Did you check out this first reveal of the “real S20” electric unicycle by KingSong? New motor, shell design, 126V system , smart BMS …. There is one thing much more interesting than all these features combined: The 126V Sensorless and Hall sensor based controller!
King Song S20 SENSORLESS / HALL SENSORED CONTROLLER
The main INNOVATION NOT TO BE OVERLOOKED in this video by the EUC community is the sensorless and Hall sensor based controller. Sensorless means that there is no physical Hall sensors telling the controller where the rotor is, and everything is controlled by back EMF ( In simple terms, the Back EMF is an electromotive force that occurs as the brushless motor turns. The sensorless controller uses back EMF information to determine where the rotor is and how many amps to push depending on wheel rotation ). We know, some of you do not know what that is and what could be advantage and disadvantage at this point, so continue to read as we try to explain what makes sensorless controllers cool!
Before we go further we want to brag a bit and tell you that we have been making sensorless e-bike controllers with Xie Chang PCB boards back in the Ebike days and that the maximum system we had was 110V with 18 fets.
Why electric unicycles are Hall sensor based?
Older technology, easy to adapt to existing systems. Easier to control starting torque and wheel rotation ( front and back ), less coding, less testing, less custom-made solutions. Easier to push the product to the market at this point!
Most EUC manufacturers do not have in-house controller development like King Song, so there is no dedicated personal working in-house engineering of the controller boards specially for EUCs!
The best example to explain why nobody did this before is because, in cheap sensorless Ebike systems, you need to start spinning the pedals to tell the sensorless controller in what rotation to rotate the motor and push amps.
Some electric kick-scooters use sensorless controllers; If a rider is not moving an e-scooter in any direction while turning the throttle to start going from a stand-still; the controller kinda tries to move the brushless motor wheel back and forward and then starts to accelerate ( the controller software does this very fast, but it gives a scooter a starting lag). This is a software feature in sensorless controllers and a thing that helps the controller to understand where to rotate the wheel!
This feature of course cannot be used in EUCs…..because of CRASH… so in other words, this is as advance as it can get. So to get the sensorless controller working with brushless motor from a dead start; an EUC company needs to write a start-up sinewave curve for the controller and then let sensorless controller continue reading back EMF, or let hall sensors tell the motor where the rotor is at starting point and continue working sensorless. This software is kinda like the starter motor for gas motorcycles! So it will be interesting to see how the starting torque will behave on King Song S20 and the acceleration from a stand-still and if it can be used 100% without hall sensors
If you want to get more techy and understand how hard the process for making this boards is, check out the famouse and awesome thread on ENDLESS SPHERE BY A GUY CALLED LEBOWSKI HERE.
There is also a hall sensor and sensorless-based systems in one box and thats what King Song did!
What are the advantages of sensorless Electric Unicycles?
First of all, hall sensors are not bad, and this tech is proven so we are by no means stating hall sensored systems are bad. We are just looking into why sensorless and hall sensored based controllers are a step up in the EUC tech!
Hall sensors can break under the improper mounting on the stator after some time. Under extreme temperatures, they can overheat or unglue from the stator causing them to send the wrong information to the controller, or break and send zero information.
Hal sensor wires ( all five of them ) exit the brushless motor through the stator axle or in the hollow motor under the certain space designed for them. So there are 5 additional wires and 3 additional sensors in the motor.
If anything from above happens, the unicycle will lose the signal from the motor and send the wrong signal or zero information to a controller. The controller will push the wrong amount of amps, or zero amps to the motor, cut off will happen or white smoke will destroy the board. EUC riders are at great risk in that case.The King Song S20 features hall sensors and sensorless back -EMP controller, so if anything breaks; you will still be able to ride it and you will not experience a cutt-off!
If the sensorless system is made correct, this will drastically improve riders’ safety.