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  • Opinions wanted on stepper driver

    Collecting up parts for an over-winter CNC plasma table build and I was wondering what's wrong with these drivers?

    http://www.probotix.com/manuals/SideStep_manual.htm

    $35 ea.,are Gecko and Larken drivers really that much better? These just look like to good of a deal to be true.Anybody have experience with these?
    I just need one more tool,just one!

  • #2
    Only 2.5 amps and 32 volts ? A gecko is 7 amps and I don't remember the voltage rating but a lot more than 32 volts.

    I'm not qualified to critique the design, but 2.5 Amps/32 volts is not a lot. Perhaps enough for your plasma table, I dunno.

    The drivers, power supply, and motors need to be compatible. Select the motors first, then get a power supply and drivers that meet the motor's specs.

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    • #3
      Wierd, There are plenty of these drives around based on this Allego chip but they are low power drives.
      At 2.5 amp and 24 volts max which is a good supply limit they are on full power and to be honest they are stretching it.

      What you get with the more expensive Gecko and Keling drives is piece of mind and some protection from shorts and overloads.

      Gecko is supposed to be bringing a new drive out called a G250 which is a small cheap stand alone going up to 3.5 amp and 50 volts.
      Can't find any release details on it but their G540 which is 4 of the 250's mounted on a breakout board is listed here.

      http://www.geckodrive.com/product.aspx?c=3&i=14469

      May not fit the bill at $299 but it does get you 4 drives and the breakout board plus simplified wiring.

      I did hear that the separate G250's were going to be about $35 each but don't quote me on this.

      .
      .

      Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



      Comment


      • #4
        I'm using the Xylotex drives which use the Allegro chip. I removed the heat sinks and the crappy thermal tape and clamped on BIG heat sinks using Arctic Silver thermal paste. I then added a good fan to cool the lot. I am running them at 29 volts from a !very! stiff supply and VERY fat wiring and have the current control on the boards maxed out. Not one bit of trouble from the drives and the performance is excellent but if the fan is turned off they go into thermal shutdown in 30 seconds. Before anyone starts to comment that this is pushing it to the ragged edge and not really a good idea consider that this is how your computer's cpu is run as a matter of standard practice.
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        • #5
          I have been running Larken drivers for over 5 years on my mill
          No problems (knock wood!)
          eddie
          please visit my webpage:
          http://motorworks88.webs.com/

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          • #6
            Depends on what you got for motors. A reasonably modern stepper is a lot more efficient than the old ones. The ones I use are about 650 Oz-in and only need 2A at 6v. You don't need a million microsteps. They make things smoother but the motors are not very linear position-wise in microstep mode. The drivers you mentioned are small and reasonably priced. Not industrial-duty but should be fine if you don't make any mistakes. They will fry in an instant if you make a wiring error or disconnect a motor with the power on.

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            • #7
              Ya,I noticed the diffrence in power output,but I'm not building a router or mill for that matter,still more is better might end better in the long run.

              I would never make it as a woman,I hate shopping

              John,yes I am also going to look at Ke-Ling their KL-6050 looks promising at $60/pop,also weighing build a power supply verses buying one.

              What Evan says is true also,I noticed computer towers are happy doubling as toaster ovens so long as there is ample breeze blowing.

              Okay,so mixed reviews it is.I was thinking of buying one their kits,no fuss no muss right?Well maybe not,anyway guy down the road built a decent 4x4' router using this one-

              http://www.probotix.com/3_axis_stepp...or_driver_kit/

              After seeing it make some fairly hefty cuts in wood and noticing how much drag his gantry has built into it I was thinking the same should work well on a better gantry design moving at a slower pace with much lower inertia to overcome and nowhere near the forward resistance.

              This guys gantry works,but it's no beauty queen.Plain b-7 althread for the screws,plywood for the frame and the linear slides are flat bar(aluminum) and grooved out skateboard wheels,yet he gets reasonable accuracy out of it.His gantry weighs a ton and the whole mess sits on furniture levelers.
              I just need one more tool,just one!

              Comment


              • #8
                Originally posted by John Stevenson
                Wierd, There are plenty of these drives around based on this Allego chip but they are low power drives.
                At 2.5 amp and 24 volts max which is a good supply limit they are on full power and to be honest they are stretching it.
                Those are all single-chip drivers based on the Allegro 3977, which has a max rated output current of 2.5A at 35V. But the datasheet has a stern warning no to exceed a Tj of 150°C, which I'd figure is a package temperature of around 125°C.

                http://www.allegromicro.com/en/Produ..._Numbers/3977/

                The bigger stepper drivers like the Gecko's have external power FETs (i.e., they're not a single-chip solution), so they can drive much larger motors. Hence the higher cost.

                Come on Marriss -- step up to the plate
                "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                Comment


                • #9
                  The data sheet for the Allegro chip also has some waffle wording about the absolute maximums, especially the 2.5 amp figure. Basically it says as long as the maximum junction temp isn't exceeded it can be run higher than 2.5 amps. That is apparently the case by my experience.

