Imagine you have a pet door, with a flap that swings back and forth along a horizontal hinge. For example, this:
The goal is to “baby proof” the door, so a child cannot crawl through.
Currently, I have a Pololu LIS3MDL magnetometer that reads a magnet field relative to the distance of the pet’s collar, which then sends a signal to a push/pull solenoid to “unblock” the flap so it can swing open. This works but draws significant current for a low power application(1A-800mA). The goal of this post is to eliminate the solenoid and replace it with something that draws less current, as this project runs of 4 AAA batteries. I figured it’s best to break down the questions into 3 parts.
After searching the Pololu website, I found some gear motors that I *think might do the trick, the problem is, there are many to choose from. I was hoping for some help to narrow down the choices. In terms of requirements:
- Must run at ~6V
- Torque is not a major factor, just need enough to lift a small plastic blockage mechanism.
- The less current the better, the caveat being that it needs enough speed to quickly unblock the door if a magnetic collar is detected.
Some have plastic gears, some are metal, I’m guessing the plastic motors are relatively low torque? And if so, does that automatically equate to less current?
One requirement that seems a little grey to me is motor positioning. For example, imagine a servo horn connected to the motor shaft. At 90°, it’s blocking the door, at 0°, the door can swing open. My thought process was that the only way the software could know the difference between 90 and 0 would be with an encoder, such as this. Maybe not the exact degree per say, but some metric of where the motor currently is. Is this the correct assumption?
Finally, given the current thought process above, if I ended up buying a low power gear motor, magnetic encoder, and motor controller, would the current generally be greater than a simple servo-based solution. That’s another thing I am struggling with; the choice between going with a servo, or a motor, gearbox, encoder, and controller. I don’t need variable speed, just go to position(x), at whatever speed is fast enough for the door to open by the time the cat enters the magnetometer range.
Sorry for the long post, and thanks in advance!