Automatic swing (Dc motor, relay, 555 timer)

Thread Starter

Experiman

Joined Aug 2, 2019
5
Hello fellow circuit people,

First off, im an absolute beginner in electronics. Also English is not my mothertongue, so if you don't get what im trying to say thats probably the reason.

Im trying to find a way to make a miniature swing. I could just power my motor in one direction with a pulse every few seconds, but it would be better and more consistent if the motor's polarity just switched every few seconds.Also I would like to learn and find out if my theory is possible at all. I have tried some easy circuits using a led light with the 555 ic, but I get stuck at the same point every time. because the circuit resulted in a blinking light, I thought I could get my motor to switch on and off at the same pace as the led. If this was the case I could just hook a dpdt relay on that led output and cross wire connect my motor to it for the reversed polarity. Now I discovered that the power input for the relay was 6V, so the output I got for the led was not strong enough to power the relay and so it didn't switch. I bought a step up module to increase the power for the relay but im starting to think that there is probably an easier way to do this. I wanted to connect a potentiometer to contol the amount of time that the motor's polarity would switch, and the duration of the pulse that the motor would get.

So my actual question is: How can I make a circuit, that reverses the polarity that powers the motor, at fixed time rates (preferably controlable) while the only action required is turning it on. I would like to use 4 AA batteries, a dc motor, a 555 ic, a dpdt relay, a step up, and various types of resistors, transistors and capacitors. Without Arduino.

Thanks in advance!
 

MaxHeadRoom

Joined Jul 18, 2013
19,394
Not sure if this solution may be a little bulky, but an automotive style wiper mechanism runs the motor in one direction which would simplify any reversal circuitry.
Either visit a wrecker to obtain one, or copy this type of mechanism.
Max.
 

Thread Starter

Experiman

Joined Aug 2, 2019
5
Not sure if this solution may be a little bulky, but an automotive style wiper mechanism runs the motor in one direction which would simplify any reversal circuitry.
Either visit a wrecker to obtain one, or copy this type of mechanism.
Max.
Alright, original solution! Will probably work indeed, but I would really like to see if it's possible with components in a circuit, and try to get it to work that way. Thanks for the reply!
 

AnalogKid

Joined Aug 1, 2013
8,220
It certainly is possible. How big is the swing? Specifically, how long are the ropes / strings / whatever between the axis of rotation and the seat.

If you just rotate a shaft back and forth with the swing fastened to it, you might be disappointed. The period of a pendulum is set by the length of the arm. For the swing to move back and forth with a motion that looks natural, the motor has to be timed to the pendulum period. Varying the motor speed will not necessarily speed up the swing.

https://en.wikipedia.org/wiki/Pendulum#Period_of_oscillation

al
 

Thread Starter

Experiman

Joined Aug 2, 2019
5
It certainly is possible. How big is the swing? Specifically, how long are the ropes / strings / whatever between the axis of rotation and the seat.

If you just rotate a shaft back and forth with the swing fastened to it, you might be disappointed. The period of a pendulum is set by the length of the arm. For the swing to move back and forth with a motion that looks natural, the motor has to be timed to the pendulum period. Varying the motor speed will not necessarily speed up the swing.

https://en.wikipedia.org/wiki/Pendulum#Period_of_oscillation

al
That's a good point, I got too fixated on the electronics part.
I was thinking 20cm in height, and from the axis to the seat 15cm. I thought that I could use the motor with a rubber wheel attached to it, and make it so that the wheel launches one side of the seat of the swing, everytime it passes the center.
 

AnalogKid

Joined Aug 1, 2013
8,220
Most electrically-assisted pendulum systems use some kind of sensor or trigger to add the electrical or magnetic boost at a certain point in the pendulum's swing, regardless of its frequency. In this way the system in self-synchronizing.

ak
 

Bernard

Joined Aug 7, 2008
5,334
A simple test. A small 6V DC motor, 1" dia. X 1.5 " long, is direct coupled to the shaft of 15 cm pendulum weighted with 2- 1" clamps = 5 oz., period about one sec. After a soft hand start, oscillation amplitude increased with timed current pulses of about 1/4 sec. Contimplating a timing disc, 1/2 opaque, 1/2 solid with a single beam break detector. The square wave signal is decoded to give a + pulse on each edge as a clock signal into a D FF. The square wave is filtered and applied to the D input ; the Q output is the direction signal which might be applied to @iimagine's
post # 6, H bridge. . Clock could trigger a 555 to give desired pulse length with a motor control switch like a PNP transistor.
Too complicated, Yes, but small & compact.
And it could be operated single direction pulsed to eliminate all of the decoding ?
 
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Thread Starter

Experiman

Joined Aug 2, 2019
5
Hey guys, thanks a lot for all of your replies!
The answers you gave got me thinking in all kinds of directions. Im leaning towards the idea of the magnetic swing, and I think I found a good circuit for it. I'll keep you posted!
 

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