Off Topic - Motor problem - Is mine manufactured wrongly?

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c00kie

New Member
Hi Guys,

I know there are going to be some motor experts out there (I'm not by any means) and I would be grateful if you would take a look at the attached picture and let me know if it looks OK or if there is a problem / potential problem. This is a brand new replacement from the supplier and I dismantled it to see if was the same as the one I sent back.

Sorry for being cryptic I just want to see if it is as obvious as i think it is...

Thanks in advance,

Mark
 

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marcos.placona

Senior Member
Well it looks good to me. I'm not a motor expert, hence my opinion here can mean peanuts, but it pretty much has everything a motor has to have, so I can't see anything wrong with it
 
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Dippy

Moderator
Brushes look a bit odd - assumming they are brushes? I haven't got all day to be cryptic.
Just plug it in, burn it out and send it back to China :)
 
C

c00kie

New Member
marcos.placona said:
Well it looks good to me. I'm not a motor expert, hence my opinion here can mean peanuts, but it pretty much has everything a motor has to have, so I can't see anything wrong with it
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Thanks Marcos, you're right, everything is there and indeed the motor runs, but I know that after an hour or two it will die in the same way as the one I sent back :(

Maybe I should have said this is a 6V motor.

Cheers,

Mark
 
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marcos.placona

Senior Member
c00kie don't you wanna post your circuit here, so we can take a look at it and see if there isn't something wrong with it?

Maybe that's causing the sudden death of the motor?
 
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c00kie

New Member
Dippy said:
Brushes look a bit odd - assumming they are brushes? I haven't got all day to be cryptic.
Just plug it in, burn it out and send it back to China :)
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Hi Dippy, sorry about the cryptic bit - I didn't want to mention the brushes in case they were supposed to look like that. As I say I'm not an expert but to my mind they have had the concave surface machined 90 degrees out. So the motors work fine for an hour or so and then fail as tiny shards of metal start to short out the commutator You can see the start of the parallel grooves that get worn in the commutator. Unfortunately the kids in the young Engineers club at school each have one of these in their buggy and sooner or later they are all going to need replacing I think.

I guess I'll have to take it up with the supplier again.

Cheers,

Mark
 
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davidwf

Senior Member
The brushes should be mounted 90 degrees to that shown - they will then contact the commutator correctly - the concave surface isn't there for looks !

sorry about the late reply I have only just seen this post
 
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moxhamj

New Member
Someone with an IQ of room temperature must have assembled that. I think a refund might be in order...
 
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Dippy

Moderator
If they are all like that don't just "take it up" - be firm. Tell him you find this cheap(?) chod unacceptable.

As a slight aside: I bought some cheap drills made you-know-where for use in a milling machine - the supplier was recommended by a friend who has since run off to NZ.
All the drills were ground backwards. Absolute rubbish. Similarly with the Boring Head cutters. Again rubbish. Recommended by same friend. As he pointed out I could get a set of 6 for the same price as one Brit made cutter.
By the time I'd sent them back I realised it would have been cheaper (and certainly better and certainly quicker) to have spent a little extra on a Western brand. Lesson learnt for me. Sadly the option is getting pretty rare now.
 
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BeanieBots

Moderator
Don't be so hasty assuming they are wrong.
If that is a high power motor such as a "540" for RC racing, then it is correct.
The concave shape is to allow bedding in and over time spreads the wear on the comutator. This happens during the three hour running in process.
However, having said that, it does not look like those are "user replaceable" brushes so it might be wrong.
 
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Dippy

Moderator
Sadly, it's true. It puts one off somewhat.
Some stuff is fine I admit.
I haven't fiddled with engineering stuff for a couple of years now, but most of the Ch stuff was rubbish. That blasted friend also recommended a Ch Chuck and JT?-R8 Arbor. They didn't even fit. I had 4 replacements. All rubbish. I got a refund and ordered Jacobs and Toolmech (or is it Toolmex?). Perfect. Twice the price, but perfect.

Get yourself an Arrand 6mm End Mill holder and a pukka tungsten carbide cutter. Slide it in dry. The fit is SO good that it tries to come back out because the air has trouble getting by. It's like a piston. Abs. superb. Price nearly £200. You get what you pay for. Almost too good to use.

I bought three Ch-made FM transmitters as presents for people. Line-in level audio to FM-out so you can listen to Listen Again BBC on your FM radio around the house. They work great. Except when they switch 'OFF' they still flatten the batteries in 3 hours. Have I sent them back? No, for a fiver each I can't be bothered, too lazy. And that's EXACTLY what a lot of these suppliers rely on. (What a cheapskate huh).

Well, I won't go on... unless provoked :)
 
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moxhamj

New Member
Re "Don't be so hasty assuming they are wrong."

He also said that the motors died after 2 hours. I've heard of inbuilt obsolescence but that is a rather short design life.

As Monty Python once said in a disclaimer: "I am over 4" "I agree not to consult a lawyer" and "I understand that if I am not completely satisfied, then I have been had."
 
