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Thread: Drive a 1.8 degree stepper at 1 RPM

  1. #81
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    Hello dominic87, I will post a picture of my design.

    I have just put together the Linistepper V2c, went very well till I got to checking with a multimeter on page 13/14. Thought I had an issue with a +5v/ground short but after a wasted hour realised that the IDC pin numbers are not the same as the picture on page 1 of the booklet.
    Maybe an ammendment to the booklet is needed or maybe it was me been thick!!! see pics:-

    I was counting the pins like this
    1 6
    2 7
    3 8
    4 9
    5 10 The same as the PIC is numbered. Think it should be like this

    1 2
    3 4
    5 6
    7 8
    9 10

    Ceefna

    Attached Thumbnails Attached Thumbnails Drive a 1.8 degree stepper at 1 RPM-book-jpg   Drive a 1.8 degree stepper at 1 RPM-liniv2b_overlay-jpg  
    Last edited by ceefna; 10-23-2011 at 10:16 AM. Reason: info on pins


  2. #82
    Community Moderator Al_The_Man's Avatar
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    Quote Originally Posted by ceefna View Post
    I am just putting the Linnistepper together, the xtal I have got is a 20MHz HC49 which has 2 pins. What i needed to know is do these just fit into the 2 outer pcb holes?(the ceramic has 3 pins) and ignore the centre hole?/ does the xtal need a spacer under it?
    and I take it it does not have a polarity?
    Ceefna
    On the 628A the xtal goes to pins 15 & 16, non polarity sensitive.
    You can download the spec sheet PDF on the 16F628A off the Picmicro site.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


  3. #83
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    Thanks Al, worked it out

    Ceefna



  4. #84
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    Hi Ceefna, yes the 10 pin connector is numbered to industry standard as;
    1 2
    3 4
    5 6
    7 8
    9 10

    However I agree that would be worth making more clear on the layout diagram and James' instructions sheet. James can you add all 10 pin numbers on the layout diagram, and put a note in the instructions? Or just let me know if you want me to do it at my end.

    The HC49 20MHz xtal is not polarised. You might want to mount it layed down or at an angle (if it is a tall one), and secure it with a blob of silicone or hot melt glue. It also requires two 22pF ceramic caps, between each outer pin and the centre gnd pin. You can add these on the bottom of the PCB if you like, they are very small caps.

    Sorry to hear you cut your hand! I've had some slips with the angle grinder but it just made a burn, you must have went deep to get stitches, ouch!

    Don't rush to work out the gearing numbers, just work on getting it built and we can put in the numbers stuff last.

    Dominic87- hi, the linistepper motor driver is already open-souce design, you can see all the info on James' page;
    PIC Linear Stepper Motor Controller
    if your laptop driver board outputs a step and direction pulse at 0v/5v logic level then it should be fully compatible with the Linistepper for your project.



  5. #85
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    Would have been ok if I was using a grinding disc but it was a 1mm thick metal cut off wheel that did the damage, ouch!

    Thats good news on the pin numbering, sure other diy'ers that don't know about industry standards have had the same issue. Numbering just makes it fool proof or is that "Ceefna proof"!

    The 22pf caps are on order.
    Just to double check am I fitting the supplied C5/C6 or should they be bigger for smooth stepping?

    Have also ordered 4x 10R 2w resistors to give me 5 ohms for the motor current.
    It said in the calculator they would only need to dissipate about 0.2w of heat.

    Ceefna



  6. #86
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    Quote Originally Posted by RomanLini View Post
    Dominic87- hi, the linistepper motor driver is already open-souce design, you can see all the info on James' page;
    PIC Linear Stepper Motor Controller
    if your laptop driver board outputs a step and direction pulse at 0v/5v logic level then it should be fully compatible with the Linistepper for your project.
    The additional board just converts RS232 to TTL. I've programmed my pic to understand the commands from the computer and control the stepper motors.
    It also sends inputs back to the computer.



