Ethel is Born
It’s amazing the collection of parts you
compile after building combat robots for
several years. Of course for some of us, it is
difficult to part with a part because you
might find a new use for it one day. After
four years of waiting, in October ’08 I went
to the Robo-Development convention and
was given a VIA Nano-ITX 1000G
microcomputer as a door prize. A month
later, I pulled out a large pile of pillow block
bearings, one inch diameter axle shafts,
wheels, and sprockets, and laid them out on
the welding table. In this collection of very
used hardware was the essence of 12
previous 220-340 lb combat machines my
father and I had built and the seeds for a
new machine called Ethel were sown.
Ethel’s drivetrain is mounted to a
welded steel frame made from one inch
square steel tubing and 1.5 inch angle iron
that is used for the 12 pillow block bearing
mounting surfaces. The overall frame is 22
inches long and 20 inches wide. Ethel is laid
out using a 4WD skid steer configuration
with two Bosch GPA 750 watt motors (one
for each side). Each side consists of a motor
that drives a jack shaft with a 4.8-to-1 chain
reduction. The jack shaft then drives the two
wheels using another 4.8-to-1 chain
reduction. This gives Ethel a 23-to-1 total
gear reduction and about 368 ft lbs of total
available torque. I call this chain layout a
bow tie configuration since it resembles
the shape of one when you look at it from
the side.
With her 10. 5 inch diameter studded
pneumatic tires, she can carry about 814 lbs.
Ethel is capable of about 4. 6 mph. I figure that’s a pretty
safe maximum speed for her to use around humans. Ethel
has 6. 5 inches of ground clearance. Her tires are overhung
outside of the frame and also extend past the frame front
and rear for maximum obstacle climbing abilities. She can
easily climb over a four inch tall board.
Ethel is built for off-road use and rough surfaces. Her
drivetrain motors are powered by two 26 Ahr Powersonic
sealed lead acid (SLA) batteries wired in series to provide
24 VDC to a Vantec RDFR38E dual motor speed controller. I
had the chassis rolling and running under standard RC
(radio control) in about four days. Basically, Ethel was just
another proven super heavyweight (340 lb) combat robot
drivetrain design at this point. However, I intended for her
to play nice. Now it was time to build her computer system,
control electronics, and write the software to tame her
down a bit.
EVA
I had become aware of the VIA Pico microcomputer
boards from an article in the September ’08 SERVO
Magazine about a Johnny 5 robot and I was quite happy to
finally have a similar board of my own to play with. The
1000G Nano-ITX board Ethel uses is pretty small. It
measures 4. 7 x 4. 7 inches — about the size of a DVD — and
contains a 1 GHz Luke processor and supports 1 GB of
RAM. The board is capable of 1024 x 768 VGA graphics
plus stereo sound, and has a microphone input and aux
audio out. The board also supports six USB jacks (if you
purchase extra cables). I found a good source for VIA parts
and accessories at an online company called Logic Supply
and purchased a 160 watt ATX computer power supply
that runs off of 12 VDC for automotive use. I also added a
Western Digital 160 GB IDE hard drive and a Sony DVD
burner that I purchased locally at Fry’s Electronics.
SERVO 08.2010 41
