Greenhouse door opener

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Greenhouse door opener

Post by ajocius » Tue Jul 09, 2019 8:28 am

I would like to motorize door opening in greenhouse, based on inside temperature. Googled for similar project, but can not find one. Has anyone done some door opener? Was thinking of printing some angled rack and pinion that could be turned by stepper motor, which would be controlled by ESP32. The challange is that I would like to be able to open door using hands too. Let's say if weather is cool in the evening and door is closed by motor, but I need to come in to pick vegetables, I would like to be able to open with hand, but that is probably not good for motor? Also, not sure how strong are those motors, could be windy outside some time.

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Re: Greenhouse door opener

Post by jimmo » Tue Jul 09, 2019 12:17 pm

You probably don't want to use a stepper motor as you're not looking for fine control of the door angle? A regular motor with some switches to detect the door position will be a lot simpler (e.g. limit switches). Or if you do want some sort of feedback on the door position, just having the door turn a potentiometer that you can measure with an ADC will probably be a good start.

Also, unlike a stepper motor, it means that you won't have to work so hard against the motor to turn it by hand. As long as the motor isn't turned on and it has sufficient protection against back EMF, then it should be fine.

If you're concerned about the door holding, don't rely on the motor -- some sort of mechanically activated latch would be better. (or a magnetic latch, which means you can choose the force that it applies, so you can still open the door by hand)

Rather than building a rack and pinion system yourself, it might be easier to find an existing linear actuator unit. Sometimes these come with force feedback (so you can do stuff like detect when someone's trying to open the door and use the motor to help them, or stop the motor if it's stuck). (Security gates use these to avoid crushing people...sadly the ones at my old work were a bit too aggressive!)

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Things to consider

Post by pythoncoder » Thu Jul 11, 2019 7:01 am

@ajocius Unless you have a reasonable knowledge of electronics I would look for a commercial motor and controller designed for opening and closing a door, and linking that to your ESP32. A DC motor or linear actuator would be ideal for the job, but we're talking about a fairly powerful machine requiring a suitable controller.

There are factors to consider in the controller design: if you have a permanent magnet DC motor and turn it manually, the motor will act as a generator producing a voltage comparable to its normal drive voltage and with high current capability. The polarity depends on the direction of motion. Without proper controller design, this EMF can do damage. Also, as @jimmo pointed out, when driving the motor the current needs to be limited to avoid risk of crush damage to people or mechanical or electrical damage if something gets stuck.
Peter Hinch

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Re: Greenhouse door opener

Post by mcauser » Mon Jul 15, 2019 6:52 am

Instead of opening/closing a (big heavy) door, how about fans with air-con ducting and 1-way valves to prevent back flow when switched off?

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