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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > Auto Tool Changer Motor G0704
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  1. #1
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    Feb 2014
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    Auto Tool Changer Motor G0704

    I am in the process of building an ATC for my G0704. I am going to use the Geneva Mechanism and wanting to get some ideas or thoughts of what type of motor to use, Geared stepper or non Geared stepper motor? If geared stepper, what would be a good gear ratio ex. 20:1 or 9:1? The carousel will be a 12 count tool holder.

    Thanks,

    Jeff

  2. #2
    Join Date
    Oct 2005
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    1145

    Re: Auto Tool Changer Motor G0704

    Anything with a geneva can take forever to change tools. I would not consider a mix of mechanisms Genevas are used with dc motors to index to the next position. THE geneva IS the idexing mechanism and require switches for teh start/stop locations with steppers there is no need for a geneva as it can move to exact position on its on. I would use about a 3:1 belt reduction for the stepper for added torque to move a HEAVY loaded carousel . The macros for such were perfected years ago.

    Just a thought, (;-) TP

  3. #3
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    Feb 2014
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    Re: Auto Tool Changer Motor G0704

    TP, just to clarify the stepper motor with pullys will require a proximity sensor to be able to home the machine at start up so that Mach3 knows where the carousel is located? From the home location Mach3 through the macro will know the other tool locations of where to stop the carousel when another tool is selected. Is that the right thinking?

    Jeff

  4. #4
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    Re: Auto Tool Changer Motor G0704

    While the geneva mechanism doesn't require use of a stepper it doesn't mean one can't be used successfully. a DC motor on a geneva still requires a way to stop the motor every revolution. Because of the way it works, the motor doesn't need to stop precisely at the same location but somewhat close at least. A stepper could be used and just command one revolution for each tool change position move. That said, if you do use a stepper, you will need a way to index it on startup (home it) and also tell it which tool position the carousel is in. I would not think you would need to gear it though. Having said all of this, it would make more sense to me to just use a stepper driving the carousel direct and ditch the geneva mechanism. That way the homing of the tool changer would take care of the motor indexing which would also place the carousel at a specific tool slot. There are examples of stepper driven tool changers that are direct drive, but a gear drive might not be a bad idea. I think Hoss did a 16 tool toolchanger with a stepper on the carousel (link below). As mentioned, the geneva mechanism would likely be slower than a stepper driven carousel.

    https://www.youtube.com/watch?v=iDT693Zv_wE

  5. #5
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    Nov 2009
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    4415

    Re: Auto Tool Changer Motor G0704

    Ballistic, yes. The tool change macro will travel x amount of steps to the next tool. That is the way it works on my 6 tool turret on my lathe. IIRC you are 1 of the only people I have seen who actually built Hoss' tool changer.
    A lazy man does it twice.

  6. #6
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    Feb 2014
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    227

    Re: Auto Tool Changer Motor G0704

    Ok Thanks for the eduction on how to go about this. I have a Gecko 203V sitting idle in my control box that I will put to use. I will put a nema34 906 or 1200 in oz. motor on the carousel. The next question, spur gears for reduction or timing belt pulleys?

    Jeff

  7. #7
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    Re: Auto Tool Changer Motor G0704

    Funny, I spelled education wrong...lol.

  8. #8
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    Apr 2005
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    1268

    Re: Auto Tool Changer Motor G0704

    Hey Jeff;
    If it were me I would use a small DC high torque motor and a motor driver with a brake. The motor I would look at is the RS-775 DC motor and the IMS-2 motor control with brake. This could save $$ for the stepper motor and driver. The advantage of using the geneva wheel is hat position is determined by wheel design and is mechanically repeatable. A sensor counter could determined tool position by homing and then doing geneva advance counts. Hope this makes sense.
    Do you have plans for the ATC or are you winging it? I've been looking for a decent set of plans for awhile now but have only the plans from hoss to date. His plans are good but I'd rather exhause all my options before deciding which design to use. I'll be designing for a Torus Pro. I'm just about finished with a compatible Power Draw Bar and an ATC is next on the agenda.
    Hope this helps.
    Bill
    billyjack
    Helicopter def. = Bunch of spare parts flying in close formation! USAF 1974 ;>)

  9. #9
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    Re: Auto Tool Changer Motor G0704

    I think direct drive is the way to go myself. I see no reason a stepper especially a Nema 34 couldnt handle this. I would trust it to a 200-300oz Nema 23 direct and not worry. How fast and quick are you trying to spin it? Enough to throw the tools out? Put a support bearing of some kind on the carousel so the stepper is only responsible for the rotation. A smaller stepper would also be out of the way if direct drive on a 10 tool carousel however a 34 might require the belt or gear drive for clearance.
    RW Skinner built one for a 45 IIRC. Though in this video I cant tell if it is direct but see no reason why it couldnt be,https://www.youtube.com/watch?v=UZWtSpbR8to
    A lazy man does it twice.

