Watch Legged Robot Run Circles Around Its Bigger Brethren

[Ben Katz] posted about bringing the Mini Cheetah (center, above) robot to the 2019 International Conference on Robotics and Automation (ICRA) held in Montréal, where it shared the floor with others for a workshop focusing on real-world deployment of legged robots. Those of you who haven’t been keeping up with legged robots may find yourselves delightfully surprised at the agility and fluid movements of this robot. Mini Cheetah may lack the effectors or sensors of the bigger units, but its nimbleness is undeniable.

[Ben] shared some footage of the robots together, and at about 7:22 in this video Mini Cheetah can be seen showing off a bit of flexing, followed by running around a larger unit. Another, shorter video is embedded below where you can see all the attendees moving about in a rare opportunity see them all together. You can even see the tiny one-legged hopping robot Salto if you watch closely!

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Testing Brushless Motors With A Little Help From The ESC

These days, brushless motors are the go-to for applications requiring high power in a compact package. It’s possible to buy motors in all manner of different configurations off the shelf, and the range available is only getting better. However, sometimes getting something truly optimal requires a bit of customization. With motors, this can involve swapping magnets or hand-winding coils. In these cases, it can be useful to test the modified motor to determine its performance. [JyeSmith]’s ESC tester is capable of just that.

Fundamentally, the ESC tester is a simple piece of hardware. It uses a microcontroller to speak the Dshot protocol. This protocol is typically used to communicate between multi-rotor flight controllers and ESCs. In this case, the Dshot telemetry is instead displayed on a small OLED screen. This enables the user to read off KV values, as well as other useful data such as current draw and RPM. This can help quantify the effects of any modifications made to a motor, as well as prove useful for learning about parts of spurious origins.

It’s a device that should prove useful to those trying to eke out every last drop of performance from their multi-rotor builds. We expect to see more similar projects emerge as drone racing continues to increase in popularity. If you’re still trying to learn the theory behind the technology, you can always build your own brushless motor. Video after the break.

[Thanks to Keegan for the tip!]

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An Open Source ESC For Brushless Motors

For something basic like a brushed DC motor, speed control can be quite simple, and powering up the motor is a simple matter of just applying voltage. Brushless motors are much more demanding in their requirements however, and won’t spin unless driven just right. [Electronoobs] has been exploring the design of a brushless speed controller, and just released version 1.0 of his open-source ESC design.

The basic design is compact, and very similar to many off-the-shelf brushless ESCs in the low power range. There’s a small PCB packing a bank of MOSFETs to handle switching power to the coils of the motor, and a big capacitor to help deal with current spikes. The hacker staple ATMEGA328 is the microcontroller running the show. It’s a sensorless design, which measures the back EMF of the motor in order to determine when to fire the MOSFETs. This keeps things simple for low-torque, low-power applications.

It’s a tidy build, and the latest revision shows a lot of polish compared to the earlier prototypes. If you’re interested to learn more, try building it yourself, or consider building a thrust testing rig for your bench at home. Video after the break.

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Supercapacitors Propel Rocket To The Skies

OK, so this isn’t really a rocket. In the strictest definition, rockets are vehicles or projectiles that propel themselves through jettisoning mass, usually through the combustion of fuel. But with electric motors getting stronger and stronger, folks are building craft that look a lot more like rockets than airplanes. [Tom Stanton] is one such person (Youtube link, embedded below).

We’ve seen “electric rocket” builds before, but where others have used lithium batteries, [Tom] has used supercapacitors instead. Six supercaps are installed in a 3D printed mount, and supply power to a 500 W brushless outrunner motor which gives the rocket the thrust to climb into the sky.

In testing, [Tom] estimates the rocket was able to reach an altitude of approximately 60 m, or 200 ft. That’s not particularly astounding, but it does prove that supercaps can run a high current load in a real world situation. Additionally, their fast recharge rate allows [Tom] to make a repeat flights in just about the time it takes to repack the parachute. Video after the break.

