Stepper motor used for rotating beacon warning light?

Is the motor which rotates the reflector in a rotating warning beacon likely to be a stepper motor?

https://www.youtube.com/watch?v=1kIVe1RrIAc

..or would a stepper motor never be used for a constantly rotating usage due to the non-smooth torque?

I seriously doubt that anyone would use a stepper for this application.
A geared brushed DC is much more sensible...

surely the stepper is cheaper?

Cheaper then 2$ ?
Also, consider the cost of the control/drive electronics - that you don't need with the brushed option...

Small DC geared motor is the best option.

Brushed DC tends to spark, so dodgy for explosive atmosphere. BLDC requires too much control electronics, and either a resolver or encoder, or back emf sensing...surely more expensive than a simple stepper?
Also, a stepper has its coils lumped into certain discrete places, instead of being expensively
spread out so as to give smooth torque...so surely the stepper is the cheapest motor
of all.?

Under what circumstance can the roof of an emergency vehicle be considered an "explosive environment"?
And if you're thinking about factory applications, then any motor has the potential to produce sparks. In that case simply using a "less sparky" motor won't be enough...

Why would you want to spend extra money and effort overdesigning a rotating mirror?

OK thanks, please forget the explosion risk.....but the stepper is surely the cheapest motor of all?....I mean
the coils are simply wound, the rotor and stator are simpler than any other motor...you agree?

No, this is only part of the picture.
when you compare the simplest stepper with the simplest brushed DC - they cost almost the same.

However, the stepper will always require a control/drive stage while the brushed DC is a plug & play solution (for the application you described).

Thanks, though with the beacon possibly being on for 20 hours per day, every day, won't the brushed dc suffer too
much wear of the brushes?

Yes they will - so what?
You're designing a mirror spinner not an arteficial bionic hand...the only thing it has to do is spin a small mass.

Yes the brushes will wear over time and yes, the shaft will have more play and the motor efficiency will decrease - but by the time the wear is significant enough to cause a complete failure your dog/cat will grow old.

Anyways, think about other solutions that don't envolve motion, for example: a blinking high intensity light, or perhaps a set of lights arranged in a circular pattern with each light going on in its turn.
This will always be more reliable - but perhaps also more expensive.

I am convinced that the dc brushed motor has a more complex construction (and thus more
expensive), than a stepper motor. In a brushed DC, the coils are "split" up and spread
around the rotor, such expensive manufacturing makes the brushed dc more expensive.
?

I'm not a manufacturing expert but I think the motors that are used for such applications are very low cost and manufactured in the thousands and this keeps the price low.

You can enquire how much it would cost to manufacture a 3 watt motor - brushed vs stepper.
But as I said before, the price doesn't end with the motor itself - steppers will require control / drive electronics...

steppers will require control / drive electronics...

Click to expand...

for the application under discussion here, the software is very very simple, pretty much just a couple of KHz PWM at 50%...no problem.

treez said:

for the application under discussion here, the software is very very simple, pretty much just a couple of KHz PWM at 50%...no problem.

Click to expand...

That assumes that you already have a processor somewhere that can run the trivial software. But in the application described, there may not be a processor of any kind onto which you can place this "trivial" drive software. So in that case there would be extra cost to drive a stepper. Even if there were a processor there, chances are it is an embedded processor with a specific job to do - not a general purpose desktop computer. So even the most trivial stepper drive software may require an extra timer, or otherwise interfere with the primary purpose of the processor, whatever that was. In short, there is no free lunch.

The free lunch would easily be provided by eg a pic10f200, , costing just a few cents.

treez said:

The free lunch would easily be provided by eg a pic10f200, , costing just a few cents.

Click to expand...

Add a regulated power supply, add a circuit board to hold the PIC, add power switching transistors, add protection diodes to protect against back emf, add transient protection which is needed in automotive or aviation applications, add a housing to protect the circuit from the elements, add a mounting for the circuit board and housing. You are way above a few cents now. And you still need an on-off switch. Compare that with the DC motor alternative, in which case the only thing you need besides the on-off switch is.....nothing.

- - - Updated - - -

There is another big difference between steppers and DC motors that no one has mentioned yet. DC motors gracefully degrade when loading increases. Their speed is variable, depending on the load and the applied voltage. You don't have to design a DC motor for a precise speed and load condition. You can pick a motor that is close to what you think will work, and if the load is a little higher than expected, a DC motor will just turn a little slower. But it will generally turn.

Stepper motors are completely different in that respect. Either they work at exactly the speed set by the driving pulses, or they do not work at all. They stall completely. They do not degrade gracefully. Therefore applications for stepper motors are designed with much more torque margin to guard against this stall condition. That translates into a bigger and more expensive stepper motor than is typically needed to "just work".

Stepper motors are great when you need precision speed or position, because when they work, they work perfectly. But a rotating beacon does not benefit from this precision. It only incurs the penalties for using a stepper motor.

treez said:

I am convinced that the dc brushed motor has a more complex construction (and thus more expensive), than a stepper motor.

Click to expand...

Have you compared prices or are you just guessing?
Have you actually looked at the construction of each or are you just guessing?

treez said:

In a brushed DC, the coils are "split" up and spread
around the rotor, such expensive manufacturing makes the brushed dc more expensive.
?

Click to expand...

Low power brushed motors I've looked at had a grand total of 3 coils. Were you hoping to find a stepper motor with less than 3 coils?

I understand a bipolar stepper has two coils only

Treez if what you say is true then every "throw away" child's toy would use stepper motors. They do not, 1000 Chinese toy manufacturers can not be wrong.
Frank