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  • Powering the leadscrew, which parts?

    After seeing tubalcain install a variable speed motor on his Atlas, I would like to do the same. Options I've seen mentioned elsewhere include using a windshield wiper motor with some sort of PWM or hobby train transformer to adjust the rpms. Someone on another forum has a 6 RPM 12 VDC GEARMOTOR from surpluscenter and is happy with it (mounted directly to leadscrew). I checked for other 12 VDC gearmors there, and they have quite a few.

    My leadscrew is 8 tpi, so 6-8 rpms on the low side ought to be peachy, right?

    Looking around for controllers, I ran across this: MXA066 PWM DC Motor Speed Controller, which looks like it'll handle what I need?

    What's the best way to go with this if I don't want to break the bank and my electrical knowledge... is... lacking. Surely someone here has already been down this road...

  • #2
    Here is how I powered mine on my SB9. Included are complete plans for a speed controller I designed.

    http://metalshopborealis.ca/pwm/pwm.htm
    Free software for calculating bolt circles and similar: Click Here

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    • #3
      The little speed controller you have linked would be ideal. I would select an available or cheap gear motor that looks like it might work and hook it up and try the speed range. Then, if adjustment is necessary, you will know exactly what to look for and get the good one or fit pulleys like Evans.

      I think mine is 8tpi and use a wiper motor....the range is useable but just a little fast. That is to say it is usually on the slowest setting for steel.
      "...do you not think you have enough machines?"

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      • #4
        Originally posted by Evan
        Here is how I powered mine on my SB9. Included are complete plans for a speed controller I designed.

        http://metalshopborealis.ca/pwm/pwm.htm
        Very impressive Evan... down to 1 1/2 rpms, sweet! 'fraid all I can do is be impressed, lost me when you started talking in electro-greek.

        Thanks Davidhcnc, I'm thinking on it.

        Couple other things I forgot to mention... reverse and power supply. Guessing that DPDT switch would handle the reverse part, right? 12 volt power supply for/from a computer?

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        • #5
          I recommend using a belt drive like I did. The belt comes off in a couple of seconds to disengage the drive for threading. You could also use an electromagnetic clutch instead which is what I did for the cross feed drive. For the leadscrew I wanted the motor well out of the way to the back so the belt is ideal. It will also slip (jump) if the drive is jammed, say by a carriage stop.
          Free software for calculating bolt circles and similar: Click Here

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          • #6
            Thanks Evan, belts it will be then. Would plain vee belts be fine or should I spring for a couple cogged timing pulley with cogged belt? Reason I ask is that my motor choice has changed, hope I picked one that will work as it seems like it might be quieter and durable but runs a bit faster than I originally planned - 130 RPM max, here's a pic of it along with the wiring:





            Ordered it this morning, so hopefully have it by the weekend from surpluscenter. If anyone is interested... they have 2 more left. Anyway, the specs:

            24 VDC VARIABLE SPEED GEARMOTOR WITH CONTROL
            New, Dunkermotoren precision built brushless DC gearmotor with mounted speed control. Planetary gear reduction. Ball bearings. Full range PWM speed control requires 0-10 VDC signal. Instant reversing.
            Part numbers: Motor BG40x50,Gear Reducer PLG52, Speed Control BGE40.

            SPECIFICATIONS Speed 130 RPM max
            Voltage 24 DC
            Amperage 2.1
            Torque 70 in - lbs.
            Gear Ratio 28:1
            Rotation Reversible
            Duty Continuous
            Mount Face mt 40mm bolt circle
            Shaft 12mm dia. x 25mm no keyway
            Size 6-1/2" x 2" x 2-1/2"
            Shpg. 4 lbs.
            The pdf instructions do not say, but do I need a 5k or 10k Pot?

            Looks like on/off switch + 2 SPDT switches?

            24V power supply instead of a 12V that I originally would have needed, anything generic 24V?

            Sorry for all the questions, but want to try to line up what I'll need to finish this out.

