The Rod End Bearing
Entry ID #: 7741
Created: Sun, Jan 12, 2020 11:06 AM
The Rod End Bearing by the Centereach CouGears Software used: Autodesk Inventor 2018, 64-Bit Edition. Build: 112, Release 2018 - Date: Thu 02/16/2017, Version 22.0.11200.0000 Designer: Kumpu Ide Why we designed this part: Over the course of time, Vex teams have found more and more ways to transmit and distribute motor power to parts and utilities distributed around the robot. With the introduction of the V5 system came the new, larger, and much more powerful V5 Smart Motor. However, the size of the motor is in itself a design constraint, as builders must leave space for motors, on top of mechanisms that will be powered by said motor(s) and space left for other purposes. With the 2019-2020 Tower Takeover season, we discovered that due to the major space limitations, linkages would become essential to keeping motors in safe and protected areas, while maintaining efficient power transfer. The options using Vex hardware was very limiting, and this is when the idea for the Rod End Bearing came about. What the Rod End Bearing is: The Rod End Bearing is essentially a ball joint with more mounting options, which effectively allows it to transfer torque in any direction. Also called a Heim Joint in the US and a Rose Joint in the UK, it can be seen in automobile suspension and steering components. How it works: Ball and Outer Race - The Outer Race is designed to hold the Ball, but also allow for free movement of the Ball within the Outer Race. The Ball has a recess for a #8-32 nylock nut, and the Outer Race has a ledge which meshes with the Casing of the Bearing. Bearing Casing - The Casing and Bearing are two separate parts, for ease of production and usage. The Casing connects to the Bearing’s Outer Race, locking its orientation. It also has a hole for a ⅜” long #8-32 screw, which can be used to attach a standoff. Attaching a rod end bearing to each side of the standoff creates a complete linkage with unparalleled freedom of movement. How it can be used: Rod end bearings are useful for providing torque transmission over long distances, where gears would be unfeasible and chain would not provide enough precision. For example, a 4 bar design could use a linkage made of rod end bearings in place of a C-channel to save on weight and materials. This often happens in robot designs because the motor cannot be placed on the arm pivot, and has to be moved lower down, whether this be for size constraint reasons, or otherwise. Another usage case is for arms that rotate in different axes. Due to the nature of the ball joint, power can be transmitted in non-linear orientations, as well as over long distances. This allows for flexibility of motor mounting, knowing that the orientation of the motor does limit the movement of the arm. Using Inventor 2018: We used Inventor 2018 (64-Bit Edition. Build: 112, Release 2018 - Date: Thu 02/16/2017, Version 22.0.11200.0000) to model our parts for the 2020 MIR challenge. The parts were modeled as adaptive parts, and many constraints were used, such that one dimensional change would reflect in the rest of our parts. We gave every moving and connecting component a 1/64” clearance, so that our slicer for our 3D printer would recognise them as separate parts. From testing, we know that 0.4mm (approx. 1/64”) will give us a smooth rotating part for parts printed within parts, which is how we intended on printing our Bearing piece. We made sure to test our assembly on a robot in CAD to spot potential problems, and then finished the part. For finishing, we gave the edges on the top and bottom of the Casing a 1/16” 45 degree bevel, and a ⅛” chamfer for all other edges on the outside. What we learned: While completing this project, we learned about the importance of having tolerances in CAD designs, which is commonly overlooked and can result in improper fit on manufactured components. Features like the Chamfer and Bevel tools were used to create a professional looking product, and the Offset tool helped us create clearances and tolerances with ease. We also learned about the power of adaptive components, which helped us with iterating the design to make it simpler and more space efficient. Make It Real: We printed out all of our components on a Creality CR-10 3D printer. We had trouble with some minor warpage, but we learned to adjust our bed heating and nozzle temperatures to minimise the warping. The parts were printed using PLA, and came off the bed almost exactly as our CAD dimensions had specified. We bolted the linkage together, and mounted it on a test rig to test the effectiveness of our design. We found our bearings to work very smoothly and quietly.