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[C-3PO]

 I have been playing with stepper motors for a while and believe they have lots of uses in radio control models.
 
They are super smooth and via a controller board (software) you can vary the speed, step from a known position to another very accurately.
 
The biggest frustration is they have no "position feedback" unlike a servo which has an integral potentiometer which enables position tracking & fairly accurate position reproduction.
 
Often when using steppers you need to identify a "home" position when you power on and from that point you can control the position accurately by counting steps, but if you experience a power failure the position information is lost and the system needs to be reinitialised - this can lead to a non viable/complex/frustrating solution.
 
I have recently been using a non contact sensor - you simply locate the sensor near the end of shaft & position a Diametrically Magnetised magnet on the end of the shaft.
 
The sensor is accurate to at least 1/10th of a degree - possibly more - the manufacturer suggests accurate to 4 decimal places, the sensor has low latency as it can keep track of the position even at an rpm of 100,000
 
In the event of a power failure as soon as the power is restored you simply read the sensor and have stepper position information
 
If you want any more information PM me

C-3PO
 

[grendel]

the very accurate motors on telescope tracking mounts use an optical sensor to count the steps and measure the angular position

[C-3PO]

Hi Grendal,

Interesting - I did not know that - I wonder what the optical sensor added to the party apart from perhaps allowing a "home" position to be identified.

Correct me if I am wrong - each time you power up you still have to initialise the system (give it a start-up home position), align it to a star etc so the PID knows the state of play even with GPS enabled scopes

I was the proud owner of this for many years - had some great fun - not sure I could lift it now!!



C-3PO

[grendel]

yes you pretty well have it, not many systems can remember the home position, but more now can be put into a power down sleep mode.