Robotics Education & Competition Foundation
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Interchangable Slip-Gear

2

njitrobotics
Entry ID #: 3547
Created: Wed, Jan 11, 2017 12:36 AM


This is a slip gear with removable teeth. The need for a slip gear was first presented to us during the previous season of VexU (Nothing But Net). We required a slip-gear to operate our catapault, so we designed a basic slip gear to meet our requirements. Upon transfering this slip-gear to our new robot this season (Starstruck), we encountered problems because our new robot needed a different number of teeth for the pullback. This made a redesign nessasary. In order to fix the shortcommings of a stadard slip gear, we designed this new slip gear to have removable teeth, a feature that allows the slip length of the gear to be changed as needed. In addition to being able to customize the slip length, the teeth are designed to be easily detached without removing the gear from the shaft. Simply remove 2 screws from each set of teeth, and you can lift up the teeth and replace them. The huge advantage of this is the ability to fix broken teeth without having to disassemble the entire robot. New teeth sets can easily be printed and attached to replace the damaged ones. This turns a potentially time consuming repair into a quick 1 minute repair, and material is saved as only part of the gear has to be printed rather then an entirely new gear. This slip gear is 3 parts, the base and two sets of teeth. The teeth are screwed into the base and secured with keps-nuts. It is designed to be bolted to a vex 60 tooth gear through the 4 screw attachment points, with a high-strength axel passing through them. The motors would then power the 60 tooth gear to provide a constant spin of the slip gear. The slip gear would then mesh with a the catpault arm's gear. The catpault would be powered through rubber bands when the gears are not engaged, and pull back when the teeth are engaged. This set-up allows a fast and accurate catapault to be constructed. We printed this gear and have used the previously mentioned set-up to launch the game objects over the fence this season. We have not encountered any breakage of teeth yet after thouroughly testing. To make this slip gear, I started by opening up a standard vex 60 tooth gear in Autodesk Inventor Professional 2016. I used the "project geometry" tool to obtain the profile of the 60 tooth gear, I used the copy tool on the sketch. I then started a new part and pasted this sketch into it.This allowed me to draw in teeth in the exact position needed to mesh with standard vex gears, along with a shape to provide backing. I extruded this feature. I then drew in the side railings to add extra support to the teeth. I used the mirror feature to mirror the rail to the other side. I then extruded holes for the screws using known dimensions for the screws plus a slight tolerance for clearence. Next, I begun design of the base. I used the known dimensions of the teeth sets' profile to make the profile of the base so they would mesh properly. I extruded it to the nesasary thickness to match the  thickness of the teeth sets. I then drew in the profile for the cut out to allow the nuts to be inserted. I mirrored this feature once i extruded it. I then added i the holes, and used geometry text to add my name. Once each part was made, I started a new asembly and added everything together. I checked for interference and fixed all interferences by revising the parts. I had to revise my base because the screws were slighly too long and interfered. Last, I revised the parts to add fillits to make a smoother final apearence, and help the part print easier. Overall, using Inventor to design this part was a very pleasurabe experience. Inventor is definately my prefered software for CAD, as it is efficent and intuitive to me. The design process for this part was optimized by utalizing the features of the software. Our team primaraly uses inventor to design the parts we 3-d print for our robot.    

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