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Thread: Weld rotator

  1. #16
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    Would plastic gears survive the heat conducted by the shaft?
    Chris

  2. #17
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by jack620 View Post
    Would plastic gears survive the heat conducted by the shaft?
    The ring gear could be mounted on ceramic spacers under the table but I would prefer to see metal gears.
    I think that's why KBPM used the term "like" in his description.

  3. #18
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    I think a plastic gear is not the best on the shaft but if it was put at the far end of the shaft and a phenolic material was used it would likely be ok but steel or cast iron would be a safer bet.
    You can limit heat transfer to the face plate/drive shaft by using stand offs, adjustable bolts ect

  4. #19
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    Michael,

    Here's another data point.

    30 years ago I built a rotator for the production MIG welding of a shaft onto a mounting plate. It used a 12V windscreen wiper motor geared down ~4:1 with a fine pitch toothed belt, there was a simple rheostat for speed control. The rotating mechanism was carried in a pair of 25mm ID sealed deep groove ball bearings. The entire welding current passed through the two bearings. In 20 years of use, and 10,000 plus welds the bearings never gave up, and it rotated as good as new. The welding current would have been about 80 amps.

    Graham.

  5. #20
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    Michael these days I wouldn't bother with a DC motor at all. It's far too limiting and may be fine if all you want to do is spin something at a constant speed, but it's not the way I'd go.

    Stepper motors are super cheap, easily obtainable, are powerful for their size and will offer far more flexibility. The drivers are also cheap and easy to get. You can either make up a simple PWM circuit with analogue control or if you really want to get fancy control it with an Arduino (super easy also). You may recall the Arduino controlled rotary table I made. While not exactly what you're after, some of the principles are the same and could be simplified for your purpose.



    I can almost guarantee you won't be the first to do this and there is almost certainly a commercial version of a simple PWM stepper controller available through Aliexpress etc. Check out cameral sliders etc as it doesn't matter if you're controlling linear or angular motion.

    Edit: something like this Pulse Generator For Stepper Controller Using AD654 - Electronics-Lab

    As far as the welding current, for the amount you're likely to be using it I wouldn't overthink it to be honest. I can see how running it through the bearing could end in tears but it would be a simple matter to have a loop of copper earth braid pressing up against the bottom of the table and acting as a brush. I definitely wouldn't want to have the ground clamp just winding up on itself and think that would be a monumental PIA. On important welds I will sometimes do a couple of dummy runs to make sure my positions are correct and comfortable, then hit the Go-Pedal to do it for real. It would be painful to have to stop and untangle the mess mid stream when the solution is so simple.

  6. #21
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Pete F View Post
    Michael these days I wouldn't bother with a DC motor at all. It's far too limiting and may be fine if all you want to do is spin something at a constant speed, but it's not the way I'd go.

    Stepper motors are super cheap, easily obtainable, are powerful for their size and will offer far more flexibility. The drivers are also cheap and easy to get. You can either make up a simple PWM circuit with analogue control or if you really want to get fancy control it with an Arduino (super easy also). You may recall the Arduino controlled rotary table I made. While not exactly what you're after, some of the principles are the same and could be simplified for your purpose.

    I can almost guarantee you won't be the first to do this and there is almost certainly a commercial version of a simple PWM stepper controller available through Aliexpress etc. Check out cameral sliders etc as it doesn't matter if you're controlling linear or angular motion.
    I agree Pete, I've been looking into suitable motors this morning and even though I already have a bunch of really nice German 24V AC synchronous motors with gearboxes in my stash am now heading this way because of speed control issues. A reasonably flexible PWM controller can be had for close to or less than the cost of components, and suitable small steppers are dirt cheap.

  7. #22
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    Quote Originally Posted by Pete F View Post
    Michael these days I wouldn't bother with a DC motor at all. It's far too limiting and may be fine if all you want to do is spin something at a constant speed, but it's not the way I'd go.

    Stepper motors are super cheap, easily obtainable, are powerful for their size and will offer far more flexibility. The drivers are also cheap and easy to get. You can either make up a simple PWM circuit with analogue control or if you really want to get fancy control it with an Arduino (super easy also). You may recall the Arduino controlled rotary table I made. While not exactly what you're after, some of the principles are the same and could be simplified for your purpose.
    Your points are most valid Peter, but some of use not electronically minded. Unless something is marked "Red wire to E2, Black wire to B1, Green wire to ground etc."
    I'm pretty useless. Years ago, I could have done all that sort of thing, but not anymore!!!
    I can design and make just about anything, but technologically I'm a failure.
    To grow old is mandatory, growing up is optional.

