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[on:]

i am trying to make an RFID safe. the mechanism will use a garden gate latch such as this one:
http://www.laornamental.com/Store/product3eb3.html?prdId=523532

The locking part of the latch is mounted on a piece of wood next to a continuous rotation servo. the servo turns and pulls a string connected to the latch which opens it, allowing the door to open. The latch opens and everything, but the problem i am having is that the servo moves past its stopping point on the previous rotation. For example, if on rotation 1, the servo stops at the 1 o'clock position, on rotation 2, it stops just before to 2 o'clock position, and on rotation 3, it stops just past the 2 o'clock position, and so on and so forth. Eventually, the servo turns but no longer opens the latch. I dont think its a software problem because the program simply tells the servo to turn for 1.5 seconds, pause for 3 seconds, and move backwards for 1.5 seconds and stop. Please help.

thanks in advance.

[Reply #1 on:]

You need limit switches, i.e. "turn until button X is pressed, turn until button Y is pressed". A lever microswitch would be the appropriate type of switch.

Without some sort of feedback mechanism there's no way to reliably make a continuous rotation servo turn a set distance.

As an alternative, you can find a few servos that will allow a repeatable number of rotations. They are referred to as "winch servos" and usually go anywhere from 1 full turn to 4 full turns. They operate just like regular servos ... with the exception of the greater range of rotation.

[Reply #2 on:]

Sounds like you really just need a standard servo. 0 degrees = locked, 180 degrees = open. Might need to create a slightly longer arm.

[Reply #3 on:]

Turning for 1.5 seconds is not really reliable, since how much the servo turns in this time depends on how much force is needed for it to move.
Much more reliable is some sort of feedback mechanism.