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Step motor - "There and back again"

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Roy Arne Nordmarken

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Hi everyone!

I hope I'm posting this question in the right forum. If not, please let me know so I can move my question.

What I want to make is a small application that will turn a (step) motor for x number of turns when power (DC 12) is on. When power is turned off, the motor should return to it's original state/turn back the same number of turns. The motor can not be very big, and doesn't need to be very powerful. If possible, it would also be nice to be able to adjust the speed of the motor. Any thoughts?

BTW:
I have never built anything with small electronics before, so please try to answer in simple noob-friendly terms.

Thanks!
 

How can the motor "turn back" when power is removed? You need power to make the motor turn in either direction. You could use a battery to do the return job, or a really huge capacitor. What do you want to allow?
 

Yes, I was thinking about maybe using a small rechargeable battery to turn the motor back when the power is removed. But I don't know what's out there. Maybe there already exists applications like this, where there are only one source of power, and something that helps the motor go back to it's original state.

What I want to accomplish is to have a small motor open a "hatch" to reveal a mounted phone in my car when the ignition is turned on. When I turn the ignition off, and lose the power signal, I want that hatch to close.
 

Roy Arne Nordmarken said:
Yes, I was thinking about maybe using a small rechargeable battery to turn the motor back when the power is removed. But I don't know what's out there. Maybe there already exists applications like this, where there are only one source of power, and something that helps the motor go back to it's original state.

What I want to accomplish is to have a small motor open a "hatch" to reveal a mounted phone in my car when the ignition is turned on. When I turn the ignition off, and lose the power signal, I want that hatch to close.
Click to expand...
You could use a power feed directly off the battery, and use the ignition switch just as a signal to trigger the stepper pulses.O
 

Yes, I was thinking about that also. That, or using the ignition to power the motor in one direction, and a seperate battery to turn the motor back. Or maybe I am lucky and can find a lead that turns positive when the ignition is turned off...

But I am really new to this, have no idea which parts to use, if I need a microcontroller, etc. Do you have some suggestions for me? I want this to be cheap and simple. Could it be possible to use the motor controlling the reading arm of an old hdd? It's no problem to buy parts, just that using something that I already have would be cooler :)
 

Another option is to use a servo of the sort used for radio controlled planes, cars, etc. They're fairly inexpensive and easy to use. A very simple (and cheap) circuit to control it could be made with a 555 chip. Only problem is (AFAIK), they all use a supply voltage of around 6V, so you'd also need a voltage regulator or something to drop the car battery voltage.

A super-simple option would be to use a motor or linear actuator to open the door when power is applied, and rely on gravity or a spring to close the door when the power is switched off.
 
godfreyl said:
Another option is to use a servo of the sort used for radio controlled planes, cars, etc. They're fairly inexpensive and easy to use. A very simple (and cheap) circuit to control it could be made with a 555 chip. Only problem is (AFAIK), they all use a supply voltage of around 6V, so you'd also need a voltage regulator or something to drop the car battery voltage.
Click to expand...

This sounds like a very easy solution! If I'm lucky, I might find a lead that gives me positive (+) when I turn the ignition off, maybe the inside "roof light". This way I can turn the current, and turn the direction of the motor. Maybe I don't even need the 555 chip? Maybe there is a kind of automatic fuse out there that turns the current/motor off when the resistance becomes too big, which also resets when the current turns?
 

Roy Arne Nordmarken said:
What I want to accomplish is to have a small motor open a "hatch" to reveal a mounted phone in my car when the ignition is turned on. When I turn the ignition off, and lose the power signal, I want that hatch to close.
Click to expand...
A stepper motor is more complicated than what you need. Same with an RC servo. You could avoid all use of fancy electronics if you use a simple 12 volt DC motor and two limit switches. When ignition is turned on, power the motor in one direction until the hatch hits a limit switch. When the ignition is turned off, power the motor in the other direction (using a direct feed from the battery) until the hatch hits the other limit switch.
 
Re: Step motor - "There and back again"

abguy said:
A stepper motor is more complicated than what you need. Same with an RC servo. You could avoid all use of fancy electronics if you use a simple 12 volt DC motor and two limit switches. When ignition is turned on, power the motor in one direction until the hatch hits a limit switch. When the ignition is turned off, power the motor in the other direction (using a direct feed from the battery) until the hatch hits the other limit switch.
Click to expand...

I have found a 5V motor from the steering of a rc car now. I think this has limit switches, as it just turns a total of 0,75 turns in each direction. So, what I have is that motor and two 12v currents. One will only give power when ignition is on, and the other will give power no matter what state the ignition is in. I guess I can use the ignition controlled current as signal, and the other current for power. But how do I invert the polarity of the current when ignition is turned off? And what should I use to go from 12v to 5v? Any regulator?

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Re: Step motor - "There and back again"

Roy Arne Nordmarken said:
I have found a 5V motor from the steering of a rc car now. I think this has limit switches, as it just turns a total of 0,75 turns in each direction. So, what I have is that motor and two 12v currents. One will only give power when ignition is on, and the other will give power no matter what state the ignition is in. I guess I can use the ignition controlled current as signal, and the other current for power. But how do I invert the polarity of the current when ignition is turned off? And what should I use to go from 12v to 5v? Any regulator?

- - - Updated - - -
Click to expand...
Just use a series resistor to limit current to the motor. No regulator is needed. To reverse polarity, interchange the two motor leads with a relay, or with MOSFETs. You will have to learn some real electronics to do that.
 
Re: Step motor - "There and back again"

I will look into it!
Thanks for all the help so far! :)

- - - Updated - - -

Will a DPDT relay and some resistors be enough for me to control that 5VDC motor safely from my 12VDC source and signal?
 

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