  10. #10
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    Feb 2006
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    7063

    Re: Auto Tool Changer Motor G0704

    A stepper or servo to drive a Geneva mechanism is a waste of money. A simple $30 DC gear-motor (see McMaster-Carr) with a ~60RPM output will do the job, with nothing more than a cam-operated micro-switch to stop it. High torque is not required. Properly designed, it only needs to stop anywhere within the nearly 180 degree arc of rotation where no carousel motion takes place. No brake is necessary because, again, properly designed, the Geneva cam will positively locate the carousel within a very small range (easily <<1 degree). Besides, if, as I would assume, you are using TTS, you don't WANT the carousel too rigidly locked - you have to allow some controlled free-play to allow the TTS holder to self-align to the carousel when the tool is being inserted.

    Regards,
    Ray L.

  11. #11
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    Re: Auto Tool Changer Motor G0704

    Well Thanks to everyone for all the ideas of how to skin this cat! I will do some thinking on the subject and come up with something from all the good info that I have taken in.

    Thanks,

    Jeff

  12. #12
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    Re: Auto Tool Changer Motor G0704

    I don't know that I would call a stepper on a Geneva a waste of money. It isn't strictly necessary but does provide some benefits that some might consider worth a few extra bucks.

    First, with a dc motor on a Geneva the tool change generally goes sequentially since the motor generally turns only one direction. In other words it is generally 1-2-3-4, and to go from say tool 2 to tool 1 means going 2-3-4-5-6...16 -1. With a direct drive stepper, or a stepper on a Geneva you could just go from 2->1 directly easily. It could be done with a DC motor too, but now you add a relay and additional logic... With the stepper it would just be in the macro coding.

    Second, with a Geneva and DC motor you still need a way to know how many times the motor has gone around to know when to de-energize the motor circuit. Either a feedback loop or something to tell the controller that that each rev has completed. So to go from tool 1 to tool 6 we need 5 revolutions, and those have to be counted with the DC motor setup, whereas with a stepper you just tell it to go 5 revolutions or whatever and since the controller is driving the steps for the motor it already knows when the last step is commanded.

    Third, with a stepper you don't need the cam, microswitch, etc. Just connect the motor shaft to the Geneva mechanism and go.

    The benefits listed above aren't revolutionary and you can get them without even building the Geneva mechanism just by using a stepper direct to the carousel. Even considering the benefits listed, it is entirely possible to do it with just a simple DC motor as mentioned.

  13. #13
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    Re: Auto Tool Changer Motor G0704

    Quote Originally Posted by 109jb View Post
    I don't know that I would call a stepper on a Geneva a waste of money. It isn't strictly necessary but does provide some benefits that some might consider worth a few extra bucks.

    First, with a dc motor on a Geneva the tool change generally goes sequentially since the motor generally turns only one direction. In other words it is generally 1-2-3-4, and to go from say tool 2 to tool 1 means going 2-3-4-5-6...16 -1. With a direct drive stepper, or a stepper on a Geneva you could just go from 2->1 directly easily. It could be done with a DC motor too, but now you add a relay and additional logic... With the stepper it would just be in the macro coding.

    Second, with a Geneva and DC motor you still need a way to know how many times the motor has gone around to know when to de-energize the motor circuit. Either a feedback loop or something to tell the controller that that each rev has completed. So to go from tool 1 to tool 6 we need 5 revolutions, and those have to be counted with the DC motor setup, whereas with a stepper you just tell it to go 5 revolutions or whatever and since the controller is driving the steps for the motor it already knows when the last step is commanded.

    Third, with a stepper you don't need the cam, microswitch, etc. Just connect the motor shaft to the Geneva mechanism and go.

    The benefits listed above aren't revolutionary and you can get them without even building the Geneva mechanism just by using a stepper direct to the carousel. Even considering the benefits listed, it is entirely possible to do it with just a simple DC motor as mentioned.
    The advantages are cost, simplicity, and reliability. A $30-40 gearmotor, a pair of $5 relays, and a $2 microswitch are all the hardware required. Using good components, it will be extremely simply, and extremely reliable. I built one years ago mostly with parts out of my junk box, and it still works perfectly. A stepper-based system will cost twice as much, and involve a lot more parts and wiring, take up a lot more space, and consume a LOT more power.

    Making a DC motor go in reverse is absolutely trivial (i.e. a single DPDT relay), so your first point is rather specious. There is no "logic", other than the absolutely trivial macro code. To make it uni-directional would to save the cost of a relay would be pretty silly. The "macro-coding" consists of a few lines of code, as it is controlled by a grand total of two output signals: a Direction signal to activate the reversing relay, and an Enable signal, to activate the relay that provides initial power to the motor. Once the motor starts turning, the cam switch is activated, and the Enable signal can be turned off. The cam switch will then turn off the relay when the motor has completed one turn. The Geneva will, inherently, stop after each turn of the driven wheel. If you want to go more than one slot without stopping, simply leave the Enable signal on, and time how long it's active. Turn it off once you're sure it's started the last turn. With a gear motor, you know exactly how long it takes to move one slot, so this is trivial macro logic. It takes a grand total of perhaps two pages of very simple macro code to make the whole thing work.

    A gear motor also connects directly to the Geneva, so your third point is also rather specious. A cam and micro-switch are hardly rocket science.

