Two Different Designs of DC Motors

[moimoi23]

TL;DR Summary

Two types of 12 Volt DC Motor designs. How to tell which one is more efficient?

Hello,

I have two designs of DC motors.

Which one is more efficient? I believe what is in question is the location of the communicator. Whether it should be closer to the out piece of the shaft turning the gears? Or should it be further away towards the end? Does this make a difference?
Please see attached images, I am not sure how to describe this.. but I can say is that type 2 seems to spin better...

Type 1

Type 2

Both Together

 

[magoo]

commutator?

 

[Asymptotic]

Hundreds of factors affect motor efficiency, but I'm hard pressed to think of any reason commutator placement would have a noticeably large effect, except perhaps if placing it on the output shaft side necessitated a higher friction bearing.

 

[Tom.G]

I would put it away from the output shaft for a couple reasons. The brushes will wear with use leaving dust behind.

• Placing them at the rear of the motor keeps the carbon dust out of the more heavily load output bearing.
• They are probably more accessible at the back for viusal inspection and/or replacement.

Tip: You will be ahead of the game if you can mount with the motor shaft horizontal, that keeps the bearings cleaner.

Cheers,
Tom

 

[Rive]

Does this make a difference?

This is just a design decision based on the actual goals the motor has to fulfill. Just this alone has no effect on efficiency.
Also, this kind of motor should not be the base of any speculation about efficiency. The primary design goal for this kind of design is to make it barely adequate, but: cheap.

For examples of efficient design you can try motors from mid-class drones.

 

[moimoi23]

This is just a design decision based on the actual goals the motor has to fulfill. Just this alone has no effect on efficiency.
Also, this kind of motor should not be the base of any speculation about efficiency. The primary design goal for this kind of design is to make it barely adequate, but: cheap.

For examples of efficient design you can try motors from mid-class drones.

My apologies, I meant to speak about efficiency in an informal way, as to say "it doesn't work as well".
Please see the below images to get a broader perspective on the differences...
I still think the difference in design allows for Type 1 not to work as well as Type 2.

Some reasoning as to why this is important...
I work as a product manager in aftermarket automotive parts, I graduated as a physics major and pursued a career in engineering but ended up in product development instead :). Manufacturers overseas will try to cut corners in any way possible jeopardizing quality in the process. I want to make a distinction between DC motors used in power operated aftermarket parts. I notice a clear distinction between the two motors and their operation, as a physics student I would like to understand why that is so... Design Differences:

Design Differences

Side View Type 1

Side View Type 2

 

[essenmein]

If you are referring to differences in performance between the two, then rotor diameter/length (here I mean the lamination's themselves, not the wire), size and strength of the magnet, number of turns are the drivers here. The two machines you have shown don't look the same as far as the important motor characteristics are concerned. Location of the commutator will have IMO no significant impact.

 

[essenmein]

You also have to define "work as well", what is it about type one that does not "work as well" as type 2, is it not able to reach desired speed? Desired torque? Too big?

 

[moimoi23]

You also have to define "work as well", what is it about type one that does not "work as well" as type 2, is it not able to reach desired speed? Desired torque? Too big?

Type 1 seems to not put out enough speed & force to properly turn the gears that the shaft is connected to. Type 1 (inside the motor) has noticeably larger magnets. The distance of the lamination on the sides are more or less the same, along with the thickness..

Starting to think there isn't a difference and maybe these little motors are just "cheap"as Rive said ↑↑↑ :/

 

[Asymptotic]

Since these motors are from aftermarket components I'd be interested to see how the OEM parts are made.

 

[moimoi23]

Since these motors are from aftermarket components I'd be interested to see how the OEM parts are made.

So I was able to disassemble one of the OEM motors. Is there a difference in the reddish copper wire? Also, what about the rotor? With type 1 & 2 I see a greenish lamination and with the OEM part motor I see a almost clear coat lamination..

see attached..

 

[Tom.G]

The wire coloring is from the particular insulating varnish used. I have a vague recollection that the Red one might be a high-temperature varnish, but don't count on it!

The windings on the middle one in the photo, type 2, appear to have been scramble wound; individual turns crossing over the turns underneath it. This is prone to early failure due to the stress concentrations at the crossovers and the small wire movements during operation. The turns are more likely to wear thru their insulation and short circuit to each other.

