x-y Table Control

Comments

• Bean Posts: 8,129

  2004-08-06 18:22 edited 2004-08-06 18:22

  You should look at using a servo (NOT a hobbie servo), these are basically a DC motor with a feedback system to tell how much it has turned.
  
  The problem with stepper motors is that there is no feedback, if the table get hung-up for an instant the rest of the pattern will be off, servos will correct for momentary snags because the "know" where they are.
  
  You would be okay if you have a very smooth table (movement wise).
  
  Terry
• Hulk Posts: 68

  2004-08-06 18:37 edited 2004-08-06 18:37

  Thanks for the response Terry.· I've used hobby servos with some success for low power applications.· Do you have any sources for the higher power units?
  
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  Basic stamp Newbie
• trend Posts: 112

  2004-08-06 18:38 edited 2004-08-06 18:38

  Is the wiring for the "big" servo motors the same as a hobby servo? (3 leads?)
  
  thanks-Lee
  
  ·
• LoopyByteloose Posts: 12,537

  2004-08-08 15:42 edited 2004-08-08 15:42

  Big servos are very different from hobby servos -- very mainstream industrial
  
  Many have an independent encoder attached to their shaft in the rear or front.
  You can buy many different voltage, torque, and RPM configurations and add on encoders that have the degree of detail you want.
  Often you have to combine parts within one manufacture's system.
  
  The places to start shopping on the net are with the major servo suppliers for information of what is out there and surplus clearing houses for cheap units in small quantities.
  
  If you buy two servos with encoders at new prices to exact specifications, you can expect to pay hundreds of dollars -- but then you will have something reliable and durable. By the way, they have their own controller systems too -- but again they are more hundreds of bucks.
  
  Their is a DIY CNC book available that may interest you - CNC Robotics: Build your own Workshp Bot.
• Jon Williams Posts: 6,491

  2004-08-08 16:04 edited 2004-08-08 16:04

  If you're going to build your own, perhaps stepper motors are a better choice.
  
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  Jon Williams
  Applications Engineer, Parallax
  Dallas Office
• Alan Bradford Posts: 172

  2004-08-10 01:32 edited 2004-08-10 01:32

  Hi Hulk,
  
  I work on XY Plasma Cutters all the time.
  The low end·X-Y machines use Stepper Motors in the open loop mode. They are cheap and thats what the little guys want. The Stamp cannot stream out the pulses fast enough to run a stepper in the microstep mode (IE 1/10 to 1/16 step) This is the type of resolution you need to run this type of drive smoothly.
  Plasma Cutters need to run·within a certain·speed window, to get good cut results.
  Too slow will not be any better than too fast. Running a stepper at 1/2 to full steps will run fast enough to cut thicker matreials, but the vibration from ther drive motors will be seen in the cut edge.
  
  There are cheap PC based CNC programs that you can buy and run from your printer port. Do a google search on PC CNC Programs. I cant recommend one over the other as I supply Stamp Based Torch Height Controls to some of the Low End Table Guys.
  
  The larger machines with the Servo based Drive systems close the loop with tachometer and encoder feedback. Tis type of machine is also too complex for the Stamp to run alone. The CNC has to do the circular interpolation, and send the right drive signald to the drive system.
  
  The last thing to think about is the type of plasma you are going to use.
  The newer Hypertherm PowerMax units do not have High Frequency Starting,(A lightning bolt) and that is a plus for cheap home brewed machines. They still generate alot of electrical noise. and proper grounding is important.
  
  The drawback is you can only cut with Air. The Oxygen Plasma Cutters all use High Frequency Starting. This is a real problem to design around. It requires a prober ground sytstem. It also requires·shielding ALL of the cables, motors, encoders, solenoids, and PC Connections. Lots of the older Thermal Dynamics and Hypertherm Plasma Units use this type of starting.
  
  Hope this helps you make your decision easier,
  
  Alan Bradford
  Plasma Technologies
  www.plasmatechnologies.com
• Hulk Posts: 68

  2004-08-10 16:11 edited 2004-08-10 16:11

  Thanks for the replies gents!
  Alan, that's a wealth of information.· My cutter has a starter aid that puts out a ton of RF so I appreciate your warnings.· I'll check on the PC based controllers, sounds like it will streamline my process.
  Much Thanks!
  
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  Basic stamp Newbie