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Roll-your-own X Axis Drive, Electric Component

Discussion in 'ELECTRICAL ISSUES - POWER YOUR MACHINES & SHOP' started by T Bredehoft, Sep 7, 2015.

  1. T Bredehoft

    T Bredehoft Active User H-M Supporter-Premium

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    I have to admit I'm a CATM, (Cheap A$$ Tool Maker). Why should I buy something I can build, anyway? I recently purchased (and am quite happy with) one of Matt's Precision Machine PM25 mills. Of course, it doesn't have table feed. I think I can build one.
    I purchased for this project a 3/8" Variable Speed, Reversible Drill Motor. ($8.00 reasonable). (It has ball bearings on the armature). I have various DPDT center off switches and Potentiometers.

    Below I have drawn, along side a plan of the electric components in the drill motor, the pot and the DPDT switch, and the Brushes and the Field Contacts, illustrated in the plan. There is no electrical connection between the switch/speed control and direction control inside the machine, it's all as shown with wires.

    I'm hoping someone here can connect the lines so that I can duplicate the speed control and direction control with out my using the existing switch/speed control and direction controls.

    Yes, I realize the DPDT diagram does not include center off, live with it.
    wiring schematic.jpg
    Thanks in advance for bailing me out of this predicament.

    Tom
     
  2. Hawkeye

    Hawkeye Canada Active User H-M Supporter-Premium

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    I wouldn't recommend using a rheostat for speed control. At lower speeds, most of your power will be burned off as heat. The drive won't have much torque.

    Some time ago, I ordered a couple of Pulse Width Modulation (PWM) motor drives off eBay. They were quite cheap and worked fairly well. The torque is higher at low speeds because the motor is still getting the full supply voltage, but it is being chopped up into shorter time intervals. You could build your own PWM drive, using a schematic off the internet, but these ones probably cost less than it would to buy the parts and build it. Just search eBay for PWM motor controls.
     
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  3. mws

    mws Active User Active Member

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    The variable speed switch in the drill is essentially a lamp dimmer which chops the 60 cycle AC into pieces to control power to the motor. You can replace the finger switch with a regular box mounted light dimmer of reasonable size (300 watts) and use the DPDT switch to reverse either the windings or brush wiring for direction.

    If you look up "Router Speed Control" you'll find this http://www.harborfreight.com/router-speed-control-43060.html link that has almost everything you need. Although, frankly I think 15 amps is a little generous for a rating, but I've used them on some pretty big loads and had no issues. You might even find one cheaper.

    I believe making the gear train and mounting the motor drive will a lot more work than wiring the motor.

    Mark
     
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  4. T Bredehoft

    T Bredehoft Active User H-M Supporter-Premium

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    Hi Mark, Thanks for the reply. the Router speed control doesn't appear to be reversible, could it be rewired to include the DPDT?

    Lamp Dimmer....I've ordered and am awaiting delivery of this--http://www.ebay.com/itm/262005011999?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT It says among other things it's a lamp dimmer.

    I've got an industrial Center off DPDT switch to couple it with. I just need to know how to route the wires through the maze of equipment.

    use the DPDT switch to reverse either the windings or brush wiring for direction. Do I send the variable speed wires to the brushes and the DPDT to the windings? that seems too easy.

    The devise illustration above shows six connections, including two from line voltage. There are two that go to the brushes and two that go to the fields. but where do they come from (exactly) within the control? that's my problem.

    The mounting and gear train are child's play.
     
  5. T Bredehoft

    T Bredehoft Active User H-M Supporter-Premium

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    Mike, thanks for the PWM suggestion. were I literate in electro speak, I'd really like to go that way, I need a power drive for the head on my PM25, without feed, just slow rapid. That looks like the way I could go. But I'll need direction.

    Tom
     
    Last edited: Sep 8, 2015
  6. mws

    mws Active User Active Member

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    Adding the DPDT for direction is easy. The six wires presently are two for line power in, two to the windings, and two which go to the brushes. Usually, the brush wiring is the part that goes through the reversing switch. Both the winding AND brush circuits are AFTER the motor speed control. Either the winding OR the brushes can have the DPDT in line, but not both. Common convention is to have the brushes reversed but the motor doesn't know the difference, just that the phase is reversed, either can have the DPDT in line.

    $2.55 for that little module is a great price for all that circuitry! You really did some digging. I'd by three and throw a few on the shelf. :) But that's me.

    Just a word however about Hawkeye's suggestion of using a PWM control (ostensibly on a DC servo motor). Universal brushed motor are really noisy. Almost anything else would be preferable for me but I suppose you can always upgrade the motor at a later date.
     
  7. T Bredehoft

    T Bredehoft Active User H-M Supporter-Premium

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    That $2.55 is Canadian, US $ is 1.90 something. Ridiculous. Soon's its here (this week) I'll see what happens. I figured at the very worst I'd be out a couple of bucks.
     
