Sawppy Cleanup After Maker Faire Bay Area 2019

Sawppy had a successful appearance at Maker Faire Bay Area 2019, where the two major novelties were an impromptu raincoat and an emergency steering servo replacement. Once Sawppy was home, though, there were a few cleanup and maintenance items before Sawppy is ready for the next event.

First of all, Sawppy’s wheels are filthy after running around San Mateo Event Center over the course of Maker Faire. There was mud, there was dirt, spilled coffee, dropped popsicles, and rain making all of those problems both better (washing off larger chunks) and worse (spread a thin layer across entire circumference.) Like what happened after Downtown LA Mini Maker Faire, Sawppy needed to kick off all six shoes and give them a nice long soak in chlorine-enhanced water. An retired toothbrush was used to scrub each wheel of dirt particles.  But despite the brushing and the chlorine, Sawppy’s wheels get a little dirtier with every public event. I’m not terribly about this cosmetic aspect, as long as the physical mechanical capabilities are not degraded by worn grousers on the wheels.

Secondly, we have a mechanical issue to investigate. The left rear wheel is now freewheeling instead of helping to propel the rover. This was discovered late Maker Faire Sunday. At that point Sawppy still had to attend Oshpark’s Bring-a-Hack at BJ’s Restaurants, but Sawppy would spend most of that event standing up on a table. So I decided to postpone dealing with that issue until later… now is later! This turned out to be the servo horn screw backing out, allowing the servo horn to slide off that servo’s output shaft. There seems to be some minor damage from chewed up teeth, but a quick test indicates there’s enough remaining to transmit power so Sawppy should be fine.

And finally, we found another consequence of a rainy Maker Faire: Sawppy’s steel drive shafts have started to rust. This seems to have made wheel removal much more difficult so I should investigate rust removal and prevention before reassembling everything.

Sawppy Emergency Field Repair at Maker Faire Bay Area 2019: Steering Servo

Taking Sawppy to Maker Faire Bay Area 2019 was going to be three full days of activity, more intense than anything I’ve taken Sawppy to before. I didn’t think it was realistic to expect a completely trouble free weekend and any breakdowns will be far from my workshop so I tried to anticipate possible failures and packed accordingly.

Despite my worries, the first two days were uneventful. There was a minor recurring problem with set screws on shafts coming loose despite Loctite that had been applied to the threads. I had packed the appropriate hex wrench but neglected to pack Loctite. So I could tighten set screws back down, but lacking Loctite I had to do it repeatedly. Other than that, Friday was completely trouble-free, and Saturday rain required deployment of Sawppy’s raincoat. But Sawppy got tired by Sunday morning. Driving towards Dean Segovis’ talk, I noticed Sawppy’s right front corner steering angle was wrong. At first I thought it was just the set screw again but soon I realized the problem was actually that the servo would turn right but not left.

With the right-front wheel scraping along the floor at the wrong angle, I drove Sawppy to a clearing where I could begin diagnosis. (And sent call for help to Emily.) The first diagnostic step was pushing against the steering servo to see how it pushes back. During normal operation, it would fight any movement off of its commanded position. With the steering behavior I witnessed, I guessed it’ll only fight in one direction but not another. It didn’t fight in either direction, as if power was off. Turns out power was off: the fuse has blown.

I replaced the fuse, which immediately blew again. Indicating we have a short circuit in the system. At this point Emily arrived on scene and we started methodically isolating the source of the short. We unplugged all devices the drew power: router, Pi, and all servos. We inserted third fuse, powered on, and started testing.

Sawppy dead servo 29

We connected components one by one, saving the suspected right-front servo for last. Everything was fine until that suspected servo was connected, confirming that servo has failed short. Fortunately, a replacement servo is among the field repair items I had packed with me, so servo replacement commenced. When the servo was removed I noticed the steering coupler had cracked so that had to be replaced as well.

Using a spare BusLinker board and the Dell Inspiron 11 in my backpack, I assigned the serial bus ID of my replacement servo to 29 to match the failed front right steering servo. Then I pulled out a servo shaft coupler from the field repair kit and installed that on my replacement servo. We performed a simple power-on test to verify the servo worked, plugged everything else back in, and Sawppy was back up and running.