  8. #23
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by KBs PensNmore View Post
    Your points are most valid Peter, but some of use not electronically minded. Unless something is marked "Red wire to E2, Black wire to B1, Green wire to ground etc."
    It's been 20 years since I wired up a stepper but watching my young bloke wiring up steppers a few months ago for his 3D printer it's almost reached the stage you are after.

    I cannot personally vouch for these but these 12-42V 4A stepper driver can be had for ~ $10 and will suit almost all 4 wire steppers. Please note you still have to add a DC PS.
    https://www.ebay.com.au/itm/Newly-Fo...97.m4902.l9144
    Screen Shot 2018-11-19 at 7.25.15 pm.png

    A new stepper will set you back starting at around $20 depending on torque requirements.

  9. #24
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    The other thing I forgot to mention is, how is a stepper driver programmed to go full circle at 1RPM or whatever speed is required, or even part circle etc.
    I do have about a dozen stepper motors that I can use, similar to these. Motor5.jpgMotor10.jpg
    They came out of a Blood Analysis Machine
    As I said earlier, I'm a technological failure. I don't even have an Iphone or similar, as they don't like me.
    Kryn
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  10. #25
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    Hi Guys,

    Kryn asked
    how is a stepper driver programmed to go full circle at 1RPM or whatever speed is required, or even part circle etc.
    In its simplest form just a counter and a variable speed clock.

    Each step is counted and since you know the number of steps per revolution and the angle per step, you just increment the counter until the number is reached, then stop.

    By changing the speed of the clock you can alter the rotational speed of the stepper !
    The faster the clock the faster the stepper will rotate.
    Best Regards:
    Baron J.

  11. #26
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    A weld positioner will have very little load on the motor, basically just friction and enough torque to turn an eccentric piece if you build one that can also be angled. Small stepper motors to suit Michael's application once further geared down (as they would be) can be as little as $10 DELIVERED. Even "large" steppers are very cheap. The result is to take any old stepper to the scrappy, get the few bucks they will be worth for the copper inside, and go buy new ones. It's unfortunate that's the world we live in, it may not save the world but that will save a world of heartache.

    Inside a typical 4 wire stepper are just 2 coils, and it's not hard to figure out which wires are which, though the manufacturer will often also tell you. When it runs it turns on each coil in turn, when the appropriate coil turns on it pulls the rotor around a specific angle (again, advised by the manufacturer) then turns off. Simultaneously the other coil turns on and pulls the rotor around the same number of degrees and the whole sequence repeats. Therefore they "step" around the circle, hence the name. As you can imagine that's a jerky movement, however the number of degrees are quite small (0.9/1.8 etc) so isn't typically noticed. It would be absolutely insignificant for a weld positioner. In the interests of completeness however, they can be made to "micro-step" by not fully turning on/off each coil and allowing the stator to partially turn, but that's beyond the required knowledge here and more for precision applications.

    The speed of stepper motors is controlled by how fast each coil is turned on/off. Turn one on and keep it on and the motor will be braked in one position. Turn one on/off every second and (for a 1.8 degree stepping motor) it will rotate 1.8 degrees per second. For a 0/9 degree stepping motor it will rotate 0.9 degrees a second. How many pulses does it require to rotate 1 RPM? 360/1.8 = 200 or 360/0.9 = 400 respectively (ignoring any subsequent gearing).

    The reason these are now the way to go is that controlling a stepper requires the controller to provide pulses that are either on or off. There is no in between. That makes for an efficient circuit, and efficient means cheap. Semiconductors like to be either on or off, if they're in between they generate heat, and heat is expensive. Even modern analogue controllers these days will turn motors fully on/off and smooth the result, but that's another story. Controlling a stepper motor reasonably precisely is therefore generally cheaper than controlling a DC motor, as you know precisely how much it will turn with each pulse. So a controller is a simply a circuit that provides a required number of pulses to a motor driver (which provides the required current, power if you like) to actually drive the motor. Both are super cheap.

