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General Hardware Setup
This guide will walk through the proper steps of setting up your gocupi with your own hardware, meaning you purchased (or built your own) gocupi board but did not purchase the available kit which includes all the necessary parts.
- Raspberry Pi
- gocupi board
- (2) 12v 1.8 degree or better stepper motors
- (2) spools
- (2) idlers
- braided fishing line (monofilament will stretch under tension causing much headache)
- gondola
- metric tape measure (yes, science calls for metric)
- We will assume that you successfully installed the gocupi source code as detailed in FIXME LINK TO TUTORIAL.
You will need to mount your stepper motors to the drawing surface, there are many ways to do this, the two preferred/popular being: FIXME PICTURES From behind the drawing surface with the shaft of the stepper going through the surface. On the drawing (offset from the surface with standoffs) surface with the shaft pointing toward the surface. Both mounting styles work equally well, the offset variant being more of a ‘mobile’ setup while the hidden motors are preferred for a more permanent installation.
The spool size contributes to time/resolution balance. Larger spools will increase the max speed of the pen, smaller will allow for a lower minimum step distance. The gocupi source will default to a spool size of FIXME which has been found to have a nice balance of speed and resolution.
Depending on the shaft length of your stepper motors you will have some options regarding the distance between your spools and the drawing surface. Good practice is to keep the line going from the motors to gondola as close to the drawing surface as possible without touching.
The further the line is from the drawing surface the more potential for backlash.
During the initial setup of the gocupi you will input the measured distance between the left and right spools into the ‘settings.xml’ file. To do this accurately the contact points between the fishing line and spools should be the end points of your measurement. FIXME PIC
As the position of the pen changes, so does the contact point between the fishing line and the spool. This causes problems with the gocupi as it is using a now an inaccurate value to calculate position. In attempts to curb this issue we use an idler pulley with a radius considerably less than that of the spool. The idler should be positioned in a place that will retain contact with the line no matter the position of the pen within the drawing area.
If you have access to a laser cutter or a 3d printer then design files are available FIXME LINKS you can also purchase either variant FIXME POLARGRAPH.UK STORE FIXME LINK TO OUR GONDOLA
There are many ways to attach the pen to the two lines, there are also quite a few things to account for when designing or choosing which style to use. Our 3d print/design was created for the Pilot G2 pen FIXME LINK/PIC OF PEN and will not allow for a large diameter drawing utensil. (i.e. a large dry erase marker)