The OxChief RC is available for 6 Bad Boy mower models:

• MZ Rambler
• MZ Magnum
• ZT Avenger
• ZT Elite
• Maverick
• Maverick HD

I hope that you won’t mind me introducing the component by way of a story.

Boys Will Be Boys

My boys are gone to camp this week. I was excited thinking that the quiet house would yield a utopia of productivity, cleanliness and order. We have been getting things done, and the house is cleaner. But it’s also too quiet around here, and I miss the boys.

Does a man ever outgrow the desire for something RC?

Above, one of the boy’s RC trucks sits atop a Bad Boy Rambler that has been retrofitted with the OxChief RC bolt-on system.

If you’re lucky enough to have a son (or a nephew, or a grandson, or a young guy that you mentor) then perhaps, like me, you often look at their toys with a touch of envy.

• Gel Blasters — where were these when we were kids?
• Go karts — we somehow survived without roll cages and seat belts.
• Dirt bikes — insane fun with a little danger mixed in.
• RC cars — pure fun until the battery runs out (or catastrophic crash).

I still remember looking at RC car magazines when I was a kid, wondering what the cars in pages were really capable of. Were the speed numbers quoted accurate? What did they sound like? Could they pull a wheelie? What did driving them feel like? There’s something about driving a vehicle remotely that tends to put a smile on your face. It’s better than fun, it’s pure fun.

Pure Fun 

There are a handful of things that are simply pure fun — exciting, adventure, and they leave you better off afterwards. For me, this includes snow skiing in Montana, jet skiing anywhere the water is warm, and watching Auburn football. One item in the prior list doesn’t belong — but it’s not because I don’t love Auburn.

But somewhere there’s apparently some memo that at some age, we’re supposed to identify as “Adult”, and this marks the point where we’re supposed to:

• Hold long conversations with others about our fav organic food choices that no-one can pronounce
• Complain ad-nauseam about politics
• Prefer watching screens inside to sweating outdoors
• Wonder aimlessly about lost time rather than imagining a fantastic future

Here’s trusting that you, the reader of this blog, like me, are working to reject the list above.

Quite often, there’s a kernel in the fun that we enjoyed as kids that is far superior to the low-T borefests we settle for as adults.

Don’t settle for binging Netflix when the joy of youth is at hand.

Adding a super solid RC control system to your mower really is a refreshing blast from the fountain of youth.

Why RC my mower?

I think you’ll find that there’s something very satisfying about driving an RC mower — perhaps it’s tied to something we enjoyed long ago that we’ve never really outgrown.

There are several compelling benefits to an RC mower, including:

• Mow from the comfort of your living room regardless of weather
• Tackle dangerous hills / suspect terrain without bodily risk
• Scratch your long-dormant itch to drive an RC vehicle
• Perfect platform to equip with FPV for a mowing experience from the future

Can Autonomous and RC mowers co-exist?

OxChief’s goal is bringing autonomous mowing to every mower. When we released the OxChief software along with the OxChief Alpha servo control for the Bad Boy Maverick HD, we were happy to offer the first mowing autopilot solution designed for anyone with a large (think multi-acre) mowing area.

While the future of autonomous mowing is bright, RC mowing is very useful in many applications.

RC mowing with an FPV setup, in particular, may just be a unique golden thread connecting the fun of being a boy with the need for productivity of being a man.

I just bought a Bad Boy mower at Tractor Supply — how long does OxChief install take?

One Afternoon.

If you presently own a Bad Boy mower, just pick up an OxChief RC control and you’re ready to roll.

Otherwise, head over to your local Tractor Supply (or, even better, your local Bad Boy dealer) and pick up your new mower.

Having secured your OxChief RC control and your mower, let’s take a quick overview of the process of installing the RC control onto your mower

RC Control on Mower Install Executive Summary

Here are the steps:

RC Control on Mower Install Detail

Enjoy your complete zero-to-hero tutorial/demo covering the entire install:

Hope you’ll head over to the store and take the plunge.

You’re going to love it.

–Wayne

We’re excited to introduce OxChief.