Let’s Learn To Love Imperfect Robots Just The Way They Are

A few months ago, as part of preparing to present Sawppy to the Robotics Society of Southern California, I described a few of the challenges involved in putting ROS on my Sawppy rover. That was just the tip of the iceberg and I’ve been thinking and researching in this problem area on-and-off over the past few months.

Today I see two divergent paths ahead for a ROS-powered rover.

I can take the traditional route, where I work to upgrade Sawppy components to meet expectations from existing ROS libraries. It means spending a lot of money on hardware upgrades:

  • Wheel motors that can deliver good odometry data.
  • Laser distance scanners faster and more capable than one salvaged from a Neato vacuum.
  • Depth camera with better capabilities than a first generation Kinect
  • etc…

This conforms to a lot of what I see in robotics hardware evolution: more accuracy, more precision, an endless pursuit of perfection. I can’t deny the appeal of having better hardware, but it comes at a steeply rising cost. As anyone dealing with precision machinery or machining knows, physical accuracy costs money: how far can you afford to go? My budget is quite limited.

I find more appeal in pursuing the nonconformist route: instead of spending ever more money on precision hardware, make the software smarter to deal with imperfect mechanicals. Computing power today is astonishingly cheap compared to what they cost only a few years ago. We can add more software smarts for far less money than buying better hardware, making upgrades far more affordable. It is also less wasteful: retired software are just bits, while retired hardware gather dust sitting there reminding us of past spending.

And we know there’s nothing fundamentally wrong with looking for a smarter approach, because we have real world examples in our everyday life. Autonomous vehicle research brag about sub-centimeter accuracy in their 3D LIDAR… but I can drive around my neighborhood without knowing the number of centimeters from one curb to another. A lot of ROS navigation is built on an occupancy grid data structure, but again I don’t need a centimeter-aligned grid of my home in order to make my way to a snack in the kitchen. We might not yet understand how it could be done with a robot, but we know the tasks are possible without the precision and accuracy demanded by certain factions of robotics research.

This is the path less traveled by, and trying to make less capable hardware function using smarter software would definitely have their moments of frustration. However, the less beaten path is always a good place to go looking for something interesting and different. I’m optimistic there will be rewarding moments to balance out those moments of frustration. Let’s learn to love imperfect robots just the way they are, and give them the intelligence to work with what they have.

Mars 2020 Rover Will Carry Sawppy’s Name

Modern advances in nonvolatile memory storage can now pack a huge amount of data in a very little space and volume. Everyday consumers can now buy a microSD card representing this advance. One of the ways NASA has taken advantage of this is offering a program where people can submit their names to be carried onboard spacecraft in the form of digital data stored on a tiny flash memory chip.

Spaceflight is still very expensive, with every gram of mass and cubic centimeter of volume carefully planned and allocated. But with flash memory chips so small and light, NASA has decided it offers enough returns on publicity to be worth carrying onboard. Such programs award social media exposure and free coverage like this very blog post!

NASA JPL’s Mars 2020 program, the most visible component of which is a not-yet-named rover successor to Curiosity, will be a participant. There will be a small flash memory chip on board with names of people who cares to submit their name via the NASA web site set up for the purpose.

I don’t care very much about having my own name on board Mars 2020, but I loved the thought of having “Sawppy Rover” as one of the names on board that actual rover heading to Mars. I’ve submitted Sawppy’s name so hopefully a few bits of digital data representing Sawppy will accompany Mars 2020 to and travel across Martial terrain.

Slowing Sawppy Response For Smoother Driving

When I first connected my cheap joystick breakout board from Amazon, its high sensitivity was immediately apparent. Full range of deflection mapped to a very small range of physical motion. It was very hard to hold a position between center and full deflection. I was concerned this would become a hindrance, but it wasn’t worth worrying about until I actually got everything else up and running. Once Sawppy was driving around on joystick control, I got my own first impressions. Then in the interest of gathering additional data points, I took my rover to a SGVHAK meet to watch other people drive Sawppy with these super twitchy controls.

