One year of building a robot dog

[Music] since my project update video last year a lot has happened with the modius controller and the mjbot's quad a1 robot here are some of the major developments and a bit of where mjbots is headed next see lots of fixing problems speed records and walking in new and varied conditions click like and subscribe to follow developments as they happen let's get started first up is the modius brushless controller new since last year is the modius r4 series with some major improvements the controller is now an stm32g4 which is smaller lower power and higher performance the communications protocol is can fd at five megabits instead of rs-485 this is both more commonly used and allows the controller to rely on hardware acceleration for framing the peak voltage was increased to 34 volts and the peak power is 500 watts the full control loop runs at the pwm frequency of 40 kilohertz and external control by a host can take place at over 2 kilohertz not only is it still open source on github but you can now buy affordable copies at mjbots.com of the controller or development kit which has everything you need to get started in addition to the improved hardware the software and validation has made big improvements all the production boards now use an automated test fixture to validate their operation i built a dynamometer with a physical torque transducer and two modes controllers back to back this can run individual performance experiments and has a full regression validation suite for the firmware while in position mode it is no longer limited to staying within a small range near absolute zero but can spin for an arbitrary amount of time there is a new mode that explicitly provides virtual walls to keep the motor within a given range i added compensation for magnetic saturation which means that the commanded and reported torque is accurate even as a motor reaches the limits of the peak torque it can produce but wait there's more a second version of the modi's controller was released this year the r 4.5 while this is a minor revision it does increase the input voltage range to 44 volts and is fully electrically mechanically and software compatible with the r 4.3 a lot of the past year was spent refining the qtd 100 quasi direct drive actuator the prototype version used in the quad a0 still had some 3d printed plastic components which were bulky and not terribly robust i spent a lot of time learning cnc machining and prototyped all the necessary components for an all metal servo actuator in-house first with a functional validation then again with a version optimized for weight and performance the final version weighs about 470 grams has a peak design torque of 17 newton meters and a maximum speed at 24 volts of around 2400 degrees per second i made a first pre-production build of these servos in a beta form which i used to build the newest quadruped the mjbots quad a1 and have made them available for sale at mjbots.com also with a development kit [Music] now motor controllers and servos are great but they're not all you need to build a robot not just because i needed them but because anyone building a robot needs them i've developed and released a series of accessories to let you put together a complete robotic system first up is the fd can usb this is just a low cost can fd to usb converter without any frills it is designed to work with the modius controller family so it comes out of the box configured for the appropriate bit rates second is the mjbox power disk board it implements a pre-charge function so you can safely power up a lot of high capacitance motor drives from a battery has a bunch of connectors to power legs arms whatever you may want and can provide a soft switch so that your robot can shut itself down cleanly when power is turned off finally we have the pi 3 hat this is a raspberry pi 3 or 4 hat that exposes four can fd buses one low speed can bus an imu and a port for an nrf24l01 rf transceiver it also provides power to the raspberry pi from an input source of up to 34 volts there are c plus libraries and example projects to control modia servos and i've used it for all of my embedded control demonstrations using all these robotic components i put together a few demonstrations that show off their unique capabilities i used an inappropriately long pull to measure ground truth torque of the qdd-100 servo and compared it to that calculated by the modius controller spoiler alert it was pretty close aping scientific's telepresence demonstration i built my own using qdd-100s and a pi 3 hat this ran closed loop control at two kilohertz which provided control response that was indistinguishable from a mechanical connection but unlike a mechanical connection the gearing ratio could be changed on the fly and even the force could be scaled between the devices without changing the range of travel many balls were thrown to further demonstrate the high rate control capabilities i made this video that showed how the position kp and kd constants can be used to implement a software configurable spring and damper now to put it all together we have the new mjbots quad a1 quadripedal robot the quad a1 is the newest version that uses the r4 modius controller qtd 100 servos and the raspberry pi 4 with pi 3 hat and power discord it started out with a lot of improvements and has gotten many more over time i'll cover the hardware improvements first then the software one of the earliest and ongoing challenging design points with the quad a1 is the lower leg and foot the quad a0 used the simplest leg that could possibly work a 3d printed rod with a rubber end cap needless to say this didn't survive very long for the quad a1 i switched to a design where the foot consisted of a squash ball with foam cast inside this basic design is still in use on the quad a1 today although it has gone through about six different refinements in design and material as each iteration failed next the chassis received a big update and that now all the components are neatly housed on the inside rather than strapped to the top further it can be disassembled from nearly any direction for easy maintenance and service now the top is free with a mounting bolt pattern to attach alternate payloads the current leg configuration requires the cables between the upper and lower leg move during each swing cycle of a leg as the robot has walked more and more that design has needed iteration as well first i went with some braided sleeving and most recently have switched to continuous flex motion conduit which i tested for a hundred thousand cycles to ensure that it would last for some time while walking while the hardware is definitely important most of the interesting new developments for the quality 1 have been in software one of the basic improvements the quad a1 has seen was performing force control and compliance in the 3d cartesian coordinate space rather than purely in the joint coordinate frames another was pronking using full rate 3d control over all feet simultaneously while not a particularly efficient form of locomotion it does signal to all potential predators that the quad a1 means business to actually make progress developing more advanced skates i upgraded the telemetry logging format and developed the tplot 2 diagnostic tool this allows you to scrub through time while viewing a log using either a tree view of all data recorded by the robot configurable 2d plots of any data value 3d renderings of the robot joints or time synchronized video to make progress without having to continually break robots i resurrected the dart-based simulation environment that i had used for previous hobby server robots and connected it to the quad a1 software i also used the nrf24l01 radio interface for the first time this uses spread spectrum frequency hopping techniques to send commands and receive telemetry from the robot in a low latency manner most debugging control still uses wi-fi but in some environments like convention centers and demonstrations wi-fi can be nearly impossible to use reliably for real-time control [Music] some of the most consequential changes were in the gate engine that controls how the legs move to achieve a particular pose or velocity over ground the feet now use a jerk free smooth trajectory to lift off the ground move through the swing phase and then re-accelerate and make contact with the ground again when walking the point in time when to lift the legs and where to place them is now selected to maintain balance around the legs that are still in contact with the ground this was the first step towards higher speeds and let the quad a1 hit its first new speed record of the year at 0.5 meters per second followed not too long after by 1.7 meters per second and then even further to 2 meters per second next the gate sequencing was updated to allow periods when all four legs are off the ground in practice the flight time can't be very long with this controller before the robot becomes unstable so much of the flight time involves the legs barely scooting above the ground it is possible in some conditions though to maintain stability like in this two-leg hopping test finally the stand-up sequence was rewritten so that the robot can successfully get on its feet without dragging legs or feet on the ground this lets it stand up from a wide range of surface conditions with all these pieces put together the quad a1 and modius controller are becoming powerful tools for research and experimentation with nearly all the non-servo structural components 3d printed a wide variety of forms and mechanisms can be quickly evaluated multiple robots now exist and are looking for more friends to play with even the current heuristic gate control algorithm running on a raspberry pi 4 is sufficient to allow the robot to navigate a range of outdoor terrain like exposed tree roots gravel loose bricks and snow combined with the ability to have short flight periods flat ground gates are now very close to proper running with an observed maximum speed of 2.5 meters per second that's all i have for now if you want to keep up to date join our discord server from the link below like and subscribe to this video and follow mjbots on any of the social networks thanks

Channel: Josh Pieper

Views: 130,621

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Id: ePdGshbKR-Q

Length: 12min 8sec (728 seconds)

Published: Mon Nov 09 2020