On 6/6/25 16:36, Chris Albertson wrote:
On Jun 6, 2025, at 12:46 PM, gene heskett <ghesk...@shentel.net> wrote:
..
I'm assuming you meant a woodworking planer? Single n. A 25" is a pretty large machine
& may use V-belts & std multi-hp induction motors. Most planers used by us hobbyists
are half that width and use cogged timing belts. Which would be destroyed by /any/
slippage. The duplicate encoder setup sounds good, until a prolonged run overruns one of the
encoders. The only thing I can suggest would involved a single hall device to give a once
per rotation trigger, driving a one shot, measure that period and feed it to another one
shot set to trigger if the first one slows by 5%, to drive an another much longer period one
shot showing on an LED from the second one when it fires. It will also flash at power up
until its up to speed, giving the user a visual clue to start the feed. If it comes on in
the middle of a board, tell the user to reduce the depth of cut for the next pass. Or cut
the power at the same time. Except for the led, that is all in the arduino file. Minimal
cost. A $10 arduino could do that. Or a multicore arm64 could do it easier but that's higher
cost.
Why would a prolongeed run over load the sensors. The sensors are measuring
either speed or shaft angle not accumulated rotation. One shots and triggers?
Why to complex. Just compare the speeds. You don’t need a once per rotation
index, you don’t care about shaft angles, only speed matters.
Actualy the dual core ARM process is cheaper then Arduino. Look at the
Raspberry Pi Pico. It is a dual core ARM that costs $4 and you can program in
in Micro Python. The Pico can easly handle reading two quadrature encoders at
the MHz speed level. Just get two $2 magnetic encoders. these are fast and
have 1024 line encoders in them. Read them Using I2C about 25 times per second
and when the speeds are a few percent or so apart, the belt is slipping.
Don’t spend motr the $2 on the encoder, 0.1% accuracy is good enough and you
can have that at the $2 price point. Somthing like this:
https://www.aliexpress.us/item/3256805971765108.html?src=google&pdp_npi=4%40dis%21USD%2110.15%215.53%21%21%21%21%21%40%2112000036033485665%21ppc%21%21%21&src=google&albch=shopping&acnt=708-803-3821&isdl=y&slnk=&plac=&mtctp=&albbt=Google_7_shopping&aff_platform=google&aff_short_key=UneMJZVf&gclsrc=aw.ds&albagn=888888&ds_e_adid=&ds_e_matchtype=&ds_e_device=c&ds_e_network=x&ds_e_product_group_id=&ds_e_product_id=en3256805971765108&ds_e_product_merchant_id=5071463479&ds_e_product_country=US&ds_e_product_language=en&ds_e_product_channel=online&ds_e_product_store_id=&ds_url_v=2&albcp=20123152476&albag=&isSmbAutoCall=false&needSmbHouyi=false&gad_source=1&gad_campaignid=20127768206&gbraid=0AAAAAD6I-hGTFVe80aKnm_qXISwfO1_L7&gatewayAdapt=glo2usa
Then the computer can be this:
https://www.seeedstudio.com/Raspberry-Pi-Pico-2-p-5940.html?gad_source=1&gad_campaignid=12740071602&gbraid=0AAAAACiAB466mzmjSu4q9jtCxQXrJQljL
Raspberry Pi Pico 2
seeedstudio.com
Now we are getting someplace, I hadn't tangled with a rpi pico, yet. .
. Thanks Chris.
Poswe can come in via the USB port from a phone charger or maybe there is
already 5 volts available some place else.
Magnetic encoders are very easy to use. If the shaft is steel the magnet can
stick to the shaft end and then the encoder mounts to a peice of plastic or
aluminum and has about a 1mm air gap from the magnet. There is room for some
imprecision, getting within 2 mm is “good enough”. The magnet need not be
exactly concentric with the chip-sensor. You can super glue the magnet if you
like.
All the software has to do it raise a pin to high if the speed ratio is wrong.
It can check a few dozen times per second and wait untill it has been wrong for
maybe a 10 times in a row and still shut the motor down a half second after it
starts to slip.
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Cheers, Gene Heskett, CET.
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soap, ballot, jury, and ammo. Please use in that order."
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