  7. #87
    Registered James Newton's Avatar
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    Quote Originally Posted by RomanLini View Post
    Hi Ceefna, yes the 10 pin connector is numbered to industry standard as;
    1 2
    3 4
    5 6
    7 8
    9 10

    However I agree that would be worth making more clear on the layout diagram and James' instructions sheet. James can you add all 10 pin numbers on the layout diagram, and put a note in the instructions? Or just let me know if you want me to do it at my end.
    Done and done.



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    Quote Originally Posted by ceefna View Post
    Would have been ok if I was using a grinding disc but it was a 1mm thick metal cut off wheel that did the damage, ouch!
    ...
    WOW! Those thin metal circular saw blades in something as powerful as an angle grinder will take your fingers clean off faster than your reflexes can even kick in! Definitely

    Quote Originally Posted by ceefna View Post
    ...
    Just to double check am I fitting the supplied C5/C6 or should they be bigger for smooth stepping?
    ...
    They are "tuned" for smoothest operation around 2 stepper revs per second. It will depend on your final gearing, but it's not that critical as the small amount of slop in your gearbiox should absorb the small step excitation from the microsteps. The more critical factor is to have a decent sized (high gearing) round pulley on the final dive (camera) as that reduces stepper and gearbox errors to an insignificant value.

    James- Thanks!



  9. #89
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    Thanks for the info on the caps. My linistepper is all finished and my gearbox has arrived. I can either have
    1024 to 1 then through my 73 to 1 worm= 74752 to 1
    or
    4096 to 1 then through my 73 to 1 worm= 299008 to 1
    Do you think the higher the better with the ratio?

    Just checked out the updates to the linistepper build page and thats perfect, would have saved me some head scratching.
    I am trying to find a small metal lathe before I start the mount as the tooling I have is not very good for what i need to make.

    Here is a little picture of my injury, makes you think twice about power tool safety!

    Ceefna

    Attached Thumbnails Attached Thumbnails Drive a 1.8 degree stepper at 1 RPM-img_0114-jpg  


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    Yikes! Made my stomach knot up just looking at the photo of your hand. Just a fraction deeper or higher up and you could have severed the extensor tendon for the forefinger and possibly lost the use of that very important finger! I agree we should ALL "think twice" about safety!

    Ok re the gearing, the 73:1 worm is doing most of the hard work, so I would use the smallest gearing you can on the other gearbox, as less gearing there will have less noise and slop.

    If your camera needs to move 360' in 24 hours to match the Earth, that's 73/24 or about 3.04 turns of the worm pinion per hour. With 1200 microsteps to a motor rev, you could pretty much direct couple the stepper shaft to the worm pinion and step it at 3650 microsteps per hour (or about 1 microstep per second). The potential problem with that is you may get some microsteps bigger than others and the potential for tiny "jerks" in the movement.

    The best stepper smoothness will occur somewhere from 0.5revs/second upward, so that is about 600 times faster. Your gearbox of 1024:1 sounds pretty good. I worry a bit about the reliability of that tiny plastic gearbox, and its multiplied gear slop. At least you could eliminate the gearslop with a small felt pad type friction brake on the main worm pulley.

    Another option, would be to use a zero slop solution like a small toothed belt and reduced gearing like 5:1 between the stepper shaft and worm pinion. That would be professional and reliable, and gives enough gearing at 5 microsteps/second to average out most of the per microstep error.

    If you are not in a hurry you could make some test rigs, even if just hot melt glued together, and try some different drive options with the actual camera. If the drive options tests out good then you could commit to a final build.



  11. #91
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    I agree the plastic gearbox is far from professional, I have a couple of the 73 to 1 worm gears. How about having the stepper driving both worms removing all the spur gear slop giving 73x73=5329 to 1
    86164.1 seconds/ 5329= 16.168905986 seconds per worm revolution

    That is still way off your 0.5 rev/second but I think it would be ok to iron out the steps?

    1 sidereal day = 23.9344696 hours
    222.6495965467311 turns of the worm per hour
    74.21653218224369 steps per second

    The worm gear instead of the gearbox will be just as good a solution as the 5/1 belt drive and also give me nearly 15 times the resolution. Plus as I have the gear already I might as well use it.

    Also got myself a Grayson 3 1/5 lathe very cheap only £50 just needs a motor!

