Reliable, simple 1rpm motor or stepper control?

Thread Starter

ReefEco

Joined Mar 19, 2022
1
Hey all, newbie to electronics here - but looking for an application for a reliable 1 rpm motor, that always turns in the same direction and revolves in the same amount. I know a stepper motor is probably the way to go, but is there a way to simply control a stepper motor without programming or a controller? I'm looking for a simple off the shelf control for a stepper then I guess, where the control is limited to applying power for a certain amount of time, and getting a certain amount of revolution. I'm trying to avoid any arduino-based control or need for programming. Thanks for the help - appreciate your suggestions! Best, Peter
 

MrChips

Joined Oct 2, 2009
26,133
Welcome to AAC!

The second hand of a clock movement moves at 1 rpm.
You did not specify the load that needs to be driven.
 

crutschow

Joined Mar 14, 2008
29,818
You can buy stepper controller boards the drive the stepper motor from a clock input, so you would just need to generate clock pulses at the appropriate frequency to get 1 RPM.
 

MaxHeadRoom

Joined Jul 18, 2013
25,226
For that low a resolution you do not need a sophisticated drive, also the PS could be exactly what the plate voltage of the motor is.
A 555 and a Mosfet would do it.
 

ThePanMan

Joined Mar 13, 2020
368
My old microwave plate rotates 6 times per minute. A simple 6:1 gear reduction would serve the need as long as what's being rotated doesn't require a ton of power. I've seen them at 24VAC and at 110VAC.
 

GetDeviceInfo

Joined Jun 7, 2009
2,096
My old humidifier drum synchro motor was a 1 rpm. Load and accuracy would go a long way in flushing out suggestions.

1647714451421.jpeg
 
Last edited:

djsfantasi

Joined Apr 11, 2010
8,330
Hankscraft Motors manufactures several low voltage, low RPM geared motors. Their motors are used in retail displays. I’ve used them in many projects.
 

MrSalts

Joined Apr 2, 2020
1,762
Do you want 1RPM to make a clock or do you want "about" 1RPM for other reasons and a revolution every 58 to 62 seconds is good enough?
 

Reloadron

Joined Jan 15, 2015
6,586
Knowing the motor voltage would go a long way as well as the motor load? Also do you just want 1 RPM continuous or did you want the motor to turn a single rotation in one min and stop? It's all in the details. Depending on how accurate you want simple inexpensive motors like this can be had easily. I have seen them for about $4.00 USD. Normally with a 50 / 60 Hz AC synchronous motor running it on 50 Hz you get 0.8 RPM and running it on 60 Hz you get 1.0 RPM. So it's all in the details?

Ron
 

MisterBill2

Joined Jan 23, 2018
11,913
Really, driving a ow powered stepper at such a ow frequency will not be a big deal if the application does not need much torque, and if the stepping nature of the motor is acceptable. The challenge will be if the application requires a very specific number of steps per revolution, as most steppers do not step 60 per turn.
Driving a stepper slowly with low torque is not a big deal as it just takes going through a few steps repeatedly.
So let us know more about the application requirements, can steps work? or is a smooth constant speed required?
 

MaxHeadRoom

Joined Jul 18, 2013
25,226
?? A stepper motor is always driven at the plate stated current to ensure constant torque through out the range from zero RPM to rated RPM.
 

D_racon

Joined Oct 4, 2021
6
you can use a 3 stage ring oscillator, combined with a 3 phase steper motor, take one of those simple stepper motors with a center tap making it usable as 3 separate coils, this way you won't need something like a H bridge. a 555 is also usable for generating a signal, however if you do that you would need to add a decoded counter like the CD4017 to turn the on and off signal into 3 or more phases so you can drive a stepper motor, and calculating the frequency of a 555 is harder due to the phases often having a different duration from each other(High vs Low) unless you add some more things like diodes to avoid that.

