Tag: drawbot

A few weeks ago I designed what I like to call “version 3.5” of my main drawbot platform. The improvements were still mainly a two dimensional design, with horizontal plates sandwiching things together. I found two main faults with this design, so I started working on improvements.

The first improvement was in the tool holder. The one with rubber bands proved to not be strong enough to hold tools in place easily. The rubber bands were a pain to work with. (They did work well enough to hold clay carving tools though, and we ran the drawbot across some slabs of clay.)

I wanted to move to a new design where a screw could be used to hold the tool. I know that the Egg-Bot uses a screw, and for the unfamiliar, it looks like this.

This is a great design, but for various reasons I chose not to attempt to copy it. Instead I borrowed some ideas…

The screw I’m using is a standard 8-32 screw with a wing-nut threaded on backwards to the head, and then a hex nut is added and tightened against the wing-nut. On the other end is another square nut to push against the tool, and again there’s a hex nut tightened against it.

In the above image showing the parts for the tool holder you’ll see the first and third pieces have holes for the screw to go through, while the second plate has a square hole to hold the square nut between them. So far it’s working quite well, and holds things without any slipping or wobbling.

Most of the rest of the plate is similar to the previous version, with the exception that now there is no bottom plate, as this mounts directly to the body.

The previous version relied on four screws and eight hex nuts to hold the motors between two plates. This was less than ideal for a number of reasons. First, there was no good way to align the motors and tighten things up. Alignment isn’t a crucial element of the drawbot, but it’s nice to have. The second issue was structural, as the 3mm wood was flexing quite a bit. I didn’t even try acrylic, but it probably would have been worse.

The new version of the motor mount is much improved! I’m sure I’ll have an issue with some of the other servos I’m using, as they aren’t all the same size, but it should be as simple as printing two new parts with the properly sized and spaced holes. Again, there’s only three parts because this mounts to… the body!

Here’s the new body platform. It’s got all sorts of mounting slots and such. The tool holder gets assembled and then attached to the body. (The “assembly” involves a lot of wood glue at this point.) The motor mounts are glued into place on the body as well. It’s nice finally having things rigid and not held together with hot glue and rubber bands. (Well, some things.)

At this point I’ve basically got a (semi-) generic platform with no specifics on electronics or components. You can fit any number of controllers and battery packs on it. That will probably change in the future as I choose the parts I plan to use.

The whole plate fits in a 280mm x 100mm area. That’s just under 12″ x 4″, which means you could fit three of them on a 12″ x 12″ sheet of Baltic Birch.

On to the next revision!

One of the issues I’ve had with the Friday Night Drawbot is the part that holds the tool has never been very solid. In early revisions I used corrugated plastic, and would just use an X-ACTO knife to cut a hole for a Sharpie, and it would work well enough, and when the plastic wore out, I’d replace it with a new piece. (The most recent body design failed miserably at producing a good pen holder.)

Since I’ve been using other things besides Sharpies, including pencils, charcoal, paintbrushes, clay tools, etc. I decided to design a proper tool holder.

I typically use Inkscape to design laser-cut things, but often visualizing a 3D object, even if it will be made from flat pieces, can be difficult, so I decided to use OpenSCAD to model it in 3D. It definitely helped me picture how it would be assembled. I also had the idea of exporting the “plates” from OpenSCAD into DXF files I could then use for the final laser-cut design but that failed miserably.

Here’s the start of my layout in Inkscape with the pieces laid flat. This let me get a good idea of the dimensions.

I wanted the tool holder to be adjustable, and handle tools from 8mm wide to 16mm wide. (In this top view, the blue circle represent the different sized tools, the yellow piece pushes the tool into a v-shaped piece to hold it tight.)

Here’s a top view of the layout with some guides to help align things. This is designed for 3mm Baltic Birch (though acrylic could be used.) The slots and tabs are all set for 3mm. There are no fasteners planned as I’ll be gluing it all together.

Another view from the top, this time with some pieces rotated 90 degrees to see how they will fit together.

All of the pieces laid out flat and ready to be laser cut. I used 3mm Baltic Birch which worked well using the Epilog Zing 40 watt laser cutter at the DCRL. (I also ended up adding yet another laser cutting workflow to my list. I now have three different methods depending on which of the four lasers cutters I typically use.)

Assembled with some wood glue, and using rubber bands to hold the tool in place. It works… sort of. I’m already planning improvements, so expect version 2 to arrive by next week. I may switch to a screw mechanism for tightening, which was my original idea, as the rubber bands aren’t working as well as I hoped.