Why Walking Robots are Easy

Tesla recently announced their humanoid robot product called Optimus it can walk around and do stuff and Elon Musk says it's going to sell for twenty thousand dollars which is cheap I mean the parts in there cost a lot more than that not to mention the r d costs and we still haven't seen the launch of the Cyber truck but how hard is it to build a robot that walks on two legs I've built quite a few walking robots in the past if you head right back to the start of my YouTube channel there are quite a few large robots that could just about hobble along made out of wood and driven by windscreen wiper motors and other parts that I could get hold of I built these earlier this Century in a room of a house here I used to live in which is why there's a bed in the corner of the shot I've moved on quite a bit since then to some robot dogs that I've built recently but a few years ago I built some bipedal robots like robot X and my walking gonk Droid these actually had a sense of balance using an inertial measurement unit to read how far they were leaning over and make the motors respond accordingly to keep them upright that can be quite tricky though and and most of what's on YouTube is the good cuts of footage where they work just about okay I've taken some of these projects to events like make Affairs and you'll always find that one person oh hello I was watching your YouTube channel with my dog and I did a stroke of Genius green Millions think alike James why don't you make a simple robot that just all it does right is lean that way right moves that leg okay then it leans the other way right moves that leg and then leans the other way right then moves that leg and then moves leans that way and and moves the other leg so in this video we're just going to make that simple sounding robot that shifts all its mass One Way moves the other leg and shifts it back the other way and moves the other leg and then it will walk along I'm gonna make this as simple as possible using a lot of linear sliders each foot can move up and down in a straight line each leg can also move backwards and forwards in a straight line to take steps and there's a carriage on top that moves side to side with a lot of Mass on it there's quite a bit of Hardware like Extrusion and nuts and bolts and so on in this project but the majority of it is 3D printed so just a quick ad for my 3D printing sponsor thanks to lulsbot for supporting my Channel with 3D printers and thanks to 3D fuel for the filament for this project and lots of other projects so check out my channel for more 3D printing projects and check out 3dfuel.com the majority of my sliding rails are basically V Wheels which are attached to some 3D prints with some bolts those have got bearings in and that allows v slot Extrusion to slot in and that makes a sliding piece so I've got a foot with some rubber feet on and we've got some linear axes that are attached to those to allow that foot to lift up and down the various parts to cross brace it including some plates on the back and the front so there's our foot with our linear slider on and of course that v slot still fits in and that's the main mechanism that's going to make those feet lift up and down so it can take steps those fees are going to be driven up and down with a bit of lead screw and a lead nut which goes on there and obviously it goes up and down as it rotates this bit of lead screw came out of an old project which is why it's quite dirty looking but it seems to move okay and of course there's a coupler on there and I'm just going to drive that with a DC motor with an encoder so that we can drive the screw and position it that fits into the extra little block on the foot so as I drive it up and down then obviously that will drive the foot up and down so my motor fits on the v-slot itself and goes into there and that means as the motor turns as you'd expect the v-slot moves up and down which we can attach to the next piece of the leg one thing I didn't mention earlier was that we actually need to make the legs rotate so that we can turn on the spot and walk around in circles essentially rather than just going in a straight line so that piece of Extrusion fits into a bearing with some 3D printed bearing blocks it's double braced with two bearings to hold it nice and securely and that allows the leg to rotate and you'll notice there's some more V wheels for the next linear slider which will come on too shortly so I've made two of those legs which both rotate and somehow we need to actually make them rotate those so they don't just go wobbly and to do that I've attached a little lever and a Servo onto that 2020 v slot and the servo onto the mounting there so with a little push rod in between that means as we move the servo we can rotate that and we can lock it in place when we want to so it doesn't just Freewheel and have the legs twist as it's trying to walk so I've put those on the middle there and made sure they don't knock each other as the legs slide past each other by putting the levers at an angle so with some more 20 40 Extrusion this time so we can hold it nice and rigid we've got the next sliding axes which is going to slide those legs backwards and forwards those 20 40s fit into some more 3D printed blocks and I've left lots of holes there for some t-nuts and bolts to attach them and those blocks are fitted to some more 2020 which makes up the frame of the robot and it'll