In this episode of Beyond Unboxing, I study and mess with something I’ve wanted for a very long time: a sensorless brushless motor controller that isn’t horrible. I didn’t even know if they could exist – after all, I’ve only associated sensorless with horrible screeching, cogging, and stuttering at any speed that wasn’t “fast”. I’ve always assumed that you just cannot get an EV to start from standstill using sensorless commutation – sensors were absolutely required for low speed performance of any kind.
I am glad to say that I am wrong – very, very wrong, and the little bits I have learned about sensorless PM motor control in the past few days, coupled with the discovery that sensors are in fact terrible things, has made me a convert to sensorless control. But only if the controller is designed for an inertial load – something I will explain the distinction of, and something which airplane controllers are totally not.
The Shady Chinese Sensorless e-Bike Controller (let’s call it Sensorless Jasontroller for now) actually has a reasonably long history behind it. Its sensored cousin, the Shady Chinese e-Bike Controller (or Jasontroller), is commonly available on eBay directly shipped from China in what I can assume is straight off the assembly room. The controllers come in a few general types and board layouts, but the architecture is almost always the same. Entire communities and bibles (example) exist around the modification and hacking of these controllers because they are very inexpensive, use common parts, and were designed to support multiple voltages and current levels on the board, with component selection determining what controller you end up getting. They form a staple of the Endless Sphere EV community, and a few members of that community have made businesses out of importing, selling, modifying, or otherwise having something to do with them.
Did I mention that they’re cheap? Generally, prices start in the $30-60 range, but overseas shipping is a signficant overhead cost, bringing the total cost to $100 or so for a high powered (72 volt, 1500W) type, or as low as $50 shipped for the fairly common 300-500W ones. I have one of them running Kitmotter, admittedly not a very strenuous task, and recently purchased another on-the-spot in Singapore because RazEr’s melontroller was damaged. The one running Kitmotter was originally purchased out of curiosity.
While making my rounds through the Shady Chinese e-Bike Store on eBay recently, I discovered (or rather, noticed – I’m sure they’ve been around for a while) that some were labeled with “Without Hall”, or “Sensorless”. I had known for a while that some people on Endless Sphere had modified their Jasontrollers with a comparator-based Hall sensor faking circuit – one that relied on comparing the back EMF of each phase with the midpoint of the voltage bus (Vdd/2) and output a 3 bit wavetrain in the manner of a set of sensors – such that they may run motors with damaged or destroyed sensors. A long time ago, I planned to do the same on Face Vector Modulation.
It was too cheap to not try to see how well it lived up to the claim. I bought a 36v unit fully expecting that it would have no startup capability whatsoever, since being an e-bike controller, it is 100% acceptable to assume that the rider has started pedalling with some forward speed. But hey, $50 sensorless controller that is supposedly sold for vehicle use and runs on 36 volts – why not?
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