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Messages - thedoctor

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General Mach Discussion / Re: Switching on/off large DC Motor
« on: November 04, 2009, 05:45:02 PM »
I hate to mention this but we use regular automotive starter solenoids for 48 and 72 volt pump motors that start at 140 amps and run at 40 amps. 12 volt coil is the only drawback and you may want to use one with a timer for your brake as the brake currents can be brutal. Our pumps run for hours at a time and the solenoids heat up but don't fail.

General Mach Discussion / Re: Feedrate override for dummies? Please?
« on: November 04, 2009, 05:35:51 PM »
Well, I finally got all mine done with a LOGITECH joypad that I took apart and wired into a REAL joystick and some quality pots. The USB connection works well through Keygrabber but two of the pots wake up in a new world every time I restart the machine. I have to run them all the way up and all the way down before they will linearize. Not a small task with 5 and 10 turn pots. I wish they were digital but maybe next time.

General Mach Discussion / Re: Plasma Table with no thc
« on: October 28, 2009, 07:22:42 AM »
Not knowing what pins and such are being used on your breakout board, I can only give you a general setup that is simple but the pin numbers will have to be determined by you. In the ports and pins config section, look at spindle output. Normally pin #1 is set for CW and CCW spindle output. That will turn pin #1 on when you turn the torch(spindle) on. This pin is where you energize your relay for plasma start. Next, go to general config and set the input #1 option on. This prevents machine motion until your plasma transfers an arc. Input #1 will stop all progress if input #1 is active or high. That allows you to hook up a current sensor (reed switch or current relay) to input #1 and make the machine wait for a good arc. This may be already built in to your plasma power supply. Input #1 will need to be run through the relay that turns your plasma on as you do not want it to stop the machine when the plasma is not energized. You can forget about input #1 setup if you don't need the "arc OK" option.  More info on your plasma brand and model would help.

General Mach Discussion / Re: Homing limits and annoying Estops
« on: October 14, 2009, 08:15:29 AM »
This is exactly where I was a year ago! My favorite tool for finding intermittent signals and noise became a $3.99 Radio Shack......OH! Excuse me!..The Shack logic probe. It not only showed me good logic-level signals but the nasty bad signals caused by stepper drivers, solenoids and other loudmouth noise generators. It even found a bad power supply filter cap for me when I couldn't even get it to show ground(0). Poor man's scope?

General Mach Discussion / Re: Feedrate override for dummies? Please?
« on: October 05, 2009, 09:36:51 AM »
Well, is is the simplicity of the thing. Digital input from a digital device. The A-pac required DC power, mounting, shielding and the use of Keygrabber. The encoder goes directly to the input section of the BOB or straight to the parport. I tried your brain and got errors (9991 I think) and the Pokey plugin I downloaded was defective. Since then, I have deleted all unused plugins and redownloaded the Pokeys plugin. I need to try your brain again because the Pokey would consolidate my inputs. providing I can get the Pokeys config to do the stuff I want. I like the concept of Brains because they are always there running in the background and they seem pretty fast. Now if I can get MY brain to agree!

General Mach Discussion / Re: Feedrate override for dummies? Please?
« on: October 04, 2009, 06:59:25 PM »
Yeah, Hood, I'll bet I could get a lot of stuff I want done if I would get used to changing things in Screen 4. I don't know why I don't just set aside the time to learn a bunch more of the options available. I am an old panel builder and I guess that makes me want to fix everything with another relay or a stacked switch. I can just barely program a simple PLC. Everything else I have tried with Mach, including the Galil plugin and J-code, has made sense and has worked for me. I tried EMC2 for a while but the lack of documentation frustrated me to no end. It ran a good, tight closed-loop with PWM output to DC servos. What more can you ask of a group with a penguin fetish? Do I put in a LOL now?

General Mach Discussion / Re: Feedrate override for dummies? Please?
« on: October 04, 2009, 04:29:17 PM »
Well, a pot requires some kind of A/D conversion to input it to Mach. Then what do you do with it? Encoders, contrary to popular belief, are cheaper than quality pots. A good Clarostat or Bourns costs me about $9.00. A CTS 2-bit encoder costs me $3.20 and no A/D conversion needed. If there is a simple way to do the A/D conversion like I was doing with that A-pac, a pot and Keygrabber, I am willing to try it. Keygrabber is one thing that works for me, most of the time. Also, does anyone know the keystroke for "reverse run"? There may not be one.

General Mach Discussion / Re: Feedrate override for dummies? Please?
« on: October 04, 2009, 09:52:38 AM »
You guys give me WAY more credit than I deserve! Dummies are people who are intimidated by such terms as scancodes, hotkeys, keycodes, oem triggers, oemcode, modbus, triggers, macros, brains, etc. I am talking MAJOR dummy! Also, I am rather unlucky. If there is a bad plugin or a misprint in an instruction sheet, I am the one who will use it or follow it. I know, this really doesn't inspire confidence in anyone kind enough to assist me. However, I am persistent and appreciative! And dumb.

General Mach Discussion / Feedrate override for dummies? Please?
« on: October 02, 2009, 07:38:45 PM »
I have tried all kinds of methods to get a knob on the front of my panel to set feedrate manually. An arcade control (A-pac) with a pot is the only one I have gotten to work to date. I would like to just use an encoder/MPG to input through two parport inputs and do its thing. I got the encoder changing the MPG#1 DRO but that is as far as I have gotten. How do I get Mach to take this input and apply it to the feedrate? Simply. For dummies. Like me.

As someone mentioned, it is a good idea to have a transient suppressor in the voltage divider circuit to kill spikes caused by the collapse of the output transformer/choke of the plasma power supply. God forbid you should run unfiltered high frequency arc-start through a pokeys! Most modern small plasmas don't use HF. As far as averaging or smoothing the input (0-3.3 v) to torch-motion, a few trials with an RC network across the output of the voltage divider can give you control of the sensitivity or fussiness of the whole THC system. Make sure you use dividing resistors bigger than 1/4 watt if you are going to do this, however!  Hypertherm uses ohmic-contact probing as a secondary system for plate detection. Their main sensing is motor current at the torch lifter. This is adjustable but I will be danged if I can figure out how they do it with a PWM motor drive. This is a good project for anyone with the need for THC and I enjoy everyone's input very much!

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