These data points agree: Sawppy’s twitchy controls are problematic to drive smoothly and it’s actually running between points fast enough for me to be worried about causing physical damage.

There were two proposed tracks to address this:

First thought was to replace the cheap Amazon joystick module with something that has a larger range of motion allowing finer control. [Emily] provided a joystick module salvaged from a remote control aircraft radio transmitter. Unlike arcade game console joysticks which demand fast twitch response, radio control aircraft demands smoothness which is what Sawppy would appreciate as well. The downside of using a new joystick module is the fact I would have to design and build a new enclosure for it, and there wasn’t quite enough time.

So we fell back to what hardware projects are always tempted to do: fix the problem in software. I modified the Arduino control code to cap the amount of change allowed between each time we read joystick values. By dampening the delta between each read, Sawppy became sluggish and less responsive. But this sluggishness also allowed smoother driving which is more important at the moment so that’s the software workaround in place for Maker Faire.

This code is currently in Sawppy’s Github repository starting with this code change and a few fixes that followed.

Sawppy and Makey

The mascot for Maker Faire is Makey the Robot. (Or possibly Mr. Makey to me…) As part of Sawppy’s Maker Faire experience, I wanted to make sure I got a good picture of Sawppy with Makey. I thought the mascot would surely be everywhere and it wouldn’t be hard to get a picture. The thought was not wrong… but finding one of the appropriate size and sitting in the right angle for sunlight and not otherwise swarmed with people proved to be a challenge.

The biggest and most promising Makey was a standing statue that [Emily] found and pointed out to me. Unfortunately the sunlight angle was not the best but we had fun with it. I started with an easy standard pose.

Sawppy and Makey 1

I went low to the ground to achieve a dramatic upwards camera angle.

Sawppy and Makey 2

Then [Emily] had a brilliant idea to pose Sawppy with Makey. She put one of Sawppy’s front wheels up on Makey’s pedestal, and turned the Kinect sensor bar with googly eyes to face the camera. This is a great picture.

Sawppy and Makey 3

After this picture, I looked for a smaller Makey closer to Sawppy’s size, and the best I found was on this sign directing people to something or another. The two robots are closer in proportion but it doesn’t have the energy of [Emily]’s pose.

Sawppy and Makey 4

And finally, when I passed the workshop area I also saw a partially disassembled Makey on display. It felt like a stage set up for something but is currently empty. But there was no time for question! I looked around, caught a brief gap in passing crowd, and snapped a picture of Sawppy here.

Sawppy and Makey 5

Meeting of Rovers at Maker Faire Bay Area 2019

The primary goal of taking Sawppy to Maker Faire Bay Area 2019 was to spread word of DIY Mars rover models to the greater maker community. But that was certainly not the only goal! There were many secondary goals, one of which was to meet [Marco] who has already received the word and built a Sawppy of his own.

Through Sawppy’s project page on Hackaday.io I learned of a few other rover builders who have built their own creations on top of my design. They are spread all around the world but I had never met one in person until Maker Faire. Even though we knew each other would be present, it brought a great big smile to my face when I saw [Marco]’s bright yellow Sawppy roll up to greet mine. We had hoped that we might see more rovers by builders that never communicated with us, but if any were present they had escaped my notice.

When walking through the area dedicated to educational maker groups, I had expected to see some sign of the JPL Open Source Rover but came up empty handed. If any completed rovers were rolling around I didn’t see them, and if any partial rovers were on table display I missed them. Though to be fair, I visited that building during one of the harder downpours so almost every attendee packed the indoor spaces making it hard to see everything with a rover underfoot.

But I did find members of the NorCal Mars Society rover project with a different focus than my project. They did not prioritize building a chassis that looked like Mars rovers, instead focusing on the control systems. There’s a camera feed for a remote operator and control system to run simulated Mars missions. Still, we were all part of the greater family of Mars rover enthusiasts and it was fun to have all the rovers meet up.

