A circuit activated by a motor which drives the motor itself ideas required

[DebarghyaChaudhury]

A retractable thread reel motor circuit ideas needed

Hello ! I am trying to design a circuit which is activated when a micro motor is spinned which in turn makes the activated circuit rotate the same motor in the opposite direction.
I know its kinda confusing but basicly I want it to use it with a reel which when thread is pulled out of it, it retracts back itself on its own. Also I want the motor to sustain even tension through out the thread when the thread is pulled out..........and all this without breaking the thread. ANY IDEAS ?! Any kind of HELP is appreciated.

 

[chuckey]

To make the motor pull at a constant tension, the motor must be run at a constant current. A crude way is to put a resistor in series with it and the supply voltage, which might have to be increased.
You could use a circuit that monitors the motors terminals, when the motor is spun , it will generate a small voltage, so amplify this to use a relay to switch the motor supply on. How are you going to stop the motor? if you use a AC coupled amplifier, when the thread is pulled back and the motor stalls the voltage across its terminals will only be DC so the output of the AC amp will disappear , so the relay drops out.
Frank

 

[DebarghyaChaudhury]

Thank you very much !! It helped me a lot. I am thinking of using a transistor to amplify the current across the motors terminals but I only need about 30s of constant retraction from the motor so I am thinking of PWM with a ne555 ic. Please suggest and once again thanks really appreciate it !

 

[chuckey]

I am not sure of your logic. Suppose you have a bi-stable, when Q1 is on then the motor runs. From stationary, when the motor moves the amplifier triggers the bi-stable and Q1 comes on and the motor runs. At the same time the 30 second timer runs, when it times out it resets the bistable and Q1 goes off and the motor stops. What happens if the thread is not pulled back? What happens if the thread is pulled back after 10 seconds?. I do not see what the timer is used for.
Frank

 

[DebarghyaChaudhury]

Sorry about that , I was just thinking of a hypothesis but I am just a newbie after all.

But basicly the idea behind this is that suppose you take a thread reel and attach two rubber bands on each of the two ends of the reel. Now whenever you pull on the thread from the reel, the reel will try to pull back the thread with equal tension regardless whether the thread is pulled out and tied to something or it is just released to roll back into the reel again- this is what I essentially want from the circuit but I want the circuit to stop pulling back on the thread on either of the following 2 cases: (i) When the thread has already been pulled back into the reel.
(ii) When the thread is tied to some external object and hence cannot be pulled back into reel at all.In this case I want the motor to pull on the thread for about 30 seconds so that it maintains even tension through out the thread for 30 seconds and then stop pulling. So now if I untie the thread again and pull a little of the thread , the motor activates again and pulls the entire amount of thread back into the reel again.


This is absolutely the exact working that is needed from the circuit so can you please help me design such a circuit for me. And thanks for everything !!