Small DC motor / switch project

[Vollmer]

I’m new to this forum - excuse my lack of knowledge. I have a project to use a DC motor, push button, motor will push an object, stop at a set point, switch motor to reverse, drive object back to original spot and stop.
Please comment on switches I will need to do this. Thanks everyone.
Vollmer

 

[wwfeldman]

please provide a little more information

What is the voltage of your battery?
What are the characteristics of your motor? (or a manufacturer and a part number)

How is the object connected to the motor, so the motor can move it in different directions?

How will it "know" it is at a set point, so it "knows" to stop?

 

[KlausST]

Hi,

Electronics works with
* voltage
* current
* power
..and so on..

Experienced or not ... without any useful values it will be hard to help.

Please understand that everyone of us will have different ideas what "small", "object", "set point" means.

For me a "sheet of iron" was of maximum 2mm in thickness and maybe 1 kg of weight. Then I worked with a bridge constructer company. They even called a 300mm thick solid piece of steel with many tons of weight a "sheet of iron".

Klaus

 

[d123]

Hi,

Depending on a lot of things, three pin limit switches could be used to detect set point then reverse motor direction. One limit switch is to reverse polarity to return object to start point, second to cut power to motor placed at start point. You would need a latch circuit to keep the motor running in both directions, reset by limit switch signals,, maybe a flip-flop or two or something like that Fun puzzle to think through, not too hard but nor too easy to implement. Using timers is messy and hard to get timing right and usefully repeatable, stick to latching devices.

 

[d123]

Hi,

Are you familiar with H-Bridges or motor drivers? Do you plan to implement this with code and a microcontroller or with a discrete component circuit? Assuming a rotating type of motor, is it a three-phase AC motor, a large powerful DC motor, a small solar motor, or a small, 5V or 12V or 24V motor?

What's the supply voltage?
What are the motor supply voltage and current requirement specifications? Does the datasheet specify the motor's resistance?
Are limit switches okay for your application or would another motor position sensing method be necessary?

If the requirements are something I can do and you tell me the four things above I need to know, I can try to put together a circuit (if the weather isn't bad tomorrow) for you to start with.

I did a very similar thing as first foray into electronics and bits of it were a learning curve, others a confusing nightmare, so if you are new to electronics, I empathize more than you can imagine and want to help. I don't know that much either but am familiar with that kind of DC circuit.

 

[d123]

Hi,

Without knowing if your application motor and object movement is horizontal, vertical, globular, opaque or transparent surface, in a clean or dirty environment, indoors or outdoors, aesthetically sophisticated or a learning tool for children... Lots of variables for better choice of switch.

Some switch (position sensing device options):

Non-contact magnetic - Reed relay (uses "a lot" of current for my tastes)
Hall Effect sensor (e.g. 3mA supply current)

"Non-contact" optical - light dependent resistor, LDR, easy to use, low suppy current (affected by ambient light conditions)
IR sensor and photodiode pair (bad for having to place one on the moving object and power it, low signal level needs shifting up)

Physical/contact sensing - limit switch (low power, easy to implement, could suffer from contact bounce which is simple to overcome, object may not force lever enough to actuate it or trajectory miss it competely but unlikely, might make project look clunky but avoidable).

There are other kinds, such as pressure sensors and so on.

Model railway designers are pretty cool precision application circuit designers who deal a lot with sensing moving objects, timing, stopping at the right place, etc. and their ideas and solutions might be a great help.

 

[d123]

Hi again,

Here's a simple circuit that should be able to implement the function as I understood it.

Remarks:
H-bridge can be sustituted with L193D quadruple half-bridge driver IC for loads under 400mA.
My debounce circuit is simple, uses a lot of parts and could be better - there are far smaller and far better ones documented all over the Internet.
I apologize for the horrible, yellow block models in places...
As there are no specs (10A, 220V AC or 125mA, 5V DC motor?) the circuit is low-power. Easily converted to higher power.
A, B, X, Y signals can be replaced with any suitable sensor/switch/logic combination.
It's an old-fashioned, simplistic approach using typical components, but very workable. Better would be an MCU.
Common sense is to see the H-Bridge is quite basic, it could be added to but is functional as seen in the schematic.

 

[betwixt]

Think I can design this with four components....
1. DPDT relay
2. 'start position' limit switch
3. 'stop position' limit switch
4. push button to get it going.

Brian.

 

[d123]

Hi Brian,

I seem to have scared the person away with my zeal or something

Think I can design this with four components....
1. DPDT relay
2. 'start position' limit switch
3. 'stop position' limit switch
4. push button to get it going.

Brian.

Well... Let's see it then, be a sport. I'm always keen to see how other people implement circuits so I can learn from them, especially engineers with far more know-how and experience. Does your version use a latching relay or latching pushbutton or neither?

 

[betwixt]

Just a dual pole change-over relay to reverse the power connections to the motor. The 'start end' limit switch turns the power off when it is operated. The 'far end' switch operates the relay to reverse the motor voltage. The 'get it going' manual switch temporarily shorts the 'start end' switch.

In an idle state, the start end switch disables all the power so nothing operates. Bypassing it with the push button starts the motor and at the same time closes the start end switch so it continues to run when the button is released. When it reaches the full extent of travel, the far end switch operates the relay coil and the motor pulls back until it again disables itself by opening the start end switch.

It makes an assumption that the push button isn't held down continuously as that would leave it in 'pull' (reverse) operation after it had returned home.

Brian.