Prototyping a Boxy Robot

In my project-based Humanoids class at Carnegie Mellon University, I chose to design and prototype a simple delivery robot. For the sake of being able to fabricate it cheaply and quickly, the design was boxy and small. Once you learn how to make a box with a laser cutter, the possibilities become endless for the other things you can make using the same principles. This tutorial will take you step-by-step through my body design and prototyping process, with many pictures and screenshots along the way.

This design has 1 compartment that is meant to hold objects like textbooks and stacks of paper that are approximately 8.5"x11". There is a little wiggle room in the design, so it shouldn't be a tight fit. Underneath the compartment, there is space for electronics. This space can fit motor controllers, Arduino boards, breadboards, Bluetooth chips, etc. The area to the right of the compartment is saved for an opening mechanism that will not be covered in this tutorial.

Step 1: Software, Hardware, and Materials

Software:

In order to design your prototype boxy robot, you need to use a CAD program of your choice. I used SolidWorks because it was available to me at my university. Another option for those who do not have access is Autodesk Inventor, which is free for student use with a .edu email address.

SolidWorks

Autodesk Inventor

This tutorial will be done in SolidWorks, but should still be easy to follow for other CAD programs.

To format and send files to laser cut, I used CorelDraw.

CorelDraw

There are many other programs that are compatible with many other laser cutters.

Hardware:

I used an Epilog Legend 36EXT 50W laser cutter. Many other laser cutters are on the market, but this best served my needs in terms of engraving area, speed, and resulting quality.

Epilog Legend Tech Specs

Materials:

• 2x Acrylic Sheet (.1"x24"x30")
• 4x DC Motors
• 4x Motor Mounts
• 4x Wheels
• Hot Glue Gun
• Glue Sticks
• Whiteboard Marker
• Cardboard Boxes (small and medium)
• USB

I used OPTIX clear acrylic sheets that I found in my university's art store. You can purchase it online here or use any other acrylic you can get your hands on.

I used Mecanum wheels with accompanying motors and motor mounts from a bare-bones RobotShop kit which is now out of stock. A similar (and much more expensive) kit is still in stock here. Any wheels will work, Mecanum wheels simply served my purpose most effectively.

Step 2: Parts

To create the same boxy robot prototype as I did, you will need the following parts:

• 1x wheelbase
• 1x top
• 1x back
• 1x left side
• 1x right side
• 1x compartment bottom
• 1x compartment side

These parts will all connect to each other using tabs and holes. These tabs need to have the width of the material thickness. In my case, I used .1" acrylic, so my tabs and holes were all .1" wide. If your tabs or holes are not correctly sized, your pieces won't fit together seamlessly!

Step 3: Wheelbase CAD

The locations and dimensions of your motor mounts and wiring holes will change depending on the types of motor mounts and motors you have. Therefore, they are not given in these drawings.

The wiring holes allow you to snake your motor wires into the area underneath the compartment where the electronics sit. This way, you can power and control your motors without dragging your electronics on the ground.

Remember that if your material is not .1" thick, your dimensions will not be the same!

Step 4: Top CAD

Remember that if your material is not .1" thick, your dimensions will not be the same!

Step 5: Back CAD

Remember that if your material is not .1" thick, your dimensions will not be the same!

Step 6: Left Side CAD

Remember that if your material is not .1" thick, your dimensions will not be the same!

Step 7: Right Side CAD

Remember that if your material is not .1" thick, your dimensions will not be the same!

Step 8: Compartment Bottom CAD

Remember that if your material is not .1" thick, your dimensions will not be the same!

Step 9: Compartment Side CAD

Remember that if your material is not .1" thick, your dimensions will not be the same!

Step 10: Creating a DXF

Before moving on to this step, it can be useful to make a SolidWorks Assembly to ensure that your dimensions are all correct and that your parts all fit.

Now that you have all of your CAD files, you need to prepare to laser cut them. Most laser cutters use a .dxf file, which is a file containing vector data. The laser cutter will follow these vectors to cut out your parts. Oftentimes, laser cutters will be connected to standalone computers with restricted functionality. It can be useful or even required to save your DXF files to a USB drive to access them from these computers.

For each part, repeat the following steps:

• Click "File"
• Click "Save As"
• Navigate to USB destination
• Click "Save as Type"
• Click "Dxf (*.dxf)"
• Click "Save"
• Click "View Orientation" (1)
• Click the face of the part you want the laser to cut (2)
• Check the "Current" box (3)
• Click the green check mark (4)
• Click "Save"

I attached my DXFs below.

Step 11: Formatting in CorelDraw

Open CorelDraw. From the opening screen, click "File", then "New". In the window that pops up, name your CorelDraw file. I named my file boxy robot1 because I will be creating one file for each sheet of acrylic that I have to cut. Set the "Width" and "Height" fields to the correct dimensions of your acrylic sheet, and make sure that the units are in inches. Click "OK".

A blank document will appear on your screen. Click "File", then "Open". Select all of the DXF files that you have created for this project and click "Open". An additional window will pop up for each file. In "Units", select "English" then "OK" for all of the windows. All of your parts will now be open in separate tabs.

You will notice that there is SolidWorks branding at the bottom of each part. To delete this, click on one of the text boxes, hold down the "Shift" key on your keyboard, and click the other text box. Handles should appear at the corners. Press the "Delete" key and they should disappear. Do this for all of your parts.

After the SolidWorks branding is deleted, return to your first DXF. Starting outside the top left corner of the part, click your mouse and drag it outside of the bottom right corner. A dashed-line box will follow your mouse while you drag it. This is a selection tool. Make sure the box completely encloses all of the lines of your part. If you make a mistake, press the "Escape" key to remove your selection and try again.

