What sensor would you suggest to make an actuator stop at a certain resistance(ie 10 lbs). I am trying to make a muscle stretching thing for my son with cp. What about as the actuator draws a certain current it kicks off? I have worked a little with arduino but not actuators.
thanks.
/not exactly sure what you are requesting.
Are you searching for a measuring device (sensor) to use with some existing actuator?
Or are you constructing an actuator of some form yourself?
Actuator meaning an animated or moving part that is the source of motion of any item connected to it.
Servo motors are a good example of something that ‘actuates’
If condition -1 is true, then we need to identify exactly what type of measurement you need…distance? pressure? electrical characteristic?
Knowing that Im sure the best fit for measuring whatever it is can be pinpointed.
That's certainly possible. The same concept is used on your car's electric windows to see they don't close on someones body parts (too hard). I'd be a little concerned about using it to limit the "stretch" on a patient. What happens if it fails ? I'd want some fail-proof method to prevent a way too hard stretch or perhaps too far a motion.skgrain:
What about as the actuator draws a certain current it kicks off?
But yes it can be done.
Measurement I am trying to get is force.
Yes, a safety will be important. I think I will determine the desired strength with something like this
http://www.e-motioninc.com/12V_Actuator … mc102h.htm
then try find an actuator that only slightly exceeds the maximum desired strength. .5 inches/s is the slowest I have found so far but would like one even slower. If it took like 30 sec to reach full stretch then a person could even use a kill switch as 3rd precaution.
Malfunctions of something like this could definitely turn a theraputic device into a middle-ages torture/dismembering instrument…lol! I gots me some bad imagery when I realised what I think its end form might be intended…
yea I should have left out the application part and concentrated on the electronics. 
If you ever get the chance to see what stretching does for a cp kid then you would understand. Its the difference between playing soccer and not being able to walk. The available actuators is pretty narrow really as far as speed is concerned and I understand that running on 6v instead of 12v will cut speed in half.(using a 12v actuator) It will be tested to no end so no worries there.
Just an FYI … you could come up with a wide variety of “actuators” and measure the pull produced via another means. As an example think of a fish scale (to weigh the fish). They usually measure the stretch of the spring and since a springs deformation is proportional to the force exerted, the force exerted by (weight) the fish is determined. So any “actuator” might be used if you insert the proper measuring tool in the loop.
Yea, one way to build in a type of safety would be to integrate somewhere between actuator and human a ‘soft’ link, like bungee cord or other rubber / flexible member that would absorb or mitigate any mechanical overruns or malfunctions that would otherwise have potential for physical harm. Find bungee link with enough strength to meet requirements of desired load, yet would flex or stretch out of spec if some limits are exceeded…
super advice CB