Cheers,
Tom

 

[moimoi23]

The wire coloring is from the particular insulating varnish used. I have a vague recollection that the Red one might be a high-temperature varnish, but don't count on it!

The windings on the middle one in the photo, type 2, appear to have been scramble wound; individual turns crossing over the turns underneath it. This is prone to early failure due to the stress concentrations at the crossovers and the small wire movements during operation. The turns are more likely to wear thru their insulation and short circuit to each other.

Cheers,
Tom

Thank you for your reply Tom,

Do you know anything about the green lamination?

 

[Tom.G]

Not really. It acts as an adhesive and as surface coating to avoid rust, but I have no details.

 

[sophiecentaur]

Starting to think there isn't a difference and maybe these little motors are just "cheap"as Rive said ↑↑↑ :/

I reckon that's the main message from this thread. If you want a very efficient motor (for a flying machine, for instance) then you would need to look at some existing high performance Drone designs and see where they get their motors from. They will probably be light weight and pretty expensive and ,magically, they will do a critical job better. Do you want to spend the money? (It's the question that applies to any Engineering project.)

 

[Rive]

I have a vague recollection that the Red one might be a high-temperature varnish, but don't count on it!

On standalone wires (sold for DIY coils) it would mean plastic insulation instead of varnish: that makes the wire solderable (no need to remove the varnish before soldering).

On a wire found in a no-name OEM product it can mean anything till' it got tested...

Starting to think there isn't a difference and maybe these little motors are just "cheap"as Rive said ↑↑↑ :/

For some product categories the price just cannot tolerate many engineer-hours spent - no need to overthink.

 

[essenmein]

Type 1 seems to not put out enough speed & force to properly turn the gears that the shaft is connected to. Type 1 (inside the motor) has noticeably larger magnets. The distance of the lamination on the sides are more or less the same, along with the thickness..

Starting to think there isn't a difference and maybe these little motors are just "cheap"as Rive said ↑↑↑ :/

Yeah so now you would need to look at more of the specifics, ie turn count, flux density of the magnets etc (more volume does not mean more flux, as there is quite the range in permanent magnet materials). Probably unnecessary, I would prod the machine supplier for data.

If you get any kind of TNI curves, or other performance data (locked rotor torque, rpm/V etc) these should allow you to compare them better. You could try to characterize the two machines, for example apply a fixed voltage and measure unloaded rpm, lock the rotor and measure locked rotor current, if you have access to a torque sensor you could measure locked rotor torque per amp. Then you can compare them better.

"Cheap" brushed machines do have their place, for a lot of automotive actuators etc, they turn for a half second or so to change an actuator then they sit idle for long periods. So there is little cost benefit to increased efficiency with something like BLDC or some other synchronous machine.

 

[Asymptotic]

Is there a difference in the reddish copper wire?

Impossible to say.
Polyurethane and polyester-based insulation is available in a range of colors, and formulations that span 105°C to 200°C thermal classes, and there is a dizzying selection of other insulation materials and blends to chose between (polyester-Nylon, polyurethane-Nylon, solderable versions that @Rive mentions in post #16, and more). Nearly all of them are available in red.

Another variable is 'build' level (how thick the insulating layer is) - single, heavy, triple, quadruple - although exact specs vary between manufacturers. Generally, the thicker the insulation is, the less prone the winding is to failure, but the fewer turns will fit into a given amount of space.

Picking which one to use is an exercise in balancing trade-offs. Can wire insulated with a cheaper material in triple build thickness fit into the available space, or is a more expensive material in single build thickness required? How hot will the winding become? Is it necessary to use a more expensive, higher temperature rated material for longevity? Will the motor be used in an intermittent or continuous duty application?

Motor type 1 has a lot of space between coils, and windage (air flow created through rotation) will allow them to run cooler. However, if there aren't enough turns to create the necessary force it really doesn't matter. Coils on motor Type 2 are jammed together so closely that cooling is compromised, and coil spacing on the OEM motor appears to be a workable compromise between these two extremes.

Dimensions on type 2 and OEM motors appear identical, but type 1 is considerably larger. I'd worry whether a replacement with a type 1 motor would fit in all designs expecting the smaller OEM part.