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tommylight wrote:

use short cables

 
 

Just noticed this. It is the answer. I think.

Move VFD much closer to motor. Shorter cable from vfd to motor.
That by itself probably fix everything without doing anything else.

Also keep all DC wires far away from AC wires.

In terms of interference, the wires going from vfd to the motor are the baddest. The longer the badder. To a lesser degree all the AC wires are bad when so close to BOB and all. Contactors are also very bad the instant they open/close.

BOB too close to relay and power wires.

is a long machine and is installed in a reduced space, the original numeric control had that function in order controlling the motion all the time for operators safety

I can't wait to try that. I have tons of cheap inductive proximity sensors (well, more like a couple handfuls). Coil one motor power lead around it. Great idea. Cheap and simple. Thanks!

Yes, I updated the magic comments to include adding material thickness.

I don't see a picture of the actual breakout board, and related wiring. I might be able to pinpoint good locations to add ferrites. Even the parallel cable might benefit, you'd have to use a clip-on split ferrite, but those are more expensive and I have never tried that type. Best put them on the VFD wires first. A customer watched me do that to his project and it made such a difference he asked me if it is black magic.

All of the above (except I don't bother with an earth ground rod on mills. Plasma maybe, if its a big one). I have covered unshielded wire by wrapping in aluminum foil then cover with tape. Make sure shields are grounded at the computer end but NOT at the far end. If aluminum foil has splices, confirm it connects very good and overlaps some.

Grounding a shield at both ends can act the same as no shield. Don't ground the motor end. Spiral steel or aluminum foil is not as good as copper braid but should help.

Add ferrite beads, the more the merrier. That alone has completely mitigated some of my most annoying interference problems. I keep a bunch on hand, and just experiment by adding a couple here and there till it is fixed.

Start by putting some on each wire that's connected to the vfd, closer to the vfd is better. They absorb some of the interference the wires radiate. Next, I'd add smaller ferrites to the limit switch wires, closer to the electronics is better.

Some vfd suppliers recommend using one big ferrite and turning the three power wires around it 3x, one ferrite for the power in side, and one for the power out side.

Ferrites come in an enormous variety of shapes, sizes, and colors. I don't know how much it matters what kind of ferrite you should use. I've read there's a significant difference in different grades of ferrite. I never bothered to figure out which are better. I had a cheap USB charger transformer quit working, so I thought I'd cut the ferrite (molded in plastic) from its cord before I discard the charger. I cut it open, it was all plastic, no ferrite inside. That was a very fake ferrite.

OK since this has gotten some interest, there are two methods of using hard stops for homing without messing with the drives at all, for DC brushed motors:
1. using hal sensors wired to inputs (be it Mesa or Pico or parallel), more windings around the sensor = more sensitive
2. using REED switches wired to inputs ...., again more windings = more sensitive
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There are two types of hal sensors, those with variable output and the on/off type, latter is easier to use for this use case.
Sensors should be wound with only one motor wire, not both.

NWE wrote:

May I ask, what use case requires adjustable home_search_vel?

+1

May I ask, what use case requires adjustable home_search_vel? Sorry for my ignorance.

tommylight wrote:

There are reasons why brushed DC motor powered machines have two sets of limit switches, one set does normal limiting while the other set is "extreme limits" that will cut all power to motors.
Brushless DC and steppers motors have no need for such measures as if the drive fails it usually causes the motors to lock and burn quietly, if all other safety measures fail.

Normally, yes. To date I've seen two Ursviken Pullmax press brakes. Both had DC servomotors all over and a shocking lack of hard limit switches. They are heavily built and very precise press brakes, but given the way the old controls were set up, the wording in the manual, and also a reprimand I once received from one of their dealers when I asked how to initialize the controls, I get the idea the users were expected to hire Ursviken techs to 'repair' the machine if any axis so much as ran into a limit switch. I consider the old Ursviken controls quite difficult to clear limit errors.

Instant runaway is certainly one of the possible hazards of brushed DC servos when the h-bridge shorts over one side. However, I have not yet seen that happen, but I will not say it can't. The few failures I have run into so far, the h-bridge was shorted completely and popping fuses instantly. I think what happened in those cases is the closed loop feedback detected the servo was a few encoder counts too far off and tried to correct by reversing the motor (by switching on the still good side of the h-bridge), causing a short and blowing fuses. Theoretically, the servo might run away far enough, fast enough to cause a positioning error, disabling the servo amp (and switching off the h-bridge) but with power still applied to it, and with half the h-bridge shorted, the motor could then run away uncontrolled.

Any way, I don't like brushes. Back when I was busy with smaller repair projects, I messed with sooo many brushed DC motors that needed brushes which were next to impossible to match up. I usually filed down bigger brushes to fit, but that is messy work. If I'm working on a project like this and have any reason to suspect a motor is weak or otherwise worn, I strongly recommend my customers to go with AC servos if possible.

Hello Guys 
For long time i trying to find any way to control the HOME_SEARCH_VEL for the calibration cycle, i'd like to link the signal to a knob that control the rapid speed as well 
Im not expert, im not sure if i got to create a  HAL thread to link the HOME_SEARCT_VEL
your help is appreciated
Regards
 

I guess if you wanted to be really safe, you could loop back a free output
to an free input and put a watchdog signal on the output and use LinuxCNC's
watchdog component to trigger a fault if the output ceases to toggle.

PCW wrote:

if the probe signal goes through multiple hal components, they need to be addf'ed to the
servo thread in processing sequence or you will add additional pipeline delays.
 

Ah!  I think I guessed that order was significant, I didn't realize it was official.  Or at least "official".
That leads me to a follow-up HAL question (sorry for the thread drift).  Can I add the same component twice?  I mean, with different names, so I don't need one central "and2" with a dozen instances, I'd rather have each function/section add its own components as needed and in the right order.
If not, getting things in the right order across all components might be difficult.

Do the rest of my ponderings still apply, since I'm using dbounce and it delays the signal ?

Thanks!