OxChief’s goal is to make driving your mower optional.

OxChief provides software and hardware to make this possible.

https://github.com/oxchief/oxchief-client

https://shop.oxchief.com/

Software written and hardware manufactured in the USA.

What I thought would take a year ended up being most of a decade.

Here’s hoping you enjoy.

In ArduPilot world, the set of coordinates (or waypoints) that your rover is scheduled to visit is often called a mission (and this mission is stored in a plain text file called a waypoints file). If you inhabit that world, you know that the de facto standard tool for basically all robot configuration and mission building is the superb Mission Planner (Windows) application written and actively maintained for nearly a decade as an open source project by Michael Oborne, an Australian super-dev. (Incidentally, the Australian people seem to be making a disproportionately big contribution to the advancement of open source autonomous robotics.)

Mission Planner is a Swiss Army knife for ArduPilot-based robots — it provides dozens (if not hundreds) of functions — but for building the kind of centimeter-level side-by-side pass missions that I like to use for mowing, I don’t think it yet has functionality to fill that exact niche.

For a while I’ve wished for some browser-based / Google Maps-based / highly zoomable (i.e. for cm-level adjustments) app that will let you define a region via a standard Google Maps polygon and then magically generate a side-by-side pass (i.e. think parallel lines instead of concentric circles) mission for a mower to completely cover the user-defined area.

Not finding exactly this anywhere else, I’ve taken a rough stab at such an application and here present it to you for your enjoyment and critique:

Precision Mule: Serving up centimeter-level missions for your mowing rover

What is Precision Mule?

Precision Mule is a centimeter-level mowing robot mission path generator. I say “mowing robot” because the motivational use case for the routes it generates is a mowing autonomous rover.

You use Precision Mule like this:

Please note that I have only tested Precision Mule with Firefox and Chrome — if anyone would like to tweak the code to work on your fav browser, feel free to submit a PR on GitHub.

Examples

So, for example, here is a mission I built with Precision Mow to mow the west lot:

Here’s a time-lapse of the mowing rover we’ve been using lately running that mission yesterday:

Here’s a mission covering basically the same area, but instead of north-to-south passes, we’re doing east-to-west, i.e.:

Just as a reminder, the heading of the waypoints is determined by the line between the first and second points of your polygon.

Here’s a time-lapse from yesterday running that mission:

Here’s a mission covering the north part of my property:

And here’s a time-lapse from earlier this morning mowing that mission:

Look closely and you’ll see Cousin Jason dropped by to check out the run.

Precision Mule Deep Dive

If you’re still reading at this point, you must have a use for this software. Here’s a video I threw together to (hopefully) make your precision path generating experience as enjoyable as humanly possible:

It’s all Open Source

The backend java server: https://github.com/waynebaswell/precision-mule-server

The ui web client: https://github.com/waynebaswell/precision-mule-ui

Look forward to hearing your feedback.

Till we meet again,

Sincerely,

Roby

1. First-date-level excitement about the capabilities of the new component and the possibilities it will open up for your projects
2. Final-exam-level dread of the process of figuring out how to use the thing

#2 can be especially pronounced when you’re an early adopter and the internet hasn’t yet given birth to much documentation about your newly acquired component.

Since that fateful day in early 2018 when u-blox announced the ZED-F9P L1/L2/L5 GNSS receiver, I’ve logged an embarrassing count of visits to their website anticipating every new piece of information that they would publish about the little ZED.

Eventually u-blox announced they would call the official development board the C099-F9P. As an old-school believer in the technology maxim that you wait ’till the 3rd iteration of some new product before adopting, I had hoped that u-blox would quickly release a few updates to the dev kit so that I could feel like a wise old sage buying the more refined product.

Well, Digi-Key began selling the C099-F9P dev kit and I could only wait a month or so before caving in and buying two:

The familiar thin white rectangular box with the beautiful u-blox logo stirs long dormant Christmas morning feelings

Unboxing the C099-F9P High Precision GNSS RTK Development Kit

When you unbox your C099-F9P, here’s what you’ll find:

Historically, the component prices of RTK hardware have been astronomical — even the multi-frequency GNSS antenna (hidden in the nondescript brown box in the upper left) has been a thousand dollar USD component up ’till recently.

