Interim Design Review: RosCoe

Travis McKenna

Current State of the Art

• Robots can navigate paths through obstacles, carry out simple tasks.

• Commercially available robots exist, mostly for research (Kobuki, Videre Erratic, PR2).

• Generally expensive

spectrum.ieee.org

PR2: $400,000

Turtlebot: $2000 Videre: ? Laser > $1000

Laptop Stays

• VGA connection on touchscreen, not on Rpi (no new screen).

• Can only interact with Pi through SSH without a compatible monitor.

• Rpi hardware probably not enough to run gmapping.

VGA Connection

Laptop Storage

• A stowable stand and container for laptop was requested.

• Cavity is 9.7” wide, 19” tall and 7.20” deep.

• Laptop is 13.54" x 9.40" x 0.98”. Weighs about 6 lbs. Base is thicker than screen.

Proposed Design

• First design based on tailgate, inverted.

• Arms made from three links, center link holds others in place when outstretched

• Links must be able to pass by/through one another

• #8-32 shoulders at joints.

Shelf

• Shelf designed to hold bottom half of laptop.

• Bent sheet metal is preferred construction, less tooling, cheaper, and easier

• Aluminum is preferred material, no rust, does not need finish or insulation from frame.

0.0019378” max deformation

0.0072752” max deformation

Alternatives

• Hold shelf with chain/wire.

• Use arm with hinges on perpendicular axes and stops (lecture hall desks).

• Add storage without desk or desk without storage.

• Leave laptop sitting on edge inside.

• Stash laptop in lower compartment.

Covering• Large weld beads exists

where columns meet base.

• Fastening material flat to the sides = poor appearance.

• Bend simple cornice to cover beads, tap holes, fasten with #8-32 screws.

Alternatives

• Cut the corners on rectangular panels to provide clearance for bead/stop short of bead

• Just cover, bend corners, leave gap, gasket/spacer.

• Grind beads down, possibly weaken.

• Continue with only foam panels, do not design new covering.

Rewiring/Organization

• Goal is to have control circuitry (3.3V-5V) mounted on board, modular.

Rewiring/Organization

or

5x

AC/DC to Pure DC• Batteries provide nominal

(inconstant) voltage.• Presently, AC inverter and

adapters are used, two stages of losses.

• To regulate/change voltage levels DC-DC, propose using buck-boost, Cuk, SEPIC or other method.

Buck Boost Circuit - www.wikipedia.com

Problem - Connections• Adapters for Laptop,

Router, and monitor have varying coaxial and proprietary ends.

• Lazy way, cut and splice AC adapters. May as well leave inverter.

• Solution might exist in auto connections, various cords.

• DC not standardized.

Is Changeover Worth It?

• Short Answer: Don’t know.• Inverters generally less efficient if using less than

rated power draw (greater percent of smaller power).

• Must add power draws from appliances, divide by estimated or empirical efficiencies at that usage to compare.

• If difference is negligible stick with inverter.

Sensors

• Options were ultrasonic, optical, stereo camera, laser scanner, Kinect, etc.

• Drivers exist for Kinect/Xtion (currently being used by Turtlebot/PR2) relatively cheap with many capabilities. Incorporated in ROS.

• Asus Xtion can be USB powered, is smaller.• Ultrasonic sensors were purchased last year. • How to incorporate ultrasonic sensors: as safety

curtain, generators for point cloud, or both.

Sensors

www.dfrobot.com

www.iheartrobotics.com

Control Systems

• Seemingly, at present, open-loop PWM control of BLDC motors is used.

• PWM applies constant voltage magnitude, varies duty cycle.

• Motor velocity is an estimate.

RPi

PWM

Sabertooth

Motors???

Closed Loop Control

• Hall-effect sensors, back emf, encoders, etc. can be used to read velocity to the control circuitry.

• Modulate input to motors based on sensor output.

• Control may have real-time requirements Rpi may or may not handle.

RPi

PWM

Sabertooth

Motors

Control

Sensor

Odometry?Velocity Command

Localization - Odometry

• GPS, without augmentation, only accurate to several meters.

• Common practice is to measure and record distance traveled (dead reckoning).

• Possible dual use of closed loop control sensor.

www.linengineering.com

Budget (tentative, incomplete)Qt Price ea. Total

For AC-DC conversion

Buck Boost Converter 3 15.41 46.23

Lenovo to Coax Adapter 1 15 15

Sensors

Asus Xtion 1 170 170

Covering

10" x 10' Roll Al Flashing 1 7.32 7.32

#8-32 screws 75 0.3 22.5

Questions