[dynamotive]

I got my Bridgeport Boss Hillbilly BOB retrofit going with Mach3, but before I start cutting metal, I would like to have a knob-controlled feedrate override. I used that as a safety device with the Boss controller, and I hate to give it up. I've been playing around with a USB gameport adapter, keygrabber, and a potentiometer. XP will calibrate the potentiometer, but the problem is that Mach3 doesn't seem to pay any attention to the calibration. The effect on FRO only seems to be dependent on the potentiometer maximum resistance. Higher values give more effect on FRO, and lower ones less. Does anybody know anything about this? Incidentally, in case it makes any difference, I'm using an Thinkpad 770e, with ACPI turned off. It drives the system very well. I've played around with the USB adapter and pot on other computers, and it doesn't seem to be any better.

[tnsmachines]

I used Pokeys and keygrabber to simply step the feed as if on the screen. Works fine that way. Pokeys now has analog input and a new plugin so it should actually do exactly what you want.

[jimmearns]

It sounds to me like you have the pot not wired correctly.
To get a variable voltage connect the "top" of the pot to a supply, the "bottom" to 0 volts (ground) and the wiper to the analogue input.

I had loads of problems with Mach3 on XP - mainky missing Z commands and crashing the work and sometimes the tool too.
Since I switched over to linux emc2 no problems - and it has the feedrate overrride on the panel. Try linuxcnc.org Best of all it is FREE!

[dynamotive]

Thanks for the replies. I looked at the Pokey device, and it looks very nice. However, the idea of having to buy an $80 device in order to do one simple thing does not appeal to me. I may wind up spending much more than that trying to figure this problem out, but it will be a learning experience. Perhaps I will build my own 'Pokey', using a PIC microcontroller. I just got some 40-pin 18F4550's ($4.40 at Newark), which have all kinds of analog and digital inputs, and a built-in USB interface.

As to the pot connections, strange as it may seem, the pots are not connected to ground. The wiper goes to the input, one side goes to +5, and that's it. The pot resistance is read by the length of time it takes a capacitor to charge up. There's no ADC. Check around at all the info on joystick/gameport interfacing, and you'll see that. I did try hooking up one side to ground, and it still worked, but the results were very strange.

I think this problem is either with Keygrabber, or Mach3. It would be nice if keygrabber actually showed analog input levels, instead of just indicating which input is being exercised. I suppose I should try the joystick plugin, to see if that works any better.

[dynamotive]

Ok, I made a little progress. I got my single potentiometer hooked up so that FRO consistently moves smoothly up and down. The problem is, FRO goes from near zero to 10 times the feedrate value that is showing. Mach3 starts up with 6.000 for the feedrate, and when I turn the pot, FRO goes from about .15 to almost 60. In other words, a maximum feed rate override of 1000%! I tried different pots, and re-calibrated it in XP several times, but it always acts the same. Is there some configuration setting that controls FRO versus feedrate?

[ger21]

I t shouldn't be able to do that. The maximum FRO is controlled by the screen file. I believe it's set at 200% in the default screen. The FRO DRO is percent override, so 60 is 60%, for a feedrate of 9.6ipm. That's what you should be seeing in the velocity DRO.

[dynamotive]

I t shouldn't be able to do that. The maximum FRO is controlled by the screen file. I believe it's set at 200% in the default screen. The FRO DRO is percent override, so 60 is 60%, for a feedrate of 9.6ipm. That's what you should be seeing in the velocity DRO.

Thanks for the reply. So are you saying the Feed Rate Override goes from zero override (no override), to 60% override? I don't want to speed up the feed, I want to slow it down, all the way to no feed, sometimes. Is there any way to do that? I don't want to stop and start the feed, I want to be able to slow it down!

[ger21]

No, I said that wrong. Typically it starts at 100%, and goes down to 0% and up to 200%. 100% is the commanded feedrate.

[dynamotive]

Ok, this is how it works: If I turn the pot to zero, the green FRO bar goes to zero, and the FRO percentage and value go to (almost) zero. When I start to turn the pot up, the bar quickly goes to 1/2 height, the FRO percentage goes to 100%, and the FRO value to 6.000 (the default feedrate). A little more turning, and the bar goes to full height, the FRO percentage goes to 200%, and the FRO value goes to 12. More turning, and the bar gets taller, and covers up the FRO percentage value. More turning, and the FRO value keeps climbing, all the way up to almost 60. Like I said, 1000% override. All the useful stuff is taking place in 1/10 of the pot's travel.

Is there any way I can change the maximum allowed override value?

[ger21]

Change the DRO format with Screen4, mach's screen designer. But, it should be set to 200, maybe 300 max by default. Are you sure it's going to 1000, and not just to 300%?

[dynamotive]

Change the DRO format with Screen4, mach's screen designer. But, it should be set to 200, maybe 300 max by default. Are you sure it's going to 1000, and not just to 300%?

It's doing what I described above. I can't tell what the percentage gets to, because like I said, the percentage value gets covered up by the bar. But, the FRO value goes to almost 60, or ten times the default feedrate value.

Is Screen4 the only way to change the maximum override value?

Thanks for the help.

[Switcher]

Do a Print Scr - on your keyboard (screenshot) of what your Mach3 screen looks like.

Then post the screenshot/image here on the forum.

Might help with the answers, to your ?'s

[dynamotive]

Do a Print Scr - on your keyboard (screenshot) of what your Mach3 screen looks like.

Then post the screenshot/image here on the forum.

Might help with the answers, to your ?'s

I can see where that would be helpful, but it seems to that I would have to post four screens to show what's going on. A lot of bytes for very little info. This is the default screen - I haven't changed anything. I'll try to summarize what's going on. This is based on the default value of feedrate, which is 6.000. The numbers are approximate.

Pot - FRO bar - FRO value FRO percentage
0.0 - bottom......... 0 --------- 0
0.1 - middle........... 6 -------- 100
0.2 - top.............. 12 -------- 200
1.0 - beyond top.... 60 -------- ? (covered by bar)

If you still want a screen, maybe the one that shows the bar all the way at the top, with the FRO value (not the percentage, which is covered by the bar) at 60 might help.

I looked at Screen4, and it appears to me that all it does is display numbers - it doesn't seem like it can change any defaults.

[ger21]

OK, my mistake again (I think). In Screen 4, you can set the limits of the FRO slider. But, in order to limit the values you're getting, you're going to have to use a macro or some other method to get the values from the pot and assign them to the FRO. Are you using keygrabber? I think you'll need to possibly use additional hardware to do this, but I'm not sure.

EDIT: and when I say set the limits of the slider, I mean when actually using the slider to control the FRO.

[dynamotive]

Thanks for the reply. I am using keygrabber. The pot is hooked up to a USB gameport adapter, so that Windows XP thinks it's the throttle slider of a joystick. It calibrates ok in XP. It works pretty well in Mach3, except for this problem of the FRO value. It's not ideal, because the value will not go to all the way to zero, which is how I stopped downfeeds on my Bridgeport Boss 5. As a matter of fact the lowest value tends to jump around a little. The gameport is not a terribly accurate device.

I suppose I can make do by using feedrates that are 1/10 of what what I actually want. I would rather that the thing work logically, but we can't have everything, right?

Now you've suggested another approach - using macros. I was hoping to get back to cutting metal without becoming a Mach3 guru, but maybe in order to do this one little thing, I'll have to do that. I did get some PIC microcontrollers to play around with, so maybe I'll try using one of those to read my feedrate override pot. That should be interesting.