Tom Carroll can be reached at TWCarroll@aol.com.
They can even be modified as
continuously rotating for very small
robots. Weighing in at 4. 5 grams, with
11 oz-in of torque, this 4.8V servo is
tiny and mighty, and two of them
could fit end-to-end in 1-1/8” to
function as a little robot’s drive
motors. I plan to use these in a very
tiny robot claw.
Futaba also has two mighty-mites:
the S3153MG (metal gear) shown in
Figure 7, and the S3154 that has a bit
over 3/4” body depth each, and over
20 oz-in of torque. They weigh in at
0.4 oz and 0.27 oz, respectively. These
two servos and the Hitec nano also
make excellent sensor movers for small
claw/arm servos. I want to complete a
small four-axis arm/claw using these
four servos to demo at some of our
robotics meetings soon.
FIGURE 7. Futaba
FIGURE 6. Hitec
gram ultra nano
The Futaba S3150 shown in
Figure 8 is a small, 0.81 oz servo with
an impressive 51. 4 oz-in of torque. I
was testing it as a possible small robot
arm/claw motor. At 1.14” x 1.18” x
0.43” thick, it is easily contained in a
small arm. The Hitec HS-7115TH shown
in Figure 9 is ultra slim at only 0.32”
thick, and has over 54 oz-in of torque
at 7. 4 volts.
Another excellent slim servo is the
Hitec HS-5125MG that is considered a
‘wing’ servo as it is only 0.39” thick.
It’s great to also hide within a small
robot’s arm structure. It has over 41 oz-in of torque and is programmable.
mid-range servo with a 1.94 ounce ( 55
grams) weight and 133 oz-in of torque
in a 1.6” x .77” x 1.5” plastic case.
These are great robot servos (and
are the two mounted in the vise in the
Figure 2 photo). They have ServoCity
servo blocks mounted on them. These
mounts offer several advantages over a
basic servo in that they provide a much
more sturdy mounting capacity than
attachment to a plastic case.
A much more important feature is
the servo block’s ability to take 90% of
the strain off the servo’s shaft and
bearings. The outboard aluminum
bracket just under the flanged output
horn contains a large bearing. Figure
12 shows a close-up. This allows the
small servo to have a large reel,
rotating arm, or arm/leg joint to be
directly attached. It would be hard to
machine these in a shop for a cost
lower than ServoCity’s price.
The Futaba S9352HV shown in
Figure 13 is a 6-7. 4 ‘high voltage’
servo that has an impressive 305.6 oz-in of torque at 7. 4 volts, though I
tested it at 7. 2 volts and it seemed to
have the same torque capacity.
Figure 14 shows a Futaba S9156
high torque (340.3 oz-in) servo that has
metal gears. Operating at 6.0 volts
(NiCd battery use only) and weighing
2. 22 oz, this is one powerful coreless
motor servo. It is well adapted to
shoulder robot arm actuation where a
17 inch arm length could lift 20 oz if
the arm’s weight is spring
compensated. It actually bent a metal
Many servos fall into the
category of what I am calling
'mid-range.' The Hitec HS-
5565MH shown in Figure 10
is a standard servo that can
operate at 6-7. 4 volts with a
torque of up to 194.4 oz-in; it
weighs in at only a bit over
two ounces. It is
programmable and can
operate off two Li-Po cells.
The Hitec HS-645MG shown in
Figure 11 is another great
FIGURE 8. The Futaba
S3150 is a powerful
FIGURE 10. Hitec HS-5565HM
with horn assortment.
FIGURE 9. Hitec HS-7115TH.
SERVO 11.2012 77