Cutting a motor commutator & motor tweaks

[cartronicshn]

cool deal, I can't wait for mine , I am already looking for arms and springs to start building my stuff

[Rig Rocker]

It's a lot of fun. I'm on my third armature right now. I'm hooked!

[WIDELOAD]

Originally Posted by Rig Rocker

It's a lot of fun. I'm on my third armature right now. I'm hooked!

It's addictive...You start finding motors you didn't even know you had to give em a cut.

[Duuuuuuuude]

I was goofing around this weekend and rebuilt (as best as possible anyway) a fried 15t hpi firebolt sealed can motor. Rewound it and cut the comm on the lathe. Not much to do for the brushes other than scuff 'em up and reuse them.

Anywho, I decided to try the "chuck it up in a drill and see the kv" thing. I did the math and it came out to approximately 3500kv. That didn't sound right at all, so I tried another, much better quality 27t motor and it came out to 4375kv.

The drill spins @ 1400 rpm, the 27t motor put out .32v.

1400 (rpms) x 3.125 (1/.32) = 4375 rpm's per volt, right?

[EddieO]

Yer formula is correct...

Keep in mind, many 27t motors are pure RPM machines....they would cut the crap out of the arm until there was nothing left. It was not uncommon to see racing stock motors make more RPM than a 19t race motor, which was required by the rules to use a full stack armature.

Later EddieO

[Duuuuuuuude]

Originally Posted by EddieO

Yer formula is correct...

Keep in mind, many 27t motors are pure RPM machines....they would cut the crap out of the arm until there was nothing left. It was not uncommon to see racing stock motors make more RPM than a 19t race motor, which was required by the rules to use a full stack armature.

Later EddieO

I thought so, the numbers just seemed high.

That 27t is one I wound on a Reedy 15t arm and it looked fairly normal, but I know what you're talking about. I've taken some 27t's apart and there wasn't much meat there.

[WIDELOAD]

Epic Binary stock comes to mind with high rpm stock motors. Checked the kv on one a while ago and it was 4880. Thing has pretty much no steel in the arm at all.

[Manning]

.....and "stock" race motors have 24 degrees timing and laydown brushes. Both affect Kv. Try checking the stock motor in both directions and see the difference.

[Cordwood]

Originally Posted by Duuuuuuuude

I was goofing around this weekend and rebuilt (as best as possible anyway) a fried 15t hpi firebolt sealed can motor. Rewound it and cut the comm on the lathe. Not much to do for the brushes other than scuff 'em up and reuse them.

Anywho, I decided to try the "chuck it up in a drill and see the kv" thing. I did the math and it came out to approximately 3500kv. That didn't sound right at all, so I tried another, much better quality 27t motor and it came out to 4375kv.

The drill spins @ 1400 rpm, the 27t motor put out .32v.

1400 (rpms) x 3.125 (1/.32) = 4375 rpm's per volt, right?

Let's get an untouched 15t firebolt and dyno them. That'd be fun.

[dkf]

Originally Posted by Rig Rocker

Got it figured out. I couldnt see pics on my phone but as soon as I saw the position of the bit, it was on!

I'm a com cuttin' Mo Fo

I have the same lathe.

Keep an eye on the ways for knicks. (I see there is already one on yours) When I first got mine there was a knick on the one way which caused the lathe to turn a taper. I stoned the knick out and it took the taper out.


Why isn't this thread a sticky yet.

[Duuuuuuuude]

Originally Posted by Cordwood

Let's get an untouched 15t firebolt and dyno them. That'd be fun.

Agreed. I'd like to see a comparison too. Especially since I'm going to be receiving a handful of used rtr sc motors to play with.

[Cordwood]

I was playing around with some graphs to show a better visual.

Here is a comparison of the Tekin Pro pre rebuild vs post rebuild/tune. Note that it's not apples to apples as the pre rebuild is the motor at 0 degrees timing in excellent condition, likely what it would be as provided from Tekin. The post is at a crawler friendly 6 degrees timing advance. I think it shows how an off the shelf motor could be better with some tuning and small timing advance.








Here is a comparison of the post rebuild/tune Tekin vs. the HHK in the P-94 can

[Rig Rocker]

Hey dkf

A nick on what? Can you please explain for me? The comms I have turned have exact OD at both ends.

BTW, that was my first com cut. I'm getting better with each one.

Thanks for the input

Originally Posted by dkf

I have the same lathe.

Keep an eye on the ways for knicks. (I see there is already one on yours) When I first got mine there was a knick on the one way which caused the lathe to turn a taper. I stoned the knick out and it took the taper out.


Why isn't this thread a sticky yet.

[dkf]

Originally Posted by Rig Rocker

Hey dkf

A nick on what? Can you please explain for me? The comms I have turned have exact OD at both ends.

BTW, that was my first com cut. I'm getting better with each one.

Thanks for the input

It looks like the corner was hit on the crossfeed which will raise the surface. That will not make it cut a taper just limit the cross feed travel.



When I got my lathe as I said it was cutting a taper. My knicked way was on the longitudinal feed though which caused the taper. I was running over the raised metal from the knick which caused the taper. I stoned down the raised portion and the taper went away. The aluminum on these lathes is heat treated but it is still fairly soft. I was just giving you a heads up so you can avoid issues.

[WIDELOAD]

Originally Posted by Cordwood

(insert pretty graphs here)

Cheers for that Corwood, it actually gives a nice visualization for people to see the difference. Maybe MattH over should take some time and have a look at them.(and maybe just read this thread in general)

[EeePee]

Nice graphs yo!

[Charlie-III]

Originally Posted by EeePee

Nice graphs yo!

+1 to EeePee & Wideload.........as well as Cordwood........

Curious to see how my "dyno" can display info.

[Rig Rocker]

Thanks for the heads up dkf

Originally Posted by dkf

It looks like the corner was hit on the crossfeed which will raise the surface. That will not make it cut a taper just limit the cross feed travel.



When I got my lathe as I said it was cutting a taper. My knicked way was on the longitudinal feed though which caused the taper. I was running over the raised metal from the knick which caused the taper. I stoned down the raised portion and the taper went away. The aluminum on these lathes is heat treated but it is still fairly soft. I was just giving you a heads up so you can avoid issues.

[JeremyH]

I was rebuilding my motors (Brood 35T HHKs) to get ready for ACC and I had one of my best cuts yet....so I thought I'd post a pic:
(I know, the camera is shitty and has a hard time focusing on the comm)

[Cordwood]

Originally Posted by JeremyH

I was rebuilding my motors (Brood 35T HHKs) to get ready for ACC and I had one of my best cuts yet....so I thought I'd post a pic:
(I know, the camera is shitty and has a hard time focusing on the comm)

That's all sorts of sweetness right there. Nice cut, too!