Help designing single revolution motor/servo

Thread Starter

llphil67

Joined May 13, 2022
4
I am trying to design a system that will trigger a motor/servo/stepper to rotate one full revolution only. This is not the project, but is an example: a coin rolls over a microswitch which triggers a motor to make exactly one revolution and stop, ready for another coin drop to repeat process. I am very new to this so I will need to know specifically what I need to obtain and how to build the system. Thank You in advance.
 

LowQCab

Joined Nov 6, 2012
2,044
You need a simple Gear-Motor that will rotate at the desired speed,,
then attach an interrupter-Wheel to the Shaft with a single hole drilled in it's periphery.

Then get an Infa-Red LED/Sensor-pair to look through the hole.

A very short pulse should "latch" the Motor "On",
and the Sensor will turn it "Off" when it sees the hole.
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MaxHeadRoom

Joined Jul 18, 2013
25,202
For simplest/precise control, probably the stepper motor may be the easiest to implement.
No feed back necessary.
Just requires a 200 pulse command generator and a simple amp drive.
 

MisterBill2

Joined Jan 23, 2018
11,877
Unless a great deal of precision and repeatability is required, an actual servo system is much more than the application requires.
Likewise a stepper motor will work but be far more complex than many applications require.

A cam and a limit switch can provide a good level of repeatability, with only a short input to move the motor past the position where the limit switch is held open.
Of course the required speed of the rotation matters a great deal as well.

So tell us:
How Fast
How accurate
And how much torque.
 

Thread Starter

llphil67

Joined May 13, 2022
4
Thinking should be about 5-10 seconds for one revolution, should be able to move 250g static load, should be accurate enough to effectively utilize whatever start/stop mech is employed. Been thinking perhaps easiest way is with a cam and leaf type switch like in old pinball machines. Priority is cheap and easy, would like to learn about steppers/servos though as well. Thanks
 

MisterBill2

Joined Jan 23, 2018
11,877
OK, now we know six to twelve RPM And the torque requirement should not be to bad. The gear reduction to get that low a speed will also provide the torque. There are probably surplus motor packages available that will do the job very well.
I should have asked about product lifetime and reliability, forgot to ask those questions.
 

Thread Starter

llphil67

Joined May 13, 2022
4
I do not think that will be an issue, I will select components durable enough. Going to do some quick searches now, think I have a cam and switches from an old electro-mechanical pinball machine I can adapt. Still wonder if there is an off the shelf stepper system I can adapt. If such a thing exists as an onboard, adjustable pulse generator and driver that would be great. Dial in pulses (adjust number as necessary), microswitch sends trigger, motor rotates, ready for next trigger. Never messed w/steppers so I may be clear off base and will simply do the old mechanical method.
 

LowQCab

Joined Nov 6, 2012
2,044
A Stepper-Motor does not normally have a "zero" or "home" position,
so without an add-on position Sensor of some sort,
there's no guarantee of stopping in the correct position,
making a Stepper-Motor a much more expensive and complex option,
with no particular advantages for your specific application.

What You need is called a "Synchronous Gear-Motor",
there's at least a million of them on Amazon and Ebay.
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MisterBill2

Joined Jan 23, 2018
11,877
LQC is correct. It could also work to use a "Slo-Syn" brand 72 RPM synchronous motor, if you can find one used surplus. That would be faster than the 5 second revolution, but if you could live with the speed that would mean no speed reduction needed. Or use that motor with a bit of reduction.
 

MisterBill2

Joined Jan 23, 2018
11,877
DD certainly has a good idea about the windshield wiper motor. Especially the much older ones that do not interface with a body computer. Some of the much simpler ones that simply include a switch to have the stop in the same position each time. An auto salvage yard may be the best source, possibly even at a better price. The down-side would be the mounting scheme that is not very standard. But those devices include the mechanism to stop and hold at the same place every time. The voltage will need to be reduced a bit for the slower speed, and the crank arm would need to be removed, probably, for your application. But those are certainly a reasonable consideration.

One thing is that we are not aware of any size constraints, which may be a big deal.
 

Ya’akov

Joined Jan 27, 2019
5,659
You said your example wasn’t the application. Could you explain the actual application to ensure that all of this advice is not for naught once some additional details about the real application is known?

It is very hard if not impossible to know one is giving good advice without knowing what the actual goal is. When you make the solution into the problem, ”solving” it very often doesn’t solve the real problem that was never stated.

[EDIT: Included omitted “it”]
 
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MisterBill2

Joined Jan 23, 2018
11,877
Y is certainly correct about needing to be aware of the application. Very few participating members are able to discern what ideas and concepts are in the poster's mind. My "mind reading" ability is very poor, and that is why I ask questions.
The alternative application of "application specific" devices is a very large area subject to a lot of creativity, but it needs a lot of information to produce useful results instead of random guesses.
Unfortunately the random guesses often are very real distractions.
 

Thread Starter

llphil67

Joined May 13, 2022
4
A Stepper-Motor does not normally have a "zero" or "home" position,
so without an add-on position Sensor of some sort,
there's no guarantee of stopping in the correct position,
making a Stepper-Motor a much more expensive and complex option,
with no particular advantages for your specific application.

What You need is called a "Synchronous Gear-Motor",
there's at least a million of them on Amazon and Ebay.
.
.
.
OK, thank you for the information, I'll do some more research
 
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