A Raincoat for Sawppy

Maker Faire Bay Area takes place at the San Mateo Event Center with both indoor and outdoor exhibits. As the dates got closer this year, weather forecast called for rain. This is probably not a good thing for attendance of the event and corresponding finances, but it’s also a concern for exhibitors as well. I, for one, did not design my roaming exhibit Sawppy for rainy weather.

The first and most obvious idea was to design and 3D print an umbrella mounting bracket for Sawppy. But I was worried about the umbrella catching wind to topple over the little rover. I was also worried about wind-driven wind flying sideways and landing on components. And lastly, carrying an extra umbrella is bulk I would rather do without.

Thus I moved on to the second idea: craft a raincoat out of plastic (garbage bags, basically) that I can secure more tightly against Sawppy’s equipment bay via magnets. Aluminum extrusion beams are not magnetic, but the M3 bolts are! This should offer marginally superior protection from the elements, and less bulk to carry around.

The project started with a large black garbage bag that I had cut open to create a single sheet. [Jasmine] (who had generously hosted [Emily] and myself Thursday night) thought the opaque cover was a shame and brought out a large clear plastic bag. This way people could still see inside Sawppy even when wearing the raincoat. I continued using the black bag as a trial run, and then used it as a template to cut Jasmine’s gift to form the final raincoat.

Sawppy raincoat template creation test

This custom-fitted raincoat only covered Sawppy’s equipment bay. To protect the rest of Sawppy, sandwich bags were placed over four corner steering motors, and a hotel shower cap was put over Sawppy’s head. Everything wrapped up nicely around Sawppy’s neck with a strip of velcro, again from [Jasmine]’s workshop. This compact arrangement was lighter and more compact than an umbrella when folded. And when deployed, Sawppy could go outdoors and romp in the rain.

Sawppy raincoat stowed

UPDATE: There’s now a video of Sawppy putting on this raincoat.

Sawppy Takes A Road Trip To Bay Area

Over the past few months Sawppy and I have been attending events in the greater Los Angeles area spreading our love of DIY Mars rovers. But now it’s time to go to the flagship Maker Faire Bay Area 2019 event. This will be a multi-day event away from home and that brings in a new set of concerns.

The first and most obvious concern is the multi-day length. Every previous public appearance was no more than an hour’s drive away from home, where I had all of my tools and parts to repair any problems at the end of the day. I could pack some tools and replacement parts but I can’t pack everything. It would be sad if Sawppy broke partway through the event in a way I couldn’t repair. On the upside, Maker Faire Bay Area would be the event to be where I could borrow or buy tools and components. Or even time on someone’s 3D printer to print replacement parts!

The second concern is the trip itself. I typically place Sawppy on a car seat however it can fit, and didn’t worry overly much about placement because the ride is short. Now Sawppy is looking at over six hours of driving, with associated six hours of bumps from the road. Would all the repetitive stress break something on Sawppy? To help alleviate this problem, I used my luggage suitcase to fill in the rear seat footwell creating a relatively flat surface for all six wheels to sit at even heights. To constrain Sawppy’s front-back movement, the battery tray and router was removed so everything fit cozily between the front and rear seat backs. To constrain side-to-side movement, the rear seat center armrest was lowered so Sawppy fit cozily between it and the door.

Over seven hours later, Sawppy arrived in the bay area and I was eager to see if everything still worked. My quick test was to reinstall the battery tray, router, and power up Sawppy to verify all components functioned. I was very relieved to see Sawppy start driving around as designed, seemingly unaffected by the long trip and ready to meet the crowds of Maker Faire.

Mounting Bracket For Sawppy Wireless Router

A natural part of a project like Sawppy the Rover is a long “to do” list. While its ever-growing nature might imply otherwise, things actually do get done when faced with motivation. For Maker Faire Bay Area 2019 my primary motivation was to get a wired controller up and running as backup in case of overcrowded radio frequencies. And now that I have a working (if imperfect) wired controller, I wanted to come back and tidy up the wireless side of the house.

