2016-02-12 (F) Weekly Summary

Another busy week working with the haptic compass. A design change removed the rubber grommet from inside the spinner and replaced it with a rubber O-ring on the outside. There isn’t a huge difference performance wise but the O-ring on the outside is easier to assess. The angle the spinner swings is easy to see since a very obvious collision occurs with the edge of the jar. With the grommet inside the spinner the swinging limits aren’t as easy to gauge. The two models spinning below show cutaway views of the old model and the new model. The new model doesn’t have ribs inside the bore for holding a grommet.

Model with grommet holder
Model with smooth bore

Most often small holes in the model don’t print exactly the correct size so they are drilled out using SAE or metric drill bits and those are usually just spun by hand. Unfortunately this doesn’t always give a perpendicular hole. One base was drilled particularly crookedly so it was corrected by heating the post with a handheld lighter then holding the post until the plastic cooled. It was a successful fix.

Aligned post and lighter

It might have been simple enough to glue magnets above an O-ring on a plain spinner but a lip was added to make it clear where the O-ring would go. This was also meant to keep the O-ring seated and aligned.

Spinner with O-ring lip
Printed model

The first O-ring wasn’t thick enough to extend beyond the magnets so there was a very significant metal-on-plastic collision when the compass was shaken. A thicker O-ring was tried but it wasn’t able to stay on the narrow lip.

Not enough clearance from O-ring

Each jar came with a thick black lid that made it difficult to see the black plastic spinner inside. One of the lids had an edge sawn off so it was easy to see inside.

Modified jar lid

The thickness of the second O-ring was measured so another model could be printed. This time there was enough room on the lip to hold the O-ring. Its thickness was enough to buffer collisions between the spinner and the jar. When the compass was shaken the most significant collisions were due to the base wobbling but this could be glued in place.

 Measuring O-ring thickness
O-ring dampening collisions

The rest of the weekly summaries have been arranged by date.

First time here?

Completed projects from year 1
Completed projects from year 2


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