The more we read about [Josh Pieper]’s quadruped, the mjbots quad A0, the more blown away we are by his year of progress on the design. Each part of the robot deserves its own article: from the heavily modified brushless motors (with custom planetary gears) to the custom motor driver designed just for this project.
[Josh], realized early on that the off-the-shelf components like an ODrive just weren’t going to cut it for his application. So he designed his own board, took it through four revisions, and even did thermal and cycle testing on it. He ended up with the compact moteus board. It can pump out 400 Watts of peak power while its 3Mbit control protocol leaves plenty of bandwidth for real time dynamic control.
The motors and gearboxes are also impressive. It took thorough experimenting and taking inspiration from other projects before he arrived at a 8108 quad copter motor modified and upgraded so heavily its own mother wouldn’t recognize it. This is all packed into a leg unit with three degrees of freedom that puts even the fanciest servo based quadruped to shame.
Finally it’s all packed into a neat four-legged robot frame with batteries and a Pi. You can get a video summary of the robot here or after the break, and we recommend reading his blog for some more images and details.
There’s an old saying about standing on the shoulders of giants, but how about doing so with an open source leg? Well, your robots might do so at least, thanks to OpenLeg, a new open source project for building robot legs. Created by [Joey Byrnes], this started out as a senior project for a course at the University of Illinois. The idea is to create a robot leg that others can use to build four-legged robots that can amble around the neighborhood, much like those built by Boston Dynamics. Continue reading “OpenLeg – The Open Source Robot Leg”→
The sound a set of machined robot legs tapping on concrete make is remarkable. If for nothing more, the video after the break is worth watching just for this. It’s what caught my attention when I first wandered by the Mech Warfare area at Maker Faire, as one of the competitors had their bot out wandering around as a demo during the setup day.
Installing target plate
Making sure the ammo is set to go
This is truly a hacker’s robotics competition. There are constraints, but there’s also a lot of room for freedom. Meet a dozen or so requirements and you be as creative as you want with the rest. My favorite part is that this is not a destructive event like many the battle-based robot TV shows that tend to turn my stomach. Instead, these robots each carry an electric AirSoft gun and seek to hit any of four target panels on their competitor’s robot. Continue reading “Mech Warfare: Like Driving A Building-Sized Robot Through A Busy City”→
Some legged robots end up moving with ponderous deliberation, or wavering in unstable-looking jerks. A few unfortunates manage to do both at once. [MusaW]’s 3D Printed Quadruped Robot, on the other hand, moves in rapid motions that manage to look sharp and insect-like instead of unstable. Based on an earlier design he made for a 3D printable quadruped frame, [MusaW] has now released this step-by-step guide for building your own version. All that’s needed is the STL files and roughly $50 in parts from the usual Chinese resellers to have the makings of a great weekend project.
The robot uses twelve SG90 servos and an Arduino nano with a servo driver board to control them all, but there’s one additional feature: Wi-Fi control is provided thanks to a Wemos D1 Mini (which uses an ESP-8266EX) acting as a wireless access point to serve up a simple web interface through which the robot can be controlled with any web browser.
Embedded below is a brief video. The first half is assembly, and the second half demonstrates the robot’s fast, sharp movements.
Stand up right now and walk around for a minute. We’re pretty sure you didn’t see everywhere you stepped nor did you plan each step meticulously according to visual input. So why should robots do the same? Wouldn’t your robot be more versatile if it could use its vision to plan a path, but leave most of the walking to the legs with the help of various sensors and knowledge of joint positions?
That’s the approach [Sangbae Kim] and a team of researchers at MIT are taking with their Cheetah 3. They’ve given it cameras but aren’t using them yet. Instead, they’re making sure it can move around blind first. So far they have it walking, running, jumping and even going up stairs cluttered with loose blocks and rolls of tape.
Two algorithms are at the heart of its being able to move around blind.
The first is a contact detection algorithm which decides if the legs should transition between a swing or a step based on knowledge of the joint positions and data from gyroscopes and accelerometers. If it tilted unexpectedly due to stepping on a loose block then this is the algorithm which decides what the legs should do.
The second is a model-predictive algorithm. This predicts what force a leg should apply once the decision has been made to take a step. It does this by calculating the multiplicative positions of the robot’s body and legs a half second into the future. These calculations are done 20 times a second. They’re what help it handle situations such as when someone shoves it or tugs it on a leash. The calculations enabled it to regain its balance or continue in the direction it was headed.
There are a number of other awesome features of this quadruped robot which we haven’t seen in others such as Boston Dynamics’ SpotMini like invertible knee joints and walking on three legs. Check out those features and more in the video below.
There was a time when a two-legged walking robot was the thing to make. But after seeing years of Boston Dynamic’s amazing four-legged one’s, more DIYers are switching to quadrupeds. Now we can add master DIY robot builder [James Bruton] to the list with his openDog project. What’s exciting here is that with [James’] extensive robot-building background, this is more like starting the challenge from the middle rather than the beginning and we should see exciting results sooner rather than later.
Thus far [James] has gone through the planning stage, having iterated through a few versions using Fusion 360, and he’s now purchased the parts. It’s going to be about the same size as Boston Robotic’s SpotMini and uses three motors for each leg. He considered going with planetary gearboxes on the motors but experienced a certain amount of play, or backlash, with them in his BB-9E project so this time he’s going with ball screws as he did with his exoskeleton. (Did we mention his extensive background?)
Each leg is actually made up of an upper and lower leg, which means his processing is going to have to include some inverse kinematics. That’s where the code decides where it wants the foot to go and then has to compute backwards from there how to angle the legs to achieve that. Again drawing from experience when he’s done it the hard way in the past, this time he’s designed the leg geometry to make those calculations easy. Having written up some code to do the calculations, he’s compared the computed angles with the measurements he gets from positioning the legs in Fusion 360 and found that his code is right on. We’re excited by what we’ve seen so far and bet it’ll be standing and walking in no time. Check out his progress in the video below.
Despite the success shown in prototypes from groups like Boston Dynamics, bipedal walking is still really hard to implement. When the robot lifts one leg, it has to shift its center of gravity over the other leg to avoid falling sideways.
The bot is RoMeLa at UCLA’s latest evolution in their approach to traditional bipedal roadblocks. Sideways walking is something we covered when we talked about their previous version, NABi, which had only two legs. ALPHRED expands that to four limbs. As the video below shows, all four limbs can be used for walking using either a wide, stable sprawl or the limbs can reorient to a narrower dog or horse-like stance for faster running.
Beyond walking, one or two of the limbs can be put to use as hands to open a door or hand over a package, which is why they refer to them as limbs instead of legs or hands. Only an animation is shown of that configuration but RoMeLa is a robotics lab which we keep an eye on so we’ll let you know if they demonstrate it.
The video goes on to show a neat actuator with active compliance which they call BEAR, Back-drivable Electromagnetic Actuator for Robots. A search turned up no further details but let us know in the comments if you have any. We also liked seeing how they use a speaker to give a rough idea of the amount of current being drawn. While it’s both practical and a hack, it also adds a nice sci-fi touch.