About a month ago Mars rover Curiosity’s computer system had a hiccup and reset itself, causing its management team here on Earth to switch to its alternate computer. These two computers – referred to as Side-A and Side-B, allow Curiosity to run on one while mission team diagnoses the other. Initial reports indicate a problem with Curiosity computer’s on board data storage systems.

My rover Sawppy is modeled after Curiosity, and it’s only be a matter of time before Sawppy emulates its big brother with a data storage problem too – the microSD card on a Raspberry Pi 3 computer is a notorious point of failure. But Sawppy doesn’t have a redundant computer system on board that can be switched remotely. Since I’m typically not far away, I can walk up to my rover and perform replacement manually.

But I could only walk up and replace it if I had a replacement handy! This is growing in importance as Sawppy started getting booked for public appearances. When it’s just a hobbyist project it’s not a big deal if Sawppy encounters a problem, I just pack it up until I can get home to my workbench. But if we’re starting to get into situations where Sawppy is actually a featured item, we need to know how to make sure The Show Must Go On.

Thus the latest addition to Sawppy’s field repair (“first aid”) kit: Highest priority is a copy of Sawppy’s microSD card already configured with all necessary software. A microSD card is very small and light, so there’s no excuse not to have one always on hand.

Lower priority, for times when there’s space to spare, is a backup Raspberry Pi 3.

And lowest priority is a LewanSoul servo USB to half-duplex translation board required to operate LewanSoul servos. And while I’m at it, pack a replacement servo as well!

One of the problems I didn’t foresee in designing Sawppy was that some children might see a fun challenge in doing running jumps over my rover. I first saw this unwelcome behavior when I brought Sawppy to Long Beach, and I knew it’d only be a matter of time before a child would misjudge their jump and smash Sawppy into a pile of broken rover pieces.

Clearly I need to find some way to discourage this behavior, but I also can’t do anything that physically harms misbehaving children. This eliminates straightforward solutions such as a Samurai blade pointing straight up. I would also like this countermeasure to be stealthy and not call attention to its anti-jump purpose otherwise some would see it as a challenge.

The answer came while preparing for this year’s Southern California Linux Expo (SCaLE 17x). I was scheduled to host the Hackaday x Tindie Birds of a Feather meetup, and I was also slated to co-present a talk with Lan Dang. For publicity purposes I decided Sawppy can be a rolling billboard, as SCaLE is exactly the right audience of people who would pay attention to a 3D-printed rover running about. I pulled out a yardstick I had on hand and started planning how to use it as a flag pole, and I immediately knew I had my anti-jumpover countermeasure as well. Two birds, one stone.

As previously mentioned, I didn’t want this flag pole to be too rigidly attached. If someone bumps my sign, or if someone decides to try jumping over my rover anyway, the flag pole must break away cleanly without damaging the person or the rover. For SCaLE I used a zip tie that was arranged so there is tension holding the yardstick flag pole in place, but pops free when stressed.

This mostly worked, but as it was built on a balance of opposing forces, it was finicky to reinstall. At Caltech Science for March, a curious toddler yanked off the flag pole and the toddler’s supervising elderly adult tried to reinstall the pole. But grandpa had no idea what he was doing, blindly stabbing inside Sawppy’s equipment bay with the yardstick applying more force as he grew more agitated. After two attempts at saying “Don’t worry, I’ll put it back myself” while I watched in horror at Sawppy electronics getting pummeled, I forcibly grabbed the yardstick from his hands in order to save Sawppy from being stabbed to death.

A better solution must be found.

In preparation for Sawppy’s appearance at Yuri’s Night, I decided to try a magnetic mounting system. Originally rejected because I thought it wouldn’t be strong enough, I thought it was worth a second look. I had a stack of these powerful little magnets and a single pair wasn’t able to hold the pole. But four pairs of them might be strong enough for the task.

For this test, four magnets were held on to chassis beam via packing tape. Two on upper beam, two lower.

Matching sets were held to yard stick flag pole with more tape.

With updated camera mast and flag pole mount, Sawppy was ready for its next public appearance at Yuri’s Night Los Angeles! That event got crowded at times and there were a few accidental bumps that triggered a clean separation followed by quick re-installation. And while this adult-focused event had few children about, there were plenty of drunken misbehaving adults. The flagpole did not discourage all misguided behavior, but it has worked well enough to become a permanent fixture of my future Sawppy public appearances.

(Cross-posted to Hackaday.io)

When Sawppy first started running around, I wanted something to sit atop a camera mast where the real rover has a camera and sensor array. It is the anthropomorphic head of the rover and it looks slightly wrong without one. (Like a chicken running around without its head.) The first iteration of camera mast sensor array enlisted a standard USB webcam sitting alongside a Google AIY Vision kit. It was mostly for appearance because there wasn’t much software behind it.

The webcam was fun for entertaining children and occasional longer distance driving, but not immediately useful for autonomy. The AIY Vision box is optimized for classification tasks. I thought there might exist code useful for robotic visual localization but if it’s out there I have yet to find it.

The most promising tool at hand for rover localization is my Kinect sensor bar running RTAB-Map or some similar software. So Sawppy will inch towards autonomy by getting a camera mast upgrade to my Kinect V1 sensor bar and see if we can integrate that into rover systems in a useful way.

I went looking for a good way to mount a Kinect bar to Sawppy. I disassembled its base looking for a good mounting mechanism, but there weren’t convenient existing fasteners for me to use and there weren’t good places for me to drill and tap new ones. It was surprisingly crowded in there! I knew there was a motor for up/down tilt but I underestimated size of the motor gearbox inside.

I then reassembled the base and went with plan B: a simple flat platform for attaching my Kinect sensor bar with double-sided foam tape.

Kinect sits slightly offset camera mast center for two reasons.

1. The Kinect sensor bar is very wide and if mounted centrally it overhangs to the right. I worry about it hitting obstacles so I wanted to bring it closer to the middle.
2. By offsetting sideways, I could expose the top of the pipe used as camera mast and run Kinect’s wire down the middle for cleaner wire management.

At the moment this Kinect is no more functional for autonomy than the previous configuration… in fact, for its first public appearance at Yuri’s Night 2019 it is not even electrically connected to anything. It’s just a matter of taking one step at a time.

(Cross-posted to Hackaday.io)