Dual PID loops with motor encoder + scale encoder per axis

I would say that its the same (resistance proportional to K * velocity error),
but the loop gain (K) is much lower than a typical servo system velocity loop.

The way you can tell that it does not behave like a torque mode drive 
is that in a torque mode drive, the current at a given speed would not change
based on motor load.

BTW, you can test torque mode behaviour easily if you have a constant current
bench supply.

PCW wrote:

I would say that its the same (resistance proportional to K * velocity error),
but the loop gain (K) is much lower than a typical servo system velocity loop.
 

Fair point, it resists but it can only resist so much.

BTW, you can test torque mode behaviour easily if you have a constant current
bench supply.

I do have a bench supply that can do CC, I think I will try that this weekend just to gain some more intuitive understanding.

thanks,
Steve

It's very straightforward; You tell a velocity-loop ZERO and it's end of story. There are no yeah-buts, ah-buts about it. A velocity loop obeys a command and if that command is ZERO...the drive doesn't decide "oh but this dude is turning my rotor by hand so let it happen"

Will set up a demo tomorrow and video it.

Craig

False

The velocity loop has finite gain (or it will not be stable)
The force applied to resist motion will be proportional to this
gain * velocity. As long as you move slowly, you can rotate
the motor shaft.

So how do you calibrate the BEMF gain? Why would our PID filter require a D-term if the motor takes care of it's own velocity damping without a coefficient?

Craig

The D term is required for bare H bridges because you typically want
much higher velocity loop gain than BEMF/motor resistance supplies.