also allow a place for that Carriage to move side to side so you can see my legs have quite a lot of movement there to move backwards and forwards and that's how it's going to take steps so we just need that Carriage now which is going to move side to side to shift the mass and again that has some V wheels at 90 degrees to each other so it slots into the v's on two sides of the 2020 Extrusion on either side of that frame and because of the V Wheels which are horizontal that locks in nicely so I can pick the whole thing up by it and it doesn't fall off I fitted some more 3D printed Parts on the end of those rails which serve two purposes one is as an end stop to stop the carriage falling off and the other one is I've got somewhere to tie a piece of belt on so I can actually drive this side to side to do that we're going to be using another one of these motors with a 3D printed T5 pulley on and that pulley has a captive nut and a little grub screw to hold it onto the flat of the shaft which is six millimeter on these motors I'm using open length T5 belt which is about six millimeters wide and that's going to go around some idlers and onto some little clamps on those 3D printed end parts so now as that slides up and down the motor will turn and as the motor turns it will cause the carriage to slide up and down to shift Mass side to side and those idler bearings are just a pair of skate bearings roughly with an eight millimeter internal diameter those legs of course need to be driven backwards and forwards so this is the sideways shot of the robot and to do that I've got another motor and another idler so it's a bit like the carriage of a 3D printer I've made this clever little belt clamp that we can put two bits of belt in or at least the two ends that wrap around there's a little block that locks in there and stops that pulling out so with both open ends of that belt installed we now have a belt drive with another motor and that's the same on both legs The Carriage has some platforms on which I'm going to install electronics on and probably also put some Mass on we can put some batteries in there although lipos tend to be not very heavy because they're designed for drones essentially but I can actually roll up one of the feet now and move that Carriage over and test whether it's actually going to balance so yep there's definitely a gap under the foot and it will just about balance on one foot even with no additional Mass on that Carriage however yeah it's pretty sketchy it will probably topple over especially if we try to move fast so I'll probably install some Mass a bit later on and see how that goes but for now it's looking pretty hopeful I can slide the legs back with some forwards as well and it doesn't tip backwards or forwards so that's looking pretty good but before we carry on with that it's time for a quick ad from the video sponsor which is established titles now what I've got here is a proclamation that says my name is Lord James Bruton and I'm going to tell you how you can get one too established titles is a fun and novel way to preserve the natural Woodlands of Scotland while helping Global reforestation efforts the project is based on a historic Scottish custom where landowners are referred to as lards or in English Lords and Ladies the title pack gives you at least one square foot of dedicated land on a private estate in edleston in Scotland and an official certificate with a Crest your certificate features a unique plot Number with which you can see the exact location of your land established titles plant a tree with every order and work with global Charities one tree planted and trees for the future to support Global reforestation efforts you can officially change your name to Lord or lady and get it put on your credit card or anything else pretty much they even have couple packs that come with adjoining plots of land the first 200 people purchasing a title pack using my link will effectively be next to my plot and depending on how many of you want to become a lord or a lady we can build our little James Bruton Kingdom it makes an amazing last minute gift and established titles is actually running a Black Friday sale plus if you use the code James Bruton you can get an additional 10 off go to establishtitles.com jamesbroughton to get your gifts now and help support the channel I'm using the encoders that are built into these motors and there's going to be five Motors and therefore 10 encoder wires I need to read those who have interrupts in the code to make sure that that's very accurate which interrupts everything as the name would suggest so I'm using a Teensy 4.1 which is a very fast micro controller so we can deal with reading all those encoders and not missing any steps there are a lot of wires to wire in all of the 10 encoders the motor drivers which are BTS 7960s to actually drive the motors with their pwm wires and the power that needs to run to the encoders and motor drivers and the servos I'm using some code from the Arduino playground website which uses two interrupts per encoder because there's two wires and that gives you the most accurate answers and you don't miss any encoder stamps so you can see all the values updating there as I'm turning the encoders so that's pretty good and it looks like they're all working together so now I can position that Carriage using the encoder value and driving it to a demand position for now I'm just using the remote control