I’ve wanted to do this for years but haven’t really come up with the ideal way to do this, and the parameters have changed a bit since I first thought of it.
Here’s what I want to do: have a device that moves the gate latch (normal fence gate, nothing special except it’s a pretty easy latch to lift) and then open the gate - but without the gate being tied to the opener so that it can still be opened manually without a problem.
I know I need to put up a solar panel and probably a 12v battery (no easy power as of now) and I think I need a servo with a pin on the fence post that will rotate into the release of the gate catch but those little tiny servos you generally get with Arduino kits might be a bit lightweight for that. Plus this is going to be in the harsh Colorado sun all summer and any cheap plastic or even 3D prints are going to just get destroyed.
The second part is much more complicated, how to push the gate open when the latch is lifted. I’ve looked at commercial gate openers and they are hard attached, meaning you either choose to always open it manually without the gizmo or you always open it electronically, which I don’t like. So an actuator might work if it wasn’t fixed to the fence but rather just pushed some form of “nub” like it catching on a small wood “L” or metal “L” that pushes it out that way but still allows for you to pull the gate opened manually.
I’ve also considered a solenoid but it would have to hit that gate pretty hard to open it far enough to be of use. Springs were a thought but the way my gate opens means the spring would be on the nice side of the fence facing the street. I really need to push this open rather than pull it open.
Any ideas? Here is the latch I have, it’s quite different than your normal gate latch but that is a strength in this case because a servo should be able to open it easily:
My use case for this (other than being able to open the gate remotely) is for my robot lawn mower to be able to pass through the gate easily to get to the other yard - otherwise I have to go out and open the gate on each mowing day. That part I can work out (API coming soon, ultrasonic sensors, etc).
Bonus would be if the device that opens it could also pull it closed. This has two purposes, the first is obvious that I need to close that gate at some point but the other is that the gate might need to be pulled in before the latch can be released due to the weight of the door (we often have to push on the gate a bit when we unlock it from the outside).
. That picture looks kind of promising maybe, I’ll have to see if I can track it down and find the details. The benefit is that it not only could close the door but keep it open when it’s opened.