A Dexterous Robotic Hand With 21 Independent Motors
BrainCo's Revo 3 packs 21 independent motors into a bionic hand with back-drivable joints, optional tactile sensing and SDKs for Linux, macOS and Windows.
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revo3
A Dexterous Robotic Hand With 21 Independent Motors
BrainCo's Revo 3 is a dexterous robotic hand
made for industrial automation, research, and robotic manipulation. It packs 21
independent motors into a compact bionic design, which gives it 21 active
degrees of freedom. A degree of freedom is one way a joint can move on its own,
and "active" means a motor drives it. The hand is 216 mm tall, and its
palm is 108 mm wide. The standard Bionic Silver style comes in left and right
versions, and the company says it can be customized in bulk.
Joints Laid Out Like a Human Hand
The company says the joint layout
"strictly adheres to human anatomical structures." The thumb has five
active degrees of freedom. Two are bending joints along the thumb, and three
are movements at its base: rotation, sideways motion, and bending. The rotation
lets the thumb cross the palm to meet the fingers, a movement called
opposition. The index, middle, ring, and pinky fingers have four joints each: sideways
motion at the base, then bending at three joints. BrainCo says this allows
"independent finger movement, collaborative grasping, and human-like fine
manipulation." The finger joints bend from 0° to 85°, and the thumb's base
rotates up to 105°.
Grip, Load and Reach
The hand can grip objects from under 10 mm to
over 150 mm wide. Each finger and the thumb can touch the palm, and the hand
supports the Kapandji opposition test, which measures how far the thumb can
move across the palm. Maximum grip force is 70 N, and fingertip pinch force is
20N. N is the newton, the standard unit of force. Total hand load is 20 kg and
four-finger load is 5 kg. Repeatability is 0.1° and motion speed is 3Hz. The
hand has fully back-drivable joints, which means an outside push can move them
without resistance.
Three Versions, Two Kinds of Touch
Revo 3 comes in three versions. The U21 has no
tactile module. The U21T adds touch sensing across the whole hand, with 0.01N
force resolution over a 0–25N range. The U21VT also adds fingertip
vision-tactile sensing, which combines vision and touch and can detect
deformation as small as 130 μm. Selected versions carry a distributed tactile
array that senses contact. The company says it can be used for grasping
fragile, soft, and irregular objects. All three versions share the same 21
degrees of freedom, back-drivable joints, and force figures.
Durability and Power Needs
BrainCo lists a joint flexing lifetime of more
than 1,000,000 cycles. The hand has been tested for drop collision, vibration,
static pressure, high and low temperatures, and salt spray. It runs on 24–80V,
with a maximum current of 10A at 24V. With 21 motors, current can spike under
heavy loads or when several fingers grip at once. The company recommends a
stable 24V DC power supply rated at least 100W. For the RS485 data link at 5M
baud, it advises using a shielded twisted-pair cable kept as short as possible.
Control Modes and Connections
The specification table lists position, MIT
force/position, admittance, and zero-torque modes. The detailed description
covers three: current, position, and MIT, and the company says more are coming.
In current mode, the controller sets motor current directly, so the joints can
move freely under outside force. This suits physical teaching, dragging the
hand without resistance, and wrapping around flexible objects. Position mode
suits replaying fixed gestures and moving at a constant speed. MIT mode mixes position,
velocity, torque, stiffness, and damping inputs. It suits contact interaction,
adaptive grasping, and reinforcement learning experiments. The hand communicates
at 500Hz over RS485, with a default speed of 5 Mbps. CAN FD and EtherCAT are in
development.
Software and the First Power-On
BrainCo provides C/C++ and Python SDKs for
Linux, macOS and Windows. It also offers ROS support and open-source demos for
robot application integration and model transfer. SDK means software
development kit, and ROS is the Robot Operating System, a common framework for
robot software. On the RS485 network, the default left-hand ID is 126, the
right-hand ID is 127 and the broadcast ID is 0, which controls every hand on
the bus at once. When powered on, the hand calibrates its position and opens
all fingers to find their starting points. The company warns that a held object
could fall at that moment and that calibration must run once before normal
control.
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