motor – Engineer On The Loose

Drawbot electronics – test driving the EiBotBoard (EggBotBoard)

Feb 172014

As mentioned in an earlier post I have decided to use the Eggbot control board (EiBotBoard) to drive my drawbot. I’ve gotten the electronics up and running, mostly just plug it in, screw down the stepper motor wires, and plug in the pen lift servo motor. Here are some videos of the EiBotBoard in action.

Some commentary on why I am using the EiBotBoard. The EiBotBoard is a nicely integrated dual stepper motor, multi servo motor driver that accepts high level motion commands over USB from a serial console.

Description of the motors selected for the drawbot. A couple NEMA 17 stepper motors I had laying around in my parts box. They are 0.8 amp motors, well within the 1.25 amps the EiBotBoard can supply.

Motion demo of the EiBotBoard driving two steppers and a pen lift servo. The script that is running is posted below. I am using a cygwin command window to echo the commands to the USB virtual comm port. Keep in mind Windows enumerates the COM ports starting at 1 and cygwin enumerates /dev/ttySxx starting at 0. In the script below I am echoing to ttyS18 because Windows enumerated the COM port at COM19.

Finally more commentary on why I like using the EiBotBoard.

Commands running in a cygwin shell script. Script with comments below.
echo "v" > /dev/ttyS18 echo "sm,500,500,500" > /dev/ttyS18 echo "sc,4,6000" > /dev/ttyS18 echo "sc,5,26000" > /dev/ttyS18 sleep 1 echo "tp" > /dev/ttyS18 sleep 1 echo "tp" > /dev/ttyS18 sleep 1 echo "tp" > /dev/ttyS18 sleep 1 echo "tp" > /dev/ttyS18 sleep 1 echo "tp" > /dev/ttyS18 sleep 1 echo "em,3,3" > /dev/ttyS18 echo "sm,1000,2000,2000" > /dev/ttyS18 sleep 1 echo "sm,1000,-2000,2000" > /dev/ttyS18 sleep 1 echo "sm,1000,2000,-2000" > /dev/ttyS18 sleep 1 echo "sm,1000,-2000,2000" > /dev/ttyS18 sleep 1 echo "sm,1000,2000,-2000" > /dev/ttyS18 sleep 1 echo "sm,1000,-2000,2000" > /dev/ttyS18 sleep 1 echo "em,0,0" > /dev/ttyS18

Send the version command to the board, establishes communication with the board.
echo “v” > /dev/ttyS18

Move both steppers at 1/16 size steps (the default) for 500 steps each and take 1/2 second to move (500 msecs)
echo “sm,500,500,500” > /dev/ttyS18

Set the pen lift servo min and max values, 6000 and 26000, determined from experimenting with this servo
echo “sc,4,6000” > /dev/ttyS18
echo “sc,5,26000” > /dev/ttyS18

Each TP command toggles the pen position from up or down
echo “tp” > /dev/ttyS18

Set the stepper fraction to 1/4 sized steps.
echo “em,3,3” > /dev/ttyS18

Step the motors for sm, duration in msecs, number of steps motor1, number of steps motor2
echo “sm,1000,2000,2000” > /dev/ttyS18
echo “sm,1000,-2000,2000” > /dev/ttyS18
echo “sm,1000,2000,-2000” > /dev/ttyS18
echo “sm,1000,-2000,2000” > /dev/ttyS18
echo “sm,1000,2000,-2000” > /dev/ttyS18
echo “sm,1000,-2000,2000” > /dev/ttyS18

Disable the motor drivers to avoid over heating the motors.
echo “em,0,0” > /dev/ttyS18

Drawbot update

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Feb 092014

Not a huge amount of progress on my drawbot but I’ve stumbled across a couple interesting ideas I want to capture as part of this build stream.

I have printed a gondola and a couple spools. I printed this gondola and it looks good.

It holds a sharpie marker great, tight with just the right amount of tip poking out. It has good mount points for the cords and a place to put some weights on the bottom. The problem is, and I didn’t think about it before printing it, there isn’t a way to mount a pen lifter servo. I could probably rig something up that would work fine, but I’d rather have a designed in solution. So I’ll likely be printing a new gondola soon. This gondola will probably work fine for a TSP single line art but I want a pen lifter so I can do pointillist style images.