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BeanieBots

Moderator
They are for a "Buggy" and used by "Kids".
Sounds like an RC buggy to me. In which case a few hours is about right!
Typical run time of 6 minutes, 20 runs and the brushes would need replacing.
50 runs (5 hours run time) and the bearings will be shot.
These "buggys" run the motors at about 10 times manufacturers spec.
Most RC cars suggest a gentle run in for several hours prior to use to bed-in the brushes. If they are run at full power from new they will only last 2 or three runs.
A browse of the RC forums will show up all the 'tricks' people resort to in order to get a little extra life from a motor.
 
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c00kie

New Member
Thanks for all the input chaps. The motor in question is this one.

We are using HPWM on a 14M to drive them at about half speed. They are only used for short runs.

The brushes are not replaceable - I did think about turning them round, but they are so small I think it would be impossible.

I can't see them being designed like that - the brushes gouge tracks in the commutator prodcing tiny shards of metal which short out the commutator bringing th buggies to a halt.

I'll try for a refund seeing as the replacement they sent me has the same problem.

The buggies were built by the children - are powered by one of these and steered using a servo.

Thanks again

Mark
 
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moxhamj

New Member
There you go. It says it has "has a virtually unbreakable polycarbonate gearcase and tough nylon gears."

Nothing there about the brushes. I *suppose* you didn't ask about the brushes?!

But that link also invites you to write a review. You could always do that *grin*.

Let us know if you have any trouble getting a refund.

Just going back to the original photo, what are those brushes made of? You say that it is gouging the metal - sounds a bit odd if they are graphite as graphite is quite soft. Or are they some special soft metal. Or was the original design for some special soft material and it got substituted along the way for something cheaper...
 
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BeanieBots

Moderator
Oh! THAT little motor/gearbox.
I've got dozens of them. Great little unit and quite an efficient motor considering how cheap it is.
Never had any problems with the motors but stripped the gears on just about all of them:mad:
The final output cog simply isn't up to the job. You can't stall the motor in the heigher ratios, the teeth simply strip off.
Never considered the motor itself. Always assumed it had metal finger brushes as it was so small and cheap. I'll have to dig one out and have a look.
 
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westaust55

Moderator
As one who has spent quite a lot of time over the years studying up on motor bushes for large industrial motors there are many things one could say but in short:

these motors are "stuffed up" with the brushes fixed 90 degrees rotated.

If all the motors are the same, its not just a simple one-off situation. I would be demanding that as the supplier not only replace all the motors but cover all costs for return and shipment of new motors.

If they do not come to the party, suggest you will be paying a visit to your local consumer affairs office.
 
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westaust55

Moderator
Just going back to the original photo, what are those brushes made of? You say that it is gouging the metal - sounds a bit odd if they are graphite as graphite is quite soft. Or are they some special soft metal. Or was the original design for some special soft material and it got substituted along the way for something cheaper...
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Funnily enough, ALL brushes are harder than the commutators or slip rings even in really BIG motors (and I deal with them up to 15,000 kW)

To prevent commutator or slipring damage, the brushes must get hot enough to litterally melt a thin layer of brush material onto the commutator/slipring surface. This skin (or patina) acts as protection for the copper or bronze commutator/sliprings. A good commutator or sliprings will have a light brown to chocolate coloured layer casued by the coating left by the brushes.

Problems arisings from lightlly loaded motors and brushes running to cool are some of the bigest problems.
 
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slurp

Senior Member
c00kie said:
Thanks Marcos, you're right, everything is there and indeed the motor runs, but I know that after an hour or two it will die in the same way as the one I sent back :(
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Daft question.... what sort of circuit are you using with this motor?

Does the drive circuit have a thermal cut out? What is the current rating of the drive circuit and what current are you actully drawing in operation?


I've a small battery operated DC motor I know runs freely at 40mA, stall is 400mA but it's still not a good idea to run it on a 1A driver.... as it tends to stall it can pull 2 or 3A! More if I really try freaky loading ;)

regards,
Colin
 
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c00kie

New Member
BeanieBots said:
Oh! THAT little motor/gearbox.
I've got dozens of them. Great little unit and quite an efficient motor considering how cheap it is.
I'll have to dig one out and have a look.
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Hi BeanieBots, that would be brilliant - I'd really like to know if they have always been like this.

Cheers,

Mark
 
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BeanieBots

Moderator
Just tried to find one but failed.
I know I've got at least three that are several years old and have hardly been used and are not buried deep in the bowels of a robot.
I'll have a look in the loft tomorrow. Good excuse to bring some more junk down:)
 
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davidwf

Senior Member
If you bought them from Rapid Electronics in Colchester, Essex then you'll have no problems with a refund - I have been using them for years and their customer service is very good, you certainly won't need to go to trading standards or anything like that !
Give them a chance to remedy the matter explaining the points & findings that you've made in this post - THEY don't make the motors remember !!!
 
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