I have been enjoying building drawbots of late. I find that they are a great way to learn about motion control systems, robotics, machining, and programing. Plus you know, robots that will do my bidding, how can you go wrong.
My next project is going to be a scaled up version of my pen plotter, this time capable of drawing on a sidewalk. Now because I don't want a 6' linear slide sticking out the front of my contraption, I am going to instead use a series of levers to get an approximate straight line that stays parallel to the ground. Here is an animation:
This linkage was designed in Linkage Mechanism Designer and Simulator an AWESOME free bit of software by David Rector. It is a wonderful program for working out linkages, and a massive improvement on my traditional cardboard and pins method.
To give you an idea of scale, the plan is to build this so that it will reach out about 6' when extended, giving me a drawing area of about 7'x4'
The construction is going to be fun, I am using 1"x1" alumium tube with 1/8" walls (Yup, despite the fact that I am in Canada a lot of stock is still sold in imperial measurements, its all arbitrary anyway really). Rather than just drilling a hole through the aluminum and bolting it I felt the need to go fancy and use sintered bronze and steel bushings press fit into the tubes. This reduces friction and makes it a lot more durable.
It took me a bit to work out how to get an accurate hole for the press fit, it has to be done to about 1/1000th of an inch tolerance (oh yeah, my milling machine is imperial as well). So if someone else is in the same boat here is how its done:
Only use this tool on a milling machine, drill presses don't have strong enough bearings to hold up to the offset and out of balance cutting forces this tool creates. Unless that is, you like excitement.