Creating Plexiglass Mounts for Robot Design

This Instructable details how to create laser-cut plexiglass plates for mounting electronic components to augment a robot. The methods described here can be applied to any robot, but I will be using a VGo Communications (http://www.vgocom.com/) telepresence robot. A telepresence robot is the equivalent to mobile video conferencing, where the user's face appears on the top screen, interacting with people and driving around a space. In the image above you can see Margo, a finished, augmented robot. To see what the robot looks like without any augmentations, see this image: http://images.fastcompany.com/upload/vgo.jpg

Materials and tools used:
- 1/4", 1/8", and 1/16" plexiglass
- Trotec Laser Engraver
- Sugru (http://www.sugru.com/)
- acrylic plexiglass bonding glue
- plexiglass polish
- calipers
- dremel
- crayons
- heat gun
- screws
- nuts
- many different electronic components, including a Hokuyo UHG laser, Sharp IR distance sensors, MicroStrain IMU, Microsoft Kinect, Logitech webcam, fitPC-2, Phidget interface board, Minibox power supply, cooling fan, tri-color LEDs, and more
- Adobe Illustrator

The steps in this Instructable are as follows:
1-5: Designing the plexiglass planes
6: Cutting and prototyping with cardboard
7: Embedding nuts and losing weight
8: Adding color with crayons
9: Putting it all together

Step 1: Mounting the Augmentation Mounting Planes

The name of this step is a mouthful, but you must think about how these augmentation mounting planes are going to fit and mount within the robot. The VGo telepresence robot has an interior space between the stocks that is about 104mm wide, 600mm tall, and 87mm deep. The stocks are also hollow with a few wires running through. To mount the plexiglass planes horizontal bars will be placed between the stocks, and the augmentation mounting planes will attach to the bars.

The inside of the stocks are dremeled to fit the 1/4" T-shaped mounting bars. This augmentation uses three bars: top, bottom, and middle. They each contained holes for screws to attach to the middle mounting plane (detailed in the next step).

Step 2: Measuring and Laying Out Components

Each component must be measured by using calipers, or some components have their measurements listed in documentation. The width and height must be used to figure out the 2-dimensional layout in terms of space, but the depth of each component must also be measured and taken into account. But, the most important detail is where the screw holes are located on each component.

Draw each component in Illustrator and begin to lay them out within the form factor of allowed space between the stocks. (from last step: 104mm wide, 600mm tall, and 87mm deep) Keep in mind which components need to be near each other, make sure they do not overlap (in the attached image in looks like some overlap, but some components are on the front of the plane and others are on the back), and make sure to account for extruding attachments such as USB connectors and other wires.

The VGo modifications are done in three planes: front (t-shirt), middle, and back. The attached drawing is just for the middle plane.

Step 3: Adding External Visual Appeal

If the augmentations are visible on the outside of the robot then whatever part is left visible must be made to be visually appealing. The front and back planes are outside of the middle plane. The front plane also serves as the front of the robot, and given that the robot is acting is the embodiment of a person, we want to make it look like a person. To achieve this I added a Hawaiian t-shirt which lights up with tri-color LEDs, not only for visual appeal, but also to serve as a status indicator.

The shirt was designed with a back, middle, and top. The 1/4" middle has the flower shapes cut out, where 2 layers of 1/8" etched flowers are inserted with LEDs. The 1/8" back and 1/16" top are used to hold the LED wires and to hold the flowers in place.

The back of the back plane was also designed with the same etched flower pattern from the t-shirt.

Step 4: Adding Three-dimensional Mounts (sensor Array and IMU)

After all of the two-dimensional planes have been designed, think about what other kinds of mounts your robot may require. The VGo telepresence robot also needed an array of sensors in the back. This was accomplished by using vertical planes, cut with square teeth to lock in to horizontal planes.

The sensor array was designed with top and bottom horizontal planes that contain holes for vertical planes to lock in place. The entire array mount connects to the back plane via a set of teeth from the horizontal planes, and the back plane connects to an internal mounting wall with a set of screws and nuts.

Another three-dimensional component was the MicroStain IMU, which must be mounted parallel to the ground. It sits on a horizontal plane with teeth that lock into the vertical middle and back planes.

