Super Simple, Super Cheap FPV Drone Tracking

What’s more disruptive to the drone first-person view (FPV) experience than dropouts in your video feed when you’re in the middle of a race? Probably nothing, and there’s probably also not much you can do about it. Or is there? Might a simple tracker based on RSSI help keep your video signal locked in?

Honestly, we’re not sure it would, but we think it’s pretty nifty to see [FlyerFpv]’s tracker following his drone around. The idea is simple and uses the full-diversity FPV receiver he already has. Diversity receivers constantly monitor signal strength from multiple antennas to determine which one to listen to, which improves reception quality. [FlyerFpv] sends the RSSI outputs to analog inputs on an Arduino which drives a servo to keep the signals as close to each other as possible. The Arduino and the DC-DC converter needed to power it fit nicely inside the receiver case with no modifications, which is a nice touch. With a 3D-printed servo mount and some fancy directional antennas, the setup keeps pretty good track of his drone now. See it in action below.

Sure, the response could be snappier, and we’d love to see another receiver and servo added to track pitch as well as yaw. For a first pass, we think it’s great, but [FlyerFpv] should enjoy it while he can in case AI takes over our flying fun soon.

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Servos Do the Plucking in this MIDI Music Box

It started with a cheap, punch-card programmable manual music box. Thirty-one hobby servos later, it ended as an automated MIDI music box, with a short pit stop as a keyboard-driven MIDI device.

If you think you’ve seen the music box in [Mitxela]’s video below before, you’re right. [Martin], musician, inventor, and father of the marvelous marble music machine, took an interest in these music boxes and their programming a while back. Like [Martin], [Mitxela] started his music box project with punch card programming, but he quickly grew tired of the bothersome process, even after automating production with a laser cutter. He decided to do away with the punch cards completely and devised a method to pluck all 30 notes using a few large handfuls of hobby servos. One servo, converted to continuous rotation, spins the drum, with the rest linked to small laser-cut acrylic plectrums via stiff brass wire. The fingers imitate the punched holes passing over the drum and pluck the notes according to MIDI messages. The whole thing can draw quite a bit of current, so in addition to a beefy power supply, [Mitxela] optimized the code to minimize power requirements. This had the happy consequence of reducing the latency enough to allow the music box to be played from a MIDI keyboard in real time.

A lot of work went into this one, but [Mitxela] isn’t resting on his laurels; he has a full slate of improvements that he wants to tackle, not least of which is SD card support for MIDI files to turn this into a jukebox. We’re looking forward to the updates.

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The Sensor Array That Grew Into a Robot Cat

Human brains evolved to pay extra attention to anything that resembles a face. (Scientific term: “facial pareidolia”) [Rongzhong Li] built a robot sensor array with multiple emitters and receivers augmenting a Raspberry Pi camera in the center. When he looked at his sensor array, he saw the face of a cat looking back at him. This started his years-long Petoi OpenCat project to build a feline-inspired body to go with the face.

While the name of the project signals [Rhongzhong]’s eventual intention, he has yet to release project details to the open-source community. But by reading his project page and scrutinizing his YouTube videos (a recent one is embedded below) we can decipher some details. Motion comes via hobby remote-control servos orchestrated by an Arduino. Higher-level functions such as awareness of environment and Alexa integration are handled by a Raspberry Pi 3.

The secret (for now) sauce are the mechanical parts that tie them all together. From impact-absorption spring integrated into the upper leg to how its wrists/ankles articulate. [Rongzhong] believes the current iteration is far too difficult to build and he wants to simplify construction before release. And while we don’t have much information on the software, the sensor array that started it all implies some level of sensor fusion capabilities.

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No, Cat, This Is Not The Litter Box user [peterquinn] has encountered a problem with his recently unruly cat peeing under the dining table. Recognizing that the household cat’s natural enemy is the spray bottle, he built an automatic cat sprayer to deter her antics.

The build is clear-cut: an Arduino Uno clone for a brain, an MG995 servo, PIR sensor, spray bottle, and assorted electronics components. [peterquinn] attached the servo to the spray bottle with a hose clamp — ensuring that the zero position is pointing at the trigger — and running a piece of cabling around the trigger that the servo will tug on. Adding a capacitor proved necessary after frying the first Uno clone, as the servo powering up would cause the Uno to reset.

The code is set up to trigger the servo — spraying the cat twice — once the PIR detects the cat for more than ten seconds. After toying with a few options, [peterquinn] is using a 9V, 2A power supply that works just fine. For now, he hopes the auto-sprayer should do the trick. If it somehow doesn’t work, [peterquinn] has mused that a drastic upgrade to the vacuum may be necessary.

