8 replies to this topic

[Jeff Whisenand]

My New Hawk 7 is defective!

I just installed a new Hawk 7, and ran the motor. It spins but the brushes are wearing 2 grooves in the commutator. Upon closer inspection I see that the brushes are installed at 90 degrees so the crest is not formed around the commutator, but the sharp edges of the brushes are in contact with the comm instead.

Did the motor factory get a bad batch of brushes and is installing them this way just for a reason? Did the production worker that installs them, not get trained right? Did quality control really inspect and pass this off as GOOD?

A corrective action needs to be implemented by the factory to make this right.

Does anyone see what I am talking  about?

Please comment. I would love to hear from you.

Thanks, Jeff

[proptop]

Welcome to Slotblog Jeff...

 

That brush issue it nothing new...they've been installed that way for many years, and in many different Mabuchi motors as well.

 

When I got back into R/C airplanes in the late 90's it was with electric power...and I noticed that same curiosity...in their 280, 300, 370 and 400 etc. size can motors.

 

There must be a (good?) reason for it...?

It's been discussed a bunch of times over the years, but I have yet to get definitive explanation for it...maybe quicker break-in?

 

Anywayze...it ain't nuthin' to worry about...they're ALL like that...

[Jeff Whisenand]

Proptop,

Thanks for the input! I am glad that I am not the first to discover it. Maybe by having less brush contact with the comm, it reduces friction or brush drag? Maybe the current needed to drive the motor is so small that it can afford less surface contact?

It would be nice to know what the engineers are thinking?

I just now noticed that the brushes are installed in a couple other hawk motors the same way.

I really appreciate your support.

Jeff W.

[proptop]

You're welcome...

Yeah...the brush thing has been the subject of many a conversation...the "break-in ritual" choices, and so on...

 

Some guys do a water break-in and some others say they'd never do that...

Some guys have had brushes last for many many laps...and some others have had brush wear much more quickly...

 

I think you'll like it here...it's a good place to hang out and keyboard race...

[team burrito]

this problem has been around for 10 years & counting...

[havlicek]

 

 

I just installed a new Hawk 7, and ran the motor. It spins but the brushes are wearing 2 grooves in the commutator. Upon closer inspection I see that the brushes are installed at 90 degrees so the crest is not formed around the commutator, but the sharp edges of the brushes are in contact with the comm instead.

 

As mentioned above, this is nothing new, and really is nothing at all!  Well, except for "wearing 2 grooves in the commutator"...that would be odd for a new motor.  I *think* what you might be seeing is simply a dark ring or rings on the commutator's shiny copper surface (which is a normal "brush track") rather than an actual groove.  The com metal is fairly thin on these motors and an actual groove appearing on a new motor would mean a really short life.

On the orientation of the brushes themselves, if the arc of the brushes is oriented at 90 degrees to the circumference of the commutator, that could actually help break-in, since the thinnest parts of the brush faces will more quickly wear and form to the surface of the commutator.  I don't know what "the fast guys" are doing with these, but this type situation would seem to me to make some sort of break-in technique/practice pretty important.  

None of this has anything to do with reducing brush drag/friction or anything like that.  As an aside, if a brush is rectangular in section as opposed to square, a brush could be installed "horizontally" (*it's wider dimension running in the same axis as the direction of rotation of the motor) or "vertically" (it's narrower dimension running in the same axis as the direction of rotation).  In either case, the brush will carry the same amount of current and exert the same drag or friction on the com, but the duration the brush is in contact with a com segment, overlapping two segments as the armature rotates and "firing" will be different which could effectively change the performance of the motor.

 

Long story short, there's nothing "wrong" here at all.  This is common practice for Mabuchi with their "motors for industry" which is what these things are.  The little "FK" motors are exactly the same as a bazillion other motors Mabuchi makes for everything from car door lock actuators and electric windows to whatever...just spec'd for slot cars running at a nominal 12V...give or take

 

-john

[Jeff Whisenand]

John, You are right. The brush tracks are not really grooves.

Thanks for the point on motor break-in. That makes a lot of sense.

I am a little smarter today than yesterday.

You guys are awesome!

[havlicek]

Hi Jeff,

 

     This type of motor typically has the brushes attached to very thin/fragile brass "arms" that position the brushes and also act as springs to keep them in contact with the com.  I don't know for sure, but the force of the armature spinning with the brushes in contact with the com could cause the brush face to move sideways relative to the com centerline because those brush arms are so fragile.  Having just the very small contact area of the brush "edges" contacting the com *might* reduce that tendency until the brush becomes more seated by breaking in.  It all looks bizarre and counterintuitive though, so I can certainly understand why seeing this make you think Mabuchi (who makes these motors for various companies to put their badges on) screwed-up!  I'd think the same exact thing.

-john

[Samiam]

With what John said about the brush support arms it is very important to use as little heat as possible when soldering on the lead wires. I use a very low watt iron just for that purpose. And when I'm testing motors looking for a fast one I swap the motor and lead wires together.  

 

Jeff,

 

What are you racing? And welcome to the blog. Grab some chips and beer(or soda) and enjoy the show.