    Now if you want to actually control and program a motor to do specific things like turn 90 degrees, pause, turn back at half speed etc etc etc then you will need a computer to handle that information. Personally I use Arduinos as they're cheap (around $20 each), and I know how to program them. That's what I used in the rotary table video above. But that's a complete overkill for a weld positioner. Yes you could, and maybe I would simply because I can (and it would be arguably cheaper than going out and buying a PWM controller), but would be like saying you need a Ferrari to run don to the shops to pick up milk.

    However the point is you can feel free to ignore all of the above. There are literally thousands of web pages, Youtube videos, blogs, etc etc describing precisely how to wire this type of thing up, wire by wire, and there's no need to understand the electronics behind what is happening. Similarly, it literally took me 30 seconds in between sips of my cuppa to open up a web page, type in Aliexpress and then "pulse generator stepper motor" to find solutions. Nobody was born with the ability to understand this type of thing pre-programmed in their brain. But I'm sorry, anyone who claims they can't do this is simply demonstrating their laziness and not their intellect. Yes it can be daunting at first, all of us who use these went through the same thing, but like any big task you break it down in to chewable bytes (sorry, in joke) and get a feel for the very basics of what each part does, and what it needs to do its job.

    So if I was starting with a blank sheet of paper I'd use a stepper motor and a pulse generator/stepper driver to do the job. It's easy, it's cheap, and it's an introduction to modern motion control systems used in pretty much every affordable CNC machine, 3D printer, laser cutter, etc etc. So for those who haven't dipped their toe in that water it's great exposure and you'll start seeing these as solutions to other problems. BUT what if somebody already has a DC motor and wants to control that for this application? Well, you know how I mentioned above DC modern motor controllers use the same principle to turn motors on/off really fast ... Do an Aliexpress search for "pwm motor controller"

    https://www.aliexpress.com/item/12-2...4-81af3f07798e

  12. #27
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by BaronJ View Post
    In its simplest form just a counter and a variable speed clock.
    Sorry I'm repeating some of Pete's response here and I forgot to include the pulse generator (connections labelled PU+ and PU-) in my post above.
    I'll use the abbreviation PU for pulse generator from here on.

    So to summarise you will need 4 things.
    A stepper, a driver, a PU, and a suitably rated (V and A) DC power supply

    A basic Pulse generator can be bought on ebay for about $5 eg
    https://www.ebay.com.au/itm/Motor-Pu...-Tsb:rk:1:pf:1

    PUs output pulses selectable over a specific frequency range eg the one in the above link output either, 5.4k-160 kHz, 540-16.6 kHz, or 80-2.4 kHz.
    The actual output frequency inside each range is set by the pot on the pulse generator.
    The motors come with a fixed angle of rotation per pulse eg for a 1.8º per step, 200 pulses are needed for one complete rev.
    If the PU is set on the 80 - 2.4 kHz range and connected to the driver, with the pot on its lowest setting the PU will output 80 pulses a second.

    200/80 = 2.5 second per rev or 24 RPM so you would need a 24:1 gear reduction to go at 1RPM, or for a 1.8º per step motor find a PU that has a 3.3Hz output.
    I've seen them as low as 1Hz. If you are going to drive the table direct you may need a stepper motor with a bit more torque.

  13. #28
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    I did wonder about using a stepper motor but being relatively uninformed about matters electrical, I discounted it. My 2 concerns were firstly that most steppers I've seen seem to get hot, so in an enclosed metal box would that be an issue, and the second concern was whether the electric fields of a welding power supply would disrupt the electronics? I once turned up my shed air conditioner while welding, so possible?

    Michael

  14. #29
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    Yeah you could have interference issues especially if you plan on doing tig welding with high frequency.

  15. #30
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Michael G View Post
    I did wonder about using a stepper motor but being relatively uninformed about matters electrical, I discounted it. My 2 concerns were firstly that most steppers I've seen seem to get hot, so in an enclosed metal box would that be an issue,
    I too recall the ones at work getting quite hot as do the ones on one of my sons 3D printers, interesting that they don't get as hot on the other printer. My so has put heat sinks on some of his and a fan on top of that, but his are in the open air. Sealed box may present a prob but some sort of venting could probably be arranged.

    and the second concern was whether the electric fields of a welding power supply would disrupt the electronics? I once turned up my shed air conditioner while welding, so possible?
    Yes, good point but basic precautions can be used to minimise these problems eg placing the electronics out of the way in a separate grounded metal box and using shielded cables. I remember the German steppers we used at work all came with beaut shielded cables.

    We won't really know until we try.

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