In using the AL5D to pick up objects of various sizes: if it is programmed to close the gripper to the size of the smallest object, what happens when it grips a larger object? Does it try to crush it and overheat the motor?
Hey,
Yes, it will overheat and burn. Actually, misuse of the gripper is a common issue with new users (especially if it is their first time using RC servomotors or robots).
Therefore, size of objects is a genuine concern for a “dumb” gripper (i.e.: without feedback). Luckily, there is a simple solution to this: adding a force sensing resistor!
You can use the recommended force sensing resistor. We also have an assembly guide for it (valid up-to step 6, since the older software and hardware mentioned in steps 7+ are now discontinued).
If you wish to know more about the sensor you can check out the user manual found.
Simply put, you place the FSR on one of the gripper side (inside) and connect it to either VCC or GND with another resistor (creating a voltage divider). You then connect the resulting signal line to an analog input on the SSC-32/SSC-32U, allowing you to derive the force from the voltage read on that input. Check page 34 of the SSC-32U manual for more details on reading analog inputs. If you are using the older SSC-32 (now discontinued), please note the commands are the same.
Concerning determining the exact force you have to derive it indirectly. Basically, you read an analog value (voltage) from the signal pin. Since you know the value of the fixed resistor used as a pull-down (or pull-up) [typically around 10 kOhm] and the FSR itself is basically a variable resistor, you can calculate from the voltage the resistance. This resistance value can be then transformed into a force!
See the FSR’s manual, page 5 for more details.
We hope this helps.
Sincerely,