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Project: Polargraph

Project: Polargraph

A Polargraph is a 2D plotter created by Sandy Noble. The expense rating is very low. The difficulty rating for the basic build is low, but, the difficulty for customization and improvement rating is high. The primary reasons for including this in our inaugural project list was to produce a technology demonstration that young children could easily identify with…most young children like to draw! Our build was initiated in November of 2014.

[Photos/Status]   [Resources]   [Examples]

Create a Polargraph exhibit that consists of a microcontrolled plotter for demonstration and manual-operated plotter for small children to experiment with.

Basic Functions Required

  • Generate GCode from image
  • Arduino sketch converting GCode to motor movements

Both are built into  Sandy’s Polargraph Server

  1. Download and Unzip the most recent release
  2. Move the UNO version of the sketch to the Arduino sketch folder
  3. Move all relevant libraries to library folder
  4. Upload sketch to Arduino
  5. Run “polargraphcontroller” program from controller folder of zip directory
  • Sayuni
  • Luke
  • Nathan
  • Caleb
  • Kevin

Tentative Schedule

  • Nov 08: Launch project. Discussion regarding basic operation and components.
  • Nov 15: Solidify gondola design and test it.  Assemble prototype for manual system.
  • Nov 22: Test Arduino shield for stepper motor control.
  • Nov 29: Assemble and test micro-controlled system.

    Details

    Connections Adafruit NEMA 17 stepper connections (Red, Yellow, Green, Gray):
    1. Red-Yellow…M1
    2. Gray-Green…M2
    3. Green-Gray…M3
    4. Yellow-Red…M4

    **2nd stepper wires are connected in mirrored order from the 1st stepper. Install “power jumper” on motor shield. Power Arduino with 9V-1A supply. Power shield motors with separate 9V-1A supply. Software

    1. Upload “polargraph_server_a1″ sketch to Arduino
    2. Open “polargraphcontroller” program from controller directory.
    3. Connect to hardware by “setup” – “Serial ports”…if not there, unplug arduino, close controller, re-plug arduino, open controller and try again.
    4. Update all parameters in the “setup” tab.
    5. On input tab:
      • Toggle the “command queue” from red to green when you want the machine to move.
      • Use “move to point” to verify machine correctly knows top/bottom/sides of paper.
      • Load image file
      • Generate Pixels
      • ?
  • Dec 06: Install and Test pen-lift
  • Dec 13:  Refine manual-operated system. Choose pictures for motorized demonstrations.
  • Dec 20: Install manual-operated system in library for beta testing.
  • Dec 27: Christmas Break
  • Jan 03: Refine the exhibit design with beta testing in the library.
  • Jan 10: Install exhibit in Children’s Museum.

Photo Record and Status

pic coming soon. Quick and Dirty Prototype. Problems:

  1. tool depth is unpredictable
  2. tool is loosely held
  3. tool pressure is uncertain
  4. exchanging tool requires knowledge
  5. tool must be modified to fit
  6. chain isn’t anchored on tool axis
  7. base is easily caught on bumps
  8. tool will catch on edge of paper
  9. plane of base contact is uncertain

1/4″ Polycarbanate gondala was cut in shape of CD. 1″ Teflon spheres for feet (3rd foot is the drawing implement). 1.5″ Cylinder plastic tube recycled for pencil guide. Light duty wood clamp to hold pencil. Ball-chain end in a loop that is secured with a zip tie

Problems:

  1. tips and rocks (should widen feet placement)
  2. high C.G. (move weights to base)
  3. chain drifts up/down on guide shaft
  4. tool will catch on edge of paper
  5. tool is limited to approx. pencil size
Polargraph gondala drawing a bitmap image

1/4″ Polycarbonate gondala cut in shape of CD. Glass marbles loosely captured in holes, retained by thin sheet of plastic (CD spacer). Thin plastic bent with heat to attach ball-chain. Brass plumbing bushing used as pen guide. Light duty wood clamp to hold utensil.

