Robotic Hardware

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Joint work with Jeffrey Mark Siskind and Siddharth Narayanaswamy

This work has contributed to the following publications:


The arm reaching for a Lincoln Log The arm looking menacingly at the camera

Robotic platform

Our custom robotic platform is built around a novel two-surface wood housing, whose upper surface serves as a workspace. A 5-DOF manipulator arm is mounted on the upper housing surface while a 1-DOF pendulum arm is mounted on the lower housing surface. A head containing two cameras with individually controllable pan and tilt is mounted on the pendulum arm which allows the cameras to rotate 180 degrees around the workspace to image that space from a variety of viewpoints.

Endogenous sensors for fine motor control

A hand with two independently controllable fingers is mounted on the manipulator arm and contains a number of endogenous sensors in addition to the exogenous head-mounted cameras: a palm mounted camera, an ultrasonic range sensor, a computer-controllable laser pointer to assist depth estimation, and two independent force sensors on each finger, one on the inside surface and one on the fingertip. These endogenous sensors allow fine motor control through servoing.

Technical drawings and descriptions of the v3 robot

The robot is composed of Lynxmotion, Hitec and several custom parts.

Arm

The arm base is a standard Lynxmotion design documented on their website. We use only one servo, a Hitec HS-5995TG, and therefor we replace the ASB-13 bracket with an ASB-04B; we weld the L bracket to the base base instead of screwing it in for a stronger joint that vibrates less. The lower (shoulder), middle (elbow) and front (hand), servos are connected similarly to the Lynxmotion SES arm. We use different servos than the SES arm; the shoulder is a Hitec HS-985MG, the elbow is a Hitec HS-645MG, the hand and fingers are Hitec HS-5475. These servos have been carefully chosen to minimize the amount of vibration, and to allow the two most taxed ones to relax by having analog servos installed in those positions. More modern Hitec digital servos can relax but the ones we had available at the time could not.

We use different link lengths from the SES arm (AT-05 for both the forearm and upper-arm), and use a different spring configuration (we add one spring attached to the lower back servo mount screw and the hub screw at the top of the shoulder C bracket). The gripper is a custom design. To the end of the wrist L bracket (part of the standard joint configuration), we connect a C bracket, ASB-09B, on to which we mount two multi-purpose brackets, ASB-04B. On each of these we mount one servo, Hitec HS-5475, one offset bracket, ASB-11B, one hub, HUB-08, one tube, AT-01. We cover the grippers using a rubber end cap, REC-06. The servos are powered by an adjustable Mean Well SP-320-5 at 7 volts.

Head

The camera mount is built on top of an MAB-01, with an aluminum replacement milled multipurpose bracket, and a welded (not screwed) L bracket joint. Two ASB-516B are joined and connected to the base, at the 4th hole. At the other end, leaving two holes empty, one hub, HUB-08, is attached, along with 3 tubes, AT-06s, connected by end-to-end hubs. The tubes are machine pressed to fit more tightly onto the hubs so as to reduce vibration. Similarly one more tube, AT-01 is mounted on top. One channel, ASB-507B, is mounted on top of this assembly with one hub, HUB-08, perpendicular to the camera mount. At each end of the top of this channel one C bracket, ASB-09B, is mounted, bent to roughly 15-20 degrees so that the cameras will face the playing surface.

Two Logitech QuickCam Orbits, with their base disassembled, are mounted to the top of these brackets. The mount has one custom plastic connector, to which the USB connector from the Logitech base is glued; the connector then is screwed into the side of ASB-09B bracket, held in place by one screw which goes through both the custom connector and the USB connector. The previous operation requires the removal of several small pieces of plastic from the sides of the Logitech USB connector. The camera then slides into the standard Logitech connector, now attached to the mount, requiring no modifications to the camera eye itself and allowing the cameras to be swapped. This setup also provides for optional stereo sound recording via a microphone built-in to each Logitech camera base.

The robot is controlled via a Lynxmotion SSC-32 controller, which comes with both ample documentation and source code. Sensors are controlled through a Society of Robots Axon. Unfortunately the Axon has too few PWM generators to replace the SSC-32.

Housing

The housing is built of out two identical surfaces, connected and build to these specifications, the bases are screwed in to these specifications.