Home
JAQForum Ver 20.06
Log In or Join  
Active Topics
Local Time 00:43 06 Dec 2022 Privacy Policy
Jump to

Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.

Forum Index : Microcontroller and PC projects : Rotary switch -- confusion over "poles"  / positions etc

Author Message
Nimue

Guru

Joined: 06/08/2020
Location: United Kingdom
Posts: 314
Posted: 01:32pm 19 Nov 2022
Copy link to clipboard 
Print this post

Hi -- slightly off topic - delete if not right for here...

I want to incorporate a rotary switch into a project.  I want to use this to introduce one of 3 resistors into a circuit to make a rudimentary speed controller.

I have two motors, each powered from the same source, but controlled independently.  The supply to each motor can be  controlled independently by varying the voltage and polarity.  This allows the speed and direction to be controlled by varying the speed of each motor independently.   All simple stuff.

All the above works fine.

BUT the default speed as constructed is far too fast, so I want to add inline resistance.  Again, fine if I do this for each motor independently.

If I constructed this from two rotary switches, I would be fine with what I think is referred to as a 1 pole, 3 position switch to bring different resistances into the circuis for each of the motors.

How do I do this for both motors using one rotary switch, so that the same resistance value is introduced to each motors circuit at the same time?

Having not used anything different than the above switch - I am unsure if what I am looking for is referred to as a 2 pole, 3 position switch?   I guess I could just buy some and bust out the multimeter...

Long question - hopefull simple answer....    

Cheers
N
Entropy is not what it used to be
 
Tinine
Guru

Joined: 30/03/2016
Location: United Kingdom
Posts: 1529
Posted: 04:01pm 19 Nov 2022
Copy link to clipboard 
Print this post

Resistors...Yuk

Grab a cheapie H-bridge and drive it from at least a 555 or better yet, a PWM from a Picomite  
 
Nimue

Guru

Joined: 06/08/2020
Location: United Kingdom
Posts: 314
Posted: 04:29pm 19 Nov 2022
Copy link to clipboard 
Print this post

  Tinine said  Resistors...Yuk

Grab a cheapie H-bridge and drive it from at least a 555 or better yet, a PWM from a Picomite  


LOL -- this is something I am retro fitting to an existing device in schools - rough and ready is best.

At presented the set up drives to motors far far too fast to use on a desktop - more like a school hall -- so this is almost like a "calibration" I am trying to hack back in.

I'll give it a go and see what happens.

N
Entropy is not what it used to be
 
Turbo46

Guru

Joined: 24/12/2017
Location: Australia
Posts: 1120
Posted: 05:38pm 19 Nov 2022
Copy link to clipboard 
Print this post

Yes, a 2 pole, 3 position switch is what you are describing. It could have more poles and more positions, just don't use them.

If there are more positions, there is often a washer on the mounting spindle with a tag which is used to restrict the number of switch positions.

You don't say what current you need to control, just make sure that the switch can carry the current (and more) and that the resistors have a high enough power rating.

Bill
Keep safe. Live long and prosper.
 
Nimue

Guru

Joined: 06/08/2020
Location: United Kingdom
Posts: 314
Posted: 05:46pm 19 Nov 2022
Copy link to clipboard 
Print this post

  Turbo46 said  Yes, a 2 pole, 3 position switch is what you are describing. It could have more poles and more positions, just don't use them.

If there are more positions, there is often a washer on the mounting spindle with a tag which is used to restrict the number of switch positions.

You don't say what current you need to control, just make sure that the switch can carry the current (and more) and that the resistors have a high enough power rating.

Bill


Perfect.

Will measure the current to check when its running in its unmodified current state.  And yes, will make sure over the resistors.

N
Entropy is not what it used to be
 
TassyJim

Guru

Joined: 07/08/2011
Location: Australia
Posts: 5005
Posted: 07:14pm 19 Nov 2022
Copy link to clipboard 
Print this post

Don't worry if you have to get a switch with extra poles. You can always parallel them up to help with current capacity.

Jim
Edited 2022-11-20 05:16 by TassyJim
VK7JH
MMedit   MMBasic Help
 
DaveJacko
Newbie

Joined: 25/07/2019
Location: United Kingdom
Posts: 26
Posted: 10:50pm 19 Nov 2022
Copy link to clipboard 
Print this post

Oversimplification warning!

Resistors control the torque of the motor, not the speed.
Voltage controls the speed, and PWM is a good way to control voltage in this context.
It's so easy to do PWM with almost anything with MMBasic.

