Wednesday 10 January 2018

Gear teeth sensors and bracket

Here's the sensor I ordered. Claims a reasonable maximum frequency ("over 100kHz") and seems to be OK with a fairly narrow tooth width. At 6000 rpm and 48 teeth, I would expect a frequency of 4800 Hz. The main question in my mind is whether or not I can persuade it to give something like a 50:50 signal, which would be helpful if I am hoping to use a pair of them to generate a quadrature signal. Or at least something approaching 50:50. The datasheet isn't exactly black and white but I think there's a reasonable chance I will get it to work. 

Honeywell's "interactive catalogue" datasheet for the GT1 sensors.

Modelled it up in Fusion 360:


And also the gear. The number of teeth, approx position and height off the deck are pretty close. This enabled me to model a simple bracket. It will be made from a piece of angle iron (probably loominum in fact), with a bend on one face. I will be able to adjust the precise separation of the sensors by swinging them, sort of like a couple of pendulums (pendula). Hopefully that will be possible from outside the machine, through the hole.


Here's the bracket drawing. I'll have to hack some of the foot away and also drill some mounting holes. Similarly I'll have to drill and tap a couple of holes in the head. There's nothing of consequence underneath, so no risk of cast iron dust getting into anything critical.

I've used the metal cover from the (now redundant) spacer block as a cover for this new opening. Cut it down to size, drilled a couple more holes in it and tapped suitable holes in the head casting. Nice thing is that it's painted the right colour. Here it is, roughly held in place with 2 of the M5 screws:


I'll make an opening for some form of connector (TBA), once I've got the thing working.


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