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[M] 2mm rods instead of 1.5mm tubes

A project log for Tetrinsic [gd0041]

A continuous, motorised slider that is force sensitive, haptic, UV self-sterilising and water resistant.

kelvinakelvinA 08/27/2023 at 14:350 Comments

I first mentioned this in this Tetrescent log, but I've spent 3hrs modelling a new solution. The main reason being that most Aliexpress listings for stainless steel rods start at 2mm:

Secondly, even though one is probably never going to push down 500gf onto any Tetrinsic when in normal use (my thumb usually hits 420 - 450gf max and 300gf when not putting in the extra effort), the safety rating of 2.0 isn't ideal. 

It turns out that the solution to the question "Should I have the rods go over or under the collector?" is actually "Both.":

This is to allow the collector to obtain minimum wall distances of 1.2mm whilst also allowing the ball chain to slide past. I've also added this smooth curve to ease the transition from air to the side of the pressure collector:

The new assembly has a much nicer looking displacement profile:

The minimum safety rating is over 3, but it's unexpectedly in the area just under the load cell: 

Now that I've slept, this could be caused by the rod-ending offsets being too close together, meaning there isn't enough overlap where all 3 rods can bear the force. Increasing this offset to 27mm (from 20mm) reduces displacement to 0.300mm (from 0.324) and increases the safety factor to 3.78 (from 3.20). Reducing it to 10 increases displacement to 0.359mm and reduces the safety to 2.78:

I'll go with a 29mm offset to leave about 20mm from the last bend:

I'm now trying to see if I can actually obtain simulations for multiple force points by making the ones that have no force applied "frictionless":

No, that failed:

I'll just have the forces without the "frictionless" constraint. I'll assume that the extra bodies have a negligible weight.

It seems that Fusion does each solve sequentially. At least that means I could be inspecting one study while another one solves on the cloud. Anyway, here are the results:

I've set the displacement to "Actual" above, but to better see what's happening on a micron level, "Adjusted" is below:

It seems that the "minimum of minimum safety factors" is 2.94, when the force is applied near the ends of Tetrinsic. The outer force position has a max displacement is only 0.35mm, so it should feel rather solid throughout, even when pushing down at 500gf.

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