    With a stepper, you need a more expensive, and physically much larger, stepper motor, a separate power supply (a gear-motor will run happily off the 12V PC power supply), a stepper driver, and the software to drive the direction and step pulses. And, if/when it stalls, you'll never know it. A properly-sized gear motor will rarely, if ever stall, and will certainly provide far more torque than you'll ever need. Overall, it will be much more reliable.

    Performance with a gearmotor will be 100% identical to the best stepper or servo system, as you are limited by how hard you want to hammer on the Geneva mechanism, not by motor torque, speed, or power. A Geneva is not fast, even under the most optimistic of conditions.

    And try direct-driving a loaded tool carousel with a stepper mo, and you'll find out real quick why that is really not a great idea.....

    Regards,
    Ray L.

  14. #14
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    Aug 2008
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    1186

    Re: Auto Tool Changer Motor G0704

    I agree with Ray, I think a geared DC motor would be cheaper and the Geneva wheel while slow is pretty reliable and if aligned properly should remain rock solid for as long as it stays bolted in that position and less likely to have a fault and cause a crash.

    The code is the hard part to me I think.. I have envisioned several ideas over the last year or so and have designed a full 12 tool changer for TTS holders, but the coding has held me back from giving it a go.. Would be awesome to have a solid design open sourced with all the electronics components detailed out and the coding work available with some instructions..

    I'm game to post up my solidworks design for the changer which I designed to be made on mills with limited Y travel if some of you macro and coding wizards want to help make that portion!!!

    Lemme know!

    Chris

    Sent from my XT1080 using Tapatalk

  15. #15
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    Re: Auto Tool Changer Motor G0704

    Quote Originally Posted by lcvette View Post
    I agree with Ray, I think a geared DC motor would be cheaper and the Geneva wheel while slow is pretty reliable and if aligned properly should remain rock solid for as long as it stays bolted in that position and less likely to have a fault and cause a crash.

    The code is the hard part to me I think.. I have envisioned several ideas over the last year or so and have designed a full 12 tool changer for TTS holders, but the coding has held me back from giving it a go.. Would be awesome to have a solid design open sourced with all the electronics components detailed out and the coding work available with some instructions..

    I'm game to post up my solidworks design for the changer which I designed to be made on mills with limited Y travel if some of you macro and coding wizards want to help make that portion!!!

    Lemme know!

    Chris

    Sent from my XT1080 using Tapatalk
    Below is all the macro code I used for my Geneva-based ATC under Mach3. Just don't ask me to explain it. I did this years ago, and haven't looked at it since. Some of what's in there was used just for testing and debugging.

    Regards,
    Ray L.

  16. #16
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    1186

    Re: Auto Tool Changer Motor G0704

    Lol.... Awesome.. I will see if it makes any sense to me.. I'm sure it will look like Greek..hahaha

    I'll post up the plans shortly, I'm going through them and making some adjustments from many years ago..lol pretty much the same situation.. Looking at them I was scratching my head wondering what I was Thinking.

    Sent from my XT1080 using Tapatalk

  17. #17
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    Re: Auto Tool Changer Motor G0704

    I was only pointing out that there are some things that some may find beneficial in regard to using a stepper in conjunction with a geneva mechanism. Whether or not anyone else agrees or disagrees is totally up to them. What one person sees as a benefit another might not, and that is fine. I will however address some points.

    Additional power supply required for using a stepper. I totally disagree. Most systems will have enough surplus available on the main XYZ power supply to sufficiently power a single additional stepper for a carousel. Especially considering that the carousel stepper need not be high performance. You say that the gearmotor will happily run on a 12V PC power supply but neglect to say that this 12V supply also needs to be added to the supply list. You can't really say that a stepper needs an additional power supply since the DC motor also needs an additional supply. In addition, the DC gearmotor needs 12V, so it will definitely need an additional supply whereas the stepper will likely be able to be powered off the existing XYZ supply.

    When I mentioned connected directly to the carousel, I meant that the relationship between the carousel rotation and the stepper rotation had a direct relationship. For example x number of steps per degree so 10x=10deg, etc. In this I was not clear.

    A geneva mechanism may be "cheaper" in dollars, but you must consider design and build time. A geneva system will take longer to design and construct than say a belt drive stepper setup. A stepper controlled belt driven carousel is about as simple as the mechanical system can ever get. I also never said anything about a geneva its wiring or components being "rocket science", I only said that there is a bit more required. Sure the cam is simple but you still have to design it, make it, mount it, etc. A microswitch still needs at least a couple mounting holes, etc. Yes it is still a relatively simple setup, and has benefits but those benefits need to be weighed by the end user.

    As for a much more expensive motor. A $30 NEMA23 stepper and a $25 stepper driver with a simple belt drive will spin the carousel, or if you want to eliminate some mechanical design you can buy a NEMA 23 with an integral planetary gearbox for $60. Sure it is a little more money, but you now have a motor/gearbox that has the bearings to support the whole carousel, therby reducing a lot of the mechanical design that would otherwise be needed.

    There are many ways to do a carousel. None is 100% right or wrong and they all have different aspects that could be viewed as pros or cons. As before the assessment for that is up to the end user.

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