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Thread: Master caster electronic automation - some questions

  1. #21
    Boolit Bub
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    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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    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 Bub
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    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 100°C+. 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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    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 Bub
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    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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    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.

  7. #27
    Boolit Bub
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    It has been a while so here is a small update
    I started programming and exploring examples of code beginning of april 2020, by summer I was programming a few days per month on this project. By november I got it all set up and mostly software bug free to a point where I could start testing. Unfortunately the automation failed because of the following points:
    - The 30Nm torque, even if huge for a step motor, is marginal. Sometimes it slips when the sprue is hard, and then I have to re-calibrate which is a pain. Recalibrating means that the sprue of the next bullet is cooling too much.
    - the direct clutch is not precise enough, the motor can get out of alignment if the sprue is somewhat hard, because of this there is a degree or so of angular uncertainty of the mold’s position.
    - the above uncertaintity trips my microswitches that limit the motors’ movement;
    - I don’t like to go to full speed for bullet extraction given this set-up, which causes sometimes a bullet stuck in the mold. However the motor is capable of much more speed than required. I’m aware that max torque is at low speed. Microstepping helped to smoothen the movement but did worsen the torque issue.

    I’m not ready yet to give up. I think the solution lies in a pulley drive to double the torque and a tight timing belt. Should do away with the flimsy microswitches and put an encoder directly on the axis of the master caster (12 bit resolution = accurate up to 0,08° = more than enough).

    Doing this electronically gives in theory a lot of possible refinement options (I’m not there yet), however I believe the air pressure concept is more robust, but may give more wear.

  8. #28
    Boolit Bub
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    Addendum
    I found it interesting to see the step motor is capable of accelerating almost instantly and stopping in such a sudden way that no impacting of the frame is necessary. I just need to tackle the stiff sprue torque issue and be more precise in the drive pulley/encoder.

  9. #29
    Boolit Master
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    Nice work, love to see pics of your progress.

    As for air giving more wear, i'm not so sure. I have cast about 800,000 with my master caster driven by an air cylinder. It does thump at the end of the stroke to eject projectiles, honestly, i see no wear on these points of impact or anywhere else really. Even the pivot points for the mould carrier, there is zero wear and i bought the main casting machine used, and it looked well used.

    I like the idea of a rotary encoder, but they are pricey and for what it's going to be used for, it seems to be an over kill. Can you not just use limit switches for it to know it's home position? I had plans of making an 8 station machine and i was going to use magnets or bolts for a proximity switch to detect when it was in the correct position. The arduino would look for this signal every cycle, so it essentially calibrates itself each cycle.

    A ribbed pulley and gear as a torque multiplier is a smart idea. Will you have an issue with heat from the stepper motor? As they have no fans to cool and if set to hold position, you get heat from the coils even when not moving.

  10. #30
    Boolit Bub
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    I could post pics but since I’m destroying everything to set up the timing belt pulleys, I need to tinker a bit more. The price for the encoder was ok, I paid something like 40€ and this is a small amount compared to the big Nema 42 step motor and the rest of the hardware.

    Considering the heat issue: while testing my software the motor that actuates the pouring with a cam wheel got a bit hot, say 50°C which is not an issue. The drivers for these motors have dip switches to change settings - halving the hold current is one of those options. Less heat get generated in that way.

    Also with full holding power the motors don’t heat up that much during the testing. The temperatures in my basement vary from 8°C in winter to 20°C in summer. The motors are allowed to reach 80°C.

    If a cooling need arises, then a PC fan and a wooden housing to conduct the air flow over the motor can help.

    If I can get everything to run precise enough and with enough torque then the standstill time is well distributed with movement, I have enough parameters in hand to manage the heating issue. Then again it may depend on your selection of motors, to answer on your concern.

  11. #31
    Boolit Bub
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    Hi Tazza,
    I just realize another reason of not having heat issues: I use step motors with a high supply voltage: my small Nema 23 motor (for the lead pour) is fed by a driver fed on 36VDC, the main Nema 42 motor is fed by a driver fed directly on the mains (230Vac 50Hz over here). Somehow the losses are lower with a higher supply voltage.

  12. #32
    Boolit Master
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    I know exactly what you mean, with how my setup evolved, i built it up, then disassembled parts that didn't work as planned. I'm not an engineer, so when i built parts, i didn't know if they would work or not, but then you find any parts that are weak or not working as planned. Jmorris helped me with issues i had with my sizer, something so simple, yet i couldn't see it, a different set of eyes or looking at it from a different angle sure can help.

    I tried setting up a stepper to run my sizer collator, i have yet to get it to run as it should, first attempt burnt up the controller, i have 4 more to play with and hopefully get it to work. I ran it at 12v, i think it was too nigh and that's why it roasted. 36v seemed really high, but the motor i had was out of a photocopier, so i don't know what voltage it was meant to be. I never knew you could get 230v steppers, we run 230/240vac here too.

  13. #33
    Boolit Bub
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    I just want to let you guys know that after three years of interrupted development I managed to make the automation work. I had to use a timing belt to increase the torque and a hall sensor over an I2C interface to adjust the motor / shaft position every now and then when the motor slips a few steps and gets out of alignment. The timing belt also helps not to destroy the machine when it stalls when I’m not directly nearby.

    Will see if I can post a picture.

    Yesterday I did a long test run, and casted 2000 bullets in sessions of 400 (double cavity). Occasionally the machine jams: sometimes a cable disconnects due to high vibrations and it is easily jammed by electrical noise. If I turn on the hood at the wrong moment the machine and/or display stalls.

    There are also a few software bugs that I need to fix that accounts to stalling, for instance about negative angle handling (then my machine corrects in the wrong way). Also a great upgrade idea is to have a acceleration sensor notice when the machine is stalling to death and have it turn of the enable button, then I can leave it unattended with slightly more confidence.

    But now I know it is worth to further refine the machine and develop a printed circuit board for it, eliminating the cable spaghetti and its unreliability and make a better screening/grounding/filtering against EMC.

  14. #34
    Boolit Bub
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    Click image for larger version. 

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    Attached Thumbnails Attached Thumbnails F778951A-6EBE-4CA2-A302-125845CF6AC8.jpeg  

  15. #35
    Boolit Bub
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    Picture of big black-silver nema42 step motor (center), also the black and blue drivers are visibleClick image for larger version. 

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    Transmission from SKF
    Click image for larger version. 

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  16. #36
    Boolit Master
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    That is some awesome work there buddy, glad you finally got it running.

    Mine took me a good 12 months, if not longer. I also had issues of stalling due to electrical noise. I'm wondering if i install shielded cable to my sensors and enclose the arduino i'm using to prevent most of the EMF would work.

    Over time, you'll work out any and all the points that have issues with vibration. My locking screws on my cylinder loosen up over time, but i have not had any parts break off due to vibrations, which does surprise me, i have cast probably 800,000 with mine so far since it was automated.

    Love to see a video of it running if you get time.

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BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
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GC Gas Check