[WIP] Hardware Upgrades

[gbalke]

Given the age of the parts, I definitely believe the performance of the motor controller can be improved at a lower cost. I'm going to do a quick breakdown of current components and specs and update this issue with alternatives.

Based on current firmware size and bootloader size, I think it's possible to get away with a much smaller FLASH section.

 text    data     bss     dec     hex filename                                 
17589    1532    5288   24409    5f59 bazel-build/bin/bootloader/bootloader.elf

(recorder size == 2000)
 text    data     bss     dec     hex filename                             
52413    1620   75180  129213   1f8bd bazel-build/bin/firmware/firmware.elf

(recorder size == 0)
 text    data     bss     dec     hex filename
52397    1620   11180   65197    fead bazel-build/bin/firmware/firmware.elf

Note that bss is just static initialized RAM and does not count towards flash space.

Currently flash is broken into 4 sections so we need sectors to support the sizes necessary.

1. Bootloader at 0x80000000
2. Board ID (1 byte so tiny flash sector preferred)
3. Motor calibration: arbitrarily sized protobuf that is currently under 1kB
4. Firmware takes up the rest of flash

Microcontroller

It appears that pretty much all STM32s are at stock volume zero ._. Truly a sad day in the world of microcontrollers.

• STM32F405RGT6 ($15.84 & current)
  • RAM: 196kB (though the ld file only uses the first 112kB)
  • FLASH: 1MB -> RM0090 Rev 19
    
  • CLOCK: 168MHz
  • Package: 64LQFP (10x10mm)
• STM32G431CBT6 ($8.01)
  • RAM: 32kB
  • FLASH: 128kB (64 sectors @ 2kB flash sector size)
    • Bootloader (~18kB): 9 sectors
    • ID: 1 sector
    • Calibration: 1 sector
    • Firmware: 27 sectors
    • Free: 26 sectors (52kB)
  • CLOCK: 170MHz
  • Package: 48LQFP (7x7mm)
  • Benefits:
    • Much cheaper & smaller
  • Drawbacks:
    • Much less flash/RAM to fiddle with

Accelerometer

Not strictly necessary. Was intended to be used for arm initialization. Part of me thinks this is reasonable to suggest as a DNP.

• IIS328DQTR ($5.85 & current)
  • ODR: 25-500Hz
  • Precision: 16-bit
  • Range: +/-2g,4g,8g
• LIS2HH12TR ($1.87)
  • ODR: 10-400Hz
  • Precision: 16-bit
  • Range: +/-2g,4g,8g
  • Seems like a great alternative... Need to deep dirve the spec sheet as the price gap must mean something haha.

Motor Controller

Heart of the motor controller... I think switching this to a pure gate driver + discrete FETs would only increase the footprint (but would bump peak current immensely).
The arm runs on 48V and each motor can pull up to 2-3A. I haven't seen a lot of options for integrated solutions operating in these ranges so the current chip seems reasonable.

• DRV8312DDWR ($7.28 & current)
  • Integrated FETs
  • Vmax: 70V
  • Imax: 3.5A/channel
  • Ipeak: 6.5A

Encoder

Currently using a 14-bit encoder. Might be worth finding a low-cost 12-bit alternative for lower precision applications (even better if it's pin compatible).

• AS5047U-HTSM ($12.10 & current)
  • 14-bit absolute encoder
• MA732GQ-Z ($6.70)
  • 14-bit absolute encoder

Supply to 12V Buck Regulator

• LM46000PWPR ($4.49 & current)
  • Vin_max: 60V
  • Vout: 12V
  • Iout: 500mA
• RT6204GSP ($2.02)
  • Same as current specs