Lightweight Electric Motorcycle With Bamboo Frame

For our high school senior project, we have created a bamboo electric motorcycle. This project has been extremely fun, challenging, and time consuming; this is not something you can do over a few weekends. The end goal for us was to create a working motorcycle with a bamboo frame and an electric motor, as well as to create an Instructable.

The main stages for this project are:

Setting your goals for distance and speed and creating a budget.
Researching and ordering drive train parts.
Testing the drive train
Creating a model in SketchUp
Obtaining and heat treating your bamboo.
Hacking apart your donor bike
Tacking the frame together
Epoxy-ing the joints
Creating mounts and attaching the drive train.
Wiring.
Final parts and safety checks.

Materials:

Bamboo (more than you think you need)

Hemp twine (or some other sort of absorbent twine)

Epoxy and hardener

A donor bike frame w/ fork

Hot glue sticks

Pipe clamps

Zip ties

Lugs or some other connectors (for wiring)

Electrical tape/heat shrink

Plywood (inch thick and ½ inch thick)

Rubbing alcohol

Solder

Tools:

Hot glue gun

Drill (a drill press is nice in addition to a drill, but you don’t need one)

Hack saw

Wood saw (a band saw speeds things up a bit, as does a circular saw)

            Jig saw
   Screw driver (Phillips and flathead)
   Computer w/ SketchUp
   Rubber gloves
   Ruler
   Sharpie
   Clamps
   Soldering iron

Parts:
   Electric motor
   Batteries and charger
   Controller
   Throttle
   Bicycle breaks (front and rear)
   Bike wheels and tires (front and rear)
   Handlebars and stem
   Two switches (one for controller killswitch, one battery circuit breaker   Rear sprocket (match pitch with motor sprocket)
       Chain (match pitch with motor sprocket)

Step 1: Setting Your Goals for Distance and Speed and Creating a Budget

Setting goals for distance and speed will help dictate your parts and budget. As an electric motorcycle, it won’t be particularly speedy unless you get a very large motor. Realistically, the top speed for this project should be somewhere between 20 and 40 mph, depending on gearing and motor choice. The upside of this is that depending on where you are living if it goes under a certain speed you do not need to get it certified to ride it on the streets.

For our project, we set the goals of a 25 mile cruising range and a 25 mph top speed. Because of some gearing complications we actually ended up with a top speed of around 35 mph.

Our budget ended up being around $1100, including one blown controller and a few tools we didn’t have already. Your budget will most likely be your limiting factor. It will determine the size and power density of your batteries (your most expensive part) and how powerful your motor is. It is important that you leave an extra couple hundred dollars in your budget for unexpected costs, because who wants motorcycle that almost runs?

Step 2: Researching and Ordering Drive Train Parts

Based on your goals and budget, you should research and order your drive train. Our drivetrain components are mostly parts manufactured for electric scooters. We decided to go with a 48 volt system as it was the best compromise between power and weight. It is very important that all aspects of your drive train are rated to at least 48 volts (or whatever voltage you decide on), because otherwise something might explode.

Our drivetrain consisted of:

A 48v 1200w motor

A 48v YK42 controller

Two 24v 20ah LiFePO4 (Lithium Iron Phosphate) batteries in series

A hall-effect electric scooter throttle

Doing some quick research I was able to find all these parts on eBay for fairly reasonable prices.

Important notes:

If you do end up getting a LiFePO4 battery (and we recommend that you do), make sure you get a balancing (sometimes called “intelligent”) charger.

It’s very helpful to get a motor that already has a sprocket attached. The standard for electric scooters fits #25 chain, which is ¼” pitch and is ¼” wide.

Step 3: Testing the Drivetrain

Once your drivetrain arrives, it is important to make sure that all of your parts will work together. Charge your batteries, and then lay your drivetrain out on a table. Use alligator clamps to wire everything up. Make sure that the throttle controls the speed of the motor properly, and note which way the motor spins. Scooter motors are generally meant to be mounted on the left side of the bike, and you’re going to mount the motor pointing to the right like a bicycle chain, so you’ll probably have to switch polarity on the motor. During the wiring stages is when you will worry about what fits, for now we just want to make sure we have all the parts, that they are compatible, and that they work.

Step 4: Creating a Model

First make a sketch, and remember triangles are your friends. Once you have an idea of what the bike should look like, assemble a model. Either make a scale model out of wooden dowels or make one on the computer. Model all your parts accurately and to scale. You will do this to make sure there is spare room for your parts, that there will be a clear chain line, and that your parts will be able to be mounted properly.

Step 5: Obtaining and Heat Treating Your Bamboo

You should be able to obtain bamboo at a local lumber supply store or online. You’ll need both 2 and 1 inch thick pieces of bamboo for different parts of your frame. The higher-stress areas should be thicker bamboo.

Before heat treating, it is important to break all of the inner membranes of the bamboo with a piece of rebar. If you do not do this the bamboo will crack, and might explode. Also, existing cracks will increase in size during this process.