    The motor/driver/gear assy will be housed in a seperate box to the camera mount, once the mount has been polar aligned then the drive box will fit onto the RA shaft of the mount.
    If you think my idea of using the 2 worm gears is good as have got all the parts I can start to put the drive part together.However I make the mount the output from this drive box will turn at 1 revolution per sidereal day so it's universal to any mount I make.


    Ceefna



  12. #92
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    Actually 2 worms is a very nice working solution if you don't mind the extra bulk and you have the ability to join one worm to one pinion with high concentricity (ie you need that lathe!). The worms can be tensioned so there is no backlash and are excellent for slowly driving a high friction load, much better than belts or gearboxes.

    74.2 microsteps per second should be fine for the Linistepper that is about 16 seconds for each stepper motor full rotation. I would leave the LiniStepper smoothing capacitors as standard for that speed.

    It sounds good! I can't wait to see the photos. of both the device and the stars!



  13. #93
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    Hi guys, now that I have your seal of approval on the drive mechanics I am going to start to put that together.

    I have already put the Linistepper together with the standard caps and 2W 5ohm resistors to set the current at 200mA. I never got a answer on the heatsink, can I get away with mounting the transistors onto the aluminium project box I will be housing the drive in?

    Ceefna



  14. #94
    Registered James Newton's Avatar
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    Quote Originally Posted by ceefna View Post
    I have already put the Linistepper together with the standard caps and 2W 5ohm resistors to set the current at 200mA. I never got a answer on the heatsink, can I get away with mounting the transistors onto the aluminium project box I will be housing the drive in?
    It's not really possible to say for sure, because we don't know e.g. how thick the al is or how large the box is, etc... but at 200mA and 12 volts (it was 12 volts right?), I would guess it will probably be ok... Best thing to do is try it while keeping a finger on the transistors and making sure they don't overheat while running it at normal load for an hour.

    Be sure to follow the directions with regard to the isolation and testing to make certain they are not connected electrically before you fire it up.

    James hosts the single best wiki page about motors for CNC hobbyists on the net:
    http://techref.massmind.org/techref/io/motors.htm Disagree? Tell him what's missing! ,o)


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    Good news,yes it was 12v. I will be sure to check temps.
    When you say "fire it up" I hope thats not literally

    Ceefna



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    James made an important point that you should make sure you have used the mica insulating washers to stop the transistor tags shorting out to the metal box!

    As for the heatsinking, it largely depends on the motor specs. If the battery (PSU) is 12.5v and the motor coil takes 6v 200mA the Linistepper transistor dissipates the remaining 6.5v and 200mA (about 1.3 watts), easily absorbed by your metal box.
    If the motor coil takes 9v at 200mA the linistepper transistor only dissipates about 3.5v at 200mA (0.7 watts).

    Either way I think you should be fine, especially with that gearing you might be able to run at less than 200mA anyway. That will reduce heat further and (more importantly) give you extended battery life on your photography treks.



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    I will be sure to insulate the transistors.
    So if I connect my 2 common wires from the stepper with a 12v from the battery to the M+, do the transistors set the voltage? does the motor just take what it needs?

    Ceefna



  18. #98
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    Yes that is correct, the Linistepper sets the motor current to the correct value (like the 200mA you specified).

    Do you have specs for the motor? Like frame size and model number, volts, amps, ohms, torque etc?



  19. #99
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    This is the motor I will be using
    Minebea Hybrid Stepper Motor
    Type: 17PM-J034-P3ST
    Size: 17
    Step angle: 1.8
    Custom Made for Pitney Bowes Franking Machines

    I have found a PDF for the 17PM series but as the motor is a custom it is not listed:-
    http://www.eminebea.com/content/html...pdf/17PM-J.pdf
    Cant find any other information on it.

    Ceefna

    Attached Thumbnails Attached Thumbnails Drive a 1.8 degree stepper at 1 RPM-stepper-png  


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    Yeah you won't really know volts:amps etc until you do some testing. I have similar length size17 steppers here that run 10v 400mA and 12v 300mA etc, so that gives you an idea of wattage for each coil. What electronics tools do you have? Like an adjustable voltage bench PSU, or multimeters etc.



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