After that initial episode of fighting on crowded 2.4 GHz band, Sawppy received a wireless router upgrade in the form of a dual-band Asus RT-AC1200. (Selected via the rigorous criteria of “It was on sale at Fry’s that day.”) Not only did this gave Sawppy greater range when operating on 2.4 GHz, it also meant Sawppy could operate on the 5 GHz band where there are far more channels to go share in crowded environments.

So that was good, and a wired controller backup is even better, but there’s a neglected part that I wanted to address before taking Sawppy in front of a big crowd: when I initially hooked up that Asus router, I connected all the wires and placed it in the equipment bay. No mount, just gravity. I intended to integrate the router properly some day and today is that day.

Sawppy wireless router

I want to mount this to the rear of Sawppy above most of the equipment bay, because that’s where real Mars rover Curiosity housed its communications equipment. Ever since I had a WiFi router at home, they seemed to have stayed roughly the same shape and size even though electronics have generally gotten smaller and more power efficient. So the first question I checked was whether the box is mostly empty space and we could transfer compact internals onto the rover?

Opening the lid did unveil some empty space, but not as much as I had thought there might be.

Sawppy wireless router opened

Furthermore, it doesn’t look like the antennae are designed to be removable. They’re firmly fixed to the enclosure, and their wires are soldered to the board.

Sawppy wireless router PCB

Seeing how unfriendly this design is to a transplant operation, I aborted the idea of extracting internals. We’ll use the case as-is, starting with designing and printing a base for the router. I originally intended to fasten the base using original router enclosure screws, but changed plans to using M3 screws like rest of Sawppy after I dropped one.

Sawppy wireless router new base

This base has two dovetails which can then fit in brackets that clip onto Sawppy’s extrusion beams.

Sawppy wireless router mounted

And voila! A rigid mount for my wireless router rigidly mounting it to Sawppy chassis instead of letting it bounce around in a tangle of wires like I’ve been doing the past few months. This is much more respectable to present to other attendees of Maker Faire Bay Area.

Sawppy Roving With Wired Handheld Controller

I now have a basic Arduino sketch for driving Sawppy using a joystick, I’ve built a handheld controller using an Arduino Nano and a joystick, and an input jack for interfacing with Sawppy. It’s time to put it all together for a system integration test.

Good news: Sawppy is rolling with the new wired controller! Now if there’s too much electromagnetic interference with Sawppy’s standard WiFi control system, we have a backup wired control option. This was the most important upgrade to get in place before attending Maker Faire Bay Area. As the flagship event, I expect plenty of wireless technology in close proximity at San Mateo and wanted this wired backup as an available option.

This successful test says we’re in good shape electrically and mechanically, at least in terms of working as expected. However, a part of “working as expected” also included very twitchy movement due to super sensitive joystick module used. There is very little range of physical joystick movement that maps to entire range of electrical values. In practice this means it is very difficult to drive Sawppy gently when using this controller.

At the very minimum, it doesn’t look very good for Sawppy’s to be seen as jittery and twitchy. Sharp motions also place stresses on Sawppy’s mechanical structure. I’m not worried about suspension parts breakage, but I am worried about the servos. Steering servo are under a lot of stress and couplers may break. And it’s all too easy to command a max-throttle drag racing start, whose sudden surge of current flow may blow the fuse.

I had wanted to keep the Arduino sketch simple, which meant it directly mapped joystick movement to Sawppy motion. But it looks like translating the sensitive joystick’s motion directly to overeager Sawppy is not a good way to go. I need to add more code to smooth out movement for the sake of Sawppy’s health.

Input Jack For Sawppy Wired Controller

I’ve got my handheld wired controller built and assembled, now it’s time to work on the other end and add a control input jack for Sawppy the Rover.

Again I wanted something relatively robust, I don’t want a tug on the wire to tear apart Sawppy internals. Fortunately the whole “tugging on wire” issue is well known and I could repurpose someone else’s solution for my project. In this particular case, I’m going to deploy the wire and jack salvaged from a Xbox 360 steering wheel. This cable formerly connected the foot pedal unit to the main steering unit. The foot pedal unit is subject to a lot of stomping abuse, which can shift the position of these pedals and result in tugs on this wire. It appeared ideal for handling the stresses I want it to endure in my application.