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            • #7
              Either pot should work fine. There is nothing special about the power supply. Even 12 volts will work. If you use 24 volts it must be full wave rectified and filtered with at least 1000 mfd at 35 volts or more. A 24 volt transformer will produce about 30 volts DC in that case. I would think the speed controller would be designed to take that but to be on the safe side use an 18 VAC transformer. As I say, 12 volts will work just fine. That motor has much more torque than you need so the reduction in torque on 12 vdc won't make a difference.

              The rpm are rather high at full speed so it remains to be seen how slow it will go and still have enough torque. Raising the voltage won't help that in which case you will need some belt reduction ratio.

              There is nothing nicer than a variable speed leadscrew drive except for also having the same on the crossfeed.

              Note: If you buy a pot from Radio Shack make sure it is Linear Taper. Audio taper won't work well.

              I would use a timing belt. Having the drive slip easily will screw up the finish.
              Last edited by Evan; 07-10-2012, 11:42 PM.
              Free software for calculating bolt circles and similar: Click Here

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              • #8
                I wonder if that gray wire might be a tachometer lead. It would be interesting to 'scope that when it is running.

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                • #9
                  caveBob, I bought a motor. Please let me know what parts & where you find them. Thanks! Eric

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                  • #10
                    Whould this motor have enough power? http://www.ebay.com/itm/221045903362...84.m1423.l2649

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                    • #11
                      Hi Evan,

                      Are you under the impression that most cheap PWM controllers available would produce a bad surface finish because they aren't "true" PWM controllers, ie the motor would be on for a long time then off for a long time, producing a noticeable surface pattern?

                      I ask because I have a motor and cheap PWM controller I have stashed for this purpose, just didn't get round to fitting them yet. I'd hate to do so only to discover the thing moves the carriage in distinct steps!

                      Cheers,
                      Rich

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                      • #12
                        Or this one?http://www.ebay.com/itm/370620470388...388%26_rdc%3D1

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                        • #13
                          Originally posted by flylo
                          caveBob, I bought a motor. Please let me know what parts & where you find them. Thanks! Eric
                          Hi Eric, I'm still figuring out which way I'm gonna go with this... going through a few more "choices" than originally thought may be available. I'll just post a few links to some stuff that I've kept notes on so far...:

                          Originally found these youtube vids after tubalcains:

                          http://youtu.be/BoFSz2LGgkM

                          http://youtu.be/3MnsBobAJ1w

                          really like the simplicity of design and use... that told me to find T5 belts... ok, fine... then a whole new universe of belts/choices opened up. This led to trying to figure out what I need of the different types, which led me again to this forum where Evan posted a link to a pdf "Everything you ever wanted to know about timing belts and tooth forms" here. I just want a stinkin belt like the one in the vids above, which led me to a couple possible places:

                          http://sdp-si.com/eStore/CoverPg/Drive_Components.htm

                          http://www.econobelt.com/e-store/Pulleys.htm

                          ...also considering serpentine belts, but it appears that that may not be an "easy" option since I've had no luck in finding pre-fab pulleys... might be easier to make your own if you go that route. Something to consider...

                          I've seen both of the motors that you posted when in "research" mode, but elected (maybe to my bad... time-wise) to go more rpms then pulley down to the range I want, keeping the torque up. Really liked the 10rpm motor you posted... but what if you want it to go faster?...

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                          • #14
                            Are you under the impression that most cheap PWM controllers available would produce a bad surface finish because they aren't "true" PWM controllers, ie the motor would be on for a long time then off for a long time, producing a noticeable surface pattern?
                            I doubt it will matter at all. There is a lot of mass in the leadscrew system, especially the carriage. As long as the "steps" are reasonably small there won't be any visible "stepping" effect. There isn't with stepper motors.
                            Free software for calculating bolt circles and similar: Click Here

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                            • #15
                              Whould this motor have enough power?
                              Yes, it will have enough torque, easy. That is ideal and a very good price too as long as you don't get soaked on shipping. I would buy two.
                              Free software for calculating bolt circles and similar: Click Here

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