VolksBot Omni: A Holonomic Robot Base Using only Robotis Dynamixel Servos

VolksBot Omni Robot Base

I recently learned that the holonomic mobile base developed at the University of Bonn's Autonomous Intelligent Systems Lab (NimbRo@Home) for the Dynamaid robot has become commercially available.  It is officially called the VolksBot Omni and is being sold in Fraunhofer's VolksBot line for 9000 EUR (~$11,700 USD).  Fundamentally, the VolksBot Omni is a powered-caster omnidirectional robot base (similar to the PR2 or Justin robots), except that its actuators are exclusively Robotis Dynamixel servos -- four modules, each with two EX-106 servos for drive torque and one RX-64 for module steering. The base is fairly light weight (around 5kg), but sports a 40x60cm chassis that supports a 20kg payload.  It has a top speed of 50 cm/sec, is controlled via USB, and has ROS / Player drivers.

Of course I like this design; it's no secret that I'm a big fan of Robotis Dynamixel servos -- I'm responsible for their open-source drivers (and ROS interface) previously documented on Hizook.    Anyway, to put the VolksBot Omni price into perspective, the combined cost of the servos alone is more than $5,100 USD -- 8 x Robotis Dynamixel EX-106 (at roughly $500 ea) and 4 x Robotis Dynamixel RX-64 (at roughly $280 ea).   I'm really curious about how the servos are integrated into the powered caster modules.  Perhaps some more detailed photos or documentation of the mechanism will be forthcoming?  In the meantime, photos of of the base will have to suffice (below).  Incidentally, the NimbRo@Home folks have a history of putting together cool omnidirectional bases -- eg. the Roomba QuadDrive.

VolksBot Omni robot base


The VolksBot Omni provides mobility for the Dynamaid humanoid robot that was developed by NimbRo@Home and demoed at ICRA 2010 and RoboCup@Home 2009-2010 (pictures and video below).  

Dynamaid robot atop VolksBot Omni robot base  Dynamaid robot atop VolksBot Omni robot base


A paper by Stuckler (et al.) entitled, "Dynamaid, an Anthropomorphic Robot for Research on Domestic Service Applications" has this to say about Dynamaid's omnidirectional base:

Dynamaid’s mobile base consists of four individually steerable differential drives, which are attached to corners of an rectangular chassis with size 60×42cm. We constructed the chassis from light-weight aluminum sections. Each pair of wheels is connected to the chassis with a Robotis Dynamixel RX-64 actuator, which can measure the heading angle, and which is also used to control the steering angle. Both wheels of a wheel pair are driven individually by Dynamixel EX-106 actuators.

The Dynamixel intelligent actuators communicate bidirectioanlly via an RS-485 serial bus with an Atmel Atmega128 microcontroller at 1 Mbps baudrate. Via this bus, the control parameters of the actuators can be configured. The actuators report back position, speed, load, temperature, etc. The microcontroller controls the speed of the EX-106 actuators and smoothly aligns the differential drives to target orientations at a rate of about 100Hz. The main computer, a Lenovo X200 ThinkPad notebook, communicates over a RS-232 serial connection at 1Mbps with the microcontroller. It implements omnidirectional driving by controlling the linear velocities and orientations of the differential drives at a rate of 50Hz.

For navigation purposes, the base is equipped with a SICK S300 laser range finder. It provides distance measurements of up to 30m in an angular field-of-view of 270?. The standard deviation of a measurement is approx 8mm. Two ultrasonic distance sensors cover the blind spot in the back of the robot.

Overall, the mobile base only weighs about 5kg. Its maximum payload is 20kg.



It looks like the NimbRo@Home folks from the University of Bonn have been busy:

Our cognitive service robot Cosero became operational in Fall 2010. Cosero has an eight-wheeled omnidirectional base (12 DOF), a movable trunk (2 DOF), two anthropomorphic arms (7 DOF each), and a movable sensor head (2 DOF). Its arms are twice as strong as the ones of Dynamaid.

The robot is equipped with four laser-range-finders, a Time-of-flight camera, two color cameras, and a directional microphone.

Cosero: Cognitive Service Robot from Nimbro@Home (University of Bonn)  Cosero: Cognitive Service Robot from Nimbro@Home (University of Bonn)

Cosero: Cognitive Service Robot from Nimbro@Home (University of Bonn)  Cosero: Cognitive Service Robot from Nimbro@Home (University of Bonn) 

—Travis Deyle

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