Ok, it is super difficult to get info about the MX2020b IC.
It is made by Chinese company sinotech, whose web site http://www.mixic.com.cn/ blocks access from outside China.
There is a 1688 (Chinese ebay thing) page which contains some info here:
https://detail.1688.com/offer/596031371053.html
LCSC (Chinese reseller) don't stock this part and don't have its data sheet, but they do have some other Mixic parts.
It looks like it's a dual motor driver chip in sop16 package. Maybe not really robust, because MichaelG92 had one fail in his picture.
I know some robot builders have used the MX chips before, they are *really* cheap, open any cheap toy and you probably find some, but they're possibly not nearly as robust as my favourite rz chinese chips.
ESC Sanity check
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Re: ESC Sanity check
Robots: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good?
Stacie - tidy flipper; 4wd driven by hair bands
Stacie - tidy flipper; 4wd driven by hair bands