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CATPOO 2021 — Power Supply

Note: This post is a work-in-progress and will be updated as requirements are fully fleshed out.

See CATPOO 2021 — A New Beginning for an overview of the whole project.

It’s about time I ruminate on power issues I’ve had in the past. In previous iterations, I cut a lot of corners with the power. Melted wires and malfunctioning steppers were the main issues I remembered facing. This brain dump will be help to avoid all the power issues in this next, final holonomic robot.

Past Power Problems

  • Previous designs considered power supply as an afterthought
  • Running all stepper motors off a single power supply proved problematic
    • The amount of current passing through would often surpass what the power supply was capable of
    • Microstepping would fail or become unreliable due to voltage irregularities
    • Even regular steps would cause problems
  • If I needed 1A max for a load, then I’d only have 1A max available
    • Designing power circuitry like I worked for Apple was a bad idea, as all that does is lead to overheating
    • Sometimes wires would melt or components would release the magic smoke from within

What’s Worked in the Past

  • Using a beefy SPDT switch to allow powering the robot externally or from battery proved helpful
    • Keeping the external and internal power physically separated avoided a lot of potential issues
    • It was very simple to troubleshoot power input issues as things were very simple
  • The battery should be easy to access and replace
    • At minimum, it should be easy to recharge.
    • Physically replacing it easily is a nice to have, especially when I show up with multiple fully-charged batteries

Strategies and Mitigation Plans for the Future

  • Have one single 12v main power rail that everything else connects to
    • There exist high powered buck boost voltage regulators that have more than enough
    • Going overkill on the main rail will leave me with more power than I know what to do with
      • I don’t want to have to remove functionality again due to lack of current
      • This will allow me to scale the robot up to whatever size I would like
    • From the main 12v rail, I’ll use a series of buck converters to get the proper voltage(s) required
  • Build and be prepared to handle lots of current (12V * 5A = 60W)
    • Once I get good, I can drop the power requirements.
    • Until then, assume the following padded numbers:
      • 5V × 5A for Raspberry Pi and peripherals
      • 4 motors * 2 coils/motor * (2.7V * 1A) for the motors
      • 5V * 1A padding for feature creep
      • Total power at worst: (5V*5A) + 4 * (2*2.7V*1A) + (5V * 1A) = 52W
      • My best guess of average power would be more like 35W
    • On battery power, it’s looking like I’ll be discharging around 1 to 2C maximum. I can’t find power ratings for the batteries that I have, but it’s looking like a lot of comparable ones are 25C, 50C or even higher.
  • Dedicated power regulator for Raspberry Pi and peripherals
  • Dedicated power regulators for pairs of motors
    • There will likely be 4 steppers with omni wheels attached.
    • Ideally, I’d want a separate power supply for each stepper motor and driver combo, but two per regulator should be good enough.
      • It’s definitely better than before
      • Have the front left motor and the back right motor on one power rail, and the front right and back left on another
        • Theory: hopefully this will cause power fluctuations to balance out
  • Have the IR illuminator draw right off the main 12v rail
    • I’d like to add a way to enable or disable this, to reduce power usage when it’s not necessary
      • It’s also nice for comparing IR versus no-IR
    • A physical switch seems like the obvious MVP, yet I’d like the ability to turn it off via software


  • Having an LED on all power rails
    • I want to be able to diagnose common issues from across the room

Diagrams and Illustrations

Rough power flow diagram
Rough layout of the robot’s back panel

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