hobby motor/servo-controlled 'flap'

[zakleerite]

hello all,
I intend to have a hobby motor control a small, lightweight door or flap.
This door would be about 8cm/3" square, and would be mechanically "normally closed". When temp reaches a certain setpoint, the door/flap/louvre would open.
I currently use a standard house thermostat to directly control a 12v PC fan.
Now, I want the flap to open when the fan kicks on, and close when the fan is turned off by the thermostat.
I envision a small hobby motor with perhaps a simple limit switch/polarity reverse, or perhaps a simple electronic control circuit.
I have been out of the hobby for so long, I'm afraid I've forgotten much of what I used to know. I'm fairly certain I used to know something, as I still have all these old resistors, capacitors, etc laying around.
Ideally the same voltage that powers the fan would serve as an input signal for the motor control - 12v = motor on in 'forward direction' to open flap. 0v = motor in 'reverse' direction to close flap. I have found some small micro controllers and digital temp sensors, and would consider moving to this, especially if it eases the motor/flap control issue.
Thanks much for any input. Nice forum you all have here!
cheers

 

[mneary]

If you can easily get 5-6V at 1A, I would consider a "hobby servo". Feed it from a 555 which can switch between two positions.

 

[Boncuk]

Use an air operated door.

No electronic malfunctions.

Mechanical malfunctions might happen with or without electronics.

Boncuk

 

[dougy83]

I envision a small hobby motor with perhaps a simple limit switch/polarity reverse, or perhaps a simple electronic control circuit.

Sounds good to me. Perhaps a relay to control the direction of the motor. See attached.

 

[shortbus=]

Instead of a motor use a solenoid and a lever attached to the door. By working out the pivot point distances ( draw to scale or use poster board and a thumb tack) you can make it move as far as you want.

With a solenoid and lever you don't have to come up with a mechanical drive system from the motor to the door. Or have to come up with a forward and reverse, or a way to limit travel. Just a simple on and off.

If you want 12VDC operation, go to a car junk yard and get a power door lock from a 1980's up GM car.

Cary

 

[mneary]

Instead of a motor use a solenoid and a lever attached to the door. By working out the pivot point distances ( draw to scale or use poster board and a thumb tack) you can make it move as far as you want.

With a solenoid and lever you don't have to come up with a mechanical drive system from the motor to the door. Or have to come up with a forward and reverse, or a way to limit travel. Just a simple on and off..

Cary

Unless you have a complicated latching system, a solenoid draws power all the time it's 'on'.

 

[mneary]

OK, I needed a servo tester and figured this would be a good project. Attached are .png schematic and Eagle files to make one. It assumes you have a robust 4.5-5.5VDC. J1 is the input, if you leave pin 3 open or low then R4 determines the initial servo position. Pull R1 up and the servo is set by R3 and R4 in parallel.

You can scale C2, R2, R3, R4 to convenient values: R2*C2 should be somewhere around 50ms. R3 and R4 (max value) around 5-10ms. R1 needs be pretty high; if too low it changes the period along with the pulse width. These aren't real critical, you can see I took a lot of latitude. The photo is of my working unit.

If your logic voltage is higher than 6V, change R7 so the output pulses aren't over 5V (some servos don't like that).

If using BC5x transistors, watch the pin out. It's opposite the 2N390x. (CBE vs. EBC)

 

[indulis]

You might want to consider something along these lines...

Linear Actuators, Linear Motors, Micro motors, Electric Motors

 

[Magen]

Another option would be to look at the windscreen wiper motor. I recall a project in EPE or Elektor that used this method to open and close an attic window.

 

[shortbus=]

Unless you have a complicated latching system, a solenoid draws power all the time it's 'on'.

The power door locks I referenced are a motor driven solenoid. The motor shuts off when it reaches the end of travel.

Cary

 

[mneary]

Please look up solenoid in the dictionary. A solenoid is a loop or coil of wire.

A solenoid draws power all the time it is 'on'.

A motor needs limit switches or some other kind of control system.

 

[Boncuk]

OK, I needed a servo tester and figured this would do it.

Hi mneary,

here is a hint how to make the transistor and R7 value easily readable. Supposedly it's a 2N3906 and R7 is 10K?

Smash the part and move name and value to a vacant space.

Boncuk

 

[mneary]

Hi mneary,

here is a hint how to make the transistor and R7 value easily readable. Supposedly it's a 2N3906 and R7 is 10K?

Smash the part and move name and value to a vacant space.

Boncuk

Thanks for the reminder. I was so happy to finally get it working that I forgot to touch up the schematic. I'll correct and replace the files. You'll probably noticed that I moved some things on the layout after taking the photo. Since I never do silkscreen the .brd was also full of labels on top of one another.