I am designing a small handheld electronic screwdriver for a university project. The motor in this screwdriver requires a torque limiter to stop it stripping screws out of plastic parts and i am currently looking to use an LM338 to do this, hoping to use as few components as possible to keep size and complexity down (atleast for V1).
I was going to do it similar to the specification sheet as seen here:
However, this clearly has some issues! 1, my motor can pull 1.45A of current and my small 100ohm potentiometers can not and 2, this also creates a varing potential divider between the LM388 and the motor, slowing the motor down. I just want the motor to be torque limited, not speed limited.
This lead me to a design like this:
However I have not been able to get this working using R1 - 1k ohm, R2 10ohm. The 1km was calulated as shown here:
The 10 ohm is just to prevent shorts and therefore small.
Would anyone be able to give me a hand who has experience with this?
The only other info should probably mention is the motor, which is this:
and has a static resistance of 9ohms (I think).
The datasheet for the LM388 is here: