A few years ago I made up some vent openers which use windshield wiper motors. They work well for the small greenhouse, but the frames have had some structural problems in strong winds. For the dome greenhouse I’m using linear actuators to operate the vents. The actuators have a lot more lifting strength and can withstand stronger wind forces.
To attach the actuator to the window frame, I took a piece of angle iron and made a cross brace. The brace will fit about half-way up the vent. I cut off a section from each end so that there were tabs that would be used for bolting the brace into the face of the vent frame. I then welded a couple of tabs into the bracket which provided the connection linkage for the actuator. After rounding over the edges and cleaning up some of the welds, the bracket was attached to the vent frame.
The rest of the braces are standard steel bar stock that are bent at slight angles. There are four of them which go from the greenhouse struts to the back side of the actuator. Because of the odd angles of the dome, a few of braces need to be bent as compound angles. If this was a traditional vent the angles would have been much simpler bends.
I temporarily bolt the top brackets to the back side of the actuator and mark where the brackets connect into the dome’s strut. It wasn’t necessary, but I set the actuator to be level when it was closed, simply for aesthetics. I drilled out the first hole in the dome strut and attached the bracket. Once the pieces start to hold themselves in place, it’s much easier to mark and attach the remaining brackets.
The bottom brackets are marked and installed the same way. It’s just a bit more critical to make sure they are placed properly so that the vent is pulled completely closed when the actuator is fully retracted. Once all four brackets are secured, the pyramid shape from the triangulation creates a sturdy mount for the actuator.
Now that it’s fully assembled, a quick test is in order. All the pieces are cleaned and painted to give the system a nice new look! Once the paint is dried, it’s a quick reassembly and then time to it get wired to the controller.
A regular two-conductor wire is used for each actuator and each vent opener has a line that runs back to the controller. The actuators have built in limit switches which stop the motors automatically. To open and close the vent, you just have to reverse the polarity of the power in the wire.
The thermostat controller is a prototype six-relay control unit that can be programmed to set each vent to open on independent temperatures. The unit can be programmed to sample the temperature at predetermined intervals and also delay the change between relays so that all the vent motors aren’t running at the same time. This keeps the unit from drawing too much power all at once. Each relay can also be disabled and forced into an open or closed position. There are more details about the thermostat in the description area of this video.
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