Introduction: Electric Mini-Motorcycle!
This instructable will show you how to design, build and test your own mini motorcycle. Small electric vehicles are a great way to learn engineering, physics and many hands-on skills. We'll start with an old pocket motorcycle frame and end up with an EV capable of cruising at 20-25 miles an hour (or more if you are crazy!). I normally use my own pocket motorcycle (i call it Chiquicycle!) for cruising around campus and getting to class in time.
This is my website: rjmelendez.blogspot.com check here for some more wacky projects.
Thanks to Abraham Garza, Charles Guan, Victor Rodriguez for their contributions.
Step 1: Get Your Rolling Frame!
First step in making your own pocket bike is to find the frame. Luckily craigslist and ebay is full of people trying to give away their old pocket bikes because they sons have grown out of them or because the electrical system got toasted by some kid doing burn outs. I have helped many of my friends find pocket bikes online and here are the models and brands that most often come up:
Razor Pocket Bikes form the majority of pocket bikes Chiquicycle is a Razor MX350 i got from some people that had taken it apart and were about to throw it away. If you look hard enough you should be able find a couple of used razors for a small cost (<50$).
Honda Minimoto is another popular model.
Also there is a lot of pocket bikes that used to be gas and you can easily convert to electric. These frames tend to be heavier but more sturdy and their brakes are much much better that child motorcycles.
After you get your frame, take a good look at it and try to find any missing parts. Sometimes you won't have the chain, or the driving sprocket. Luckily you should be able to find most of these materials in the internet here are some good resources for pocket bike specific parts!
Many times you can probably replace the original parts by bicycle parts (Chiquicycle has a bicycle handlebar + bicycle seat). In addition the brake levers/cables can definitely be bicycle parts.
We have a "pocket bike gallery" in cambridge MA, we have all sorts of bikes we can convert so don't limit yourself to a specific brand or style!
Make sure your rolling frame (wheels, handlebars, chassis and brakes) are in good condition before you start modifying it.
Step 2: Design and Get Your Electric Drive!
Next is to get an electric drive for your pocket motorcycle. The drive has 3 components: the motor, the controller and the batteries.
Before selecting components its important to get a sense of the voltage and current you will be dealing with. Voltages for pocket bikes range from 24-40V and current limits can vary from 20-60A.
First question is if to use a brushless motor or a brushed motor. Brushed motors are cheaper but they may need more maintenance. Brushless motors are generally higher performance but also generally more expensive.
Brushed and Brushless motors have an important parameter to pay attention to this is the Motor Back EMF constant commonly reference to Kv. Kv is measured in RPM/volt and represents the speed that the motor will obtain in no-load conditions. A high Kv means the motor will spin faster at steady state but it will also produce less torque per unit current. It is the "gear ratio" of motors, a lower Kv will generally give a lower final speed but more torque for the same amount of current. Think of a high Kv being like higher set of gears on your bike/motorbike or car (harder to pedal but faster). i recommend a Kv of less than 200 for a pocket bike. Chiquicycle has a 245 Kv motor and i wish it was lower so i could have a better acceleration.
Make sure the motor you select can handle the currents and voltages you select. However keep in mind most motors can actually surpass their ratings quite a bit. My friend is running 40V on a motor rated for 24V for instance. Always look on forums for and tips and hints about motors to use.
Here are some great brushless motors from hobbyking: (when ordering from hobby ALWAYS make sure to use PAYPAL payment option)
The kind of controller is specific to wether your motor is brushed or brushless. Again keep in mind the voltages and currents you want to run on. The controller is what ultimately will decide how much current will get pumped into your motor so make sure you are happy with its current rating.
Kelly makes good controllers here are some links:
kelly brushed: http://kellycontroller.com/mini-dc-controller-kds12v-72v-c-27.html
kelly brushless: http://kellycontroller.com/mini-brushless-controller-kbs12v-72v-c-60.html
Another cheaper option is to use a chinese electric bicycle controller from Ebay. These controllers are cheaper but come with no guarantees and no manual. Chiquicycle currently has one of these controllers and it works fine. My friend charles has a good tutorial about these chinese controllers: http://www.etotheipiplusone.net/?p=2387
Most stock mini motorcycles operate either on 24V or 36V lead acid batteries. Lead acids are cheap but are pretty heavy. You can get lead acids pretty much anywhere, you can also reuse the batteries that came with the original bike if they are not burnt out.
