The 3D printing phenomenon had more or less passed me by. I had learned to use one at the TechShop in Raleigh, NC, but that wonderful resource closed days
after my course and I never got a chance to use their
machines. However, things changed when I got a chance
to use one at my new job. I’m a product development
engineer and had always just ordered the more
sophisticated high resolution SLA and SLS prototype parts
at my previous employer.
The new company has a more hands-on approach,
so they have their own MakerBot Replicator® 2X. These
printers cannot yet really replace the more expensive
prototyping methods for fine parts and appearance models,
but they can let you try out the basics of many designs
before spending the money on the more expensive
methods. The company also encourages employees to learn
to use the equipment and allows its use for the occasional
personal project ... I felt a bot coming on!
In the March 2014 issue of SERVO, I had looked at the
Pololu tracks system and had designed some different sizes
of drive sprockets to allow more variation in how the tracks
could be used. I had put the files for these new sprockets
up on www.shapeways.com and had a couple of small
six tooth sprockets printed by them. These smaller sprockets
can be combined with the standard 12 tooth sprockets
and 22 tooth rubber tracks to make an interesting wedge
layout (Figure 1).
I decided to continue something of a tradition in
combat robotics — my tracked wedge bot was to have a
cheese theme. I designed a main chassis with thick walls
and then added “holes” to give it a Swiss cheese look. The
“bubbles” in the cheese are simply subtracted spheres as
can be seen in Figure 2. Now is probably a good time to
explain how 3D printers can handle making thick wall parts.
You can print them 100% solid, but it’s usual to specify
how many layers in the skin you want and then specify
what fill you want. For my first chassis, I specified three
layers (each 0.2 mm thick) plus 20% fill.
The design uses the same small 500 RPM (at 6V) motor
and gearboxes I use in my Saifu kits, a Finger Tech Robotics
power switch, and a small 3S LiPo battery (Figure 3).
I protected the tracks with full side walls; those and a
cover for the battery, etc., are held in place with #4 screws
(Figure 4). The wedge itself is removable, and I can make
various configurations so that I can match the attachment
to the opponent like I do on my bigger bots.
Now, I have a confession to make. This bot was to be
my first Fairyweight, and I had it in my mind that this was a
250 g weight limit. It wasn’t until someone pointed out
that it is, in fact, 150 g that I realized my mistake. I decided
to press on, but make the bot an Antweight 1-lber instead.
My first attempt at printing the chassis failed when the
print did not stick properly to the bed of the printer, but the
SERVO 07.2014 41
● by Pete Smith
FIGURE 1. Track model.
BUILD REPORT: Printing Cheese