Actualy for this they use motion capture from a human dancer to collect “target points.” The points are (x,y,z, time). Then, of course, the robot does not have the same mass distribution as a human and would fall down if it exactly copied the human’s moves.
So they use an “MPC” controller. MPC is like the far simpler PID, but MPC looks to minimise predicted future error, not the current error. OK, not the “future error” but the “future cost”. Cost is the difference between where you are and where you want to be. An MPC controller can parallel park a car given only the current position (in a traffic lane) and desired location (at the curb). It searches for the lowest cost solution and will find the back-and-forth motions and steering wheel turns needed. The robot searches in real time for the best solution for hitting those target points, even if it means widely deviating from them. The cost funtion is coded by engineers and likely has a low cost for slightly missing a point and VERY high cost for falling down or for exceeding the motor’s limitations. The real-time optimizer finds a path that has the lowest predicted integrated cost from present to some future time, usually a few seconds ahead. “integrated cost function” is a very mathematical-sounding term, but simply said, it is placing its foot now, so as to create the lowest cost future. Basically the controller “thinks” “I was told to place my foot at (xy,z) at time “t", but if I do that I will fall on my face, so I place it differently, but then again, I need to minimize the effort needed to reach the next foot postion and so on. MPC is using a physics-based simulation to predict about 10,000 possible futures and then selecting the one that is “best”. Then it does this all over again about 50 times a second. The controll pretty much does what humans and other animals do. We think ahead a little. We will walk around a tree, not through it, because the longer path creates a better future. The robot can in theory be told “build a brick wall” and then search for the motions that create the desired state. But not today. computers are not powerfull enough This new Atlas robot is nothing more than about 28 BLDC servo motors. I'm sure many of us could design the mechanical system. Where Boston Dynamics shines is in its mastery of advanced control theory. They say it is based on this: https://en.wikipedia.org/wiki/Model_predictive_control > On Jul 16, 2025, at 9:53 AM, Stuart Stevenson <stus...@gmail.com> wrote: > > We had to sign DOD forms to allow a 15MB control in the shop. Something > about a control for nuclear subs. It is a '28' axis control. > > I could see using the center of gravity with an orthogonal cartesian > coordinate system. Then calculating the limb positions for each pose. > > Gcode - nah > > > > > > On Wed, Jul 16, 2025 at 11:26 AM Chris Albertson <albertson.ch...@gmail.com> > wrote: > >> In the old days there were huge differences in how they were controlled. >> But today we use microcontrollers for everything. SO there is some >> convergence but still I think we can see differences in the physical motors >> >> 1) Stepper is just a BLDC motor is “dozens” of poles and perhaps two or >> three phases. Traditionally there were controlled with square waves, But >> now we we some “closed loop steppers” controlled with analog sine waves. >> >> 2) BLDC is typically a three-phase motor that in the past might have been >> run with square wave generated by switches. But today we have Bosch more >> sophisticated “FOC” controllers even if some still do use Hall effect >> switches. >> >> 3) A three-phase motor that even in the old days was powered by >> three-phase AC, Now that BLDC motors can be controlled this way too I >> wonder two things (1) are they really different and (2) how were they >> traditionally controlled before we had microcontrollers that could generate >> waveforms in software? >> >> >> Of the above for my interrest ig robotics the exciting kind is the BLDC >> controled by FOC. These give the best power to weight and best control >> over acceleration and position. If you see a humanoid robot, it is because >> of these motors and the huge energy stored in lithium batteries. >> >> How would you like to write the “g-code” for this machine (28 axes). >> https://youtu.be/I44_zbEwz_w >> >> >> >>> On Jul 16, 2025, at 4:56 AM, Stuart Stevenson <stus...@gmail.com> wrote: >>> >>> What is the difference between: >>> >>> 1: stepper/servo (Hanpose, et al) >>> >>> 2: BLDC servo >>> >>> 3: A/C servo >>> >>> It seems to me to be describing the same technology. >>> >>> Thanks >>> >>> Stuart Stevenson >>> 4638 Farmstead Ct >>> Bel Aire, Kansas 67220 >>> 316 258 0953 >>> stus...@gmail.com >>> >>> -- >>> Addressee is the intended audience. >>> If you are not the addressee then my consent is not given for you to read >>> this email furthermore it is my wish you would close this without saving >> or >>> reading, and cease and desist from saving or opening my private >>> correspondence. >>> Thank you for honoring my wish. >>> >>> _______________________________________________ >>> Emc-users mailing list >>> Emc-users@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/emc-users >> >> >> >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users >> > > > -- > Addressee is the intended audience. > If you are not the addressee then my consent is not given for you to read > this email furthermore it is my wish you would close this without saving or > reading, and cease and desist from saving or opening my private > correspondence. > Thank you for honoring my wish. > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