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3D Printing A Water Jet Drive

[Ivan Miranda] is always experimenting with 3D printing, and recently has been taking his work on the water. His latest creation is a racing paddle boat, but its performance left [Ivan] with a need for speed. Cue the development of the 3D printed water jet engine (YouTube link, embedded below).

The basic principle of operation is simple. Water is sucked through an inlet, where it is accelerated by a turbine driven by a brushless motor. This turbine, in combination with stator fins, forces the water through the outlet, propelling the boat forwards in the process.

The first prototype is printed in PLA. Tolerances are good, thanks largely to [Ivan]’s experience and well-calibrated printers. After assembly, the engine is fired up, to great results. After sourcing a series of larger tubs in which to test the device, the engine is finally run up to full throttle and appears more than capable of shifting a serious amount of water.

We’d love to see a proper instrumented thrust test, particularly one that compares the device to other water jet drives on the market. Brushless motors make a great drive solution for RC boats, so we’re sure [Ivan] will be tearing up the lake real soon. Video after the break.

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Brushless R/C Rocket Tests Different Flight Regimes

Quadcopters are familiar, and remote control planes are old hat at this point. However, compact lightweight power systems and electronic flight controllers continue to make new flying vehicles possible. In that vein, [rctestflight] has been experimenting with a brushless electric rocket craft, with interesting results. (Youtube, embedded below.)

The build uses a single large brushless motor in the tail for primary thrust. Four movable vanes provide thrust vectoring capability. To supplement this control a quadcopter was gutted, and its motors rearranged in the nose of the craft to create a secondary set of thrusters which aid stabilization and maneuverability.

The aim is to experiment with a flight regime consisting of vertical takeoff followed by coasting horizontally before returning to a vertical orientation for landing. Preliminary results have been positive, though it was noted that the body of the aircraft is significantly reducing the available thrust from the motors.

It’s a creative design which recalls the SpaceX vertical landing rockets of recent times. We’re excited to see where this project leads, and as we’ve seen before – brushless power can make just about anything fly. Even chocolate. Video after the break.

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Designing Tiny Motors Right Into The Robot’s Circuit Board

Motors are not overly complex, but this one is downright simple. Carl Bujega has been working on a motor design that heavily relies on the capabilities of the printed circuit board (PCB) fabrication processes. His talk at the 2018 Hackaday Superconference covers how he built a brushless DC motor and speed controller into a PCB. You can watch the newly published video after the break.

There are two main parts of an electric motor; the stator is stationary while the rotor spins on bearings. Electromagnetic forces are used to cause that spinning action. In this case, Carl has built the electromagnets as coils on a 4-layer circuit board (six coils on each layer). When electrified, a magnetic field is generated that pushes against the rare-earth magnets housed in the rotor.

A couple of things are really interesting here. First, those coils are usually made of “magnet wire” (enamel covered wire that is very thin) wrapped around an iron core. Using the circuit board instead saves both physical space, and the time and expense of wrapping coils of wire in the traditional way. Second, Carl has been designing with manufacture in mind; you can see in the image show that his motor design is dead-simple to assemble by inserting a 3mm bearing in the PCB, inserting magnets into the plastic rotor and snapping it into place. The end goal is to make robot actuators that are part of the circuit board itself.

The genesis of this idea came from Carl’s interest in drone design, in fact, he jumped right into a drone startup immediately after finishing his EE. The company didn’t last, but his thirst for interesting designs is ongoing. When looking at reducing the total parts necessary to build a quadcopter he happened on the idea of PCB-based coils and he’s followed it to this motor design, and beyond to some very interesting flexible-PCB robot design work which you can check out on his Hackaday.io page, YouTube, and Twitter.

There are of course some trade-offs to this. The motor is low torque since it uses an air core and not an iron core. And he’s had trouble implementing a sensor-less Electronic Speed Controller (ESC) as the back-EMF from the coils appears to be too weak. Not to fret, he added a hall sensor and has succeeded in designing an ESC that measures just 14mm by 8mm. In fact, he’s holding up the ESC and motor in the image at the top of this article!

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