ptp
USA
Asked
— Edited
I'm looking for a method to stop the gripper servo when holding an object. 
I tried a few options:
1) servo potentiometer analog read
The values are noisy, and needs constant calibration, requires short delays between the readings (flood issue?)
2) Force sensor analog read (picture)
The values are noisy and depends on the touching surface.
3) Tactile button/pad digital read (picture)
similar to a bumper switch (picture) seems more simple to detect (digital signal) but so far nothing small to fit the gripper.
Any suggestions ?
they are small, and they only work with a strong pressure.
plus i will a need a bunch of them to cover the touching area.
This is the same pcb as my SMART servo board just with different firmware. One thing you have to bear in mind is the start inrush current of the motor (start current spike) this must be ignored by the processor.
There is a very simple way to do this but it is only simply digital with one grasp pressure, but you would not need to add any switches, potentiometers, force sensors etc to the claws.
Take a reed switch then wind a coil around the glass envelope, the winding turns have to be found by trial and error - now the coil is wired in series with the claw motor. When a stall occurs (object grasp) current to the motor will increase significantly which will increase the EMF of the coil, with the correct turns on the coil this will make the reed switch close and this would then signal to a v4 port line that something was grasped which is what you are looking for. Do not forget that on motor start up you will get a false indication on the line (inrush current) so this pulse needs to be ignored. You will probably need to take into account position holding current and make sure that the reed is not triggered at this level.
Tony
May I ask what value and wattage resistor you use as the in-line current sensor?
You can see the resistor in the top left hand corner of the board above the H-bridge. The opamp I use is a (Microchip) MCP601
Tony
Thanks for the suggestion, last night i made some tests and i got mixed results, basically the servo was sweeping back and forward and i got some current spikes.
I'll need to try different circuits and amplify the signal to get higher resolution.
If i cannot remove the spikes, i'll do continuous reads plus a software filter e.g. median
Thank you for the information.
Nice tech... i can't see the price neither the availability it must be expensive...
Precision Coil
for sensing the current going through a wire. If motor stalls current will be high,
so define a treshold and that might work.
Good luck,
Greetz