MOD: Please merge with an existing topic if appropriate.
Here is yet another servo point-motor hack. As you can tell from the pix, I'm not kidding when I say "hack"! I would not go as far as calling it as a prototype - it's more a "proof of concept". I have a version that uses 3D printed parts and a much smaller micro-switch rather than the finely crafted plywood and gigantic micro-switch you see here. The "production" version has the micro-switch mounted alongside the servo body rather than at right angles to it, and the actuator bears on the underside of the cam, but it's a lot easier to see what is going on with this version.
"But, how does it work?" I hear you ask - or more likely you don't.
This is how you connect it.
It's very similar to a light that's controlled by two switches. When you flip the panel switch, the motor starts and keeps going until the cam flips the micro-switch. When that happens, as both motor connections are now at the same potential (either 0 volts or plus volts), the motor stops. When you flip the switch the other way, the motor reverses until the micro-switch flips in the other direction at the other end of the cam rotation.
The micro-switch does not immediately flip when the cam starts to rotate because its actuator arm is pressing against a segment of the cam that has constant radius and positions the actuator at its mid-point. This works because of the hysteresis produced by the over-center "snap switch" inside the micro-switch. The actuator always has to move beyond the mid-point of its travel before it will snap into the other state.
The advantage of this method is that there is no current draw at all when the motor reaches the end points, and it is completely immune to electrical interference. Also, no momentary switches are required, so the panel switch position indicates the point setting.
It works best on 1.5 volts. To make it easy to set up, I cut the end stops off the final gear in the servo, but that is not essential. For automation, a relay or electronic buffer could be used instead of the panel switch.
Edited by AndyID, 10 March 2015 - 14:14 .