I'm building an arduino-based robotic arm which is meant to pick some objects with a two-finger-like structure. The problem is I need to detect the servo stress (the moment when the servo really holds the object) to stop the servo and prevent it from squeezing the object. Is there any way to do this with an Arduino Uno?
Electronic – arduino – Detecting servo stress/load
arduinoservo
Related Solutions
What you want is a motorised slide potentiometer. These are used in top end mixing desks. When a preset is recalled from memory the sliders all move to the right position.
For example, sparkfun has this one: http://www.sparkfun.com/products/10734
It sounds like you want to move the car manually and have the Arduino record this movement, then "play it back" later.
If this is the case, using a rotary encoder (example part) of some sort would be a simple way of doing it. There are various options to detect the rotation and mounting methods, magnetic sensors, optical sensors, etc so have a look around and see what suits your project. Use to sense the amount of rotation, record and then simply tell the stepper to do the same.
Since the stepper has magnets and windings that will generate pulses on movement, you can also use the stepper itself as an encoder, so you may want to experiment in this direction. Here is a good page on the subject with an example circuit shown below (written by a very knowledgeable and enterprising chap on the Piclist)
Best Answer
Force/pressure sensors will be more "real life" accurate, reporting directly the force being applied to the object. Whereas current measurement only gives you one piece of data for extrapolation among many other parameters which may be variable. Precise pressure sensor are pretty expensive. The current "sensors" may be much cheaper and possible smaller.