Most machines seem to end up ready to draw A1 sized pictures at the most, so that means a machine around a metre wide.

I have built a machine 8m wide, and seen another 6m tall. Each have their own problems.

• Huge Portland Design Week Project is a good example of a big machine.

While there is not a practical limitation to the size of a machine in software, there are plenty of physical, mechanical reasons why things get tough at larger sizes.

• Access: It's a pain to have to go up ladders to get to the motors.
• Speed: A large machine doesn't go any faster, so it ends up taking days and days to detail a very large drawing. Path optimisations help here (Vector Optimiser), but there's no getting away from it. Any given pen has a certain top speed.
• Quality: A big machine has a bigger sweet spot, so quality is good overall. Because the weight of the gondola does not change with position, but the weight of the cord does change, then it is possible for the cord to pull the gondola around in undesirable ways. When the gondola is right down in one lower corner, the cord from the opposite motor is likely to be slightly curved, so pulling the gondola further in towards the centre than it should be. In fact, it is likely to be impossible to move the gondola right to the edge. This is true of small machines too, but the hanging catenary problem only becomes worse as machines get bigger.
• Set-up time & cost: A cross between the first two above. It takes longer to set up a machine using stepladders, then if it goes wrong it costs it all again. If you've got a roll of paper 2m wide, it's going to take you some time to prepare the next canvas when you forget to home and draw a stripe through your nice clean paper. The paper itself is expensive and difficult to handle. Do not underestimate this.
• Markers: One reason that spraycans are popular is that they can put down a large mark, fast. With pen-based drawbots, it is difficult to go much larger than standard marker pens. It is usually intended that large images are viewed from a distance, so up close detail is reduced. With drawbots with small pens, no such reduction in detail is possible.
• Orientation: Physically it's quite easy to go wide, and a lot harder to go tall - most walls are wider than they are tall. A Polargraph machine with counterweights needs to have a physical drop that is equal to, or greater than the diagonal distance across the machines surface. A 1x1m machine has a diagonal of about 1.4m, so the motors need to be able to drop their counterweights at least 1.4m. The distance from the ground should always be at least 1.4 times the machine width, so this makes wide, landscape-orientation machines challenging mechanically. Aha though, you'll see many machines use a pulley system to half the drop required. This is smart. A little hard to do with beaded cord, but not impossible.

The fundamental limitation in the firmware is that is uses a signed long integer to record the length of the cords, and the size of the machine. This is a 32-bit number, and has a maximum of 2,147,483,647. The basic unit of measurement is the motor step, so the machine can handle machines with cords of that many motor steps.

You can calculate the maximum machine size: 200 motor steps * 8 microsteps = 1600 steps per revolution of the sprocket. Each revolution extends 95mm of cord, so each millimetre takes about 16.84 steps. If you extended the cord until the maximum value of motor steps was reached (2,147,483,647 motor steps), then you would have paid out 127km of cord.

So that's what I mean by no practical limitation in software.