The jack has strong resemblance to standard landline telephone cable and may actually be the same thing, but because I salvaged both the jack and compatible wire for my project it didn’t matter if it was actually the same as phone jacks and lines. Using calipers I measured the jack’s dimensions and created a digital representation in Onshape CAD. I then modeled the rest of the bracket around that jack and printed its two parts.

Sawppy joystick jack printing

Here’s the mounting bracket front and back pieces along with salvaged jack, whose wires now have freshly crimped connectors for interfacing with LewanSoul BusLinker debug board.

Sawppy joystick jack unassembled

When assembled, the bracket grabs onto one of Sawppy’s aluminum extrusion beams. Tugs on the wire should transfer that force to aluminum beam instead of pulling wires out of the board.

Sawppy joystick jack assembled

I installed this jack between two major pieces in Sawppy’s structure. This ensures that it will not slide when tugged upon, which should help with strength.

Sawppy joystick jack installed

Sawppy Wired Controller Enclosure

I now have an assembly of circuit boards that has all the electronics I needed to create a wired controller for Sawppy the Rover. Now I need an enclosure to make it easy to hold, protecting both my skin against punctures by header pins and also protecting the soldered wires from damage.

The first task is to measure dimensions and iterate through design of how I would hold the assembly using 3D printed plastic. It evolved into two separate pieces that mate up with left and right sides of my prototype circuit board.

The next step is to design and print two small parts to hold on to the wire. The idea is to have it take some stress so tugs on the wire do not rip my 4-pin JST-XH connector from my circuit board. And finally, an exterior shell to wrap all of the components.

Sawppy handheld controller unassembled

The exterior shell was an opportunity to play with creating smooth comfortable hand-conforming organic shapes. Designing this in Onshape was a bit of an square peg in round hole situation: standard engineering CAD is tailored for precision and accuracy, not designing organic shapes. That’s the domain of 3D sculpting tools, but I made do with what I had available in Onshape.

Given a bit more time I could probably incorporate all the design lessons into a single 3D printed piece instead of five separate pieces, but time is short and this will suffice for Maker Faire Bay Area 2019.

Now that I have one end of my wired serial communication cable, it’s time to look at the other end.

Sawppy handheld controller assembled

Arduino Nano Forms Core Of Sawppy Wired Controller

At this point in the project, I have an Arduino sketch that reads an analog joystick’s position and calculates speed and position for Sawppy’s ten serial bus servos to execute that command. Now I turn my attention back to the hardware, which up until this point is a collection of parts connected by jumper wires. Good for experimental prototyping, not good for actually using in the field.

The biggest switch is from using an Arduino Uno clone to an Arduino Nano clone. The latter is far smaller and would allow me to package everything inside a single hand-held assembly. Both Arduino are based on the same ATmega328 chip and offers all the input and output I need for this project. Typically, beginners like to start with an Uno because of its selection of compatible Arduino Shields, but that is not a concern here.

This specific Arduino Nano will be mounted on a prototype perforated and plated circuit board. It is placed on one end of the board in order to keep its USB port accessible. Two other components were soldered to the same prototype board: a 4-pin JST-XH connector for power and serial communications, and an analog joystick module.

My mess of jumper wires were then replaced by short segments of wire that are soldered in place for greater reliability. This is a relatively simple project so there aren’t very many wire connections, and they all easily fit on the back.

Arduino nano with joystick on PCB back

In theory the Arduino sketch can be seamlessly switched over to this board. In practice I saw bootloader errors when I plugged in this board. It turns out, for this particular clone, I needed to select the “Tools” / “Processor” / “ATmega328P (Old Bootloader)” option in Arduino IDE. As a beginner I’m not completely sure what this meant, but I noticed sketch upload speed is significantly slower relative to the Uno. My source code was unchanged and it all still worked. A few test drive sessions verified this little hand held assembly could drive Sawppy as designed.

Next step: an enclosure.