                  ABSOLUTE MAXIMUM RATINGS
                  at TA = +25°C
                  Load Supply Voltage, VBB ............. 35 V
                  Output Current, IOUT .................. ±2.5 A*
                  Logic Supply Voltage, VDD ........... 7.0 V
                  Logic Input Voltage Range, VIN
                  (tw >30 ns) ..... -0.3 V to VDD + 0.3 V
                  (tw <30 ns) ........... -1 V to VDD + 1 V
                  Sense Voltage, VSENSE ................. 0.5 V
                  Reference Voltage, VREF ................ VDD
                  Package Power Dissipation,
                  PD................................. See page 3
                  Operating Temperature Range, TA
                  (A3977Kx) ............ -40°C to +125°C
                  (A3977Sx) .............. -20°C to +85°C
                  Junction Temperature, TJ ......... +150°C
                  Storage Temperature Range,
                  TS ......................... -55°C to +150°C
                  * Output current rating may be limited by
                  duty cycle, ambient temperature, and heat
                  sinking. Under any set of conditions, do not
                  exceed the specified current rating or a
                  junction temperature of 150°C.
                  BTW, the Allegro chip can handle significantly larger loads if synchronous rectification is disabled and external flywheel diodes are installed. Such diodes only cost a few cents each and take the load off the internal H bridge.

                  Disabled Mode. When the SR input is logic high,
                  synchronous rectification is disabled. This mode is
                  typically used when external diodes are required to
                  transfer power dissipation from the A3977 package to the
                  external diodes.
                  Last edited by Evan; 08-05-2008, 10:02 AM.
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                  • #10
                    How quiet are the steppers with the Allegro driver chip? Allegro says it's nice and quiet (of course,) but I ran across this thread at CNC Zone where Mariss openly talks about the development of the mini-Gecko:
                    http://www.cnczone.com/forums/showthread.php?t=51083

                    Quite a long thread, I spent a whole week reading through the 200+ pages(!!) Very interesting to see a new piece of stepper technology being created. BTW, the ~$30 "target price" listed on post #1 jumped to something like $50 or $60 for single volume pricing, which is a bit premium for 3.5 amps, but then so is the product.

                    On page 28 in that thread, Mariss says this:
                    A chopper (L297, Allegro, et all) has two free-running 20 - 25kHz oscillators. These oscillators phase-lock and break phase-lock hundreds to few thousand times a second. This "make, break" phenomena produces beat frequencies that fall smack-dab into the audible range producing the grunting, hissing, squealing and whistling everyone is so fond of.:-)
                    So how noisy is that Allegro drive? I'm guessing it's probably quieter than the previous generation of stepper drivers, but probably not as good as a Gecko drive.

                    -Matt

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                    • #11
                      How about this one.

                      P/N: CW250
                      INPUT: 20-60VDC
                      OUTPUT: Selectable up to 5A max.
                      STEP ANGLE: 1.8 deg:200steps/Rev.
                      Microstep: 1/8: 1600 steps/Rev.
                      Full bridge driver for hybrid stepmotors.
                      Switch Selectable output current.
                      Over temp & Output miswire protected.
                      Opto isolated Step pulse input (Clock input +5V Level).
                      Opto Isolated Direction input ( +5V Level)
                      Terminal strips in/out.
                      L: 5-3/4" W: 3-3/4" H: 1-3/4" WT: 1.5

                      No endorsment or reccommendation. Just something I stumbled across.
                      https://www.mpja.com/prodinfo.asp?number=17452+MS
                      Last edited by Forrest Addy; 08-05-2008, 12:51 PM.

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                      • #12
                        Originally posted by Evan
                        The data sheet for the Allegro chip also has some waffle wording about the absolute maximums, especially the 2.5 amp figure. Basically it says as long as the maximum junction temp isn't exceeded it can be run higher than 2.5 amps.
                        That's the 150C Tj I mentioned in my post above. That's not waffling -- that's how most power devices are spec'ed: how high the junction temperature can get before the power transistor fries. There's also a reliability issue: the lifespan of the transistor is inversely proportional to the Tj.

                        Microprocessors, for example, are usually designed for a 7-year lifespan, so they're usually spec'ed with a much lower Tj: 90 - 95C. If you overclock the processor, the Tj goes way up, and the lifespan of the chip decreases proportionally.

                        Just remember that the internal junction temperature is a lot hotter than you can measure on the surface of the package. That's why modern microprocessors have on-die thermal diodes...
                        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                        • #13
                          Originally posted by Forrest Addy
                          That's the Chinese CW250. The datasheet is amusing -- it's a "Micorstepping Driver".
                          "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                          • #14
                            your plasma gantry should be light and require minimal torque. OTOH it needs to move the torch fast for a smooth cut so you can't gear down the motors much. Be sure you've put a pencil to that aspect.

                            Best,

                            BW
                            ---------------------------------------------------

                            http://www.cnccookbook.com/index.htm
                            Try G-Wizard Machinist's Calculator for free:
                            http://www.cnccookbook.com/CCGWizard.html

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                            • #15
                              That's the 150C Tj I mentioned in my post above. That's not waffling -- that's how most power devices are spec'ed: how high the junction temperature can get before the power transistor fries. There's also a reliability issue: the lifespan of the transistor is inversely proportional to the Tj.
                              That isn't what I mean. They are waffling on the current limit, not the temperature limit. First they say 2.5 amps and then they basically tell you how to circumvent that limit and say it's the temperature that really matters instead, which it is. 150 C sounds rather high to me.
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