> > From: Frank Tkalcevic [mailto:fr...@franksworkshop.com.au] > > > You subject line says RS485/CAN which are dramatically different from the > > SPI based synchronous clocked serial interfaces. Even RS485 and CAN are > > dramatically different. > > > > Thanks for the replies... > > > > The question was around slower RS485/CAN. I'm seeing a lot of actuators > > (motor/gearbox/driver combinations) that are driven by CAN bus (MIT > > cheetah). > > > > Brute speed seems to be a common solution, which I'm guessing protocols like > > EtherCAT rely on. > > > > Given the CAN bus speed limits - 1MHz, it doesn't seem possible to > > send/receive messages to many motors at a typical LinuxCNC 1kHz rate. Is > > there some kind of "smarts" that let these control systems work smoothly at > > lower update rates? > > > Most CAN based Step or Servo motors can operate in position or speed mode. > In speed mode you can also set torque values. They work well for say pick > and place or tool changers etc. And anything else where you might want > precision motion or torque control. > > Generally the motors come in two flavours supporting either J1939 or CANopen. > Recall I mentioned that CAN messages have 11 bit IDs and up to 8 data bytes. > To set up or control a motor you send Service Data Object messages (SDO) > writing to the device object dictionary (OD). You get information back by > reading from the OD. > > When working with CAN bus it's handy to have some sort of dongle for > receiving and sending messages. Once such device is a CANUSB from Lawicel I > Sweden. > www.canusb.com
And an application to read/write the dictionary using an .eds or .dcf file. _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
