A Robot Dog With One Servo Per Leg — minirobo #11

I've been building robot dogs for a long time, and they always end up complicated. This one doesn't. Barkley has one servo per leg — four moving joints in the whole robot — so the only things left to change are the length of the leg and the shape of the gait. That constraint is the episode. With four things to tune instead of forty, you can actually search the space: measure the robot, model it, and let a simulation try gait after gait while you do something else. But a simulation is only worth running if it tells the truth. So before any of that — what does he weigh, where is his centre of gravity, and what do these MG90S servos actually do when you tell them to move? They lag about 36 milliseconds behind the command, and they will not exceed 500 degrees a second. Modelling those two numbers is what makes the simulation match the bench. Then we take the best legs and the best gait back to the mat, film it at 120 frames per second, and put it next to what the simulation said would happen. What's in this episode Why one servo per leg, and what that constraint buys you Weighing him four ways, because that is how you find a centre of gravity Bench time: measuring servo lag and the speed ceiling Why modelling the lag is the thing that makes a simulation honest Hours of searched gaits, and what "best" turned out to mean 120 fps on the mat, against the simulation that predicted it Centring four servo horns with a printed jig instead of computer vision Flashing firmware that listens to the minirobo controller Everything is free and open — every STL and the CAD behind it, the minicore, the controller, and the firmware on both boards. minirobo.io --------------------------- Chapters 0:00 A robot dog with one servo per leg 0:27 Dials, or simulate 0:46 What does he weigh? 1:14 Bench time — what the servos actually do 1:45 36 milliseconds, and 500 degrees a second 2:08 Simulating, for hours 2:42 Back to the mat, at 120 fps 3:26 Arguably great 3:47 Or just print a jig 4:16 Flashing the firmware 4:35 How to build a Barkley 5:09 See you next time --------------------------- Parts used (affiliate) MG90S metal-gear micro servo ×4 — https://amzn.to/4xeFcZg MG90S multipack (cheaper per servo, and you need four) — https://amzn.to/3SREP7h ESP32-C3 SuperMini (14-pin) — https://amzn.to/3RYS9qi Boost Converter Module (set to 5V) — https://amzn.to/4gLbt3X 470µF electrolytic capacitor, 10V or higher — https://amzn.to/4bW3EFW 2.54mm female header strips (the module sockets) — https://amzn.to/4bpj7y7 Pre-wired LEDs with built-in resistors (the eyes) — https://amzn.to/4yzQ053 1S LiPo with protection, 1100mAh + JST — https://amzn.to/4dqeNPV M2 self-tapping screws (6mm) — https://amzn.to/4xpkNQR Hot glue gun (the battery is glued into the bay) — https://amzn.to/4wJcXkY Soldering iron + solder — https://amzn.to/4pUFwt3 The 3D printer I use — Original Prusa MK4S — https://amzn.to/4wRBe8m (As an affiliate I earn from qualifying purchases — costs you nothing, supports the channel) Free downloads — the whole robot, not a picture of it Every STL and the CAD behind it, the minicore, the minirobo controller, the firmware for both, and the centring jig: https://minirobo.io/projects/walker Printed parts The body, the lid, the four legs and the toes are all PLA. The centring jig is printed too — a plate with a fence that holds every leg at a known angle while you seat the horn, which is a two-hour print instead of an afternoon of computer vision that still has error in it. The bench The numbers that make the simulation honest are both measurable on a desk: the servo lags a command by about 36 ms, and it will not move faster than 500 degrees a second. Model neither and the simulation lies to you; model both and it matches what the mat shows at 120 fps. Community Join the minirobo community at https://minirobo.io/community — free downloads for every episode, and the place to post what you built. Drop your build in the comments below and check the channel's Community tab for polls, photos and behind-the-scenes. New to minirobo? Subscribe — one off-the-shelf part per episode, and real mini robots built with it.