Tinkerdays 2012 | prototyping a wall plotter

Tinkerdays 2012 | a 60 hour prototyping event

Already the second day of tinkering and we are starting to make progress on our current project, "the hemiphterograaf".
We are creating a wall plotter / printer based on the kritzler schematics.

Check http://tinkerdays.wordpress.com to keep yourself updated, join the conversation, tell us what you want us to improve and let us know if you think we should write an extensive tutorial.

Today will be exiting.

  • With the use of thermoplastics (beats lego & meccano for certain applications) we will tinker the pen holder.
  • install the arduino blue tooth shield
  • update the testcode to synch the steppermotors
  • complete the stand on which we will secure the steppermotors (which hold the penholder via thread)
  • install the stepper motor pulleys (and pray they work, if it does, it deserves its own tutorial, more on this later)

current state: we'll continue the day at 24/07/2012 | 12:30 GMT

hemiphterograaf V0.2.1 closeup

to keep our cool

Let me know if you need any advice... I have currently replaced the salvage motors with gear reduced steppers but haven't hung it and run it yet.. Should have 64x the resolution.

It's a simple and fun project. The hardest part is the unidirectional version of bresenham's line algorithm.

When I rehang mine (I use 48" spacing) I will also try the idea of replacing the dry erase pen with a couple of other marking devices, including a salvaged inkjet printer head and maybe even a dremel mount...add a plunge depth and you have a suspension router.....

Thanks for the offer focalist!
Within an our or so, i'll update our latest findings and post some new photos.

Here's my thread from last year on the Thinganator...


By the way, in the end, to compensate for radial distortion, I went with Heron's formula and successive approximation. In both the Bresenham code and the Heron code, the key is error inclusion math.

Is there a special reason to cal your project as "the hemiphterograaf"?
Also I want to know whether that the circuit that is available in lower right hand corner of the first picture similar to the circuit which is shown in the bottom of the picture that I have posted in below.



Do you mean the way the breadboard is connected?
Either way, the arduino is the same one, and the breadboard in the first picture is a later version with all the wire connections made to the h-bridge chip. If this is not what you wanted to know, please clearify further :slight_smile:

@ focalist
Thanks for the link to the thread.

We have build the test setting by now and are doing the math ("Code wizard" Mark that is) as I type this (;
Also the Fritzing schematics will be online (very much) later this night as well as the some new photos.
FYI, the test setting is (only) a ± width 24 x heigth 30 cm. canvas.

I have updated the blog

with some pictures of the current test setting
(stand, pulleys, penholder, wires, the whole sjebeng)
Currently updating the .ino

A couple of thoughts...

Your pulleys are going to become a problem as is the thickness of the cord. The thickness will make it wander all over as it winds on the spools. I would suggest something more pulley like, I glued washers to a nut.. And thinner line. I found 12 pound fishing monofilament line to be easy to work with.

Assuming you are not going to put in limit switches, I would also suggest a four way navigation pendant so that you can easily set to 'home' position.

As you can see, without radial compensation, horizontal movement actually ends up curved as a function of the three tensors (right, left, and gravity) instead of the two tensors which exist if the system moved the pen with, say, a gantry or other two tensor solution. That is where Heron's comes into play. The pen location is the vertex of two imaginary right triangles formed by the vertical tensor of gravity. Heron's formula allows you to calculate the height of the triangle formed by a side and the vertical, which gives you your y coordinate, and then the x is calculated using Pythagorean. Just remember the third tensor, gravity, will form a right triangle to the horizontally equal tension lines. Gravity makes the invisible ninety degrees from the horizontally mounted motors. This by no means was my idea,but the idea of another wall plotter maker (have to find the link, it's in my stuff there someplace), but was written so as to perform all the math on an attached PC, the plotter being a printer device, the computer simply sent pulses to a parallel printer port on the PC, which was linked directly to the stepper motor driver, not an intelligent device. Arduino easily handles the math, and although I never did write a HPGL or GCODE interpreter in, doing so is pretty standard, they are delimited text files of coordinates. Parse and go. Even performing the math on the Arduino, I needed to put in delay statements to slow the movement speed to a reasonable pace, or there's a ton of jitter as the marker drags across the board. Slow and steady...

