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Thread: Master caster electronic automation - some questions

  1. #21
    Boolit Mold
    Join Date
    Feb 2017
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    Antwerp area, Belgium
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    21
    A small step motor and a cam is exactly what I had in mind. Will create a less noisy circuit.

    For the main step motor I found earlier a 30Nm step motor for 200USD and its driver is about 100USD. I plan on watching the current and switching the thing off if the current is becoming bigger than a certain adjustable setting that I can tune with a potentiometer. That way I dont need a limiter switch to protect my master caster.

    Actually the 14Nm were not calculated but measured with a counter-clockwise torque wrench.

    So it looks I have answered my own question that I started this thread with.

  2. #22
    Boolit Master
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    Oct 2013
    Location
    Brisbane, Australia
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    1,455
    I like the idea of limiting current, when it detects a current spike, it knows something is stuck and stops.

    Double the torque sounds like a good idea, running a motor at it;s limit all day surely wouldn't be good. Do steppers have issues with over heating, as they don't have cooling fans?

  3. #23
    Boolit Mold
    Join Date
    Feb 2017
    Location
    Antwerp area, Belgium
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    21
    Small update - I purchased the step motors and am currently trying to write software for it. I settled for an arduino. C code programming is like 16 years ago but the internet came since then.

    It is just going very slow as I can program for something like 2 hours per week with my current obligations. I settled for a Nema 42 step motor for the main drive and a Nema 23 for the pouring. I decided to use a wheel instead of a cam.

    The motors get hot if they stand still. But they can handle 100C+. May install a cooling fan if needed.

    I dropped the idea of a V-groove transmission and two pulley wheels. I will use a direct transmission with a sacrificial clutch made out of a kind of hard plastic. The clutch should break before my master caster does, as the Nema 42 looks quite impressive.

  4. #24
    Boolit Master
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    Oct 2013
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    Brisbane, Australia
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    Good to hear you're working on it.

    How did you come to the conclusion that 30nm that the nema 42 will put out will be enough? are you running this motor as direct drive? If it's done with a belt, you can increase the torque by changing pulley/gear sizes.

    As far as i was aware, you can run the motor so it will not "hold" that is the main cause of heat build up. It means that even when it's not moving, it's still powered. Ideally, you only need the motor powered when it's moving for this setup. They will need to hold for CNC work so it can't be moved around by a load on the work piece/spindle, but for this project i think the hold feature isn't required.

    Do keep us updated

  5. #25
    Boolit Mold
    Join Date
    Feb 2017
    Location
    Antwerp area, Belgium
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    21
    Hi Tazza,
    I used a left-hand torque wrench to measure the force required to cut the sprue of my largest diameter mold I currently have. I measured 14Nm max. I am aware that there are a lot of variables that affect this result. The amount of time the bullet can cool down is a big factor, together with size and alloy.

    The hold feature for the step motor is important to make the machine operate at a known position. The step motor I use has no feedback as to where the spindle is pointing. That’s what encoders are for but then again here is not much choice in 30Nm motors, this pushed me a bit in the direction of a step motor (and I admit they are easier for me to understand and operate).

    Once I set up the machine, the step motor may not slip or the arm of the master caster may hit its metal frame and break something. The motor I use has no dynamic current limitation. The max current it draws is set by a dip switch so i can not program a safety in that way. Therefor I use a weak machined plastic link between the motor and the caster.

    A V-belt would also offer this safety feature. But I must also ensure the position is sure, I mean: no slippage. If I program the motor to do 100 steps to the left then the result should be exactly that.

    If the 30Nm are not enough then you are absolutely right about your suggestion of changing the transmission ratio. an advantage of the direct drive are the lower costs, the motors were expensive enough for me.

    If I would need two pulleys, the mounting plates, the ball bearings, one or more V-belts and a way to tension it so I get no slippage below 30Nm I would at least spend 100-200 Euro more I guess.

    Thanks for thinking along

  6. #26
    Boolit Master
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    Oct 2013
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    Brisbane, Australia
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    Ahh, that's right, i remember you mentioning the torque wrench earlier, sorry i forgot about that.

    Another thing you can do is to add a limit switch so you can "zero" the machine every time it starts up. That way there will be one point that is the same every time, even if something binds and it does a step but does not move, no need for a rotary encoder that way, those are way too expensive.

    Mine uses air, so it needs to know when the arm reaches set points, i have one under the pour spout and one for when the mould hits the stopper. There is no reason why you can't set switches on yours like this, so you still get the strike when it hits the end of travel, unless you wanted smoother operation without the impact at the end to shock the projectiles out.

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