Max Velocity regulation via external inputs

I am using a 3 axis CNC router with stepper motors (interface: axis direction, step axis)(see "mydiycnc.com")

Before I start digging through the source code, I wanted to verify that the following features don't currently exist in the emc2 software:
1. de-power the stepper motors when not moving.
2. I really like the "Max Velocity" slider. Is there anyway to adjust it based on external digital feedback? Ex: use 2 digital inputs to encode "tool can cut at faster x-y-z velocity", "slow down cutting velocity", "slow down cutting velocity as fast as possible".

Feature #1 I can live without (it just makes it so I have to leave the driver box open for ventilation), but it would be very nice to at least have a "decelerate fast but don't stop" input so it could better handle irregular surfaces without damaging tools.

Thanks for the fast reply! I honestly didn't expect any easy answers.
Now I just have to figure out how to write & load HAL components.

1. de-power the stepper motors when not moving.

Not sure what you want to do here. If you completely remove power from the drives you risk loosing your position. With and without power the steppers may jump to the closest detent.
When you power up the steppers you may hear a slight thump as they jump to position and any forces applied to them without power could move them.

If you have an available output pin you can use hal to toggle that pin based on a signal.
It is more common to reduce the driver output when the axis is not moving some drives do this automaticaly some have an input for it.
If your driver has an input for low power you can use one of the velocity pin in hal to do this.

Rick G

>without power the steppers may jump to the closest detent.
I'm not doing actual microstepping at the moment, though I guess I don't actually know if the detents are at each full motor electrical cycle or at each 1/4 cycle. If they are at each full cycle then I suppose this might be an issue. I'm hoping that the friction created by the anti-backlash mechanisms will be enough to keep me from losing my position.

I think I'm starting to understand how to customize emc2 I/O pins, but in order to troubleshoot the hardware mods I need a way to monitor the parallel port.

I found & compiled a program to do this and discovered that even though emc2 communicates fine with my PCI parallel port card (once I entered the correct address), there doesn't appear to be a file such as "lp0" or "parport0" in my /dev folder (which the port testing program needs to function).

Any suggestions?

Thanks! It worked perfectly and I only had to edit the device address.

I took a break from looking at LinuxCNC documentation to actually build the spindle motor current monitoring circuit. This ended up being much harder than expected. Both power and ground had high frequency noise from the switching power supply plus a noisy sine wave as it tried to keep up with the varying current draw of the DC motor.

It's been so long probably noone is looking at this thread anymore, but here's a picture of the bread board rat's nest after I finally found a configuration that worked. The board has its own power source (a battery), and the voltage/current set point is doubled and each sent out to a different output comparator so that I have a hysteresis to work with.


Dustin Soodak