The offshoot of this is that the most efficient way I have found is to actually calculate the error for each possible right and left tensor (eight possible.. Plus, minus, or stay the same on the right and left tensor), and then move in the direction with the least error, and repeat until the goal error range is met. Lather, rinse, repeat.

Dammit, you just made me need to pull the Frankenbotic Thinganator out of the closet.....

And dedicated you seem :slight_smile:
Pull that Thinganator to 2.0

The suggestions you made in your post all seem valuable and they will surely prove themselves in the next phase of the project.
However, our tinkerdays have come to an end (for today).
Thanks again for your comments.

If you are like me, and it seems you are at least in this respect, you will find yourself drawn (ugh!) back to this project again and again. Simple, elegant, and a ton of fun.

Here's my suggestion.. This scales. As long as you have string, you have workable area. Replace the marker with a can of spraypaint actuated by a solenoid, or hack an automatic air freshener for the cam mechanism. Use short puffs to paint "pixels". Graffiti anything, whole sides of buildings. Of course, I would never suggest doing such a thing to a building that you don't own.....

I have this admittedly crazy idea of using a laser as the head, and "printing" on concrete and some rock by either ablating or oxidizing the top layers. Ablated graffiti on the side of a mountain or hydro dam? They would be trying to figure out how to fix it for years... Okay, I'd better stop, my evil is showing...

The thinganator is probably just the 1.0 outcome of your (crazy, as you admit yourzelf (; ) ideas.
Off course, you'd have to prototype before you can think about scaling the project to bigger size.

The setup (as we use it with two motors in the upper corners) would be suitable for prints / plots in areas that are beyond reach, such as a hydro dam.
I guess al you have to do is mount the "engines" on each side (high up), connect the spray contraption and it will do the job. Might have to do some calibration, but that won't be a problem (some sort of wireless connection would be necessary, and a decent power supply, etc.)

The marker replacement sugestions also come in handy. We were also talking about the use of a spray can. The use of a solenoid could indeed do the job.

The limits would really be the step size and the amount of weight of the "print head" plus suspension line. Both can be made much more easy to take care of by using a gear reduction system. The rest is just software...

I replaced the original motors with gear-reduced motors that are designed to operate venting for air conditioners and that sort of thing. They are very inexpensive, around two bucks each, and mate wonderfully with a ULN2003 darlington array for power switching. I believe most of the hobby vendors carry these now, and they are easily found on ebay.

They are usually labelled " 28BYJ-48 " followed by a voltage designation, either 5 or 12.

Here's the first vendor that popped up with the search on ebay, it's even already sold with the ULN2003 driver board. I just entered the search term, I'm not connected with any vendor! Anyway, this vendor sells them for just over three dollars with the board, including shipping (to USA anyway, not sure about shipping to UK other countries..) :

I still haven't put it back up on the wall and messed with it since... now you've relit the fire of interest in the project again :wink:

In any case, these motors are great because the gear reduction gives it a ton of torque, you cannot turn the shaft with your hand. Not sure of the final stall torque on it would be, but I suspect it's pretty impressive for the cost and size.

I've used them as drive motors for a three wheeled bot, to turn a drivescrew for moving a CNC table.. I bought a ten pack of them about a year ago for something like twenty bucks off one of the ebay vendors. Love them, highly recommended.

The limits would really be the step size and the amount of weight of the "print head" plus suspension line. Both can be made much more easy to take care of by using a gear reduction system. The rest is just software...

You can also use another stepper driver.

Most use these on their 3D printers, Pololu - A4988 Stepper Motor Driver Carrier at 1/16th stepping the resolution is pretty good.

I'll be posting a little vid, at the blog of the "wall bug" in action, in an hour or so.

update: video making of short -> Tinkerdays 2012 | arduino wall plotter - YouTube

Yes, i got a little over excited with the music...