So I would suggest The following:
Note that this is a very simple solution, it doesn't require expensive parts, doesn't require many parts, It doesn't require complex calculations, and yet it is quite effective and accurate if you get the parts from a proper maker and seller, as well as that it allows for tuning the power usage of the motor.
You'll need:
1* 74HC14HexInverter withSchmittTriggers(default for this one).
1* 3phase stepper motor with center tap(or 3 separate coils).
THIS STEPPER CAN BE EASLY MADE YOURSELF FOR VERY CHEAP if you don't need it to run a heavy load
to do so you need:
1* very thin emailed copper wire(electrically isolated copper wire like you find in speakers, it is best to have a few meters.
3* iron nail, stapler, or other small metal or scrap metal core, if you use a nail you can keep it long for cooling.
1* small magnet for in the rotor, like what you find in a compas or a more powerful one for more power and accuracy.
pieces of iron might work to.
1* some material to make the motor chassis from
1* some gears to slow down the rotation from whatever frequency your ring oscillator runs on to 1rpm
theoretically seen you can even use cardboard for the chassis and gears if it is allowed to be weak.
just make sure the magnets don't get hot.
wind 3 roughly similar coils, one around each iron nail, you can use a drill or contraption to speed it up.
make the rotor on a small axis like a metal or wooden pin so it will stay in place in the chassis, yet still rotate.
add in the magnet in the centre, make sure to position it similar to in a compas,
north and south need to be pointing to where the coils will be.
make the frame, place the rotor in it and place the 3 electromagnets/nails around it.
connect one wire of each coil to each other, this will be connected to +/Vin.
make sure all electromagnets have the same polarity by turning them on one after each other.
Make sure they all attract the same side of the rotor.
If one doesn't then connect the other wire to +/Vin instead.
Now it should be done once you've added the gears.
However might you not like to use gears then you can also:
Place the 3 electromagnets very close together and add many magnets with the same pole facing outward.
or just pieces of iron or a other feromagnetic material.
this will reduce speed and increase accuracy since each step will be the size of the distance between the electromagnets.
and then those steps can be changed in size using some gears.
but in this second example we use the distance between the coils so we won't need gears.
1* some resistors
1* some small capacitors
1* some transistors, mosfets or other things to amplify the signal.

now you can make a Not ring oscillator, there are many guides online about how to do so with the .
the formulas for calculating the frequency are also with them often, this is based on the schmitt trigger Hysterese(often around 0,7V at a certain voltage), the capacitor size and the resistor value. the hysteresis is in the datasheet, but it won't hurt to use a potentiometer and a oscilloscope or voltmeter to figure out the hysteresis for sure if you want high accuracy.

now you would have 3 outputs and a 3 phase signal. this signal can be amplified by the mosfets or transistors with a resistor in front of them. depending on their power you can directly use them to drive the coils.

after this you should be ready and have it rotate at the speed calculated or estimated, you can replace resistors and such to alter the speed, etc.

Now there is one thing I would recommend to add however and that is pwm/power limiting, this reduces power usage and heat in the coils, it makes it more safe as well. to do this you need almost nothing because there are still 3 inverter gates free in the IC, and you only need one to make a PWM generator, to do this you can use a one of the not gates, a capacitor, 2 diododes and 2 resistors or 1 potentiometer.
it charges the capacitor and discharges it at a different rate which creates the PWM. using a potentiometer will allow for around 100% to 0% duty cycle, but the 100% and 0% might fry the chip due to one of the connections having no resistance anymore, so if you use a potentiometer, add a resistor at the end of the not gat/inverter to prevent overcurrent, this will limit the duty cycle somewhat, however you can still easily reach 5% to 95% if you use a small enough capacitor and high resistors in front of the diodes.
The diodes are both faced another way, so when the output is on it enters through one resistor to charge the capacitor until it turns the gate of, then it discharges through the other resistor this allows the on and off cycle to have a different duration aka. pwm.
this pwm can be added using a extra mosfet or transistor, or another much better way which is combining the logic of the PWM signal with the 3 phase signal before entering it into the transistor or mosfet, this increases efficiency and can be done using simple resistors and capacitors, or transistors. it is a simple AND or inverted AND gate, you can also use a resitor and use the PWM frequency and a diode to discharge it, so the 3 phase outputs each have a current limiting resistor behind them, then a diode to the PWM signal is added, this diode will pull the voltage after the resistor low if the PWM signal is low, so this will blend the 3 phase signals with the PWM, the point between the resistor and the diode is your new signal. you should however also add a diode between the signal and the transistor, mosfet or IGBT running the electromagnet(for all 3 of them). this is because a diode has a voltage drop, so the signal might not fully be 0V and might instead be something like 0,7V which can activate the mosfet, transistor, etc. by adding a similar diode between the blended signal and the transistor we make sure that also has the voltage drop meaning it will get 0V when the signal is low instead of 0,7V or such.
 

MaxHeadRoom

Joined Jul 18, 2013
25,226
If a stepper is operated at this low a RPM, PWM is not required. if the plate voltage of the motor is used.
Simpler with a uni-directional Bi-Polar stepper motor also.
 

MisterBill2

Joined Jan 23, 2018
11,913
The very od "superior Electric" stepper drivers used two TTL l, I think, and some decoding logic to control the power transistors. With a couple amps current and most of the power heating some large power resistors they were horribly inefficient. Not my choice at all. But they did work, and if high speed was never required a lower voltage supply could be used without those resistors. Very few folks ever did that. What application support????

Given that we don't see any TS response to the question of how much torque, no suggestions. we really do need to know the torque requirement.
 

MaxHeadRoom

Joined Jul 18, 2013
25,226
Series Resistors in Stepper drives have not been used in decades, now PWM, in this case, 1rpm unidirectional, only the plate voltage supply is needed, plus a suitable step pulse rate generator to suit.
No PWM needed.
 
Top