Gobble Squabble: Tips For Designing Your Robot For 3D Printing

Creating your own unique combat robot design for 3D printing will be one of the most rewarding parts of your project. This post contains guidance, tips and recommendations to help you succeed — but you’re welcome to use a wide variety of other methods, as long as your robot complies with the rules.

  • You’ll need a 3D design tool. For students who are just beginning in 3D design, we recommend tinkercad.com . The pictures below are captured from TinkerCAD screens. There’s extensive information available to help you get started using TinkerCAD. But you can even use more advanced tools like and Solidworks or Autodesk Inventor for this project; using these tools will help you prepare even more for FRC design activities.
  • You’ll need access to a 3D printer that can print an object at least 6″ W x 6″ L x 2″ H in size. Your school robotics team, engineering program or library may have one. And in Colorado, many public libraries and makerspaces have one or more. Make contact early and find out how you can have your design printed.
  • Decide what type of 3DP filament you will use: your choices are ABS, PLA or PETG. ABS is lightest and has good impact resistance, but can be difficult to print with. PLA and PETG are easy to print and have a good slick surface, but weigh almost 20% more than ABS. If you’re new to 3D printing, we recommend you use PLA or PETG. All these filaments come in many colors, allowing you to customize the look of your robot. Example sources on Amazon are: ABS, PLA, PETG.
  • Decide how much space your robot’s internal components (e.g., motors, battery, RC receiver, motor controllers, power switch, wiring, etc.) will need. Sometimes this is best done by placing them all on a sheet of paper, and seeing how you can arrange them to minimize the space required — then measure that space, expand it just a little bit to be sure, and document the arrangement.
  • Consider the robot body design shown below as an example. This is a versatile design that’s been adapted to a defensive wedge bot, a flipper bot and an attack bot with a horizontal spinning weapon. The slots in the base are to reduce body weight and provide some air flow to keep the internal electronics cool
  • If your robot body design is bigger than 6″ x 6″ (150 mm x 150 mm), it’s getting too big to make weight. Overall, the robot body shell will be the single heaviest component of the robot. If you make it too big, you’ll have to modify it before you compete.
  • Design fastening screw holes into the robot body, as shown. You should use metal screws called “metal screws” for your component fastening, usually of #4 size. Measure the size of the thread displacement on the screws and make your screw holes 20% smaller, so the screws will bit the plastic and hold. Leave about 3 mm of plastic material around each screw hole for strength.

Here are some specific design tips for the body (shell) of your combat robot (refer to the picture for more insight):

  • Do your designing in millimeter dimension mode in TinkerCAD, since it’s much easier to define and use small dimensions this way. This is the default mode for TinkerCAD. Accuracy of 0.1 mm (.004 inches) is available.
  • The robot walls should be 2 to 3 mm thick. If thinner than 2 mm they will be very weak; if thicker than 3 mm they will be very heavy.
  • Put a ruler tool on your TinkerCAD Workplane. This will give you precise dimensions, and allow you to change part dimensions directly by typing in the new settings.
  • Here’s a quick overview of the practical realities of mechanical fit. You cannot fit a cylinder with a diameter of exactly 1.0 inches into a hole with a diameter of exactly 1.0 inches; the hole should be slightly larger, perhaps 1.05 or even 1.1 inches, depending on the accuracy of the tool making the hole. 3D printers tend to make holes slightly smaller than the specified size, and positive-displacement objects (e.g., a cylinder) slightly larger than specified. Do some test designs and 3D prints to determine how much you need to adjust respective sizes for items to fit together, before you do your final designs.
  • Figure out early how you will mount or attach the motors to the robot body. The straightforward way of screw attachment via the motor mounting holes often doesn’t work well because the screws are so small. Other proven methods include motor mount brackets, plastic mounting blocks (as shown above; these require careful design and sizing) and zip ties to hold the motors tightly on curved mounting blocks. Tip: try some small test designs early, 3D print them, and test how well they work; keep making improvements and testing until you’re satisfied with the results. Motor mount brackets or zip ties are the easiest of these methods.
  • Test your schemes for screw mounts and fasteners early and keep improving them until they work well. Include your ability to align screw holes across multiple parts so you can assemble your final robot parts easily and with strength. Tip: design a small multipart box with screw holes for final assembly. Align the screw holes and size them for #4 metal screws. 3D print the box and see if the assembly works well enough; if not, revise and reprint until it works well — then use the techniques you’ve learned to design your combat robot body and weapon.
  • For printing, 3 or even 4 shells are recommended, and something in the range of 25% to 50% infill. The more shells and greater infill will make parts stronger but also make them heavier. Don’t be surprised that if you print your robot body to be as strong as possible that it turns out too heavy, in which case you’ll need to make modifications to reduce the weight and re-print it (or drill many holes in the body when trying to pass inspection at the event).
  • Place 15 mm square tabs at the corners of large objects to help them 3D print very flat. These tabs can be removed after the print is completed.

For this view (below), a separately-designed control section lid has been placed on top of the robot shell in TinkerCAD, so the screw holes can be aligned exactly. Using TinkerCAD and a 3D printer, accuracies of 0.1 mm are feasible.

This information is original work by Techno Chaos and is published under the terms of Creative Common license mode Attribution-NonCommercial-ShareAlike (CC BY-NC-SA).