  8. T Bredehoft

    T Bredehoft Active User H-M Supporter-Premium

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    Mark, I'm not at all sure I understand the above.

    110V: one wire goes to the to the speed control then to the DPDT? Two wires from the DPDT go to the brushes?

    The other wire from 110V goes to one of the windings? That's only three wires to the motor....

    I need another wire to the DPDT and another wire to the other winding. Can you draw a picture?

    As I think I said, I'm a toolmaker, not an electrician.

    tbredehoft to be contacted through alink.com

    Tom
     
  9. Keith Foor

    Keith Foor Active Member Active Member

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    OK, there are 4 wires going to the motor. Two are connected to the brushes, and two are connected to the stator (outer windings). To reverse a motor like that you have to switch one or the other. We are doing to switch the brushes for simplicity. We are not talking about the variable yet, just the forward and reverse. We will get to the variable in a minute. The feed coming to the motor (will be from the variable) will wire as follows. From the center of the switch terminals 3 and 4, you will run the two wires feeding the motor assembly. From those two wires you will also connect the stator wires from the motor so they have 110 that is unswitched. Run two wires from the bottom of the switch to the top of the switch (6 connections on a DPDT ) and cross them so that terminal 1 goes to terminal 6 and terminal 2 goes to terminal 5 (looking at the switch from from left to right with the terminal rows up and down so you have 2 vertical terminals with 3 terminals in each vertical row) as follows

    1 2
    3 4
    5 6

    Connect the brushes to terminals 1 and 2
    This will allow you to reverse the motor.

    The variable.

    You can use a light dimmer to control this type of motor

    A dimmer will typically only have 3 wires, a line in (110 feed)
    a neutral wire (typically white)
    a load wire that would go to the light or in this case a motor.

    Connect the load wire terminal 3 on the switch.
    Connect the neutral wire to terminal 4 on the switch and connect the 110 power cord to terminal 4 as well.
    Connect the BLACK wire on the line cord to the line wire on the dimmer (should also be BLACK)

    The DPDT switch will give you reverse ability on the motor, the dimmer will give you variable speed and will also control the on/off function of the motor.
    Now, USE A 3 WIRE cord on this and connect the green wire to the machine ground or some close metal part. No sense in having something get shorted to the machine and shocking the hell out of you.
    The line cord only applies if you are going to power this from another source besides the machine. If you have 110 elsewhere in the machine and can access it safely, then you can simply run a piece of SO / SOW cord (rubber extension cord type wire) from the source to the unit. Or put a line cord on it and plug it in where ever. Choice is yours. Remember that if you tap the machine power you will need to fuse / protect the wiring and assembly. The machine may be fed from a 30 amp breaker so that is a bit too much for a drill motor and 14 gauge cord that you will typically use for this. I see guys all the time needing a 110 outlet on a machine so they just tap one leg of the main feed and run it straight to a 15 amp output they mounted on the machine. Problem is the machine is rarely fed with a 220 15 amp breaker. There are 15 amp panel mount breakers available if you want to go that route and it's perfectly safe to do that. I just finished putting a 4 square box on my phase converter cabinet and installing a set of outlets with a breaker like this for running the drill I use to spin up the motor on the RPC. The RPC is fed with a 50 amp breaker (15 HP motor) and that would melt down a standard 14 gauge cord if the cord was to fray and short.
     
  10. turnitupper

    turnitupper Australia Active Member Active Member

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    Just a note of caution, most cheap drills are wound to work on about half voltage at full speed because the triac/chopper network only works on the positive half cycle. Using a full wave controller will double maximum speed and usually spin the armature into oblivion. You can try this on a variable speed drill with a u/s trigger, wire mains directly to motor, secure drill to something solid,connect a long extension lead, stand well back, turn power on and wait for smoke, fire or shrapnel.
    John.
     
  11. T Bredehoft

    T Bredehoft Active User H-M Supporter-Premium

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    Keith, I think you've covered it. I'll have to study your details, but I think it will work out. Life has intervened, I've got a couple of short run productions to do, and wait for some parts to be delivered. I'm still designing the connection between the drill motor and the feed screw, too.

    Before I hook everything up permanent wise, I'll patch it all together and see what happens.
    Yeah, John, that's the plan, wait for shrapnel. First time through, the pot I had self destroyed. Since then I've included an on-off switch.
     
  12. T Bredehoft

    T Bredehoft Active User H-M Supporter-Premium

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    I can't believe almost two years have passed. The 3/8 drill somehow let the magic smoke out, it was replaced with a 12 volt automotive window motor, the belt drive was replaced with a direct drive with a dog clutch, it feeds from not moving up to 10 inches a minute, reliably.
     

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