[thingstodo]

The router mounting proved too much trouble. Every coupler that I came up with required more mechanical skill than I have. I split couplers, I clamped things with straps, clamps, screwed things down ... all failed. Holding a router with one hand, making adjustments to speed with the other, and remembering the data does not work for me.

So I found something different. I have a 10,000 rpm side grinder. The middle of the disk appears to be about the same size as the encoder disc.

So I can use the Variac to adjust the speed of the grinder, mount the grinder to my shelving, then use a friction drive between the encoder and the grinder disc. I used electrical tape and that worked OK for me.

See the picture for a bit more info. I have the PLC on the middle shelf, the 12V power supply below, the Variac on top. The tach is strapped to a piece of scrap lumber and aimed at the encoder disc. The encoder disc has electrical tape on it to block reflection of the laser tach for most of the revolution and a small window is shiny aluminum that reflects well. The side grinder is clamped to the top shelf and the handle drops through a hole in the shelf.

The blue laplink cable connects to the 25 pin serial port on the PLC, set for 19200 baud, BCC error protection, no parity, 1 stop bit. The laptop is an older Dell D820 running DOS 7.0 and the old Allen Bradley 6200 series programming software. The laptop display is showing the calculated RPM by measuring the pulses in one second and scaling to rpm as well as the number of pulses in 10 seconds and scaling to rpm.

Variac tach encoder/60 encoder/6
10 112 120 114
15 600 540 588
20 1179 1260 1212
25 1780 1740 1752
30 2720 2760 2550
35 4000 2160 1824

The encoder has 1024 pulses per revolution. At 2720 rpm, that is 2720 * 1024 = 2785280 pulses per minute. Since there are 60 seconds in a minute, that is 46421 pulses per second, which is pretty close to our rated maximum of 50 Khz.

So under ideal conditions - well shielded cable, good connections, etc - I should be able to measure 2929 rpm.

From the ev calculator, that's over 90 mph (which is 2875 rpm). I think that a reliable 2200 rpm (just under 70 mph) is a reasonable target.

This part of the investigation is done - the encoder signal can be read for the speed range that is useful for me.

Next - how can I drive a 'dashboard' so I don't need to keep looking at the PLC programming software to see information that I need.