Limbi/Spring ’19
Magnet Test
Author/s: Samonte, Ridel A. PM and D&M
Table of Contents
Introduction
For the module-to-module docking, our team have decided to use permanent magnets; specifically, neodymium magnet discs for symmetry. So, how strong should the magnets be?
Well, we want it just strong enough for the two modules to securely dock; if it is too strong, then it might reposition the idle servo (joints of the arm) during module-to-module docking.
Magnet Test
Cross sectional view of module showing the permanent magnet placement.
This is the design that our D&M team came up with. For the module-t0-module docking, there will be about 0.05 inches (x2) = 0.1 inches of material between magnet pairs.
Our team experimented with 5 magnet pairs with 5 different pull forces: 1.7 lbs, 5.2 lbs, 9.5 lbs, 10 lbs, 15 lbs.
*Pull force is the amount of force needed to detach a magnet away from a flat surface.
Our team found that pull forces greater than 5 lbs are too strong and caused idle servos to turn during docking. On the other hand, the 1.7 lb pull force magnets are just the strength for our application.
Limbi Magnet Test for 1.7 lb magnetic pull force for the module-to-module docking. 4 Magnets holding two parts together with about 0.1 inches of PLA plastic in between.
Side Note:
The reason why we chose magnet discs (instead of magnet strips/magnet blocks/non magnetic mechanism) is because of its symmetry for easy placement and it does not require power. We want to be able to implement the module-to-module docking design in the arm-to-module docking. We currently have our requirement (2.1.15.1) as two separate docking faces for module-to-module and arm-to-module for the module design but we later aim to have a universal (the same module-to-module and arm-to-module) connection later in the design process.
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