Hooking up the components yields this:

The ZED-F9P hooked up and ready for for action. Note the GNSS antenna is sitting on the circular silver magnetic ground-plane. The metal ground plane significantly increases antenna performance by reducing signal multipath issues. Nearly any metal ground plane (i.e. the roof of your car) will do the job — in general, the bigger the plane the better.

If you go on a late-night RTK GNSS wiki binge, you’ll likely have your brain numbed as you start to uncover the considerations involved in distilling the faint chirps from several dozen non-homogeneous satellites orbiting our planet 12,000 miles away into a centimeter accurate position in your front yard 20 times per second.

Let’s be clear: this blog post will not add to that scientific body of knowledge at all — instead, I’m assuming you’re a layman from some field other than RTK GNSS and you’ve stumbled across this ground-breaking technology as it’s effectively the only game in town for repeatable absolute centimeter-level outdoor positioning.

Those wishing to understand the technology underpinning RTK GNSS more deeply will find capable mentors in Tomoji Takasu^[1], Clive Turvey^[2], and Tim Everett^[3].

Shortcuts to High Precision GNSS with the Revolutionary ZED-F9P (or “Early Adopter Tax Evasion”)

This blog post should serve as a crash-course in getting your ZED-F9P rolling. Success on my part will be measured in helping you avoid much of the early adopter tax that I had to dutifully pay through the usual fog of frustration and confusion that eventually gave way to the thrill of using a game changing component.

At this point I’m going to suggest something that (I think) you’ll eventually thank me for: Go ahead and buy two C099-F9P dev kits so that you can stand up your own Base Station. Trust me, at some point this will almost certainly feel like the best $250 USD investment you’ve ever made.

We’re going to set up one of the C099-F9Ps as the “Base Station” (to provide “Corrections”) and the other as the “Rover”. You have the option to use some local correction source if available, or to use a subscription correction service (i.e. the dev kit comes with a free trial subscription to a remote correction service called HxGN SmartNet — I’ve not used). Your mileage may vary, but I’ve never regretted setting up my own base station and relaying the RTCM corrections on a dedicated radio link.

Let’s start with the simplest possible use-case — hard-wiring the corrections output directly from the “Base Station” board to the “Rover” board (via a male-to-male breadboard wire). Once you have the setup running with a wired RTCM connection, you’re just a pair of 3DR radios away from a long-range wireless RTK setup.

RTK success with two C099-F9P boards wired to each-other

Here are the high level items we’ll accomplish to get our self-contained RTK system running:

1. Connect to your ZED-F9P from within u-center
2. Update the ZED-F9P receiver firmware on both C099-F9P boards to the latest from u-blox
3. Set up one C099-F9P board as the Base Station, one C099-F9P board as Rover, and wire RTCM output from Base Station to Rover

1. Connect to your ZED-F9P from within u-center

On Windows 10 (no knowledge if this procedure works on other versions of Windows), before you plug in the C099-F9P, open up the Device Manager and expand the Ports item. Now plug in the C099-F9P and you should see 3 new ports that appear — one for the ODIN-W2 radio (COM7 in the example below), one for the ZED-F9P (COM6 below), and a USB Serial Device port that’s apparently some kind of all-in-one port where you don’t have to guess baud rates correctly. It’s much easier IMO to use this port (COM3 below).

On Windows 10, I seem to have the best success connecting to the “USB Serial Device” port that appears when you plug in the C099-F9P

From within u-center (I’m using u-center 19.04 which is the latest as of May 2019), click the down arrow next to the port icon in the upper left and you should see a port number corresponding to the USB Serial Device you noted above (COM3 for me). Select this port and we’re now connected to the dev board.

2. ZED-F9P firmware update

Updating to the latest firmware may not be required, but it’s quick and easy — so I’d say go for it.

Here’s a little video I made of updating the ZED-F9P firmware.

