Robot, all wired up
If you’re just tuning in, I’m building an Arduino powered drawing robot. If you’re the least bit interested in making one of your own1 then please take this quick DrawBot poll to let me know what you’re interested in. You can come right back and check out all the nifty little details in my drawing robot project, promise.
Okay! I’ve finished designing, printing, and installing all the plastic parts necessary and wired up all the bits that need to be wired. Despite the big curl of rainbow colored ribbon cable, which I left in because I didn’t want to measure the cable for an exact fit and because it just looks pretty, the wiring is extremely simple. Each of the stepper motors I’m using has four leads which, through some connections and cables, make their way to the PolargraphSD case. Once these eight wires are connected and the robot supplied with power, you’re ready to start drawing.
Wiring detail
To help tame the wiring mess I lightly braided2 the motor leads and added a drop of hot glue to keep them in line. I made sure I left more than enough slack so I can remove the motors and move them around. On the left side of the above photo you can see a curved piece of plastic. I’m using an old version of one of the monofilament spools to somewhat contain the rainbow ribbon cable.
Wiring and connectors
As mentioned above, the wiring is exceedingly simple – four wires from two motor are connected to eight terminals on the circuit board. Insisting on the rainbow ribbon cable as I did simultaneously complicated and simplified this project. The simplest possible solution would have been to wire the right side motor directly into the terminal blocks on the circuit board, solder four wires to the four left motor leads and plug these newly extended wires into the circuit board and call it a day. It would have involved only four soldered jointed and it would have been a breeze.
But, I had a dream. A dream of a sweet looking awesome drawing robot. And this dream involved soldering 16 separate connections and 8 additional wire ends.
On the left and the right I soldered the motor leads to a 4-pin break away 0.1″ header. Since I didn’t have any brown heat shrink tubing, I decided to color code the motor leads by covering the green lead with a little green heat shrink, the brown with blue heat shrink, the red lead with red heat shrink, and the yellow with yellow heat shrink. If you’re following along at home, alwaysremember to put the heat shrink on the wire before you solder the connection. Once I had soldered the four wires to the 4-pin connector and shrunk the heat shrink, I added a really wide piece of black heat shrink which I shrunk around the whole thing. This way I can easily grab all four wires at the same time. I also think it looks nice.
Before doing this soldering I made sure that I knew the exact order I needed to wire the motors to the circuit board. In case you’re using the exact same setup as me, the colors are, from left to right: yellow, red, brown, green. If I had wired the motors directly into the PolargraphSD board, you would see them, again left to right, as: yellow, red, brown, green, yellow, red, brown, green.
I then took the 4-pin female-to-female connector cable I bought from SparkFun and cut it right down the middle. I took my 10-wire rainbow ribbon cable and pulled away the two least colorful wires leaving brown, red, orange, yellow, green, blue, purple, and light gray. The I soldered the cut ends of one of the 4-pin female connectors to the brown, red, orange, and yellow ends of the rainbow ribbon cable and the other 4-pin connector to the green, blue, purple, and light gray side of the cable.
I spent more than a little time debating exactly how I would include these connectors. Should I solder the motor leads to the female connector wires or is it better to solder the leads to male pins? In the end I decided that if I ever took this project apart I might one day need to change the order of the wires coming out of the motor. If they were soldered to female headers, my only solution would be to add more connectors in between or cut the female connectors off. Since I soldered a 4-pin break-away block to the motor leads, I could theoretically break the four pins apart at a later date with little effort.
I suppose I could have chosen to be slightly less paranoid/OCD about checking and re-checking the wire order when I was soldering. There’s no actual harm in accidentally swapping the order of one of those connections – I could always just swap the appropriate wires going to the terminal block on the circuit board and no harm done. However, it was important to me, for purely aesthetic reason, that the ribbon cable actually look rainbow-y when it was connected to the terminal block.
Besides using one drop of hot glue with each of the motor lead braid bundles, I also added an additional drop underneath the green-through-gray section of the ribbon cable to help keep it in line.
Finished, Mounted Robot!
This is what the robot looks like installed on my wall! I’ve plugged it in and powered it up, but drawing will have to wait for another night. It’s a little difficult to see, but there are four additional plastic parts installed in this picture which were not included in the first picture above. To simply installation and removal, I’ve bolted two white dovetail slides to the wall. Then two black plastic mounts slide onto the remaining dovetail slide on the top of the project box and onto the white dovetail slides on the wall. Tighten a few M3x16 bolts, and everything is solidly in place! ((Just so you know, that the black cord running down the right side of the picture doesn’t really look like that. When I stood back far enough from the wall where the robot is installed, something was in the way which I didn’t want in the picture. When I smudged it out of the way I had to smudge-out the end of the power cord.))
The paper roll seems to unroll pleasantly from behind the project box with just enough resistance so there’s no way it will just unfurl unexpectedly. While it was a little difficult to get started behind the box, ideally I won’t have to repeat the process very often. While I was mounting the project box on the wall I realized that the wall bows out slightly. I don’t think this will affect anything much – it’s just an odd quirk of my home which I noticed for the first time.
I’m very much looking forward to starting a drawing tomorrow. I’ve got several in mind which I’ve prepared in anticipation of Maker Faire. :) While I’ve taken the necessary steps to fine tune the steppers by adjusting the potentiometers, I’m sure they will both need to be dialed in. Even once I’ve gotten a successful drawing done, I foresee additional room for improvement in this project. The pen holder/gondola is a constant source of innovation. I’m looking forward to trying out several designs. I’ll need to install the servo motor so I can do drawings with pen-lifts. Lastly, I think Sandy is hard at work developing the code to support endstops. I think this would be a really helpful addition as it will allow for automatically calibrating scripts to run just before a drawing. Edit: I almost forgot! I also need to experiment with different kinds of pens to find out which ones work best on nearly vertical surfaces.
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