Looking to capitalize on his familiarity with the Raspberry Pi, [Sebastian Zen Tatum] decided to put the diminutive Pi Zero at the heart of his “antweight” fighting robot, $hmoney. While it sounds like there were a few bumps in the road early on, the tuxedoed bot took home awards from the recent Houston Mayhem 2021 competition, proving the year of Linux on the battle bot is truly upon us.
Compared to using traditional hobby-grade RC hardware, [Sebastian] says using the Pi represented a considerable cost savings. With Python and evdev, he was able to take input from a commercial Bluetooth game controller and translate it into commands for the GPIO-connected motor controllers. For younger competitors especially, this more familiar interface can be seen as an advantage over the classic RC transmitter.
A L298N board handles the two N20 gear motors that provide locomotion, while a Tarot TL300G ESC is responsible for spinning up the brushless motor attached to the “bow tie” spinner in the front. Add in a Turnigy 500mAh 3S battery pack, and you’ve got a compact and straightforward electronics package to nestle into the robot’s 3D printed chassis.
In a Reddit thread about $hmoney, [Sebastian] goes over some of the lessons his team has learned from competing with their one pound Linux bot. An overly ambitious armor design cost them big at an event in Oklahoma, but a tweaked chassis ended up making them much more competitive.
There was also a disappointing loss that the team believes was due to somebody in the audience attempting to pair their phone with the bot’s Pi Zero during the heat of battle, knocking out controls and leaving them dead in the water. Hopefully some improved software can patch that vulnerability before their next bout, especially since everyone that reads Hackaday now knows about it…
While battles between these small-scale bots might not have the same fire and fury of the televised matches, they’re an excellent way to get the next generation of hackers and engineers excited about building their own hardware. We wish [Sebastian] and $hmoney the best of luck, and look forward to hearing more of their war stories in the future.
Be more fun if it was ‘autonomous’ – there’s easily enough grunt in the zero to run opencv and simply identify what isn’t arena and attack it.. I’ve never seen arena hazards in anything so lightweight.. And being wireless enabled data to and from a pc is an option, so could set up a bigger PC to do the vision tasks – which you could try with normal RC gear, but won’t be able to get any feedback beyond the basics RC systems sometimes include, where being a zero you can program it yourself.
Just using it as an RC receiver seems wasteful to me, interesting but overkill for the task at hand… Also don’t see how even with the zero being so cheap it works out considerably cheaper in electronics on the robot, I’d have though slightly more expensive…
Oh trust me, its completely overkill, but considering that a good RC transmitter with mixing capabilities goes for $150 then you have to add the cost of a receiver to that, a $10 pi zero and $40 Bluetooth controller is always gonna be cheaper.
True, the transmitter is expensive, but its a single purchase, not built on to the robot that is good for every project damn nearly forever if my second hand one is anything to go by (its one of the early fancy computerised ones with modular radio for different frequencies/ encodings etc that really isn’t friendly to set up the way new ones are, but damn if it doesn’t work fine last time I needed it, even if I do always have to dig the manual out too)..
I was only thinking on the robot anyway – the bits that might be damaged, through use and need replacement. As your basic hobby RC receiver are stupidly cheap really – or at least can be, as fancier model for long range/ with extra telemetry etc do exist..
The biggest problem regarding cost is that every bot at every competition must have a failsafe feature and the cheaper you go, the less likely it will have one. I am going to be building an RC bot soon, but when I first started, I didn’t have the money for a one time purchase of $100.
Would definitely be interesting to see the Pi take a more active role in controlling the bot as time goes on. I wonder if there are any rules about that sort of thing in a competitive scenario?
That was another reason I chose to use a Pi because there are no rules on computer assistance. Currently I have the bot running a two joystick layout for movement which is uncommon, but with enough money you can get that out of RC components. The first assisted implementation that I have been meaning to add will be a button that switches the polarities of the drive motors so when it gets flipped upside down, I can continue to drive it normally. Assisted bots aren’t too common, but a notable example is The Machine Corps 2018 Chomp. The most notable autonomous feature was its proximity triggered hammer.
Something I’ve seen so much in fighting robots are hammers which get used very poorly. The driver will get right into an ideal position *then fails to trigger the hammer* until the opponent gets out of the impact zone. When teams separate driving and weapons control, it often gets worse. Spinning around, driving aimlessly, flailing the hammer, hitting everything except the other bot.
Makes me want to yell out “Hammer NOW! NOW NOW! Well, too late, you really taught the arena floor not to mess with you!” “Good grief! When the other bot is right in front of yours HIT THE HAMMER! Don’t wait for five seconds!”
I’m surprised they’re using the L298 drivers. It was my understanding that they have terrible power efficiency, meaning they waste power. I would imagine a couple of drivers like https://www.pololu.com/product/2990 would be better.
Lots of “hackers” and hobbyists keep on using the L298 because … probably because it’s a chip they’ve heard of first. Maybe just because it looks impressive? Maybe because they do not like reading datasheets, and do not realize a small SOIC8 can be a more “powerul” motor driver?
The Polulu board you mention uses the DRV8838.
some similar chips which can deliver more power are the DRV8871 and the A4950.
All these more modern chips also do not need all those high current (and therefore bulky) bypass diodes. Just a single SOIC8 or smaller. Does not look impressive at all.
Addition:
Just discovered the L298n has it’s own tag here on Hackaday, while probably none of the others have. There are also just 7 articles under that tag, while a search finds around 20 articles with that string.
There are 37 articles though under the tag “H-bridge”.
I’m gonna be honest, I chose the L298N because it was easy and cheap. Sure it has a lot of drawbacks, but it definitely has a lot documentation. Will look towards those others though soon.
Every fight will be a ‘Tie’?
I’ll see myself out
Does the weapon of choice make this bot a tie fighter?
You should take a bow for that one.
Sure it[‘s all fun and games until someone puts out an I2C ……..
So proud of you Sebastian. You introduced me to Raspberry Pi.
Thank you so much, I hope to continue messing with Pi’s until I am as old as you lol.