Monday, May 7, 2012

RailScooter

This semester I decided to be a hipster 2.007 and opted out of the mainstream 2.007 robot competition. Instead, I enrolled in the Electric Vehicle (EV) section of 2.007. In this section, led by Charles GuanShane Colton, and Eli Davis, each student had to come up with an idea for an electric vehicle. Any electric vehicle, from a go-kart to an electric kid-tricycle. We would then get to design, machine, race, and keep our vehicles! Deciding what vehicle to make was a tough decision between practicality and novelty. But in the end, I decided I would make a scooter because it was something that I could actually use to commute across campus.
$40 A3 scooter from Amazon
The first item I bought was an actual scooter. To make my life easier, I decided to use the scooter's pole and folding mechanism. This meant I had to design and machine a new frame and fork for mine.

Noobishly printed the parts from solidworks
I then bought a large 1/4'' aluminum plate from McMaster-Carr (amazon prime for Meche's) which I used to machine the new fork for my scooter. My initial plan was to print out the shapes from SolidWorks and then trace them on the plate to accurately cut it with a bandsaw. Unfortunately, I somewhere in between the transition from SolidWorks to printer to paper, the ratio between the solidworks sheet and the physical sheet stopped being 1:1. So I ended up with a fork that was larger than I had originally accounted for. Fortunately, I realized this before drilling the holes and assembling the fork.
my decapitated scooter :(
With the drive train done and the fork assembled, I was around a third of the way done with my scooter. But I still had to figure out a way to attach the handle to the frame of the scooter, attach the latch and poly-carbonate cover, and finally, wire the whole thing together.
Playing the sensor game
 After finally finishing the mechanical frame, I got to the tedious and annoying find-the-correct-combination-of-wires game. There are 12 combinations: 6 from the three motor wires times 2 from the ABC sensor wires.
the latch works :D

Awesome pcb sensor mounts designed by Charles G.
Charles made our life way easier by designing and ordering some circuit boards that would hold the sensors and make it easier to slide them on the motor in order to find the right position for them. This is important because the position of the sensors will affect the amount the current the motor pulls from the controller.
Finally found the correct combination
 I got lucky and found the wire combination pretty quickly but I got stuck a really long while finding the right position for the sensors.

My scooter works!
WUUUUUUWWWWW!!!!! It works!!! Sadly, in an event that reminds me of Charles' reverse polarity battery connection before the 2.007 competition. As I was riding my scooter from N52 towards TDC I decided to go full throttle on Mass Ave and over the railroad tracks.... Needless to say, I flipped over and went flying around 15mph and fell on my left arm. A car, a bicycle, and several bystanders stopped to ask me if I was ok as I stood up, picked up my scooter and the broken fork from the ground and sadly carried my scooter back home :(

This occurred less than twelve hours before the EV Race :(

In memory of the obvious event, I christened my scooter, "RailScooter". :D

Yay! No broken bones.
Things I learned this semester:
  • Use a mill whenever you can! I had so many problems making a fork for my scooter because I would try to use my calipers to make aligning holes on two pieces and failed every time. The main problem was that I had band-sawed all the pieces for my fork so they were not exactly.. straight. This meant that measuring the proper positions for the holes was very difficult. Finally, I should have used more center point drill bits to make sure that I drilled the holes in the (already inaccurate measured) positions I had chosen.
  • Very important! Use at least THREE screws (on each side) in the plate that holds the shock absorber. Most of the torque caused by your weight and by going over bumps (and conveniently, railroad tracks) acts on this plate. The problem with screws is that their threads weaken the material and make it very susceptible to shearing. This is why in my new (very hastily built) fork, I made sure that the plate was sitting on the 1/4'' aluminum fork side AND then screwed together. This way the aluminum would have to break before the screws are sheared off. My new fork will probably be waterjetted since I've already made the design in solidworks. It will use t-bolt slots and be substantially prettier and sturdier than my current fork.
  • In retrospect, I should've done more research on the other scooters that other students had built because, honestly, I did not know what I was doing 80% of the time. Most of my time went into fixing slight misalignments and other errors I made. 


My injured wrist,  RailScooter, and me.

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