for open dog 3 that I showed at the beginning of the video and for now it's just trying to get to the position as quickly as it can I move on the stick but that's rather jerky so I've moved on and written some Arduino code to make a step sequencer and I've also got some proportional control so as the distance between where the encoder is and where it needs to be get smaller it decelerates and that means I get a nice smooth motion and no overshoot so you can see that motor is turning away nicely there and you can see it's decelerating as it gets towards its targets I've also got some motion filtering on here which I talked about in another video and that video was just using cheap servos and an 8-bit Arduino Uno to make an animatronic head and you can check this out on my channel I've actually got some additional motion smoothing here which basically takes a large percentage of the old value in each Loop and a small percentage of the new value that's coming in from the remote that means the value can't change too quick and so we get a nice smooth motion you may have noticed I've also added some extra mass in the form of two one kilogram lead diving weights I got off Amazon so now there's definitely enough Mass to over balance the robot onto one foot while we pick up the opposite foot I'm using the encoder control again on those feet Motors to turn those lead screws and I've used lead screws here rather than belts so they're not easily back drivable they can be back driven a bit but with the motor holding power in place that robot can definitely hold the mass of itself plus that additional lead that we now have which is another couple of kilograms spinning backwards and forwards on top so that was an early design decision to make sure this thing would definitely work and it looks like it's going to be a okay so now it's time to probably use those sliding axes to slide the legs backwards and forwards and move them in opposite directions when one foot's off the ground and hopefully we can take steps so let's give that a go we can move the mass to the right there and move the foot up and slide those legs in opposite directions and then we can take a step and now our robot walks along just like we wanted it to it's pretty slow though and we'll talk about that in a moment but essentially it can't move too fast because then it will over balance because of that huge inertia from that mass moving which would basically be enough to tip it over so it is statically stable that means it hasn't got any sense of balance and that basically means that we have to go quite slow to make sure the mass is over one foot before we do anything I've also Incorporated the servos here so we can rotate the legs although you can see that there's quite a bit of wobble and that's mainly down to the fact that they're holding that whole rotation with those 3D printed levers and the servo itself which only has a certain amount of holding power we have all that Mass on top that we need spinning battles and forwards and you know essentially being an off-center load from where the rotation is so we definitely get some wobble there and again we have to go quite slowly otherwise we've got no chance of it working whatsoever foreign [Music] difference [Music] well it looks great in five times speed but why can't we make it go faster in real life the problem with accelerating Mass fast is that mass has inertia which means it wants to stay still if I move a large Mass from a stationary point or move it repeatedly side to side then it causes a reaction force that pushes me in the opposite direction so as well as the mass of the robot being enough to offset the mass of the opposite leg while it takes steps if we accelerate it enough it would also cause enough of a reaction that it would tip the robot over to manage that we're back to measuring the angle of the robot and dynamically controlling the velocity of the mass to keep the robot from over balancing as well as all the other axes which are essentially Mass moving around my robot axol Gunk droids look like they were moving more fluidly although they were often temperamental and that's when you realize how much work has gone into robots from Boston Dynamics and other large companies although they still have their issues at some point I'd like to build a bigger bipedal robot again with some of the things in it that I've learned from doing the robot dog projects like the cycloidal drives those back drivable axes and a bit of dynamic stability and the inverse kinematics mainly but for now I'm pretty happy with that for a two-week project I'm going to publish all the cad and code and that's on my GitHub and the links in the description to this video so if you'd like to support me through patreon or YouTube channel membership then those links are in the description as well and patrons and YouTube channel members can get access to all the videos up to a week early and sneak peeks and pictures of what's coming up alright that's all for now 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Channel: James Bruton

Views: 244,330

Keywords: Tesla Optimus, walking robot, bipedal robot, how to build a walking robot, testing bipedal robots, simple walking robot, 3d printed walking robot, walking machine, simplest robot, how to build a robot, homemade robot, 3d printed robot parts, maker, why are robots expensive

Id: WJKhpGFg4uU

Length: 15min 58sec (958 seconds)

Published: Tue Nov 01 2022