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Suggestion on where to ask for help in designing a simple RPM/rotation checking device?

skysquid

Oct 10, 2023
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Where best to look for help to identify how to build and assemble a simple device to alert me (with a load buzzer and flashing light) that a shaft on a gear motor is no longer turning? I have a piece of food equipment that gets stuck and burns out the 1/2 HP motor. This is my third time getting it rewired. Ideally, looking for a simple solution that doesn't require a board but simple components that can be wired together,

It can be optical, magnetic, or mechanical. I was thinking of gluing a magnet on the rotating flat part on the backside of the gear motor with a reed switch tracking movement.

I seek help identifying the correct part numbers and general guidance on putting it together. The design constraints are each and cheap. I am not a programmer, but I know how to solder.

Thanks for any leads/advice.
 

skysquid

Oct 10, 2023
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this is the end of the gear motor that needs to be tracked to know that it is constantly turning during operation.
 

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skysquid

Oct 10, 2023
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Hi. No. We are trying to prevent another motor burn out and want to track the rotation so we know if it stops so we can turn the motor off and clear the jam.
 

kellys_eye

Jun 25, 2010
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You can get current monitoring relays with programmable delays that will trip if the set current is exceeded for any given time period. This might be a better option:


Use the relay contacts to either stop the motor and/or sound an alarm.

The alternative is to fit a sensor that outputs a signal whilst the shaft is turning (could be a rotary encoder or optical reflecting IR LED/sensor) and circuitry that detects the loss of this signal.
 

skysquid

Oct 10, 2023
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Hi, thanks for this. The design constraints for this project are cheap and fast. Your idea of a rotary encoder or optical reflecting IR LED/sensor) and circuitry that detects the loss of this signal is more like what we are looking for.
 

kellys_eye

Jun 25, 2010
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The design constraints for this project are cheap and fast.
'Fast' is the relay solution. I don't know (off-hand) of an off-the-shelf IR/rotary solution but Google 'missing pulse detector' schematic. This is (basically) a retriggerable monostable used to hold a relay (switch) contact closed until it detects a missing pulse for whatever detection circuit you decide to use.

There are also lots of IR reflective sensors and rotary encoders out there too.

The IR solution would be best as it is a non-contact solution requiring zero mechanical mods. This only necessitates the sticking on of 'slotted' disk (or even carefully spaced black painted lines to interrupt the IR beam). Here's a typical (lots of other styles out there) version of detector but it needs the appropriate receiver amplification to get the pulse stream from it: (could be as simple as a schmitt buffer/gate device)

 

kellys_eye

Jun 25, 2010
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Here's a slotted opto module that'll deliver a pulse stream if you can fit an 'interrupter' on the motor:


You should also consider a hall effect device and sticking a magnet on the motor disk.
 

Minder

Apr 24, 2015
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Honeywell have a line of small proximity sensors SS400 series, they require a small button magnet, if going with this, then you should probably fit two magnets at 180deg to retain balance.
Retained by epoxy?

1696970949969.png
 
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Bluejets

Oct 5, 2014
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"shut the gate after the horse has bolted approach" I have to say.

Accepted approach is normally to fit an overload device to the motor.

Firstly it does not need and human recognition of any fauly condition.
Secondly it protects the motor.

Beats me why you don't fix the current jamming problem.
 

skysquid

Oct 10, 2023
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Interesting. How about something really simple like a Reed switch, powered by a battery (or 12 v supply), wired to a piezo buzzer and resistor? I'm trying to stay away from Adrino because I am not a programmer.
 

Delta Prime

Jul 29, 2020
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Beats me why you don't fix the current jamming problem
Cuz it's filled with IR detectors,epoxy, magnets and Reed switches. You should have went Megger.
Adrino because I am not a programmer.
Welcome to Maker Pro.You don't have to be a programmer. But you have to be "Down with OPP,you know me" Others People's Programming.
They call them libraries.
You'll fit in nicely! :D
 

skysquid

Oct 10, 2023
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"shut the gate after the horse has bolted approach" I have to say.

Accepted approach is normally to fit an overload device to the motor.

Firstly it does not need and human recognition of any fauly condition.
Secondly it protects the motor.

Beats me why you don't fix the current jamming problem.
I wish it was that easy. I'm test milling a number of different materials and different loadings to see how much it can handle.

Also, the art of it for me is how cheap and easy can the rotational monitoring solution be done for. Value engineering. It is easy to through money at a problem, but that's not as rewarding.

My previous solution was to put a temp probe of a yolink temp/rh sensor and have it send an alert to my phone once starting to over heat, but the problem there is sometimes i forget to turn on notification and or someone else is running it. So I looked at it and thought that the slow moving object can probably be easily detected and a buzzer sounds when it stops rotating.
 

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Harald Kapp

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I agree with the other answers that monitoring the motor current is probably the best option. Plus shutting off power if the motor current is to high, indicating a stall condition.

How accurate does your monitoring have to be?
A simple solution, albeit not very accurate, is using a resettable fuse in the power cord leading to the motor. Under normal conditions (motor running) the current is low and the fuse is inactive.
When the motor stalls, the current will rise and the fuse will be triggered, turning off the motor. As long as the stall condition is present, the fuse will be held in the active state, limiting the current to the motor.
Once the stall condition has been removed and the fuse has been given a bit of time to cool down, the motor can be operated again.
Of course the fuse value needs to be determined such that both normal operation and stall condition are adequately covered.


I can't imagine any solution more simple than this.
And you don't get notifications :(
 

skysquid

Oct 10, 2023
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I agree with the other answers that monitoring the motor current is probably the best option. Plus shutting off power if the motor current is to high, indicating a stall condition.

How accurate does your monitoring have to be?
A simple solution, albeit not very accurate, is using a resettable fuse in the power cord leading to the motor. Under normal conditions (motor running) the current is low and the fuse is inactive.
When the motor stalls, the current will rise and the fuse will be triggered, turning off the motor. As long as the stall condition is present, the fuse will be held in the active state, limiting the current to the motor.
Once the stall condition has been removed and the fuse has been given a bit of time to cool down, the motor can be operated again.
Of course the fuse value needs to be determined such that both normal operation and stall condition are adequately covered.


I can't imagine any solution more simple than this.
And you don't get notifications :(
it currently has it's own breaker, but by the time it pops, it's too late and the motor has fried. Also, if I don't catch the stoppage in time, there is enough powder that backs up in the cyclone to which will sieze the rotary valve.
 

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kellys_eye

Jun 25, 2010
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I'd go with the 'missing pulse detector' (MPD) version and then decide which method of pulse detection you want to use. Naturally this solution will involve building (or having commissioned) the construction of the MPD and the experimentation with the signal detection circuitry so, as far as 'speed' is concerned, this isn't going to be an overnight solution.

But....

As expensive as my original 'relay' version suggestion is - but it's likely available elsewhere, cheaper - RS aren't known for low cost (rather they are better at reliability) there may be other versions of the same device, probably a cheap Chinese equivalent, if you're that cost conscious.

Buy cheap, buy twice usually ends up the case and when you consider the development/build time and associated costs, that relay gets to appear to be very much more value for money than you first imagine.
 
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