> -----Original Message-----
> From: N [mailto:nicklas.karlsso...@gmail.com]
> Sent: August-22-20 5:28 AM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] OT: Synchronised motion using RS485/CAN bus motors
>
> > I thought of one bus per leg, but the Raspberry Pi only supports two CAN
> > busses and I think this is a common limitation not just on the Pi. But
> > I think we just figured out that one CAD FD can do 12 motors at 20 Hz.
>
> It is more or less possible to configure mapping of dictionary into PDOs sent
> in real so I expect values for more than one servo motor
> could be sent in each message, maybe a few. If driver use internal position
> control loop you could send back feedback at a lower rate,
> looking into standard for CANopen lower numbered PDO have higher priority and
> for each PDO number TPDO have higher priority
> than RPDO while it may make sense to do the opposite if possible to send back
> feedback at a lower rate.
>
>
> Nicklas Karlsson
>
I think it all depends on what a motor requires.
One byte for Enable/Direction/MotionType
Four bytes for signed position
Two bytes for Current/Torque/Velocity value?
That leaves one byte Maybe a max Current Limit value?
A reply with 6 bytes might be position (4 bytes) and velocity(2 bytes)
Both of those messages can't easily be packed into one shared with a second
motor. Not without going to perhaps signed relative position and signed
velocity.
The problem with relative is it turns again into the equivalent of a toggle
message. Miss one and your position is wrong. So I would never do that.
John
>
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