Prototype Arduino Wired Controller For Sawppy

Once I had basic control of LewanSoul LX-16A serial bus servo via analog joystick with an Arduino Uno, it was time to write code to perform trigonometry math necessary to calculate Ackerman steering angle and speed for each of Sawppy’s six wheels. Conceptually this is a port of code I wrote for the SGVHAK Rover project. However, that had the benefit Python, a high level friendly language.

The first concern came from reviewing Arduino Language Reference page. Under Trigonometry section it lists cosine, sine, and tangent functions but I didn’t see their counterparts arccosine, arcsine, and arctangent which I needed. I was never worried that I might have to reimplement my own math library: surely one would exist! They’re too useful and the Arduino ecosystem is too large for them not to.

It turned out I didn’t have to go very far in my search: underneath all the beginner-friendliness the board still runs an ATmega328 chip of the AVR microcontroller product line. And Arduino has not deviated from core language for programming that chip, so I could pull in the standard AVR <math.h> library to gain acos(), asin() and atan() functions.

I only had to duplicate the math for an Arduino counterpart, I didn’t try to replicate all the features of my Python code since some of them relied on the nature of Python for their flexibility. Still, even with the simplifications (or possibly because of them?) the code was different enough for some bugs to slip in. I ended up retracing through my steps using pen and paper to debug a few problems.

Once debugged, I had a crude wired controller for Sawppy. An analog joystick connected to my Arduino Uno with jumper wires provides user input. My freshly written code translates the joystick position to four corner steering angles and six wheel velocities, and sends out commands to all ten LewanSoul serial bus servos using Arduino’s UART TX pin connected to LewanSoul BusLinker via another pair of jumper wires.

Next task: make this Arduino wired controller more compact and more reliable with soldered wire connections to replace these jumper wires.

(Code for this project is publicly available in the arduino_sawppy subdirectory of Sawppy Rover’s Github repository.)

Arduino Control Of LewanSoul LX-16A Servo Via Joystick Commands

Once I climbed a few early steps on the Arduino IDE learning curve, I was off and running writing code. Fortunately the underlying code for programming an Arduino is still the C++ I’m familiar with. I picked up where I left off earlier with the analog joystick tutorial, now shuffled off to its own C++ class. I then looked over the sample code released by LewanSoul for controlling LX-16A servos in the form of a single flat Arduino sketch file.

I don’t plan on using most of the functionality of that sketch, but I thought it was easiest to lift the code wholesale rather than putting time into extracting just the parts I wanted to use. The code was written as flat top-level APIs, but it wasn’t difficult to write a small class that exposed a few methods which called into the two API I cared about. One to make a LX-16A move to a specific position, the other to make it rotate continuously.

There were a few rounds of experimentation on how exactly to communicate intent across this API. Using values as directly dictated by LewanSoul would have worked fine for this one case, but I didn’t want to be tied to one specific servo. Like my SGVHAK Rover software project, I wanted this code to be adaptable to multiple motor implementations which meant a more general description of motor action.

I tried percentages for both, ranging from -100% to +100%. For position servo, this would mean -100% is full deflection left, 0 is center, and +100% is full deflection right. And for continuous rotation, -100% is full speed reverse, 0 is stopped, and +100% is full speed forward.

Speed worked well but position did not: different servo will have different ranges of motion, so full deflection would mean different angles for different servos. So that was changed to angle in degrees. In the case of LewanSoul, -120 degree to +120 degree.

This was enough to let me control two servos with an Arduino, based on position of the connected analog joystick. This is sufficient control for my standard “rover wheel on a stick” test case, a good milestone before proceeding onwards.

(Code for this project is publicly available in the arduino_sawppy subdirectory of Sawppy Rover’s Github repository.)

Sawppy Will Be At Maker Faire Bay Area 2019

I’ve been taking my rover Sawppy to various events, from small school science fairs to large exhibit hall of Southern California Linux Expo. One of these stops was the Downtown Los Angeles Mini Maker Faire. A Maker Faire is the right kind of environment to attract the right kind of crowd that is perfect for a motorized model of Mars rovers.

