I ordered this motor from amazon recently since it seemed to have matched the needed specs to drive my smart-curtain project. When programming the encoder channels, I realized the encoder may not have the accuracy I thought it would have. The PPR spec for the motor is 11, which if I understand how these encoders work correctly, would only give me an resolution of 32.72 of a degree rotation (360/11).
I continued my search and found this one today, which claims to have "828" PPR. However, it gets this resolution by multiplying the actual PPR (12) by the gear ratio (69). I don't think this really gets me any closer, since I can not 'Poll' the sensor channels fast enough in order to tell the motor to stop somewhere within this resolution. I would only be able to tell the motor to go to the mechanical position by a factor of 30 degrees (360/12).
For my project, I would like to turn the motor with an accuracy of at least 1 degree, almost like a stepper motor. This way if the length of my curtains change after relocating to a different apartment, I could have a high degree of accuracy to still be flush to the bottom of any window frame.
I also considered a magnetic sensor from the bottom which could signal this instead, but this would introduce another piece of hardware to install, make cable management more difficult and I feel complicates things. I think it would be a much better design overall just have a single motor with a good encoder resolution to be able to determine this instead.
The speed of the motor would need to be between 86-100 rpm or so (give or take) to open 6 ft length of curtain between 6-8 seconds (given the diameter of the PVC being used).
Stepper motors almost sound like the thing to use here, but they were not considered because I need high torque, continuous rotation, and my speed requirements seem to be considerably high for these types of motors. Speed is apparently a specification that is left out of the product details for steppers, so it has been very challenging to find one that is fast enough for the project when browsing catalogs.
Given the information above:
Am I understanding how these encoders work correctly? The PPR on these encoders seem surprisingly low to me!
Should I be using for a stepper motor instead? If yes, where can I find one specific enough to meet my project requirements?