Hi all, I was referred here by the Pi form as the arduino might be more appropriate. I have had a look around on the forum already, and although there are similar projects, I can't find all the answers I'm looking for (assume I know nothing please).
So, the project would be an automatic door opener on a timer. My questions are:
This was originally a Pi idea, and I am familiar with the Pi. Not too familiar with the Ardunio, so is this possible? I was told that the Pi uses too much power for this, so how does the Ardunio differ?
Is there anything that can power this in isolation for about a week?
Do small 12v motors hold their position when powered down. Ideally, I would like the motor to hold about 2kg (an over estimation) with no power. I've read different things on this forum, so I was hoping someone could clear it up for me (and maybe show me an example of one which can do this, if they exist).
A PI probably consumes 500mA at 5V? An arduino can consume say 40mA-80mA (depending on the board) at 5V. Also you can put arduino to sleep to virtually consume "nothing". You did mention a motor so that might be consuming the majority of the power when arduino is controlling it. Geared motors have some torques from the gear box when powered down, not a lot. What are you planning to do? Holding a door in the open position without power? Supply the whole story. You can always put counter weights on your door so that the motor needs little to open it and keep it open.
1 and 2 already answered. 3 A small 12v motor covers a very wide range, and are not designed to open doors and hold them in position. A motor has only rotary motion so need some mechanism to translate and link it to the door (unless you place it a the door fulcrum). Instead of a motor try an electrically operated Linear Activator (eg Gimson Robotics).
A motor drive through a worm gear will hold position when the motor is powered off. However you could not move the mechanism manually without breaking it so it may not be appropriate for your door.
Another idea to think about is adding a brake to the mechanism. A simple servo could be used to apply a brake - or, perhaps, to release the brake when the motor needs to work.
This was originally a Pi idea, and I am familiar with the Pi. Not too familiar with the Ardunio, so is this possible? I was told that the Pi uses too much power for this, so how does the Ardunio differ?
I've never used the Pi, but the Arduino is good for "simple" input/output, such as detecting a button-press or turning-on an LED or motor, etc. (I don't believe the Pi has similar I/0 pins that can be easily programmed & controlled.)
Is there anything that can power this in isolation for about a week?
A car battery? It depends on how much current the motors require and how much you run them. The amp-hour or milliamp-hour rating on a battery is an indication of battery life... A 1000mAh battery can run at 100mA for 10 hours, etc. The Arduino will consume some energy when "idling", but the motors will consume a lot more when they are running.
A garage door opener or an automatic security gate probably really would require a car battery and a big motor.
Do small 12v motors hold their position when powered down. Ideally, I would like the motor to hold about 2kg (an over estimation) with no power. I've read different things on this forum, so I was hoping someone could clear it up for me (and maybe show me an example of one which can do this, if they exist).
No. Most electric motors spin freely when not powered. If there is a gearbox to gear-down the motor, the gearbox often provides a lot of resistance when turned "in reverse".
Depending on the application, you may need some kind of latch. If some kind of friction-latch (like a kitchen cabinet, etc.) won't work for you, a solenoid can be used as a "lock" that releases only when energized.
Sorry for not having elaborated more on the project: The door is a chicken coop door, and is a guillotine design. I would have the arduino set on a timer to power up, and lift the door in the morning, and lower the door in the evening.
I was wanting the motor to hold the weight of the door when powered down to save the power supply, as the power supply will have to be portable.
The worm gear thing sounds interesting, as I have no need to manually use the little door - so I'll look into that!
Does anyone have any external power supply recommendations for this kind of project?
Your statement "I would like the motor to hold about 2kg (an over estimation) with no power." makes
not logical sense. You need to specify something like 2Kg at 10cm or 2Kg at 100cm.
Motors are rated in torque. A force at a distance( in metric, often Newtons and not Kg ).
With the proper clutch that slip under load, something like a windshield wiper
motor comes to mind.
Dwight
crelding:
The door is a chicken coop door, and is a guillotine design.
If the door will fall closed under its own weight then I suggest a motor with a worm drive to wind up a string attached to the top of the door. This has the advantage that the motor does not have to be near the door where it might get fowled (sorry ).
If your door weighs 2kg then you need to figure out the turnning force (torque) that that generates. There is a simple idea for doing that in the Thread Stepper Motor Basics
Yeah I've seen other threads on this topic, but non have all the info I need (hence this thread).
@dwightthinker - Ok, so I clearly know very little about motors, lol. The door will be held vertically, so does the 2kg not stay as 2kg regardless of the distance? (it would only move about 1m) (sorry, I really don't know these things).
I had a look at the marine batteries, and they seem crazy expensive! I've seen elsewhere on the forum that 3 AA batteries could power this kind of system for a few months, so was thinking more about a battery back like this (solar pannel would be cool too).
@Robin2 - Just to clarify how these worm gear motors work - it can lift the door. When the motor powers down, it can hold a weight, and then when it powers up, it can turn the reverse way and close the door, right? If so, this is exactly what I want!
crelding: @Robin2 - Just to clarify how these worm gear motors work - it can lift the door. When the motor powers down, it can hold a weight, and then when it powers up, it can turn the reverse way and close the door, right? If so, this is exactly what I want!
Yes.
A cheap source of a powerful 12v worm drive motor would be the screen-wiper motor from a crashed car.
You will also need limit switches to tell the Arduino when the door is open (or closed) and to turn off the motor. And relays or a suitable motor driver between the Arduino and the motor to handle the high power for the motor.
Yes you need something to limit the travel.
If it is going to be exposed to the elements you
need to worry about moisture effecting the switches or optical
interrupters.
It will need a clutch for safety reasons. The motor will jam
once stopped and without ripping it apart, it can not be moved.
Most garage doors have a current sensor on the motor that detects
something blocking and also a light beam across the base
of the door.
It would be easier to detect an object jamming it is if the door
had a counter balance of some sort. That way the current value is
smaller for the trip.
Wiper motors are more than strong enough to handle 2Kg,
depending on the lever arm length.
Dwight
Rather than the complexity of a clutch I would choose "string" that is strong enough to lift the door but weak enough so the motor can break it without damage to the motor or gears.
For safety, you might have a self resetting
circuit breaker. That way, if the motor had high load,
it would draw enough current to trip the breaker.
The arduino can detect a the loss of voltage to the motor
and reverse the motor if it tripped.
A diode across the circuit breaker would allow this.
Something like polly fuses comes to mind.
This way, if someone or critter got caught it would reverse
and attempt to correct it.
The string failure is not a bad idea.
Dwight
Yeah I've seen other threads on this topic, but non have all the info I need (hence this thread).
I think some of the discussions had ideas of using counter balanced doors where the motor did not actually hold any weight, just moved the door. Somewhat like the counter weighted sash windows in the school I went to way back when.