From Failure, Success

There’s been another mishap around here. I guess building robots has its ups and downs and last week was no different.

I’m kinda ashamed to say that while I was working on the KR01 robot I’ve now managed to burn out two Thunderborg motor controllers and one Ultraborg servo controller. Well, not quite “burn out”. The motor controller parts of the Thunderborgs still work but the RGB LED used to display the battery level has somehow gotten fried on both units, and the Ultraborg (which is used for sonar and servo control) seems to have died during the first Thunderborg catastrophe (sympathetic death). I have no idea really how this has happened, but of course the only real possibility is that I’ve done something wrong. I mean, I’ve been very careful with checking my wiring before applying the power, but at some point I must have got my wires crossed. The PiBorg folks who make these boards have been quite helpful and I’m sending them back to the UK to see if they can figure it out. But that will take awhile.

King Ghidorah anatomy by Shoji Phtomo
Not to be confused with Monster Zero 1

This means that for at least a few weeks I would be without a robot (the horror)! I really can’t have this happening just as I’m getting the robot operating system up and running. So last weekend I went ahead and built out one of my design prototypes, which I’ve been calling the KRZ-01 (Kiwi Robot Zero), as it’s based on a Raspberry Pi Zero W. It uses a Picon Zero for a motor controller, a Pimoroni Breakout Garden to mount some of its sensors, and a trio of infrared detectors rather than a front bumper.

Happily, the build posed only a few problems and I had it up and running rather quickly. I rewrote the Python modules that had been used to control the KR01’s motors to instead use the Picon Zero and I had it dancing around on the carpet today for the first time:

KRZ-01 Motor Control Demo

The KRZ01 is meant to be small and relatively cheap, but still have the ability to carry some impressive sensors. It actually isn’t a whole lot less capable than its larger sibling, the KR01. Without including shipping the parts come out around NZ$250, so it’s not the cheapest robot you could build but it’s got a lot of functionality2.

Side View of KRZ-01
Side View of KRZ-01

It’s based on a Raspberry Pi Zero W, which has 500MB of memory and supports both WiFi and Bluetooth. The OS is Raspbian Linux. The Picon Zero motor controller and a Breakout Garden Mini are both mounted on a Mini Black HAT Hack3r breakout board. This is an extremely compact setup. You can see this on the side view photo.

The sensors include: three Sharp infrared detectors; a VL53L1X Time of Flight (ToF) distance sensor mounted on a micro servo, which can measure distance up to about 4m with a 25mm accuracy (this is the same sensor I used on my night light); and two 298:1 ratio micro gear motors with encoders so we can measure how far we’ve travelled.

Bottom view of KRZ01
Bottom View Showing the Motors and Motor Encoders

There’s still two free I²C Breakout Garden sockets so additional sensors can be swapped in and out without any soldering. I added a couple of 11×7 LED Matrix boards as status displays but they’re hardly necessary. The whole thing runs on a common USB battery. The chassis is made out of 3mm Delrin plastic. For locomotion it uses a pair of Moon Buggy wheels, a lightweight plastic ball caster in the front, a heavier stainless ball in the back (so its balance is towards the back caster).

Since the robot supports WiFi I connect to it remotely using ssh, which is how I’ve been installing and loading its software, starting and stopping programs, and shutting it down 3. Remarkably, the Raspberry Pi W includes a tiny HDMI connector so I could plug it into a monitor, but that hardly seems necessary. This seems like a command line robot.

The chassis is 75mm wide and 120mm long. Without a battery the whole thing weighs 120 grams. For comparison, that’s 17 grams less than my iPhone 5. I have a 5200mAh battery that weighs 136 grams and a 4400mAh battery that only weighs 40 grams, so unless battery life is an issue I’ll probably use the smaller battery. I have a 10000mAh battery (200g) that would last many hours but I can’t imagine leaving the robot alone that long. What kind of trouble could it get into?

For more information about the KRZ01 Robot, visit its NZPRG wiki page.

Note: as of today the NZPRG has its own YouTube Channel.

Edit: after some back in forth in email and finally posting the boards back to PiBorg in the UK, I learned from them that what seemed to have happened was that the UltraBorg tested as faulty, and that was apparently what was burning out the LEDs on the ThunderBorgs. They’ve since sent me replacements for both and all is working well now. A well-deserved thank you to PiBorg for their patience and help!

  1. Kaiju Zukan image by Shoji Ohtomo
  2. you could start with the Pi, motors, controller and chassis for about $150 and add sensors as you go
  3. properly, since it’s running Linux and using an SSD card for storage, so powering off suddenly can corrupt the SD card

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