My dilemma of finding a suitable bike to use (on the cheap) has been found! Sadly, it comes at the cost of my dear roommate's bike's demise. Seems like it was backed into by a car while locked up on campus and the back wheel got decently smooshed. She hadn't really been using it and she graciously offered to donate it to my project.
He suggested that I look into local recycling plants that will often sell you buckets of batteries for cheap with the idea that some of them may work and others may not. This would be a great option over buying one huge battery for both saving money and gaining a better understanding of how batteries work. Of course, there's potentially more of a safety risk using questionable batteries, but I'll enlist the help of my more experienced EE friends to make sure I don't blow anything up. Since my battery needs depend on the motor, and the motor depends on the bike (for the most part), it appears that the next step is to find a motor. The convenient coincidence is that in my Systems Analysis and Circuits classes this semester, we've just begun to talk about DC motors. Based on the preliminary research I've done, I want to look a motor that I can incorporate a torque sensor into. A torque sensor would make the motor "smart", in the sense that it would give more juice when it senses the rider applying more torque (going faster or going up a hill). I do want this pedal assist feature above anything because I want to be as safe as possible while riding this bike. An electric bicycle with a motor that's just either "on" or "off" starts to stray into motorcycle territory to me, and that's really not what I want. I still want to use my bicycle as a source of exercise and not take away pedaling altogether. The website The New Wheel is proving to be an incredibly useful source. I'll be looking for second opinions but their comparisons of different e-bike motors will give me a good starting point. Some motors available like the models by Bionx and Bosch have torque sensors built in, but you need to shell out some extra cash for the fancy ones. Could I integrate a torque sensor of my own? How does a torque sensor send signals to the motor? I need to know much, much more before I narrow down my motor options. I'd like to DIY as much of this as possible so I'd prefer to make my own, but I'm concerned about feasibility. The question of hub motor vs drive train motor is still up in the air, but with a torque sensor being a priority, I can push off that choice until later. An aside:
I'm getting a bit ahead of myself here but I'm thinking about how I'll need to make this whole system waterproof. I want to design a case myself and 3D print it. The students I mentor in the freshman engineering class will be doing a project exactly like this in a few weeks (to house an arduino and breadboard), so the timing works out well. I want to make sure that the case can keep splashes out but not prevent an air intake for temperature control. I believe that I'll have to make sure the batteries and motor don't overheat, or melt the plastic of the case, but I really don't know at this point what kind of heat I'll be dealing with. It's amazing, the more I learn, the more I realize I don't know.
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I'm going to interrupt my progress for a little while to do some much needed research. The last lecture in my advanced writing class was about literature reviews and their importance to both their authors and the field they explore. One of the initial steps of writing a literature review, my professor pointed out, is that you read *literally* all literature that exists on a particular topic to write a proper literature review. That being said, the scope of the topic can be very narrow or on such a leading edge of science that not much literature exists, but it got me to thinking that I ought perform a literature review myself on the topic of electric bikes, so that I'll understand what I'm getting into.
Luckily, I can kill two birds with one stone this semester as one of the assignments in the advanced writing course is to write a literature review on a topic of my choosing. I'll need to focus in on one particular aspect of e-bikes, as trying to write a literature review on the phenomenon of electric bikes would be an undertaking too large for one semester. I haven't decided yet what nook I'll focus in on, but as the first draft is due Friday, I'd better get going! I I am now the proud owner of my very first Specialized bike, a used Vita that I found as a great steal at a local bike shop. I didn't realize how clunky and impractical my bike was until I saw what this Vita had to offer. It's a step-through frame size that actually fits me instead of a too-small, men's bike. It's about twice as light as my current bike, which is perfect for dragging up multiple flights of stairs in a Boston apartment building.
Purchasing a new (to me) bike has better illuminated my needs for an electric bike. I don't think I'll be using this Specialized Vita for this project. Ideally, I want to find a bike that's:
Another item I need is a large battery. I heard through the grapevine that a particular club at Northeastern has some spare lithium ion batteries that I might be able to borrow for making my e-bike. A peer who has experience using big batteries told me that my battery needs are going to depend on the requirements of the motor I choose. The motor I choose is going to depend on the payload I anticipate (weight of me, the bike, and whatever I carry on it). According to Evelo Electric Bicycles, two commonly used types of motors for electric bikes are mid drive or hub drive. The main distinction between a mid drive and a hub drive motor is that a hub drive motor is attached to the hub and drives the wheel of the bicycle directly, but a mid drive motor is inserted in series with the drive train and drives the crank. I am a student, which means that my most limiting factor in this project is cost. A comparison guide from E-Biking Now claims that hub drive motors are more readily available and cheaper, and that mid drive motors can be proprietary. I'd like to do as much of this project by my own construction as possible, so for that reason, I intend to choose a hub motor, but my mind isn't set on it yet. The website warns that the handling of a bike with a hub motor can be affected due to a raised center of gravity, and I worry that handling is something I need while weaving through pedestrians and cars in Boston. In my next post, I hope to have secured down a battery and reached a final decision on a motor and motor configuration. All logic may fly out the window if it turns out that my cost considerations lock me into one option or another, whether that be the battery capacity or motor cost and availability. |
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