Suggest use any transistor, Maybe Darlington, or 20p ULN type chip to power motor.
Don't forget a freewheeling diode though.

Alternatively.. post project requirement in details here,
TBS is full of clever helpful people !
 
Turbo46

Guru

Joined: 24/12/2017
Location: Australia
Posts: 1120
Posted: 05:53am 20 Nov 2022
Copy link to clipboard 
Print this post

If the motors can be connected in parallel, you could get away with a single pole 3 way switch and 3 resistors, each resistor in series with both of the two motors.

Bill
Keep safe. Live long and prosper.
 
palcal

Guru

Joined: 12/10/2011
Location: Australia
Posts: 1562
Posted: 06:10am 20 Nov 2022
Copy link to clipboard 
Print this post

I'm guessing they are DC motors, why not use a motor speed controller like this
Motor Speed Controller
AC Version
Edited 2022-11-20 16:15 by palcal
"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"
 
Mixtel90

Guru

Joined: 05/10/2019
Location: United Kingdom
Posts: 3141
Posted: 07:26am 20 Nov 2022
Copy link to clipboard 
Print this post

A resistor drops the voltage. The torque falls. Assuming the load remains reasonably constant the speed will fall, although the speed:resistance_value ratio isn't usually very linear. A simple PWM controller with a single mosfet output is pretty much ideal. Avoid H bridges unless you have voltage to spare as you'll usually lose at least 2V, possibly more, in one. A 555 can be used as a PWM generator, you don't need a micro.

For the simplest system I'd keep a resistor in circuit as many switches will break the circuit between positions and this will keep a supply to the motor. It does no harm to wire it this way anyway. You just have to choose parallel combinations for the speed steps. Just copy the whole circuit for another pole of the switch on a 2-motor system. If the current is low then the cheap rotary switches can be 4-pole 3-way as standard. You can wire two poles in parallel for each motor. Beware though, the maximum rating of these switches is only about 300mA per pole and you'll probably get about 500mA with two poles in parallel.


+ --------+
         |
         +------------+
         |            |
        R1            O
         |           /
         |         O  O  O
         |            R2  R3
         |            |   |
         +------------+---+
         |
        motor
         |
- --------+

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs
 
Volhout
Guru

Joined: 05/03/2018
Location: Netherlands
Posts: 1809
Posted: 12:31pm 20 Nov 2022
Copy link to clipboard 
Print this post

Post 1: you have independent control over voltage and polarity. Why resistors?
If nothing goes right ... turn left
 
Nimue

Guru

Joined: 06/08/2020
Location: United Kingdom
Posts: 314
Posted: 04:42pm 20 Nov 2022
Copy link to clipboard 
Print this post

  Volhout said  Post 1: you have independent control over voltage and polarity. Why resistors?


This is a commercial product that I am "hacking", so I am limited to adding something in - the MCU is a "blob".

Control as in - each motor is controlled independently - and is either "on", "off" or "reverse".  I can't control the voltage -- its almost like I just need to bring the level down.  The "on" is far far too fast so I need to scale it back.



All the feedback here has been great --- I'll be building something over the week and will report back.


Cheers all
N
Entropy is not what it used to be
 
PeterB
Guru

Joined: 05/02/2015
Location: Australia
Posts: 617
Posted: 10:47am 21 Nov 2022
Copy link to clipboard 
Print this post

G'Day All

Perhaps you may consider using diodes instead of resistors. I have no idea of your voltage and current requirements but 1N400x diodes are cheap and can be strung in series to give a range of voltages.
I am reminded how years ago the son of my late wife's friend wanted to drop the speed of two windscreen motors. He had tried resistors, but the regulation was poor, so I designed a switching circuit that did the job but when he saw that it incorporated a pot. which varied the speed a whole new world of possibilities opened up. It was a classic example of me, the Engineer, not asking questions of the end user at the start.
I was very good at that  

Peter
Edited 2022-11-21 20:49 by PeterB
 
Turbo46

Guru

Joined: 24/12/2017
Location: Australia
Posts: 1120
Posted: 11:21am 21 Nov 2022
Copy link to clipboard 
Print this post

That's a good idea Peter, it would give a more or less constant voltage that would not vary much with load but still very simple. Don't know how much voltage Nimue wants to drop though.

Bill
Keep safe. Live long and prosper.
 
Print this page


To reply to this topic, you need to log in.

© JAQ Software 2022