3. Set up one C099-F9P as the Base Station, the other C099-F9P as the Rover, and wire RTCM output from Base Station to Rover

You’ll need to know your Base Station antenna’s coordinates to complete this section. If you’re not familiar with how to get those coordinates, check out Addendum 1 below.

The configuration procedure we follow in the video below configures the receiver to output NMEA PVT (Position, Velocity, Time) to the UART2 (June 2019 update: output on UART2 has been spotty — so I’m just using UART1 for PVT output) UART1 Tx port at 5Hz (i.e. a new reading every 0.2 seconds) at 115k baud. It also configures the UART2 Rx port to receive RTCM corrections at 115k baud. These settings are convenient for the mower rover we blogged about last time. Note that you can set the output rate up to 20Hz, but you may need to bump up the baud to something higher than 115k (otherwise the line may get clogged up and the readings would be delayed). On the slow rover we’re using to cut the grass, 5Hz is plenty and the Pixhawk 4 we’re using communicates nicely at 115k baud.

If you’ve followed the steps above, then you can easily send RTCM correction data from the Base Station to the Rover by connecting the the Base Station UART1 Tx to the Rover UART2 Rx with a simple breadboard wire.

Caveat: the one-wire approach will work if you’re powering both boards with an electricity source with a common ground. If not, you can just connect the two boards’ GND sockets together (you’ll find multiple GND sockets on the dev board) with another breadboard wire.

It wasn’t obvious to me from the documentation which sockets on the C099 board map to UART1 and UART2 — perhaps all other humans were born with this knowledge. Here’s a little mapping diagram that will hopefully help future travelers:

Showing the u-center screens for the ports on the Base and Rover. Note the curious black lettering (like “J3 >1” and “J9 > 2”) — the official C099-F9P documentation adopts the names “J2”, “J3”, “J8” and “J9” for the terminal blocks — just showing what the terminal is called in the C099-F9P u-blox documentation.

You’ll note that we’ve taped off the ODIN radio antenna jack (remember that I don’t use the on-board ODIN radio). This just gives me one less thing to remember when connecting the GNSS antenna to the dev board.

ZED-F9P real world performance demonstration

Here’s a little video showing why this small RTK receiver is so significant:

Rolling our own long-range corrections link

If you’ve been using u-blox high precision gnss components since the NEO-M8P, then you may have previously used the superbly easy-to-use and capable C94-M8P development kit for that (L1-only) module^[4]. The C94-M8P basically did everything right from an ease-of-use standpoint for a builder wishing to probe that gnss module’s functionality. For instance, the development kit was sold as a pair of modules (i.e. so that you weren’t tempted to skip setting up your own local base station), the radio was based on SiK telemetry achieving great range, and the procedure for setting up a base station / rover system was very simple and well documented^[5].

I spent several unrecoverable hours trying to get two C099-F9Ps to communicate with each-other via the on-board ODIN-W260 radio. Efforts tried include downloading multiple versions of the s-center radio evaluation software, feverishly googling for any kind of documented success story setting up the link, setting jumpers, and flashing various firmwares and configuration settings to the dev board. I’m not sure if you’d describe my efforts as total failure or absolute failure, but I never saw any sign that I was close to actually making the communication link work.

Fortunately, long-range radios have become very cheap in recent years, so snag a pair off eBay, Amazon or SparkFun and you’ll have a long-range RTCM corrections link between the Base Station and Rover with minimal effort.

3DR radio configuration

Mission Planner has built-in functionality to configure the radios.

2 SiK radios connected to the Mac (running Windows via VM). Note that some SiK radios don’t have micro-usb ports — you connect them to your PC’s USB via a USB-to-Serial adapter.

Here’s a close-up of the relevant screen in Mission Planner, along with the settings of the radios that I’m using for the link:

Now that the radios are communicating, it’s time to remove the RTCM wire connecting the ZED-F9Ps to each-other and instead connect them wirelessly via the radios.

C099-F9P dev boards powering 3DR radios for wireless long-range RTCM corrections.

