Friday, August 5, 2011

DIY Telepresence Robot - Part 4

Building the Body

Construction of the body frame is an easy task because of the simplicity of working with the EZ Tube construction system.  The body design has to be as light as possible but strong enough to withstand the weight and stress of the head.  I considered using Styrofoam, PVC pipe, and even wood, but these materials were all heavier and bulkier than I expected and not nearly as sturdy as aluminum.  It would have been necessary for me to build a "box" like structure to gain the required rigidity.  Aluminum allowed me to simplify the body down to just a single strut and the EZ Tube part dimensions, shapes, and ease of assembly coincided exactly with what I needed.

The body is formed by creating a support strut and mounting base from the EZ tube parts.  First cut a 30" length of tube using a hack-saw or table saw.  This will be the vertical shaft and its length will position the robot head at just the correct height to talk comfortably with someone seated at a desk.  Now cut two short 3 7/16" lengths of aluminum tube and use them to attach the three composite T connectors so that they form an H shaped foot with one of the connector ends pointing vertically from the center.

The H foot should be wide enough so that when placed on top of the Create, the ends sit directly over the four 6-32 screw holes on the top of the Create.  iRobot conveniently designed the Create so that a five pound load centered between these four screws will counter the weight at the front of the unit and balance the Create robot almost perfectly.  Thus the mounting screws in the H foot should be positioned so that the vertical shaft  is perfectly centered between them.  Create a paper template of the screw holes and use it to mark, position, and drill the holes in the H foot.  Using progressively larger bits, drill a large hole straight up through the middle of the foot into the vertical connector large enough to shove a Type-A USB connector through.  We will use this hole to hide some of our cables within the aluminum shaft.

Next cut off the tips of the H foot (excluding the vertical one) since they don't add any stability, are not used as connectors, and are simply dead weight.  Then remove the cargo bay tailgate to eliminate more dead weight.  Gently connect the 30" shaft to the H foot.  DO NOT FULLY HAMMER THE SHAFT ONTO THE FOOT YET.  We only want a temporary connection for positioning.  Use 1 1/4" long 6-32 screws and thin washers on top and bottom to attach the H foot to the Create.  Be careful not to over-tighten or allow the foot to angle.  Use a level tool to ensure that the shaft is perfectly vertical.  If not level then use additional washers under the foot to level it.  The mounted foot should look this.

The next thing we will do is to create an attachment between the vertical aluminum shaft and the Eagletron PowerPod.  Luckily the PowerPod has a standard camera tripod mounting screw hole on the bottom of it, so all we need to do is create a sturdy screw mount for it.  To do this we take the EZ tube adjustable foot end-piece and remove the foot.  That leaves an end piece with a perfect little hole in it.  All we have to do now is take a 1 1/4" x 1/4"-20 bolt and push it upwards through the hole.  Now use a flange nut with the flat end facing upwards to lock the bolt into place.

Screw the PowerPod onto the bolt until it is fairly tight.  Turn the bolt in the socket and continue tightening until both the PowerPod and the bolt feel tight and locked into place and are facing straight forward.  Now apply some super glue to lock the bolt in position.  Finally, tap the end-piece into the aluminum shaft.  You may need to use a knife to shave off some of the plastic to accomplish this.  The finished end piece and bolt should look like this.

We are now done with the structural elements of the robot.  In the next post we will implement the electrical system so we can power the laptop from the Create battery.