I don't think it actually runs that fast, I think you calculated the maximum rate possible with one motor on the bus.
More reasonable is to assume 20 updates per second and 12 motors on the bus. This rate could work. I looked for 10 minutes through the Chetha code in Gethub and foud they do update all the motors every "dt" but I could not find where dt is set. But itis likely about 0.05 second. One other easy trick is to have two CAN busses one for left and the other for right. You would never need to send data from one leg to the other so this could work. On Fri, Aug 21, 2020 at 4:45 PM Frank Tkalcevic <fr...@franksworkshop.com.au> wrote: > I was looking in more detail at the MIT Cheetah and found this page - > > https://www.robotdigg.com/product/1667/MIT-Robot-Dog-high-torque-Joint-Motor > -or-DD-Motor > <https://www.robotdigg.com/product/1667/MIT-Robot-Dog-high-torque-Joint-Motor-or-DD-Motor> > > It says that each motor takes an 8 byte payload to drive a motor, and that > motor then replies with a 6 byte packet. After you add the CAN headers and > trailers that is a total of 200 bits, best case, or about 416 updates per > second for 12 motors on 1MHz bus. > > I was expecting the update rate to be a lot lower than that (I should have > done the math). > > > -----Original Message----- > From: N [mailto:nicklas.karlsso...@gmail.com] > Sent: Saturday, 22 August 2020 5:34 AM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] OT: Synchronised motion using RS485/CAN bus motors > > > ... > > On CAN you can take advantage of the fact that all devices read the bus > at > > the same time. Each reader decides what information it wants to read and > > ignore the rest so a time-sync heartbeat could be implemented if the > nodes > > all needed to be time synchonized. ... > > Yes all devices need to read bus within the time it take to send one bit > because of the arbitration used to send the message with highest priority > first. With CAN-FD speed is increased after address is sent so that message > could be larger. > > > _______________________________________________ > 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 > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