That’s all there is to it! Note the solid yellow light on the Rover indicates it has an RTK fix — I love seeing that light.

Sincerely yours,

Roby

Addendum 1: Finding Latitude/Longitude/Elevation for your local Base Station Antenna

This simple fact, combined with both a rapid fall of hardware component prices and a steady refining of history altering open-source autopilot stacks, means that many passerby have begun seeing sights previously uncommon to man.

Exhibit A:

In this blog post we’ll introduce the main components of our mowing rig. In future posts — hopefully not 2 years from now — we’ll try to flesh out some more system details. As always, feel free to post questions in the comments and I’ll try to address anything I haven’t explained well.

The Pursuit of the Perfect RTK GNSS System

As we’ve previously discussed, for several years the long $$ poll in the hardware tent hamstringing our autonomous mower dreams has been centimeter-level robust GNSS gear¹.

2 years ago we marveled that ComNav had built a precision GNSS module for ~$1000 USD capable of positioning to within 1cm at 10hz (i.e. 10 readings per second — or a new position output every 0.1 seconds). Our excitement was justified because the big agriculture/surveying GNSS vendors were concurrently exacting perhaps 5-10x that price for similar technology.

It is with considerable excitement we report that now in 2019, your affordable autonomous field-navigation robot dreams are more approachable than ever.

The reason for this, of course, is largely the gift that u-blox has recently introduced to mankind: the ZED-F9P L1/L2/L5 GNSS module.

Example hardware components for an Ardupilot based precision auto mower

If you live thousands of miles away from Switzerland like me, then you may also shamefully admit that your knowledge of that beautiful country has hitherto been effectively limited to the following:

1. The Alps
2. Remarkable banking
3. Swiss Army knives

Well sister, get ready to add a 4th item to that list:

Who are u-blox and why do they matter?

u-blox is a Swiss publicly traded, highly profitable, growing, financially healthy, dividend paying fabless chip designer that is quietly introducing a line of low-cost ultra high precision GNSS modules that will likely change the entire world².

Over the past 20 years, u-blox has been developing an ever improving line of high performance GNSS receivers that have become the de facto standard GNSS component in several important markets.

If you’re not very familiar with the world of drones here’s a way to think the place u-blox occupies in that market:

u-blox is the Intel of IoT GNSS

u-blox really is that dominant as the provider for drone GNSS receivers, and it’s reasonable to speculate that they’ll soon provide the high precision GNSS modules onboard a big percentage of the ~70 million automobiles annually sold worldwide.

Many more glowing words could be accurately penned about u-blox, but our task at hand involves using their ZED-F9P high precision GNSS module as the position solution for an autonomous mower.

So what’s the big deal with the ZED-F9P?

In laymen’s terms, the ZED-F9P allows any outdoor thing to know it’s exact position on the face of the earth to within ~1cm with up to 20 position updates per second at a price-point that’s an order of magnitude lower than similarly robust incumbent solutions.

It does this for a flat one-time price of ~$500 USD. That price is for 2 ZED-F9P modules (along with 2 antennas) to build a stand-alone system (i.e. one of the ZED-F9P modules is set up as a Base Station / “correction” provider). If you have an existing correction source, then you’ll only need to purchase one module, and so your cost is halved to ~$250 USD.

The fine citizens of Precision Ag / Land Surveying world, arriving at this page and reading the ZED-F9P specs and pricing, will likely have a visceral appreciation for the u-blox accomplishment that perhaps few others can fully understand⁷.

For $500 you can purchase a 2 receiver / 2 antenna (a capable active patch antenna is included in the dev kit) L1/L2/L5 multi-constellation 20hz system that’s comparable in performance (and arguably much more approachable in terms of ease-of-integration) to a $10,000 system from one of the existing old school RTK manufacturers.

Readers familiar with RTK technology jargon may be interested in a flyover of the ZED-F9P’s technical specs:

ZED-F9P Technical Highlights

Price: ~$250 USD³

Multi-Constellation: GPS / GLONASS / Galileo / BeiDou — In other words, it’s processing position signals from satellites from all 4 of the major GNSS constellations.