From the official Maker Faire website I learned that “Mini” in “Mini Maker Faire” is not necessarily a comment on the scale of an event. The “Mini” signifies a community event that is organized and held by local entities, like the Los Angeles Public Library in the case of DTLA Mini Maker Faire. Maker Media, who has the registered trademark and associated legal rights, allows such communities to call their events a Mini Maker Faire and share some infrastructure if certain guidelines are followed.

So what about events curated and produced by Maker Media? They are the Flagship Maker Faires. And the original one of them all is Maker Faire Bay Area held in San Mateo, California. When exhibit applications opened up, I was tempted but also intimidated about submitting Sawppy in an application. It is not just a Maker Faire, it is the Maker Faire! This intimidation kept me from submitting by the early deadline, but a few encouraging pushes (Thanks Jasmine! Thanks Emily! Thanks Glen!) got me past my psychological barrier to submit my application.

I was very excited when I received a notification telling me Sawppy had been accepted. It is amazing to see Sawppy listed on the event’s “Meet the Makers” page. And I have my own Maker Sign that I will display on Sawppy during the event. I was intimidated before, but now I’m looking forward to the event!

Sawppy Sign MFBA19 69882

Sawppy Builders

I started my Sawppy project in March 2018. By May 2018 I had my first rolling chassis but it was fragile. Every time my rover broke, I learn a little more about mechanical design, and Sawppy improved over the following months. I also started writing assembly instructions and supporting documentation to help any other interested people build their own Sawppy, not knowing if anyone would take me up on my offer. It was extremely gratifying to see other people have indeed accepted my invitation!

On my Hackaday.io project site I’m going to start recognizing those who have embarked on their own Sawppy adventures, roughly in the order of when I learned about their efforts. Sometimes I learn about their ambitions before they got started, sometimes I learn about it only after their rover had been completed. Given this, it is likely there are other Sawppy builders out there I don’t know about at all! But that’s fine, I just love the fact there are more Sawppy rovers running around.

I used to list a few Sawppy builders on my Sawppy project description text, but the list has grown too long to fit in that space. I’m going to track Sawppy builds by continually updating a project log entry created for the purpose, editing it as I go to add more rovers as they come online. I don’t know if there’ll ever be a day when even this would become too unwieldy to track all the Sawppy builds out there… but as far as problems go, that’s one I would be very happy to have.

To everyone who decided my project was worth your own time and money and effort to build: Thank you.

It’s my privilege to link to all those Sawppy rovers in one place.

I Found My Motivation To Enter World of Arduino: Make Sawppy Easier

When talking to people about fun electronics projects, it has come to people’s surprise that I have yet to do anything with an Arduino. It is the platform of choice for introduction to hardware computing and how many people got started in this hobby, but for one reason or another I never went through that phase.

Generally, if I need something with computing power or network connectivity, I use a Raspberry Pi 3. If I need low-level control over precision timing, I use a PIC. Sometimes those two are paired up, like our VFD driver board project. An Arduino’s capabilities fit in between those two platforms, but as I already have proficiency in coding for a Pi and for a PIC, it doesn’t leave much motivation for me to learn Arduino. But it’s something I kept in mind, expecting that one day an Arduino’s beginner friendliness will be an asset for me to build a project with one.

That opportunity has surfaced!

backyard sawppy 1600

As I took Sawppy around to various events, I had many opportunities to talk with people who show interest in a DIY motorized Mars rover model. My own personal ambition is to make Sawppy autonomous, but not everyone shares that goal. I learned that many people would be content with a remote controlled rover. Furthermore, I’ve seen a lot of interest in parents who wanted to gauge if Sawppy is a good project to build with their children. And in this scenario, my SGVHAK rover software running on a Raspberry Pi is far more complex than strictly necessary.

For this audience, a simple Arduino-based rover control system would fit a niche separate from that of a Raspberry Pi rover control scheme. It will be less powerful, but will also be lower cost and more approachable as a learning exercise for beginners.

So for the sake of making Sawppy more accessible to everyone, I’m going to start investigation into an Arduino-based control scheme.

Sawppy Field Repair Kit: Backup Electronics

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!

Sawppy backup electronics