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# Need advice from math gurus: ballscrew>sprocket>chain force

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• Posts: 3,681
I posted this image earlier. It is a way to have a swing arm with sprockets on it that that allow constant tension on the belt. The idlers are on a swivel plate that is held in the center position by tensioner springs. If there is excess tension in either direction a switch gets depressed. This worked out well on the previous high torque worm gear design. It is more quickly tripped versus current sensing on the motor.
• Posts: 3,681
Here is the concept for the back side idlers acting as stress detection. Springs hold a swivel please in place. The LOAD side will only see a known load unless there is obstruction so the springs can be set to allow the load to not trigger the switch, but any stress on the idler above the load will press the switch. On the slack side, there should never be a load on that side other than belt tension.

I have looked for a while but cannot find a formula for a force acting on the idler pulley to get some estimates for the load on the springs normally and under stress.
• Posts: 1,061
Debbie Downer chiming in again:

I can't help but imagine all kinds of nuisance trips with this mechanical sensing method. It might be just as cost effective to employ a shaft load sensor, commonly used for web tension control (?).
PropBASIC ROCKS!
• Posts: 3,681
edited May 2017

I will get in the sparkfun load cells and HX711 boards today and build a special enclosure to house those with and LCD display to see and set all the parameters of the 2 load cells. The LCD will show upper and lower load limits for OPEN, upper and lower limits for CLOSE, options for defining the average load sample size and also method to use mean load values and discard transients.

BTW with the original spring/switch concept, you never just read the first switch event, you so something like:
```If Switch1 == 1
waitcnt(1_000_000 + cnt)
If Switch1 == 1
waitcnt(1_000_000 + cnt)
If Switch1 == 1
waitcnt(1_000_000 + cnt)
```

This way you can toss out transients after analyzing what a transient might look like, then set a sampling method to mask it.
• Posts: 3,681
The suggestions for the load cell and HX711 combo worked out incredibly well. I bought the 50Kg load cell and HX711 board from spark fun. There was an object posted in obex. I wish I had of experimented with these load cells years ago. Thanks to whoever put that object in there, I used the read raw and with minor changes to show it on the LCD I am very pleased. Too bad nobody carries this HX711 but I intend to try to locate some and build a board for it.
• Posts: 1,061
Nice job! Sounds like you're having fun.
PropBASIC ROCKS!