PlotBot: Building the Machine

With the research all done, I started thinking about how I wanted to build my PlotBot.
Having looked at the other designs, I found they were either mounted on a wooden frame and then a piece of paper is taped onto the wooden panel, or they draw directly onto a surface like glass or a wall. Given that the aim is just to make something that catches peoples eye, rather than making posters or drawings for people, I think the best course of action would be to use a whiteboard. I can get one reasonably cheaply, and the mounting is pretty much already sorted.

The whiteboard and mountings.

Once I had bought a whiteboard (600mm x 450mm) I started lining up the parts I had as to how I would mount them.
I had also bought 2 Pololu 1204 Stepper Motors and an Adafruit Motorshield v2 (AFMSv2). I did have a few concerns with these parts combined together, in that the motors only draw 600mA and the motorshield provides 1.2A per channel, therefore the motors might get a little hot if they start drawing more than they should – but we’ll see how it goes!

Roughly lining up the parts on a sheet of acrylic.

To mount the acrylic sheet to the whiteboard I used two of the mounts supplied with the whiteboard secured on the top of the sheet. These then hook onto the edge of the whiteboard, and the mounts on the side are adjustable to “lock in” the sheet to the sides of the board. Finally I decided to neatly mount the arduino and AFMSv2 in the center of the acrylic sheet.

     

     

I picked up two remote control car wheels at a local hobby store, along with 50m of fishing line, which would form the basis for my reels.

I found some nuts in the garage that fitted the inside of the wheel, and used Araldite (metal glue) to fill the gap around the stepper motor shaft hoping that this wouldn’t go wrong.

Araldite’s in, I was a little bit messy dripping it everywhere!

 With the luck of the gods, after leaving it 24 hours to cure I was able to punch the stepper motor shaft out of the nut, leaving a nice shaped hole. The advantage of this method being that I can very easily remove the reels and use the steppers in other projects.  

  

Now that I have the reels mounted on the steppers, I was able to complete the main build; mounting the steppers onto the acrylic sheet, and winding the fishing line onto the wheels – happy days!

  

 

 

 

PlotBot: Brief

So as time draws on we are getting closer to the start of the new academic year, and of course that means Fresher’s Fair!
At Kent we have several creative societies including SpaceSoc and their “Build a Rocket” sessions, Engineering Soc  with their focus on robotics, and TinkerSoc who want to help people build without limits.
With TinkerSoc it has become somewhat of a tradition to build and showoff a project at the fresher’s fair. In previous years we have had a laser engraver making custom name tags and furbies singing bohemian rhapsody, basically something to grab peoples attention and imagination.
Having seen a number of vertical plotters online I have decided now is the time to build one.

The standard vertical plotter is made up of 2 stepper motors, a servo, a motor controller and a microcontroller. By providing a stream of polar coordinates to the robot, the two motors can be wound in and out to move a pen across the whiteboard. This produces drawings where the pen never leaves the surface however that does not limit the styles of drawings that can be produced. Drawings can be developed further by adding a server or linear actuator to the pen carriage in order to push the pen off the drawing surface, thus allowing mush more freedom to implement different drawing styles.

Obviously we cannot draw above, or on either side of the motors, however the effectiveness of the plotter changes depending on the position of the pen carriage.
As such the most effective drawing area is a rectangle in the centre of the drawing surface with the tension on a cord being too low on either side, and the resolution is too low at the top due to the large angles. (http://2e5.com/plotter/V/design/

 

There have been a great many vertical plotters in the past, a great list can be found at plotterbot.com.
Overall there seem to be two different styles of drawing with vertical plotters.

Single line, where the pen never leaves the surface, is technically less challenging and can provide great results however you can be left with the odd scrawl across the surface that you didn’t want.

Multi line, where the pen can be lifted/pushed away from the surface, allows much more flexibility with regards to what can be drawn as the robot won’t scrawl connecting lines across the surface however does add the extra complexity of having a servo or linear actuator to push the pen carriage away from the surface.

Bearing in mind the saying, the more complex it is, the more likely it is to break.

 

Tinkerlog’s “Der Krizler” is definitely one of the more popular V-plotters out there, drawing on glass to amuse passers-by.

https://www.flickr.com/photos/8123185@N02/8181763825/

 

Dan Royer’s Makelangelo is a very impressive V-plotter. Commercialised as a kit, it’s reliability has been tested extensively!

Makelangelo 2.5

 

And probably the oldest V-plotter around from 1988 developed at MIT using lego!