How to make a trainable robot reel

[RickDeNatale]

I’m looking for a way to make a reel of monofilament or thread which can be trained to play out and reel in the line and then play back the sequence like the trainable robot arm which uses the analog feedback micro servo.

The problem I want to solve is that during the training I need the reel to provide enough force to attempt to pull the line back in, but not enough to prevent the line from being pulled out or overcoming the tensile strength of the line.

Do you think this is possible with the analog feedback servo motor, or if not are there alternatives?

[adafruit_support_bill]

The analog feedback servos have only 180 degrees of rotation. Most continuous rotation servos have no feedback at all. You would need to add some sort of external feedback mechanism such as an optical encoder.

The Parallax Feedback 360 servo combines continuous rotation capability with digital feedback and might be a good choice here: https://www.adafruit.com/product/3614

Measuring tension could be approached in a couple of ways. You could add a current sensor to monitor the load on the servo motor. But that is not likely to be very precise. A better approach might be to design a strain-gauge into your mechanical structure to measure the stress between the reel and whatever it is mounted to.