Problems:

  1. Needs a pen-lift to improve performance on most images (click for example on vector image)
  2. Clamp needs 2nd attachment screw to ease utensil installation
  3. Ball-chain retainers have fractures at the bend (need stronger parts for public use)
DIY polargraph gondola

Pros: Pen lift is effective. Fewer parts without balled feet. Larger guide tube accommodates wider range of drawing implements.

Problems:

  • Pen-lift motor robbed essential power from stepper motors. The system became unstable and inconsistent. We now use a separate power supply for the steppers.
  • Weight distribution and height of chain force causes tipping/wobbling. Carefully, minimizing the pen height helps with this problem some. Adding washers (approx. 40% of assembly weight) to the bottom lobes helps some.
  • Ball-chain isn’t perfectly captured and occasionally slips out of grooves during maintenance.
  • Pen-lift foot cannot pass over edge of paper when “down.” Therefor, home position must be on the page and reduces the printable space considerably.
DIY polargraph gondola parts

A. 1/4″ polycarbonate B. 1/2″ copper tube C. Tower Pro Sg92R D. old CD E. 1/16″ plexiglass F. water-hose seal G. plastic clamp

A was cut with jig-saw and sanded smooth. B is pressed into a 5/8″ hole (heat and hammer required). C is mounted with screws into side of A. D was pressed onto B. D was required to prevent E from getting caught on servo motor and wire. E was first bent with heat and then drilled-slotted to receive the ball-chain. F is a rubber washer that presses onto B to hold E in place. G is mounted by replacing the manufacture’s axle screw with a much longer machine screw. The new screw threads into the base, A, and holds G 3/4″ above the base.

DIY polargraph gondola assembly

under development
…that we experimented with and what we found.

Mod #42HS4013A4

57 oz-in 12V 1.3A NEMA 17

Pros: availability (free 2-day shipping arrived in time for club experimentation)

Cons: Exceeds current capacity of Adafruit motor shield (v 1.2)

Observation: Heat buildup on motor shield cannot be ignored for even short run times. Shield needs to be modified by piggy-back chip or heat sink or both.

Adafruit 12V 200x stepper Product #324

Pros: It has proven compatibility with Adafruit motor shield (v 1.2).

Cons: The 3mm mounting screws are difficult to find.

Observation: Works well. However, we would like a less expensive alternative for smaller individual polargraphs. Also, the motor builds up considerable heat when driven by 12V for more than an hour or so.

28BYJ-48 (5V geared mini-stepper with driver board)

Pros: It is prolific and 1/4 the price per motor when purchased in sets. Can be driven by Arduino without a motor shield.

Cons: It is relatively slow. Will take some coding to integrate with PolargraphController software.

Observation: The low-cost goal demands that we explore further:

Video of latest version

Resources

Examples
Makelangelo 2
Detailed developer’s journal
Example of improved speed achievable when supplementing with micro-processor
Gondala design by polargraph creator

Help advance the design and make Design Decisions by replying to the comments below.

43 Comments

  1. Micheal, I have a three days swim competition, so I can’t attend Bot club!

  2. Sorry Micheal, I have tennis competition so I can’t attend this bot club, so sorry!

  3. I just want to make sure, we have botclub on this week Saturday right?

  4. Happy New Year to everyone, welcome to 2015!!! XD

  5. Merry Christmas everybody!!!!!

  6. Take a look at the Gondola 4 section. The pen-lift greatly improves the picture quality. However, the tipping/wobbling looks “messy” and I think it adds some unpredictability (might prevent the possibility of Norwegian pixels in the future).

    Also, mounting the servo in the front wasn’t as trivial as we thought. Let’s try on the top of the base (even though the weight will be off center).

    • Yes

      • Did I miss anything important?

        • You missed how to rebuild the Polargraph and that is all, and where have you been??

          • I had finals, region auditions, and visitors at our house. SO BUSY!!!

  7. Sorry Mwienen! I can’t go to the bot club on this Saturday, our robotic teacher, Ms. Pina have a paintball party, so I can’t go. But I will work on the robot on this weekend!!

  8. Take a look at the Gondola3 tab. IT WORKS!!! Looking at both types of drawings, we really need a pen lift mechanism.

  9. This Saturday (Nov 29th)we will look at the various software steps required to get from a digital image to motors spinning. The one mechanical piece of the puzzle we still don’t have is a sprocket that matches the ball-chain that we have.

