12 SERVO 09.2016
unit is able to recharge two batteries simultaneously, greatly
easing the burden of keeping them operational. It will
certainly make my life easier (Figure 4)!
The Banshee three-axis controller is powered by its own
9V NiMH battery. I already had a couple of these, so I
should always have one powered up and in reserve.
All of the other components operate on their own
power supplies. The light-up brain uses three watch
batteries; the LEDs and the wireless microphone use AAs;
and the speaker, GoPro camera, and phone are recharged
via USB. I think the biggest challenge in operating Jarvis will
be making sure all his batteries are kept charged!
Servos — My servos of choice come from Hitec. When
I first started building my own animatronics, they are the
ones I used and I have become very comfortable with
them. They have been extremely reliable and have done
everything I have reasonably asked of them. The variety of
options they offer means I can always find just the right
combination of features and price to fit my build budget.
The output shafts, connectors, and direction of rotation
can vary between brands, so it is less complicated if you
pick one brand and stick with it.
I selected the Hitec HS-5485HB servos for this project
(Figure 5). I would be powering these at 6V; at that
voltage, they provide 89 oz-in of torque. This is
compounded when combined with the SPG400A-CM
gearboxes from ServoCity, and they provided all the power I
required. By switching the gear ratios, you can achieve a
variety of torque ranges and speeds. It is a tradeoff, so pick
the combination that best fits your needs.
I had started with the 2:1 gear sets since my
requirements did not call for additional torque. However, I
found that even though these are digital servos, I could not
slow them down enough to get the smooth motion I
wanted. I switched to the 5:1 ratio gears for the elbows
and the 7:1 sets for the two shoulder joints. The slower
speed gave me the fluid movement I sought.
Linear Actuator — The addition of a RC micro linear
servo from Actuonix Motion Devices (formerly Firgelli
Technologies) was instrumental in solving the issue I was
having with the head nod (Resources).
Moving the head assembly ended up to be an
unexpected challenge. I designed the mechanism so that
the attachment point for the head would be in the back.
This allowed all the components to be visible and
complemented the Steampunk look I was after. After
making all the decorative and electronic additions to the
head, it ended up being much heavier than I had planned.
Even with the addition of a spring to take a bit of the
load, the servo I had planned on using could not handle it.
The solution I came up with was to use an RC linear servo
(Actuonix model #L12-30-50-6-R). I had plenty of room to
mount it and the added torque was up to the task (Figure
6). These actuators use the same wiring harness as a
standard servo, and function in the same manner. Since
they provide a linear motion instead of a rotary motion,
they can offer another alternative when you are designing
your mechanisms. I have found them to be very easy to
work with and they have solved a number of design
challenges for me.
I still incorporated the Actobotics servo block, but
replaced the servo with a broken one (my fault, not the
servos) from my spare parts bin.
Head Construction — Initially, I had planned for Jarvis
to have a very robotic design that would incorporate many
Figure 6. This RC micro servo has what it takes!
Figure 5. Supercharged Hitec servos and gear sets.