There are two ways of heat treating bamboo. The first method is to put the bamboo in the oven. This is the easiest, the fastest, the safest, and the cheapest way, but not all your pieces of bamboo will fit unless you have access to a really large oven, or decide to make an oven. If you use an oven, set the temperature to 350 degrees Fahrenheit and put the bamboo in for as long as it takes for it to become slightly browned. It is hard to tell how long this will take, but it took about 40 minutes for us. It helps to rotate the pieces every 10 minutes or so.

The second choice is to use either a blow torch or an electric heat gun. We suggest an electric heat gun, because the heat will not burn the bamboo as easily as the blow torch. If you do this the finish on the bamboo will look nicer, but it will not be as thorough, and the heat treating process takes a lot longer.

Step 6: Hacking Apart Your Donor Bike

In this step you will cut apart the donor bike frame to remove the front fork/headpiece assembly and the rear triangle. Keep the handle bars unless you plan on making your own.

For cutting we suggest a Sawzall with blades meant for cutting metal. This makes it extremely easy. It is also important to secure the bike to something. We clamped the bike to a large metal table. C-clamps work great for this purpose, but there will be a lot of tension so be careful when placing and removing the clamps.

See illustration for cutting directions

Step 7: Tacking the Frame Together

This step is fairly simple, but extremely important. The purpose of this is to make sure everything fits together, help determine the angles, give you a chance to change things, and make it much easier to epoxy. You will not be able to change the angle of anything once you epoxy it so tacking everything together with hot glue is an important step.

Step 8: Epoxy the Joints

This is a major stage, and takes a long time. We used West Systems epoxy, and it worked rather well for us. The epoxy must be pretty thin, you want to avoid really viscous stuff.

Setup: You should be in a well ventilated area, or outside. You do not want to be breathing in fumes from the epoxy. If you have gas masks go ahead and use them, but particle filters won’t do anything. Lay out lots of newspaper, this is a messy process. Rubbing alcohol is a must, and you’ll need a lot of it. You use this to clean the bamboo before you epoxy it as well as to clean up any errant drips of epoxy. Disposable rubber gloves that are designed to handle chemicals are also important. Don’t wear clothes that you care about, and it’s not a bad idea to wear an apron of some sort. Having your arms protected with clothing or plastic bags is ideal. Pre-cut your string into 3 or 4 foot sections. The last thing is to have two disposable dishes or containers, one for mixing the epoxy in and one for rubbing alcohol.

Process: It is best to have two people working during this process. One person mixes epoxy and hardener in one bowl and then dips in string. This person then pinches the string and pulls the string through their fingers to get off excess epoxy (like papier-mâché). Once the string is free of excess epoxy, the “dipper” hands off the string to the “wrapper”. The wrapper then wraps the string around the joint, trying to keep it taut and trying to keep the joint symmetrical. Expect to do one to two joints at a time, depending on where they are. The epoxy starts to harden after about ½ hour to an hour, but takes about 12 hours to become secure.

Clean up: Paper towels with rubbing alcohol. This will get epoxy off skin and objects, but you’re not going to get it off your clothes. Try not to move the frame or get rubbing alcohol on the setting joints.

When mounting the rear triangle, try to be as sure as possible to make the rear axle perpendicular to the rest of the bike.

Step 9: Creating the Mounts and Mounting the Drive Train

However your mounting system is designed, remember that you cannot drill into the bamboo. We found that the most effective and secure way of attaching things to bamboo is with pipe clamps. Make sure that your motor mount is very solid, as it will be taking a lot of torque.

Mounting the drivetrain:

Here’s the rear sprocket we bought: http://electricscooterparts.com/sprockets.html Item # SPR-2590

What’s nice about this sprocket is that it threads directly on to the rear wheel of a bicycle. This is awesome. Just unscrew whatever cassette is on the wheel, and screw that baby right on.

Attach the rear wheel w/ sprocket and the motor, making sure that the chain line is clear. You may have to fabricate a chain tensioner to keep your chain off your rear fork.

Next, attach the power source and controller. We suggest fabricating a battery box and then attaching that to the frame, instead of directly attaching the battery. You can then just screw the controller to the top of the battery box.

The throttle you bought should slide nicely onto your handlebars, you should attach this too at this point.

Step 10: Wiring

Once all the pieces are attached, begin wiring them together. Be extra careful to keep one battery lead taped over until the very end. There’s not much we can say here, just keep an eye on the circuit diagrams and you’ll probably have to flip the polarity of the motor. Wire a switch in between the final battery lead and controller, along with the kill switch coming from the controller. We learned the hard way that the controller’s kill switch only cuts throttle input, and doesn’t actually break the circuit.

We assume you have prior experience wiring things, if you don’t, find someone who does to help you out.

Step 11: Final Parts and Safety Checks

At this point, you should be in possession of a running, albeit somewhat uncomfortable, electric motorcycle. It is at this point that we recommend adding foot pegs and a seat of some sort.

Our seat was made by folding rags into the general shape we wanted, and then wrapping the rags with with duct tape. Still uncomfortable, but slightly less so.

As far as safety goes, we recommend a motorcycle helmet (a bike helmet at the very least) and that you probably should avoid riding this in the rain.

Introduction: Lightweight Electric Motorcycle With Bamboo Frame