Multi-Frequency: L2OF, L2C, E1B/C, B2I, E5b, L1C/A, L1OF, B1I — This is the real kicker — historically you have only obtained multi-frequency receivers by parting with thousands (or ten-thousands) of USD dollars.

20HZ output capable: Stated differently, just to be clear, it can give you 20 unique cm-level accurate positions every second.

Well-documented and mature presence: i.e. autonomous autopilot stacks (such as the gold-standard Ardupilot) have supported u-blox gnss receivers for years⁴.

Supports standard RTCM corrections.

Low power consumption.

If you’re coming from the world of Precision Ag or Land Surveying and you read those specs, due to your experience with the companies that have supplied that market for 2 decades, you may be thinking “yeah but how much does The Man charge me for software un-locks for all 4 constellations, multiple frequencies, and 20HZ output?”

Answer: 0.00 USD.

Yes, the ZED-F9P comes with all those features out of the box — the only catch I know of is our shared inability to stockpile these modules and then time-travel back to 2015, making a fortune through resale.

Rover Build

The rover we’re describing today is built on a repurposed electric wheelchair powertrain as we’ve previously detailed. But note that we’ve upgraded a few components since the previous discussion about this rover.

The significant modifications are these:

1. Replace our beloved ComNav K501g with the superior u-blox ZED-F9P.
2. Upgrade rover wifi system with Ubiquiti mesh network⁵ (i.e. we run a Ubiquiti access point on the the rover that’s joined to our local Ubiquiti network. This offers many benefits, for example: it’s now trivial to shell/VNC into rover’s onboard Raspberry Pi from any computer on our local network).
3. Replace Pixhawk 1 autopilot with Pixhawk 4 autopilot. Just to be clear, this is not because the Pixhawk 1’s functionality is yet significantly outdated for this application (even though Pixhawk has been around since 2013) — instead, when Holybro introduced the Pixhawk 4 I got curious about it’s performance, and liking it’s specs (and Holybro’s solid reputation) but not finding many user reviews of the module, curiosity overtook and I just bought the little guy from Sparkfun.

Rover front view from above

Note the next-level red/black clamps connecting the + – battery terminals to the AC/DC inverter

The box on the left is the power box — box on the right is the brains box.

The “RTK” radio at the bottom is dedicated to receiving RTK corrections from the base station.

Another angle of the brains box.

Mowing Deck Build

We hacked together a mowing rig⁶ as follows:

1. After eyeing the big 60″ deck on our old Scag mower, we cut out a similarly-shaped (albeit scaled-down) hexagon from 1/8″ sheet metal.
2. Procure 3 24v 150W ZY6812 150-GM150115 DC motors from eBay (somehow those powerful motors are shipped to your door @ $25 a pop).
3. Hook up some shaft coupler extensions (from eBay) to the DC motors. This buys us a couple extra inches of clearance between the mower deck and the blade disk. Note that I had to Loctite the nuts that snug these extensions to the motors. Also note that if you want to purchase extra nuts for this extension (for example, if you want to hold those Honda disks in place by sandwiching the blade disk between two nuts), that the nut size ia a little odd: M10 Left Hand 1.5. This Amazon query should get you what you need.
4. Bolt the 3 DC motors to mowing deck sheet metal.
5. Attach Honda blade disks to the shaft coupler extensions. I like the Honda disks because they’re metal (and because they’re Honda). I had to drill out the hole in the center of the disk slightly — i.e. you have to make the hole’s diameter a little bigger to use the shaft coupler extensions that we’re using.
6. Ask Pops to weld together a carriage structure to attach to the rover. If you study carefully the metal and swiveling wheels on this structure you may recognize they’re just parts we’ve salvaged that were laying round from prior power-chairs.
7. Suspend the mowing deck from the carriage by 4 loops of 1/8″ galvanized 7×19 steel wire cable (this ultra-strong wire rope was leftover from building the backyard containment fence a few years back). Those aluminum brackets attached to the deck that the cables loop through were laying around the shop.
8. Run ground wire and fused 24v power wires back to the mowing deck.
9. Create mower deck sides by bending & cutting sections of 3″ Aluminum flat bar. Bolt aluminum sides to deck using these brackets.
10. Bolt two Spiderman bicycle training wheels to front left/right sides of mowing deck — this helps the deck to “float” along without getting hung up on uneven terrain.