I also printed out some spools, the ones I mentioned in my earlier post, the ones makerblock recommended I shouldn’t use. They printed fine and I think I can glue them together to avoid the coming apart and unspooling problem. But they aren’t ideal, for a lot of the reasons makerblock pointed out. They press fit onto the motor shaft, no set screw, they are kinda narrow so you get cord build up changing the spool diameter. They looked good on paper but after printing and holding them in my hand I can see some of the issues makerblock pointed out. So I’ll be printing new spools.

On to the interesting part. I found a link on youtube to a guy who made a drawbot using the Eggbot hardware. So far I haven’t found any more details but at least someone tried, and succeeded, at this before.

Second, and I think more cool. I stumbled across a video for building a drawbot on the cheap. This guy uses some super cheap stepper motors, less than $5 USD each with motor drivers, simple 3D printed spools, and cup hooks for cord guides. No motor mounts, he just screws through the motor mounting tab into the wood drawing surface. Doing a quick BOM using the cheap motors and drivers, a super simple bare bones arduino clone, 3D printed spools, cup hooks or eyelets for guides, a cheap wall wart power supply, and a hand made or 3D printed gondola I think you could make a drawbot for less than $50 UDS, maybe less than $35 with some searching.

To me this is a super exciting way to introduce robotics to newbies. The drawbot itself is cool, people just seem to like watching the drawing appear physically. The cost is pretty cheap, it seems within the range of a learning or science project, and it’s super simple to build. I think a high school or middle schooler could easily assemble a simple drawbot in a day. Build up some kits and sponsor a build a drawbot day at your local school.

Drawing board, melamine coated shelf board from HD
Stepper motors with drivers
A cheap arduino clone, preferably already assembled to avoid soldering
Cables and wiring harness, preferably already assembled for plug and play
3D printed spools and gondola
Cup hooks and screws
Some fishing line
A sharpie marker

The software would need to be developed to drive it but that problem is being worked. I think this is a cool idea that could be pretty interesting for young wanna-be nerdlings.

Search DealExtreme for stepper motors, I’ve found some motors with drivers for less than $4 USD each.

Polargraphic Plotter – printing the motor mounts

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Feb 022014

I just finished printing both motor mounts for my work-in-progress Polargraphic Plotter / Drawbot / Plotterbot. I decided on these motor mounts on Thingiverse. They fit a NEMA 17 motor and they looked simple and easy to print. Although I am a little concerned about the print layers being parallel to the mount bolt holes.

I printed these on my MendelMax 3D printer in ABS. I printed the mounts one at a time and each mount took a little over an hour to print. The prints needed some clean up with a pen knife to trim off the danglies but after that they look good. The motor mounting holes line up nearly perfect and the mounts are good fit to the motor bodies. We’ll see how they hold up under load but if I use a washer on the mounting holes it should distribute the stress.

My MendelMax printer

A two-for-one special, 0.5 mm printhead off of ebay. It seems to print ok.

The motor mount finished and ready to remove from the bed.

A video of the motor mount being printed

Another part down. Now on to the filament spools….

Polargraphic plotter – parts and pieces

Tech 2 Responses »

Feb 022014

I’ve decided to use an Eggbot control board, the EiBotBoard, to drive my polar plotter.

Not for any particularly wonderful reason. The board costs right at $50, which is the cost of an Arduino uno R3 ($30) plus an Adafruit Motor Shield ($20).

It seems the software to drive a polar plotter already exists for the Arduino / motor shield combo. Eggbot board, not so much.

So I’m looking at the same cost and more work to use the Eggbot board. But hey, if it was too easy it wouldn’t be fun :). I like the form factor of the EiBotBoard and if I can get it working as a polar plotter I can add a little back to the community.

I ended up buying the EiBotBoard from Sparkfun, the stepper motors from Pololu (on black friday sale for $14 each), the power wart from Adafruit.

The motor mounts, filament spools, and gondola I’ll download from Thingiverse and print them myself.

I’ve decided on the following parts:

Motor Mounts