[fovea1959]

Working with Richard Wallace: put a plastic nut on the back shaft to use as a spacer, then superglued a K&J Magnetics diametrically magnetized ring magnetic (R424DIA, $0.61). He salvaged an Allego A3291 Hall Effect Latch from a washing machine motor. added a couple of filter caps and a pull up, and we put it on a scope. Beautiful square wave. Student wired up a harness to connect it to the side car, added the code to LABview to set up a counter, read width of last period, take the reciprocal, and plot the resultant revolutions/s. Rock steady with up to a full speed Banebots, about 310 rps (18600 rpm), and it work with about 1.5 or 2 cm from the face of the Hall Effect sensor to the edge of the ring magnet.

I imagine for the Hall Effect what we did was very similar to Team 2729's boards. The ring magnet just glued to the backshaft was pretty slick; K&J has a pretty neat selection.

Can't find the Allegro chip in a non-surface mount package, so ordered some UA1881 and UA5881 chips using our Digikey voucher, and we'll just use vectorboard to fab a couple up for the bot. Those chips are about a buck. We're gonna try a team 2729 board also.

So: I could use an encoder for this, but it looks like about $3 in parts and some sweat equity, we have get lots and lots of RPMs....

Will try to get a white paper detailing some comparisons between the various chips and doing this optically, but probably not until after bag day. Post here or PM if you want more information before then.