Honda blade disk part #72612-VP7-C50

Blades (not pictured) swivel on 3 bolts welded to the disk

Wrapping Up

Let’s bring this post to a close with two time-lapse videos (one run — but video taken from 2 cameras — note that the second camera’s battery died before run completion) taken this morning.

Note the number of obstructions that would challenge an RTK system of lesser capability.

The mowing rig works quite well, keeping the back yard neatly trimmed and letting my clothes stay clean in the process.

Sincerely yours,

Roby

June 27, 2019 update — Here is my current Ardupilot Rover Pixhawk 4 param file for the rover: Pixhawk4-Rover-Params

Roboticists Often Find That Kids Are Eager Helpers

Rover 1 has been a fun project, but Rover 1 is too small for our ambitions. It’s time to start working with a wheelchair-based robot platform. However, before we make the move, let’s make one last modification to Rover 1.

Voiding the Warranty

M60 — 2 x 30a $40 Motor Controller

I want to test out a cheap 60 amp (2x30a) dual motor controller (hereafter called “M60”) available on eBay that I’ve not seen reviewed elsewhere. Is it possible that this motor driver is a viable alternative to the venerable $125 Sabertooth?

M60 Specs: Notice the Control Pin Operation is Very Similar to the L298N

Now think back to your 9th grade Mandarin class and review the spec sheet for the M60. If you don’t remember Mandarin, I’ll give you a quick hint: the 6 control pins (labelled PA, A1, A2, PB, B1, B2) behave just like the L298N control pins (labelled ENA, In1, In2, ENB, In1, In2).  In other words, we’re going to switch over from the L298N motor controller to the M60 motor controller without touching a line of Arduino code.

Now, you’ll notice that the voltage range on the spec sheet is 12v-30v. This means that we are compelled to ramp up the voltage for Rover 1. This is accomplished by adding another 8-place AA battery holder to the platform and wiring it in series with the existing battery holder.  This should give us a potential voltage of 16*1.2v = 19.2 volts. In practice, due to limitations of the batteries and loss in the driver, this will give us around 14v at either motor.  Keep in mind these are 6v motors.  Clearly, we are violating sensible design behavior.

It turns out that the positive wire from the battery to the M60 needs to be a little longer.  This gives me a perfect opportunity to try out some of the fancy new heat shrink solder connectors that you can pick up just about anywhere including Amazon. I purchased these several months ago, but have been suspicious of their fitness, and haven’t tried them out ’till now.

Heat Shrink Solder Wire Connector: Too Good to Be True?

The Original Wire Wasn’t Long Enough to Reach M60 Motor Controller

Slip on the Heat Shrink Solder and Twist Wires Together

Slide the Heat Shrink Solder Over the Twisted Wires, Centering Solder Over Wires

Apply Heat (Careful Not to Melt/Burn Anything Unintentionally)

Voila! Looks Pretty Slick! Super Easy. Note: Long Term Performance Unknown

M60 PA, A1, A2 maps to Arduino 10, 8, 9, respectively

M60 PB, B1, B2 maps to Arduino 11, 12, 13 respectively

Check out these pictures of Rover 1 fully assembled:

The boys like helping, particularly during the testing phase:

Here’s a little video of it running around the back yard. Note that the oldest boy is quite dejected since he’s not driving.

Wrapping Up

Somehow Rover 1 appears to have survived exceeding the motor’s recommended voltage by over 2x. Let’s quit while we’re ahead! Next time we’re going to pull the M60, Arduino, and radio off Rover 1 and try our hand at a big-boy robot.

Here’s looking forward to seeing you then,

Love,

Roby

Rover 1 Arduino Speed and Steer “Mixing”

In our last post we spent a good bit of time speculating why folks are often afflicted with Codeaphobia. At the end of the post we gave a super-small Arduino program that makes the Arduino’s LED blink.

