The goal for the second semester of the year is attaching batteries to the bike, to try to add a toggle clamp mechanism so the motor will not always be in contact to the wheel, and make a carbon fiber clamp to hold these implements. For this project I had a milling machine, drill press/drill, wire strippers and crimps, a voltmeter, a chop saw, sandpaper/file, ovens, and CAD software(Rhino and Solidworks) as my tools. For materials I used wood, aluminum sheets, nuts and bolts, Teflon tape and film, nylon film, and carbon fiber.
Step 1: Carbon Fiber Clamp(Conventional Oven Process)
To hold the batteries and clamp to the bike, I decided to make a clamp with carbon fiber composites. To do this I had to make foam mold for the carbon fiber to heat and set into while heating and outer edges would stay in place. I originally tried compressing the uncured carbon fiber layers together in the foam with electrical tape and heating it >300*F for 2 hours which melted the tape out off the mold and not keeping the shape of the clamp. I then tried making a second clamp at a lower temperature and it kept shape, but because the carbon fiber was uncured, the layers did not fully laminate together and made it brittle, cracking while trying to put it on the bike. I then decided for the next clamp that I would add layers of carbon fiber with extra resin so that all the layers would be fully bonded together. After doing another trial of making the clamp, the carbon fiber was fully laminated but it still struggled to stay in shape with the electrical tape.
Step 2: Carbon Fiber Clamp(Vacuum Seal Process)
To not risk the next carbon fiber clamp loosing shape, I then decided to use a vacuum bag to have the carbon fiber keep its shape. To do this, I used an inner cloth, that had a similar shape to the clamp but was wider to go over the clamp 1 inch longer and then I did the same again except with a nylon film which was able to wrap around the whole part and have an extra inch around the edge to seal it. To seal it , I used a polymer sealant tape to connect the edges of the nylon film, along with a nozzle to vacuum seal the part. Once the bag was sealed and vacuumed, I put it in an oven with an internal vacuum so it could be sealed the whole way through the ~2 hour heating process. When finished heating, I removed the part from the oven and the films encasing the carbon fiber clamp and sanded/filed the edges to prevent scratches or other cut related injuries. I then drilled a 1/4inch hole into the ends of the clamp so it could have the toggle clamp and battery box attached to it
Step 3: Designing Battery Box
When making my battery box, I wanted it to be able to switch out batteries easily while it was attached to the bike by the carbon fiber clamp. I then came up with a setup which had two different batteries that would be help by a board of wood with brackets holding adjustable Velcro straps so if I needed to use a different battery that is a different size. To attach the plank with the batteries I also designed a different pair of brackets that attach to the carbon fiber clamp. For my battery box's switch, I decided to use a toggle switch so I could change the voltage used to power the bike at different speeds. I also designed a platform the switch for the batteries I used which were 6 volt batteries which gave me an option to use either 6 volts or 12 volts through Rhino.
Step 4: Motor and Batteries
I first used a chop saw to cut the plank of wood to fit inside the bike. After cutting the wood I began working on the brackets to hold the Velcro straps. I cut out 6 1 inch by 2 inch aluminum metal sheets. to have the Velcro slide through, I marked the center part of the brackets to bend into shape to allow the straps to pass through. I then made the brackets connecting the battery box to the bike by cutting out 2 2 inch by 1 inch aluminum sheets and bending them in the middle to have a 90 degree angle in the center. I then attached them to the plank and marked the entry hole to attach it to the carbon fiber clamp. I then laser cut out the toggle switch platform to attach it to the battery box with screws, and engraved on the options for the voltage amount being used. For the toggle switch I used female and male disconnectors on the ends of the wires to be able to remove the wires and allow it to use other batteries and not risk the wires from coming loose.
Step 5: Toggle Clamp Design
To design the toggle clamp I used Solidworks and Rhino to see what dimensions I needed to lift the motor off the back wheel. Using Solidworks, I looked at what could allow the clamp to both lock in place when in contact with the motor and lock in place when being lifted by the motor. After making a final draft of the clamp, I changed the Solidworks file into a Rhino file so I would be able to laser out a draft clamp to see if it would work.
Step 6: Toggle Clamp(build)
Once I made the final draft of the toggle clamps I used aluminum sheet metal to make the clamp. I first marked out the laser cut parts of the draft on the aluminum sheet. Then I cut out each part of the clamp from the metal and then used a milling tool to remove the remaining edges of aluminum that was not needed for clamp as it would take up space and not allow the clamp to move the full range of motion I wanted it to. To do this I, screwed the metal pieces to a piece of wood by its joints which I first drilled out, with a 1/4th inch bit, and clamping it between the chuck. I then milled the edges off by starting on the outside and then raising the part up until the bit being used would hit the wood. Once the bit makes contact with the wood, I moved the bit towards the aluminum part so it would contact and mill out the aluminum outside the marked area. After repeating this process with all of the parts of the clamp, I then connected them to each other, the clamp, and the motor, using 1/4inch nuts and bolts.
Step 7: Final Assembly
After assembling the clamps, battery box, and toggle clamp, the bike was successful in running on its own with a pedal start. The only problems I have had when riding is that the bike would not have enough power to go up slopes, but it can be solved by increasing the voltage the motor is receiving by changing out the batteries. I also experienced trouble with the toggle clamp as the joints I on the clamp that I made restricted the desired movement I wanted, but the bike still runs fine. The only problem this creates is that it puts the motor under more force than needed when not in use.