Once the entire part is selected, you will notice many handles around each line. To avoid having to move and format these lines separately, click the "Group" button in the top ribbon. This will let you drag all the lines at once.

While you have the part selected, copy it. Then navigate back to your empty boxy robot1 file and paste it. Place it in the top left corner with at least 1/8" margins around the edges. Repeat this process with as many parts as will fit on your first sheet of acrylic. Make sure that the parts all have at least 1/8" margins on all sides.

Select all the parts in the document. In the top ribbon, select the line weight dropdown menu and choose "Hairline". This tells the laser cutter that you want to cut the lines rather than engrave them.

Use the same process to fit all your remaining parts onto your second sheet of acrylic.

Step 12: Laser Cutter Parameters

Click "File", then "Print". This will open a similar dialog box to printing a normal Word document. You will notice that in the top right tab there is a message that says "1 Issue". After we set up the laser cutter parameters correctly, this should resolve and say "No Issues".

Select your laser cutter as the printer. Then, click "Preferences" next to it.

The next window is Epilog software. There are several steps here, but the order doesn't matter. Just make sure to get them all!

• Check "Auto-Focus" in the "Options" section
• Select "Vector" in the "Job Types" section ("Raster" is for engraving)
• Set the "Width" and "Height" fields in the "Piece Size" section
• Set the "Speed" to 15%
• Set the "Power" to 100%
• Set the "Frequency" to 5000 Hz

The Speed, Power, and Frequency settings are all recommended for 1/8" thick acrylic in the laser cutter manual. There are other thicknesses and other materials listed as well.

Epilog Manuals

Click "OK". You should be returned to the print window. The top right tab should now say "No Issues". If it still lists issues, check your preferences again. Once no issues are found, click "Print".

Step 13: Cutting Process

I used wood and designs from another project for these example photos because clear acrylic is practically invisible under the glass lid of the laser cutter.

Once the document is sent to the laser cutter by clicking "Print", move over to the laser cutter. Locate the compressed air valve and make sure that it is on. Also, ensure that the laser cutter is turned on. Open the lid and place your acrylic in the upper left-hand corner. This is the origin or (0, 0) point of the laser cutter's area. Close the lid of the laser cutter. In the small front screen, you should see a job number and name. The job name should match the CorelDraw document name that you sent. If the names do not match, make sure that the laser cutter is properly connected to the computer and repeat the printing process. Press the green "Go" button once you have verified you have the right job on the screen. The laser should move over your material and auto-focus. After it is focused, it will move to its first location and begin cutting. Do not leave your laser cutter unattended.

Since the Speed, Power, and Frequency values on laser cutters are only recommended, you may need to cut more than once to cut completely through the material. It is CRUCIAL that you do not move your material or move any lines in CorelDraw. If you do, the cut could be ruined! The only things you will change are your Speed and Power settings. After the initial cut, you want to make quicker and less powerful passes.

For subsequent passes, increase the speed by 10% and decrease the power by 10%. Continue to make passes until you see that all of your cut-out pieces have "fallen" or "dropped". This will indicate that all of the parts have been completely cut through and that you will have no difficulty removing them. A completely cut piece will fall slightly below the level of the uncut pieces.

Be aware that as the laser hits the engraving area when it cuts all the way through the material, it could send up sparks or bright flashes. Don't be shocked, but do be ready to pause the laser cutter if the material is highly flammable because it may catch fire. There are two ways to stop the laser cutter. The red button pauses the cut and turns off the laser but stays in place. The job can be resumed by pressing the green button. The reset button pauses the cut, turns off the laser, and completely aborts the job. This means that the laser goes back to the origin and you have to restart your cut completely.

After you're confident that your parts have been completely cut through, remove them from the laser cutter and repeat as necessary until all of the parts are cut.

Step 14: Assembly

Assembling these parts is a little bit like doing a jigsaw puzzle! Something that I found helpful before I heated up the hot glue gun was using a whiteboard marker to mark which piece was which and what side was up or down. I then loosely assembled all the pieces without glue, just to double check that everything fit properly.

When using hot glue, make sure that you're working over a sacrificial material like cardboard or scrap wood. Hot glue can ruin many surfaces such as carpet, table cloths, or table surfaces.

Start with the right side and back. Push hot glue sparingly inside the back holes on the right piece. Push the right side tabs on the back piece into the holes on the right piece. Use a cardboard box to make sure that they are at a right angle and let the glue dry.

Next, use the left side piece, and repeat the same process with the left side holes and back left tabs. Again use the cardboard box to make sure that the pieces are at a right angle.

Next, take the compartment bottom. Spread hot glue sparingly inside the left side center holes and back center holes. Push the compartment bottom tabs into these holes. Prop up the compartment bottom on a cardboard box to make sure that it's level. Let the hot glue dry.

Almost done! Take the compartment side and push hot glue sparingly into the compartment side bottom holes and the back upright holes. Place the compartment side into the appropriate holes and tabs and let the hot glue dry.

Finally, take the top piece. Spread hot glue sparingly into all of the holes on the top piece. Push the top piece onto the fitting tabs and let the hot glue dry.

Separately, follow the assembly instructions for your wheels, motor mounts, and motors. Attach the assembled pieces to your wheelbase.

Being very careful not to get hot glue into your wheels or motors, push hot glue into all of the holes on the wheelbase. Take the assembled left, right, back, top, and compartment and push it into the wheelbase holes.

You now have your very own boxy robot!

Here are some helpful tutorials on how to continue with this project by powering and driving the motors using Arduino:

Control a DC Motor with an Arduino

Motor Controllers with Arduino

Thanks for reading! Please post any questions or tips you may have, and have fun making!