An MIT student's adventures through engineering and beyond.

efficiency curve of CIM motor

efficiency curve of CIM motor In which your protagonist characterizes a horrifically underpowered motor for use in an EV.

Hey, y'all. Just got done with the Edgerton Center Engineering Design workshop, where I mentored high school students on engineering principles. Check out the site at Anyways, one of the projects during the program was a window opener, and their prototype used the standard motor used in the First Robotics Challenge, also known as the CIM motor.

CIM Motor — Image credit AndyMark

Now, this motor has quite the amount of torque for its small size, designed to run at a maximum of 337 watts at 12

Megantereon, alongside a friend

Megantereon, alongside a friend In which your intrepid engineer-to-be explains the impossiblity of getting parts for a go-kart cut on an abrasive waterjet machine.

That happened around late April 2014. What you didn't see was that the controller going up in smoke due to the back EMF, trying to reverse the motor while it was still running, and this controller doesn't support regenerative braking.

Rewind back a couple of days, and I finally get all the parts made of 1/4" aluminum, along with the brake rotor, cut on the CSAIL waterjet. This happened after trying for a week to get access to a

Detail of stator and rotor assembly

Detail of stator and rotor assembly Where two young, intrepid engineers attempt to electrify two bicycles for under $200 using an odd motor without any magnets.


  • Electrify two bicycles for under $200 each
  • Demonstrate axial-flux switched-Reluctance motor technology
    • Using hubmotor built into rear wheel
    • Using motor driving a chain or belt on rear wheel

Preliminary model of SRM hubmotor

The switched reluctance motor

Switched reluctance motors rely on the electromagnetic attraction of ferromagnetic materials (such as steel) to an applied magnetic field, instead of relying on permanent magnets or magnetic induction.


  • Can be made cheaper due to the lack of permanent magnets
  • No detent

Megantereon rendered with SolidWorks Photoview 360

Megantereon rendered with SolidWorks Photoview 360 So last time I covered the basic drivetrain design. Now I'll get to the CAD design of the go-kart itself.

While I was pondering the design of the gearbox, I went ahead and designed the frame. I knew I wanted a three-wheeled go kart (for simplicity and because I was somewhat inspired by the MIT EVT eBike which I helped design), and to use 80/20 framing because I'm not experienced with welding aluminium (and I wanted to avoid steel to minimize weight).

Megantereon's frame in SolidWorks

I went with a triangle-ish layout to ensure stiffness (triangles are the stiffest polygon).

I decided to

traditional gearbox

traditional gearbox Where your intrepid engineer to be attempts to make an electric gokart that goes 35 mph with 80/20 aluminum

It seems like a rite of passage for many MIT engineering students to make their own powered vehicle to get across campus quickly.

I had these goals in mind:

  • Be capable of going 35 miles per hour on a flat surface (not on the streets, though)
  • Be as light as possible (use 80/20 aluminum extrusion for the frame)
  • Have 3 wheels

So, to begin this ritual, in October, I purchased this:

Turnigy Trackstar 1/5th Sensorless Brushless Motor Turnigy Trackstar 1/5 Sensorless BLDC


And, unfortunately, like any other first post, this will be weird and awkward, so i'll just cut to the chase.

Who am I?

I'm Jacob Fisher, the engineer to be/foodie/fixer/do-it-yourself-er/person who tries to be the jack-of-all trades in whatever he comes across.

My interests, to name a few:

  • 3D printing
  • Electric Vehicles
  • Cooking

Why do I have a blog?

It's been suggested to me many times that I keep a personal log of the projects I work on. In addition, my aversion to social media in general must be compensated by something, and my compensation is