Creating a Marker Holder for the XRP in Fusion 360

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2024-01-25 | By Travis Foss

Currently, I am working on a project using the XRP to draw the DigiKey logo. To draw it properly, I need ‎to be able to lift a marker with the robot’s servo as the robot travels from letter to letter. I initially used ‎rubber bands and treads from XRP wheels, but they had a problem with the marker slipping and not ‎maintaining the desired position. To overcome this issue, I created a 3D-printed holder using Fusion ‎‎360. The holder would attach the servo arm and solve the slipping problem.‎

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To start the model, I measured the marker that I would be using and found the diameter to be 18mm, ‎so I drew a circle that size. I offset that circle 1mm to the outside to give the holder a wall thickness.‎

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I extruded the ring of the model 8mm high. This gives the holder enough height to be able to grip the ‎marker as it is lifted.‎

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I drew a 10mm x 4mm box on the right side of the ring, 9.5mm from the center of the ring.‎

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I extruded the box 8mm high to match the rest of the ring.‎

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Then, I created a sketch on the new box. I drew another box that was 8mm wide by 6mm high since I ‎was planning on printing this out of TPU, and I wanted it slightly undersized to fit tight against the ‎servo arm. I also added radiuses to the corners of the box to make it easier to print and stronger.‎

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I used the extrude tool to cut the newly drawn box symmetrically out both sides of the box. In this ‎case, the sketch plane was the center of the previous box instead of the face. If it had been the face, I ‎could have changed the direction to one side and the distance to 4mm.‎

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However, I decided that 0.5mm might be a little too thin for the outside wall, so I extruded it another ‎‎1mm to give it extra strength.‎

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With the design finished, I needed to export it so I could slice and print the part. To export an STL file ‎from Fusion, there are two different ways to do it. The first is to click on the new page button to the ‎left of the save button and click on the Export button.‎

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An export popup box will then appear. Under the Type dropdown, scroll down until you find STL Files, ‎and click on that. You can also change the name of the file if you so choose. Once that is completed, ‎click the export button. You may get a Job status popup like the one shown below that will show the ‎progress of the export. Once the status shows complete, your STL will be in the folder you chose to ‎export to.‎

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The second way to export an STL from Fusion 360 is under the same menu shown before. Look for the ‎‎3D Print option.‎

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Click on this menu button, and a small 3D Print toolbar pops out. Select the object or model that needs ‎to be exported by clicking on the select box next to the selection section and then click on the model. ‎It should then say 1 selected on that box. Next, there is the option to select a format (STL is what I use ‎most. However, most slicers also accept 3MF files as well) and the refinement of the model. This is a ‎very basic model, so I left the refinement set to low. If the model was much more detailed, you could ‎increase this to make sure you don’t lose any of that detail during the conversion process. On the ‎bottom of the toolbar, under the output section, it gives the option to send the file directly to a 3D ‎print utility such as PreForm, Cura, or Custom. The Custom option allows you to select the slicer ‎program that is typically used to slice your models. I use the LulzBot Edition of Cura, so notice below ‎the Custom box, next to Application, it shows CuraLE. To choose which program, you will need to find ‎the Application .exe file location for the slicer is that used on your hard drive. Once everything is ‎complete, click the OK button at the bottom of the toolbar.‎

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I set up my slicer for Polymaker TPU and sliced the model. I transferred the GCode to my LulzBot ‎SideKick 747 and started the print. After about 30 minutes (including preheating, leveling, and print ‎time) I had the finished part. With a bit of testing, I learned that it was better to place the holder on ‎from the servo arm side and slip it up to just before the lifter portion of the arm (see image below for ‎reference). This keeps a bit of tension on the marker to hold it in place and allows it to flex enough to ‎not cause too much resistance. ‎

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