Charline build-out, take two!

The second try:


This build I am using 1mm thick fiber washers everywhere.


Almost done.

All she needs is her antennae and a right-angle USB connector.


Oh - eye lashes… Adorable.

Very creative.

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Charline is looking good.

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Well. . . .

Every time I’ve seen two identical characters that are supposed to be opposite genders, the difference is usually red lips and eyelashes.

Since it’s kinda hard to give Charline lips, I was stuck with eyelashes. . .

Hmmm. . . .  Lips?  Let’s see. . . .

I could paint her Grove connector red, 'eh?

I am planning to give her pink antennae though.


Charline’s debut:




Built using the new V3 camera, an 8-gig Pi-4, and a newer rev controller board.


  • Basic build with the camera and the pan-and-tilt installed.

  • Photo-shoot for all the major fashion magazines.

  • Basic “Am I alive?” functional testing.
    (i.e.  It powers up, the servos seek to home position, the “bitness” eye LED’s are the correct color, and it shows as a networked, (as opposed to an access point), network connection.

    • Pro tip:
      To avoid inadvertent heart-attacks, make sure the SD card is fully inserted before applying power!


  • More extensive testing using the GoPiGo O/S.

    • Camera
    • Movement.
      (I haven’t even spun the wheels under power yet!)
    • Remote desktop.
    • GoPiGo O/S Web access and FPV testing.
  • GoPiGo calibration.

  • Enable development access.

  • Test with my joystick enabled FPV robot code.

  • Install a front bumper.

  • Build and install an automatic on/off circuit for the supplemental 5v supply.

    • This is for both Charlie and Charline.
    • Schematic and build-out to follow.
  • Retrofit Charline’s battery with replacement 510Ω calibration resistors for the power meter.

Longer range goals:

  • Integrated status display like Charlie.
    (Possibly a touch-enabled OLED?)

  • Test with my Pi-5.

  • Test with my Jetson Nano.

Important note:
So far, (knock wood!), with the fiber washers installed, there have been no cracks in the acrylic despite the fasteners being torqued tight.

I have also been updating Charlie to use fiber washers on an ongoing basis.  (If I take something apart that can use fiber washers, I install them before reassembly.)

I thought that the “lipstick” was a nice touch, though I’m thinking of using a more subdued color in the future as it seems a bit garish.  Did you notice the “rosy cheeks”?  :wink:

Finding that particular shade of pink was a godsend since I thought I was going to have to mix it myself!  It took several tries before I got the amount, its position, and the shape of the “rosy cheeks” right.


It turns out that I couldn’t find “pink” wire like I needed, so I used the green and green striped wires from a piece of network cable instead .  That works since Charlie’s antennae are green network cable wires.


Looks great. I look forward to reports on how well she runs. I hope GoPiGo O/S is up to the challenge.


For those who are interested, here is the schematic of the supplemental power control circuit.


  • V+ should be no greater than 60v

  • Sense should go higher than 2.5v.

  • The input to the FET contains a 5KΩ current isolation circuit and a passive noise filter for the SENSE input.

  • The optional circuit on the output, (CONTROL), is to eliminate output “stickiness” due to extremely high impedance inputs.

  • Buck converters based on the 4005 chip have an active HIGH enable pin on pin-4 so this circuit won’t be necessary.  I noticed that the time constant of the input is a bit high on that chip so I added the filtering circuit to it.

  • Buck converters based on the XL2596 have the active LOW enable pin on pin-5.

  • The enable pins are tied to either ground, (LM2596), or +V, (XL4005), so they will have to be carefully lifted from their circuit pads before use.




On the 4005 buck converter used on Charlie I included the entire input current isolation and filter circuit to the enable pin on the 4005.  This provides both a “grid-leak” to prevent charge accumulation and input filtering.

  • Note that the maximum input voltage to the SENSE pin should be no greater than the applied V+ voltage.

  • Also note that the enable inputs to the respective buck-converter chips are high impedance inputs, (MOS gate inputs), and the absolute maximum rated leakage current is rated at something like 10μA up to a maximum of V+, output loading of the Raspberry Pi shouldn’t be an issue.  However, as a design best-practice, and since the Raspberry Pi’s GPIO pins are limited to an absolute, drop-dead maximum current of 30 miliamps (±, later models might withstand 50μA), the 5k isolation resistance is highly recommended to prevent any circuit failure or defect from burning out the associated pin.