I am working what should be a simple project. Its two stepper motors spinning two devices that have physical stop limitations. If over run the devices will be damaged. One of the devices specifically is a vacuum variable capacitor which has no real "stops" as such but if turned too far in one direction will destroy the part. There is no way to mount any kind of limit switch and no room to "rig up" a screw block for the purpose of mounting limit switches. I have come to the conclusion that a NEMA 17 or 23 stepper motor with absolute encoders would be the simplest safest solution. I have searched and do not see much out there. Can anyone offer up a source and part number for such a stepper motor? Not being an expert on the subject I figured someone here may have a suggestion.
Is this what you want?
https://www.pololu.com/product/2278#:~:text=This%20NEMA%2017-size%20pancake,both%20edges%20of%20both%20channels.
Absolute encoders are available that can be attached to a stepper motor shaft using a shaft coupler. Choose a stepper with output shafts extending from each end and attach the encoder on the back side.
In a properly designed setup, stepper motors don't skip steps, so it is not common to see them combined with an absolute encoder (which are expensive).
Thank you for the quick reply. The action after the controller losing power is where we run aground as the last exact position is lost to the controller. That is where the stepper can run the devices past their stops and be damaged when restarted. The controller knowing exactly were in the rotation the motor / device is, even after a reset is key. I have a small set footprint so adding additional apparatus is difficult and why I was looking for motors with encoders built in. Can't imagine my simple project and this type of situation is rare and uncommon.
I gave you a link to built-in encoders.
I looked at that one but the encoder appears to be by definition more of a "incremental" encoder . The result is it does not store the last know position in the cycle prior to a reset of the controller. They claim it is a quadrature encoder. (which is new to me...) Here is more tech on the subject. https://forum.digikey.com/t/beginners-guide-to-the-quadrature-encoder/40827
I didn't suggest that it was. However, as you discovered, you are extremely unlikely to find a stepper with a built in absolute encoder that matches your requirements.
Was not inferring you did,. Yeah, just lamenting as this was going to be a simple remote operation over WIFI and is turning into more work than its worth (and $$$. haha.)
I learned something.
Fascinating subject I thought too.
What about an IR light aimed such that a remotely mounted IR receiver can detect it, maybe using some sort of light gathering and focusing device in front. These are fairly sensitive devices (IR Xmt/Rcv) so the distance can be several metres/yards.
I understand your project, but wonder if the tuned circuit cannot give feedback so your program will know the direction to turn and when it has turned enough?
Once I can manually remotely operate the tuner, that will be a next step to sense SWR and auto tune. Initial project is to hit the Arduino via WIFI to a web page on the Arduino and move sliders to operate the cap and dual coupled roller inductors accurately and have memory settings assigned with the ability to jog adjust fine tune. Others have done similar but not thru WIFI. The inductor I can put limit switches on for home but the vacuum cap I have no way to track that shaft accurately so the need for s stepper motor with absolute encoder is critical. Last thing I want to do is trash a $250 cap...
I will use WIFI to attach to the Arduino over my home network, if that is what you are referring to/
It seems your post got scrambled or something.
Not sure what you mean.
The AS5600 hall-effect magnetic absolute encoders are pretty small. I see them offered on boards with magnets and headers at $10 for $3, and there's a library: GitHub - RobTillaart/AS5600: Arduino library for AS5600 magnetic rotation meter
If either a NEMA17 or NEMA23 would work, maybe there's space to stick an AS5600 in the size difference between the two.
Have you considered attaching a 10 turn pot to the motor shaft. Use a cog belt to transfer movement.
Thank you. I will look into that.
It did cross my mind but the vacuum cap has a 23 turn travel from start (hard stop) to end. Twenty four turns and it starts to come apart at the shaft. (unscrews the shaft from the cap) The cap is by far the biggest pain in this and why I have to have an absolute track on its position even after reset of the controller. It does perform much better than a traditional open plate cap.