Chiquicycle has a custom soldered battery pack made out of A123 LiFe cells. These cells are harder to come by but are lighter and more powerful. My friend Victor has put a nice tutorial together on how to make these packs: http://viictorrodriguez.blogspot.com/2012/09/how-to-make-battery-pack.html
My friend Abraham and I have put together a physics model on MATLAB/Simulink that simulates the acceleration profile of an EV. This can show its top speed and their acceleration. You can download it here: https://dl.dropboxusercontent.com/u/4686960/sims%20EV.zip
In the Matlab script you can fill out the value for your specific EV (wheel size, sprocket gear ratio, voltage, current etc) and when you run the script it will plot for your the accel. profile of your EV. I suggest you play around with the settings in order to tune your design.
After you have your motor, controller and batteries you are ready to begin modifying your bike!
Step 3: Mounting the Motor/Drive Train
Mounting the motor is pretty straighfoward. Most motors have mounting holes where to screw them onto supports. If you are lucky some motors even have their support built in and you will just have to screw it to the flat part of the frame.
Chiquicycle has a a very simple mounting set up. I grabbed an aluminum L-bracket and mounted the motor on it and then mounted the bracket to the frame. If you play it smartly you might not even need to drill holes into the frame and reuse the old ones. Be sure you consider the chain tension when choosing how to mount your motor, you might even consider using slots rather than holes for your motor mount so you can move the motor forward of back to adjust chain tension.
Once the motor is mounted you need to mount the sprocket to the motor. Some motors have a sprocket mounted on them already. Other motors have a sprocket that has a D hole. You can file/sand down your motor shaft to fit the D and then make a spacer with a set screw to constrain the sprocket axially on the motor shaft. You can also order shaft collars on mcmaster to constrain the sprocket axially.
After your fit the motor sprocket, try putting the chain around both the rear and front sprocket. Make sure there is appropiate tension. If its not tensioned appropriately you can shorter then chain, or move the motor mount if you designed for that. Some pocket bikes might even come with a chain tensioner so be sure you know how to use it.
Step 4: Mounting Motor Controller and Batteries
After your drive train is assembled, it is now time to put in your controller and batteries.
The controller is pretty easy to mount, they normally have mounting holes you can use to mount the frame. Many times you will have to build an interfacing plate (something that mounts to the controller and the holes in the frame.
Batteries are a little bit more tricky to mount. what I found is best is to put them in a box where they fit snuggly on and the mount the box to the frame. You can the zip tie it for extra security.
Once you are done with the mounting, you are DONE with the mechanical work on your bike!
Step 5: Electronics!
The electronic wiring is dependent on your specific motor controller. The motor controller normally has two leads for the batteries and then 2 or 3 for the motor (2 motor leads for brushed motor, 3 leads for a brushless ones).
You will need to connect a throttle to the motor controller (this is what tells the motor to go faster or slower). And the throttle normally has 3 leads (power, ground and signal) they often have these colors (red-power black-ground green-signal.
For a good schematic you can refer to your motor controller datasheet and they go into the details of how to connect everything.
For the chinese controllers that have no manuals refer to the picture.
Step 6: Testing!
Please be sure you are wearing appropriate safety equipment (helmet, gloves etc).
I use my android phone with its built in GPS to generate GPS plots of my EV rides.
My Tracks (from google) is the app I use. Very intuitive to use and easy to export data. After collecting my data I use the website www.gpsvisualizer.com to visualize the data. You can use the data from here to see how well your experimental data matches with the design you performed in step 2.
Here are some plots/videos from my testing with chiquicycle!
Step 7: Share Your Experiences!
I am very big fan of sharing what you learned! After you finish your pocket bike, share your work with other people and inspire them to pursue similar projects!
Let's keep the EV/hacker community growing!