You've probably seen the two wheeled self-balancing scooters, also commonly known as hoverboards, in the news (for reasons both good and bad). These hoverboards are portable transportation devices with rechargeable batteries.
The popularity of this device increased quickly in the gadget market, before slowing down due to safety concerns over issues with the large rechargeable lithium cells used for power. However, the overall principle of movement in this device is intriguing. A hoverboard consists of two wheels arranged side-by-side with two small platforms connecting the wheels. The built-in gyroscopic sensor pads in the platforms detect body movement by the rider who stands on.
Breakdown of two wheeled self-balancing scooters
Low cost and simplified solution from Arrow
This sort of "body weight directed" movement has tons of applications in the transportation and robotics world. The Arrow Engineering Solution Centre (ESC) team has developed a motor control solution built around this idea. General design uses 3 control chips, thus significantly increases the cost of the device. The solution from Arrow cuts down the design to 2 control chips, significantly reducing the cost. The simplified principle diagram (see figure below) and PCB board design also remarkably decreases the production complexity. In the new 2-chip design, 2 pieces of STM32F103C8T6 from ST are used to control the Brushless DC (BLDC) electric motors to receive and handle signal of gyroscope on both wheels. Thus the two wheels can operate independently, but the communication interface between 2 chips connects the BLDC motors in order to make the wheels rotate coordinately.
12 pieces of the new 60V N-channel MOSFET from STMicroelectronics (the STP77N6F6) are adopted to this new design. We find it is more suitable for a 2-wheeled self-balancing scooter than the STB75NF75 because of its extremely low Rd(on) (6.3mΩ). The lower voltage in STP77N6F6 matches perfectly with the application voltage of 8 lithium batteries.
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Save the cost, go to market fast
With only two chips and new MOSFET, this solution is a cost effective and time to market design to increase the motor efficiency for two wheeled self-balancing scooters and other potential designs utilizing a two-wheeled, body-weight directed movement system. A support team in Arrow Shenzhen, China is dedicated to provide the support to this solution. Source code is available to customer for further development.