Tuesday, August 2, 2011

DIY Telepresence Robot - Part 3

Building the Head

Robot Head

Construction of the robot "head" is the the most delicate part of the project.  It involves the creation of a custom bracket to mount the laptop on the Eagletron PowerPod.  The PowerPod forms the neck of the robot.  It is a small motorized platform that can rotate both horizontally (pan) and vertically (tilt).  The mounting platform itself measures about 2"x2" across and comes with a removable camera mounting bolt that can be used to attach a variety of video cameras.  To avoid making modifications to the netbook shell, the mounting bolt will be removed and the netbook bottom will be attached to a flat platform surface using velcro.  (Adhesive tape can also be used but velcro allows the netbook to be easily removed and reattached)  At 2"x2" the PowerPod is too small to form a sturdy connection with the laptop using only velcro, so a larger mounting surface will be created using a thin sheet of aluminum.

Another reason to create the custom mount is to reduce weight.  The PowerPod is designed to support video cameras up to 3 lbs.  Our netbook is lighter than 3lbs, however its weight distribution is very different than a video camera.  A video camera holds all of its mass in an evenly distributed box with the center of gravity just an inch or two above the bottom.  Our laptop has an L shape when open, and its center of gravity sits high and towards the rear, so to avoid stressing the PowerPod motors we should ensure that the weight is well below 3lbs.

The easiest thing we can do to shed weight is to remove the battery from the netbook.  It's heavy and since we will be powering the netbook from the iRobot battery, it's also redundant. The Asus battery forms the lower rear surface of the netbook, so removing it leaves a large cavity on the bottom of the netbook instead of a smooth surface.  This cavity sits right below the center of gravity of the open netbook.  We will need to mount the laptop as close as possible to the center of gravity right under the battery cavity.

To provide support under the battery cavity we create an aluminum curve.  The flat bottom part of the curve will support the base of the laptop and provide a large surface for velcro adhesion.  The top part of the bracket will gently curve into the battery compartment to support the center of gravity.  To create the curve bend a 6.5" x 12" x 0.04" aluminum sheet around a 3/4" wooden dowel rod.  Then use a hack-saw to cut the two ends of the sheet to the proper length and a mallet and pliers to refine the shape.  (a vise and a table saw would have been helpful but I had neither.)  Finally file down the sharp edges to avoid scratching the laptop.

Curved Aluminum Sheet

Now the aluminum curve must be attached to the PowerPod.  Remove the 4 screws that hold the mounting clamps to the PowerPod mounting plate.  Measure and drill out four holes in the aluminum sheet that match the holes of the mounting plate.  The holes must be oriented so that the mounting plate will be centered laterally and sit as far back as possible on the curve.  The hole alignment has to be near perfect.  Create and use a paper template to ensure that the holes are spaced precisely and be careful not to let the drill drift.  Use a drill press if possible.  Attach the aluminum curve to the PowerPod with the four screws.

Use some electrical tape to pad and soften the top of the curve surface where it contacts the battery compartment to avoid scratching.  Finally stick a couple of wide velcro strips to the aluminum surface and to the bottom of the laptop.  The finished product should look like this.

Finished Platform

The netbook should be able to sit on the bracket in an open position without toppling it and the velcro adhesion should be strong enough to easily withstand tilting and shaking of the unit.

That completes the neck and head of the robot.  In my next post we will construct the tower "body" and attach the neck to the body of the robot.

Next -> Part 4: Building the Body