Auto-Tracking Sentry Gun Gives Deer a Super Soaking

Things rarely go well when humans mix with wildlife. The problems are exacerbated in the suburbs, where bears dine on bird feeders and garbage cans, raccoons take up residence in attics, and coyotes make off with the family cat. And in the suburbs, nuisance wildlife can be an intractable problem because the options for dealing with it are so limited.

Not to be dissuaded in the battle to protect his roses, [dlf.myyta] built this motion-activated sentry gun to apply some watery aversion therapy to marauding deer. Shown in action below against a bipedal co-conspirator, the sentry gun has pretty much what you’d expect under the hood — Raspberry Pi, NoIR camera, a servo for aiming and a solenoid valve to control the water. OpenCV takes care of locating the intruders and swiveling the nozzle to center mass; since the deer are somewhat constrained by a fence, there’s no need to control the nozzle’s elevation. Everything is housed nicely in a plastic ammo can for portability and waterproofing. Any target that stands still for more than three seconds gets a hosing; we assume this is effective, but alas, no snuff films were provided.

We’re not sure if [dlf.myyta]’s code can discern friend from foe, and in this litigious world, hosing the neighbor’s kid could be a catastrophe. Perhaps version 2.0 can include image recognition for target verification.

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Solenoids and Servos for Self Actuated Switches

The new hotness in home automation is WiFi controlled light switches. Sure, we’ve had computer-controlled home lighting for literally forty years with X10 modules, but now we have VC money pouring into hardware, and someone needs to make a buck. A few years ago, [Alex] installed WiFi switches in a few devices in his house and discovered the one downside to the Internet of Light Switches — his light switches didn’t have a satisfying manual override. Instead of cursing the darkness for want of an Internet-connected candle, [Alex] did the only sensible thing. He installed electromagnets, solenoids, and servos behind the light switches in his house.

The exact problem [Alex] is trying to solve here is stateful wall switches. With an Internet-connected lamp socket, the wall switch no longer functions. Being able to turn on a light when your phone is out of charge is something we all take for granted, and the solution is, of course, to have Internet-connected switches.

Being able to read the state of a switch and send some data off to a server is easy. For this, [Alex] used a WeMos D1 mini, a simple ESP8266-based board. The trick here, though, is stateful switches that can toggle themselves on and off. This is a mechanical build, and although self-actuated switches that can flip up and down by computer command exist, they’re horrifically expensive. Instead, [Alex] went the DIY route, first installing electromagnets behind the switches, then moving to solenoids, and finally designing a solution around four cheap hobby servos. The entire confabulation stuffed into a 2-wide electrical box consists of two switches, four hobby servos, the D1 mini, and an Adafruit servo driver board.

The software stack for this entire setup includes a NodeJS server connected to Orvibo Smart Sockets over UDP. Also on this server is a WebSocket server for browser-based clients that want to turn the lights on and off, a FauXMo server to turn the lights on and off via an Amazon Echo via WeMo emulation, and an HTTP server for other clients like [Alex]’ Pebble Watch.

This is, without question, the most baroque method of turning a lamp on and off that we’ve ever seen. Despite this astonishing complexity, [Alex] has something that is also intuitive to use and, to borrow an applhorism, ‘Just Works’. With a setup like this, anyone can flick a switch and turn a lamp on or off over the Internet, or vice-versa. This is the best Home Automation build we’ve ever seen.

You can check out [Alex]’ video demo of his build below, or his GitHub for the entire project here.

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Warhammer 40K Model Rocket Launcher

[Daniel L]’s friend has a passion for Warhammer 40K. [Daniel] himself has a similar zeal for perfection in details. When he remembered a long-forgotten request to build a working rocket launcher for one of his friend’s Warhammer 40K models — well — the result was inevitably awesome.

The MicroMaxx motors — one of the smallest commercial rocket motors on the market — he had on hand seemed to fit the model of the Hyperios Whirlwind anti-air rocket tank. Modeling and 3D printing all the parts proved to be easier than assembling the incredibly detailed model — on top of sanding and filling gaps, a perfect paint job was no simple matter.

The launcher has two main circuit boards: a STM32F407 microcontroller brain, a low-power A20737A Bluetooth module, and a voltage regulator. The second has the constant current source and MOSFET output stages for the rocket igniters. Pitch and yaw handled by a pair of RC servo motors. [Daniel L] has also gone the extra mile by creating an accompanying iPhone app using the Anaren Atmosphere IDE — it’s simple but it works!

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