  10. What happened yesterday? Sorry I couldn’t go.

    • We discussed the different types of electric motors as covered on Everything About Electric Motors. Please read take a look on your own. We then connected our first servo motors to the Adafruit motor shield in order to see what we’re in for.

      • Thanks, I’ll take a look at the link.

  11. Sorry I can’t go to Rotclub, I have to go out of town! I’ll work on my lady bug on Thanksgiving!

  12. Motor issues for Nov 19th

    1. electrical connections to Arduino motor shield
    2. mounting motor to drawing board
    3. mounting sprocket to shaft
    • We got the Arduino we you gave us working and that was pretty cool!!!!!. Tomorrow we are going to get the stepper motor hooked up and see if we can’t get that to work.

  13. One thing I wondered, although I know it far ahead from were we are now, is for the motorized one, are we going to have it remote control or where it figures out how to draw a given picture.

    • Take a look at the examples listed…

  14. Please look at the picture of Gondola 2 and its problems. If we really want to limit the tools to pencils/ball-points, then we can move the clamp closer to the base…maybe all the way (the white spacer block was need for typical markers). This will address problems 1,2,3. Please reply to this comment to discuss solutions to the problems listed for Gondola 2.

    • This seams like a good idea. It would limit to pens/pencils and help with balance, although I don’t get how it would limit tool depth. Also, if we did do this wouldn’t the thing that fits pencils perfectly have to be shortened.

      • Oops, I was looking at the wrong gondola design.

  15. I don’t think we should.
    It would be hard to make a pen up/down mechanism, plus we also have to make something to protect the holograph- so there wouldn’t be anywhere to mount it.
    Also, if you’re using the manual operator, it would be hard to use the pen up/down mechanism.
    Basically, it should work like an Etch-a-Sketch(which doesn’t have an up/down mechanism).
    We can always find pictures that you don’t have to lift your pen to draw.

    • I mean-I don’t think we should make a pen up/down mechanism.
      Sorry, I’m still trying to figure out how to use this!

  16. Design Decision 3: For the manual-operated system, How do we protect the system from the small kids while making it easy for a parent to change the drawing surface (either replace paper or wipe slate clean) and replace the drawing implement (for a color change or when depleted)?

    • What if the writing surface is like a giant clipboard with many papers clipped on to it? The “clipboard” will also have a clear plastic shield in front of it.
      That way, when the kid is done drawing, the parent simply had to un-clip the paper from the giant clipboard!There will be many more papers on the clipboard so you can use it many times!
      Also, on the last page on the clipboard, there should be a message like: “Sorry, we’re out of papers. Come back later!” or something.
      For the pen…I have to work on that one…but I know that the pen-holder has to have a custom fit so it can accept any type of writing utensil.

    • I’m sorry I couldn’t make it today, I had a region orchestra competition.

      • ok

      • We look forward to your input this week. We need to settle the gondola design via comments. At the club meet, we’ll move right along to motor issues.

        • The only motor issues I can think of are how much to turn and mounting. Are there others you have thought of?

  17. Design Decision 2: What will the “floor” of the Gondala be like? Some people have used flat disks (like a simple CD). Smooth is good. Relatively large is good (to keep things flat and stable). However, without “feet” the pen-up/down mechanism takes more design. Remember, if we have two Gondala feet and the pen serving as a third foot, it establishes stable/predictable contact between the pen and the paper. The downside of having feet is it requires more design to keep them from damaging the art/paper.

    • What if we used a paper or foam plate?
      A CD is good.
      For the feet-what if we use some of those sewing pines and position them so the round, plastic part head of the pin touches the paper?
      If you have no idea what I am talking about, I’ll bring some of the sewing pins next time we meet and explain my idea.

      • To add rigidity to the base, I made a CD sized disk out of a thicker material. It is more rigid and also allows for countersinking fasteners.

        The feet are now teflon spheres. If they are selected for the final design, I think we can find wood spheres locally that will work just as well.

        • i am pretty sure we are going use the big white balls for feet

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