Greetings from Mexico<br>Leo G.</p>
Got the diff from Jeffrey Samagaga at www.samagaga.com <br>It was about $100 new including axels.
<p>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.</p><p>Wayne</p>
<p>Kindly give the battery spec please..</p>
<p>please I need more informations about this car</p>
<p>Happy to answer specific questions,</p>
<p>Happy to answer specific questions,</p>
<p>please I need more informations about this car</p>
<p>please I need more informations about this car</p>
<p>please I need more informations about this car</p>
<p>Thank you for making this instructable. Very entertaining and thought provoking.</p>
<p>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.</p>
Ganhaar,<br>My apologies if you'very answered this one...what was the aprox. diameter of pine log used for the plug?
Only a guess as I didn't record measurements - probably 600 to 800mm diameter or between 2ft and 3ft.<br><br>Regards<br>Wayne
<p>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.</p>
We found these components online and ordered them from a supplier in China, Samagaga. I think the components are made primarily for pedal tricycles.<br>I focused on the 3 wheeler for the drivetrain in the instructable as it was more efficient, simpler and cheaper than the 4 wheeler. <br>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.<br>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. <br>Regards<br>Wayne
I don't know if you answered this... But approximately how fast does it go?
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. <br>Where were you getting the motors from to get a pair of 2hp motors for $40? Sounds like a great price. <br>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. <br>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. <br> <br> <br>
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 ;)
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 <br>they are aerodynamic ridged and are cheap second hand <br>i bet you could make a EV car for alot less $$ then 1500 bucks! <br> <br>awesome build i prefer the 3 wheeler myself! <br>maybe because your using a differential between the two rear wheels <br>one wheel drive on the 4 wheeler would same weight and might help your initail rolling resistance on the drivetrain. <br>&lt;3
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.
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. <br><br>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.
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?
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.
Amazing design and construction. Job well done!
Hi Gan, great work.<br> <br> I am surprised that you get such a difference between 3 wheels &amp; 4 wheels - how is your steering alignment? Suggest removing 1 front wheel &amp; running (if it will balance) check amp draw wheel on, &amp; wheel off. If significant diff, try adjusting toe in to min amp draw.<br> <br> My guess is ~ extra 5% for 4 wheels - not more than 10%?
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. <br>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. <br>I also suspect that bearing alignment was not perfect and adds extra drag. <br>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 &amp; 4 wheel) weigh? Are other factors the same? <br> i.e how much is the extra driven wheels weight penalty?
GREAT WORK!!! And congrats on the race. Where did you get your parts?
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.
Well done! Great job on a purpose-built vehicle. I tested an &quot;Electrathon&quot; 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: <br> &quot;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.&quot;
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. <br> <br>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.
impressive project!!
Fantastic! Thanks for taking the time to share this.

About This Instructable




Bio: Designing, making, eating, thinking, growing, drawing, exploring, drinking.
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