Step 5: Adding Three-dimensional Mounts (kinect + Webcam and Base Laser)

Some three-dimensional mounts are not achieved only with plexiglass; some require physically modding the robot also. For Margo, the Hokuyo UHG laser, kinect, and webcam had to be added outside of interior mounting planes due to their size and orientation. The laser had to be added to the base and the kinect + webcam had to be mounted together on top of the robot.

The laser won't fit inside of the base, so the top panel of the base had to be dremeled to fit the shape of the laser, as it extrudes out of the top of the base. The mount for the laser also contains a Sharp IR sensor that is placed in the front of the base. It props the laser up by utilizing screw holes that already exist in the base and some interlocking horizontal and vertical planes. The top of the laser is orange, but by adding a layer of white Sugru over it it matches the sleek color scheme and look of the VGo robot.

The kinect + webcam had to fit into the form factor of the width of the robot, as you don't want to compromise the aesthetic look by adding something that is wider than the robot. The Kinect was made less wide by detaching it's longest circuit board (the board was then placed into the middle planes) and dremeling any parts of the metal case that exceeded the size of its other board. The webcam needed to look down towards the base of the robot so its mount is an angled box that locks into the webcam mount.

Step 6: Cutting and Prototyping With Cardboard

Before committing to cutting and etching plexiglass you can use cardboard to prototype your designs. It cuts quick and is very cheap, or just use the cardboard from the box that the plexiglass came in! The thickness of the cardboard may not be equivalent to the thickness of the plexiglass you plan to use, but it can give you a rough idea of whatever or not components will fit two- and three-dimensionally.

The laser cutter used was a Trotec Laser Engraver which interfaces with Corel Draw. To make my design plans cuttable I exported the drawings in Illustrator as Illustrator 8 EPS files. Cut lines are changed to red 0.004 thick lines, and etch shapes are changed to black fills.

The images in this step are of early prototypes, while the designs in previous steps were final designs, so they may not correspond.

Step 7: Embedding Hex Nuts and Losing Weight

Before cutting plexiglass, there is one very helpful modification to make. Given that each component will be held in with screws, you can design the mounts such that their hex nuts are embedded. This means that each mounting plane will actually be 3 planes: 1/16" with screw holes, 1/4" with hex nut shaped holes, and 1/16" with screw holes. By doing so the hex nuts get held within the 1/4" plane by the two 1/16" planes on either side. This also allows for each side of the planes to get etched with labels for where each component goes.

To hold all three layers together, clamp them and use acrylic bonding glue along the edges (it will sink into the rest of the surface area between layers). Acrylic bonding glue is also used to hold together any interlocking horizontal to vertical joints.

In any case a robot's motors controlling its movement are only so powerful, so we have to lose as much weight as possible. To do so perforation holes were added to the 1/4" planes, about 132 per square inch, losing roughly 45% of the weight.

Step 8: Adding Color With Crayons

To add more visual appeal crayons can be used to color the etched portions of the plexiglass. After the etched portions are colored use a heat gun to melt the crayon wax. This will make the color disperse and fill the etched area. On Margo this was done on the red flowers on the t-shirt, the white flowers on the back plane, and the etched labeling on the middle and back planes.

Step 9: Putting It All Together

Now all of the plexiglass mounting layers are cut, glued, colored, and all of the components are attached. The middle plane attaches to the mounting bars, the back plane attaches to the middle plane with screws, and the t-shirt attaches to the middle plane.

To stand the Kinect and webcam up on top of the robot, 3D printed stocks were made (not by me, so their design is not covered in this Instructable) that sit inside of the VGo stocks. They are placed on stands inside of the stocks, through a dremeled hole in the top of the stocks. A 3D printed top was also placed on top of the Kinect case. Plexiglass rings were added over the dremeled holes in the VGo stocks and the dremeled hole in the base for the laser. To hold them in place and make the holes look clean and sleek, Sugru was added under and around the rings.

That's it! All done. 9 months of work condensed to an Instructable (whoa!). This work could not have been done without the University of Massachusetts Lowell, the UMass Lowell Robotics Lab, Holly Yanco, and Kate Tsui, whose dissertation was the driving force behind augmenting this robot.

http://robotics.cs.uml.edu/