Today, I’m going to skip the long essay and immediately give you the Rover 1 RC-Arduino-L298N code. You can view the Arduino sketch here and download the repository here. Just unzip and open Arduino/rover1_rc_arduino_l298n/rover1_rc_arduino_l298n.ino with your Arduino IDE.

You’ll note that we created a project on GitHub to host Rover 1’s code.

If you’re new to programming, you may not be familiar with GitHub. It’s the de facto standard place to host open source code.

I attempted to add a few more comments in the code than usual — if anything is unclear, let me know in the comments below!

Until next time,

Sincerely,

Roby

Wheelchair, Cold Milk, and Makeblock Starter Kit

Welcome back my friends! Immediately after hitting publish on the last post, I knew that we had to point the true beginner roboticist to a wonderful tool for starting out in robotics. I highly recommend you consider purchasing a skid-steer starter robot like the Starter Robot Kit by Makeblock. I think you’ll be impressed with the quality of the Makeblock’s machined parts and it’s clear assembly instructions. Are you too proud to tell your significant other that you’ve purchased a lowly educational robot? Here’s an idea: purchase it for your kid, your niece/nephew, your grandkid, or the kid down the street. When it comes in the mail, go ahead and pre-assemble it for them. BAM! Just like that we’ve added another future roboticist to the fold!

The Makeblock robot is not perfect. The model I have has a tendency to shed the tracks if you turn too fast while you’re supplying excessive voltage to the motors (which, of course, we’ll do). Also, I don’t know the exact specs, but the payload capacity isn’t much — perhaps 2 pounds (1 kg) — you likely will outgrow this robot very soon. If you like to go rogue, perhaps you’ll have luck with one of the tank robots readily available on eBay.

The reason we recommend tracked robots instead of a simple robot powered by two independent rear wheels is off-road performance. If, however, you plan on running your robot on pavement, you’re far better off sticking with traditional wheels.

So why do I like the Makeblock robot? It’s a good product and the company stands behind it. Perhaps you’ll let me illustrate with a little story. I purchased the kit you see above new from an individual on eBay back in 2015. Apparently, one of the times that RadioShack went bankrupt, they liquidated their Makeblock robots for cheap, and a few people jumped on the inventory and made a little profit reselling them on eBay. I’m perfectly happy with this and regard it as a great example of a well-functioning market system. Well, I wasn’t so happy when the robot’s motors weren’t strong enough to make sharp turns with the tracked setup (the robot kits comes with parts to use either wheels or tracks). It turns out the Makeblock had put out a memo acknowledging that some of the motors were defective. I contacted Makeblock through their website and indicated that I had purchased the robot new, but second-hand via eBay. They promptly mailed me 2 new motors free of charge. If you’ve spent much time sourcing products in these markets, you’ll likely realize that this is an exceptional display of corporate integrity. Perhaps it’s old-fashioned, but any time I’m fortunate enough to find either a company or a person who displays unquestionable integrity, I’m inclined to hold on to them.

Gallon Milk Jug as a Size Reference — Note That Rover is Upside Down

Whichever platform you choose, try to ensure it’s mostly made of aluminum or some other non-ferrous (non-magnetic) metal. The reason is when we attach an autopilot to the rover, we’ll rely heavily on a magnetometer (compass) for heading — if you surround a compass with too much iron, you’re going to seriously degrade it’s performance.

So what’s up with all these pictures of gallon milk jugs you ask? First, I love milk. Second, there are few things more frustrating than pictures on technical blogs without reference points. I realized in the previous posts I’ve started down this same horrible path by posting pictures of things that you may not be familiar with but without a reference point to something familiar. This, of course, is a considerable blogging sin, and I ask your forgiveness. Oh, and while we’re at it, yes that is cold milk I snatched from the fridge. And, no, Mrs. Roby DOES NOT know about this.

In our next post, we’ll build a radio-controlled rover on the Makeblock frame with some common hobbyist electronic components.

Peace,

Roby