Cutting a motor commutator & motor tweaks

[EddieO]

You can just clean them off with motor spray after. I have the same cutter and it works fine. Good unit and you can get them for dirt cheap now.....I always used a stock motor in mine though, 27t p2k2 usually....or something similar.

The fussy brush is cool and worked well in the racing days, but they were very tedious to use and time consuming....don't know how much that's worth in the crawling days now. I actually used to have a motor just set up for the fussy brush to cut stuff. I didn't really use the serrator much from Fussy brush, as the integy worked fine when we needed it.

I would not worry much about the slots on the rear of the brush, many top brushes do not even have them. Someone did a test way back when of having it not in the slot or in, not noticeable wear differences, no HP difference...



Later EddieO

[EeePee]

The slot would technically reduce spring pressure given the same spring.

Nor do I see the point in them at all other than locating, but that's got to be beyond not mattering.

[JohnRobHolmes]

I use a xipp brush cutter too, takes a lot of pressure to cut because the bit has no rake. I run mine with a 13t crawlmaster and 12v. The fussy brush is really handy for getting laydowns ready to seat on a 10mm comm and prepping silver brushes. Only takes a few seconds to shape with the Fussy brush VS waiting half an hour for a laydown or silver brush to wear in. Totally worth it for me, I had them fire off a run with 10mm bits just so I could have the tool for production.

[kurtus]

Well I do like tools so I see a fussy brush in my future plus I'm not building motors to sell so I have nothing but time. Good to hear that what i am noticing with the xipp cutter is normal. I think I'll run the 45t with a 3s pack and use some cutting oil to see what happens. Should I just put a bit of oil on the brush or the cutter? Also is it advised to recut the comm after breaking in 767 serrated brushes?

Thanks for the input guys

[EeePee]

Originally Posted by JohnRobHolmes

I had them fire off a run with 10mm bits just so I could have the tool for production.

Oh yeah? Sell those separate?

I would think oil on the bit will fly off as soon as you turn it on. I'd put it on the brush, but I don't think you really need it at all.

I've been at a point that every time I did another step to the motor, the comm was recut. So, cut clean, broke in, cut again, broke in again. Perfect contour, and perfectly clean in the end. Ready to be killed in the Losi.

[kurtus]

Originally Posted by EeePee

Oh yeah? Sell those separate?

I would think oil on the bit will fly off as soon as you turn it on. I'd put it on the brush, but I don't think you really need it at all.

I've been at a point that every time I did another step to the motor, the comm was recut. So, cut clean, broke in, cut again, broke in again. Perfect contour, and perfectly clean in the end. Ready to be killed in the Losi.

I'm starting to think my issue is more motor rpm than anything, based on what you, eddie and john are saying it should run in the 27000rpm range but the best I can get out of the 45t is 15000rpm at 12.6v. I need to find a can to put one of the stock arms I have into and use that instead . I'll follow your lead here EeePee, thanks

[kurtus]

One strange thing about my atx power supply that you electronic gurus might be able to help me with is that everytime I hook a motor up to the 12v lead it just cuts the power supply out. It has plenty of amperage on the 12v side, I think its 20amps or more so this is really confusing me, I pull 10 amps charging lipos all the time from it with no issues. It will cut out using my charger though if I power the power supply on first then plug the charger in, cuts out again. Leave the charger plugged in, cycle the power and it fire up just fine. It's like there is a signal being tripped causing and overload or something. Motors run fine in any situation on the 3v and 5v taps just the 12v that causes it to cut out.

[EeePee]

Originally Posted by kurtus

I think its 20amps or more

At what voltage?

Might be at only 3.5 volts, so you're pulling too much at 12.

[kurtus]

Originally Posted by EeePee

At what voltage?

Might be at only 3.5 volts, so you're pulling too much at 12.

This is what I did with it and it is very convenient.

[JohnRobHolmes]

Originally Posted by kurtus

One strange thing about my atx power supply that you electronic gurus might be able to help me with is that everytime I hook a motor up to the 12v lead it just cuts the power supply out. It has plenty of amperage on the 12v side, I think its 20amps or more so this is really confusing me, I pull 10 amps charging lipos all the time from it with no issues. It will cut out using my charger though if I power the power supply on first then plug the charger in, cuts out again. Leave the charger plugged in, cycle the power and it fire up just fine. It's like there is a signal being tripped causing and overload or something. Motors run fine in any situation on the 3v and 5v taps just the 12v that causes it to cut out.

The inrush current is tripping the power supply. Your charger has main power caps that will pull a few hundred amps for a split second while they charge to the mail rail voltage. If you take off the main cover of the ATX and get the cap specs, you could calculate the inrush.

The reason it doesn't trip if it's already hooked up is because of the soft start and boot up time. The caps charge a bit slower and the inrush is already over by the time your ATX is ready to watch for overcurrent situations.


There is probably a shunt inside the ATX you could beef up to get around this. Or you could just make sure the charger is always plugged in before the ATX is plugged in. You could also remove the resistor that discharges the caps so it doesn't recharge every time you plug it in. You could also use a precharge resistor on the positive side. So plug in the negative, precharge positive (100 ohm in series with positive charger rail), wait 5 seconds, plug in main positive and unplug precharge resistor.



I have a 50a supply we modded for breaking in motors. Does the same thing. Also, can't hook up motors on the 3.5v rail without it tripping the supply. Have to use an ESC to ramp up motor speed, which defeated the purpose of having a bare 3.5v rail for breaking in motors.

[kurtus]

Originally Posted by JohnRobHolmes

The inrush current is tripping the power supply. Your charger has main power caps that will pull a few hundred amps for a split second while they charge to the mail rail voltage. If you take off the main cover of the ATX and get the cap specs, you could calculate the inrush.

The reason it doesn't trip if it's already hooked up is because of the soft start and boot up time. The caps charge a bit slower and the inrush is already over by the time your ATX is ready to watch for overcurrent situations.


There is probably a shunt inside the ATX you could beef up to get around this. Or you could just make sure the charger is always plugged in before the ATX is plugged in. You could also remove the resistor that discharges the caps so it doesn't recharge every time you plug it in. You could also use a precharge resistor on the positive side. So plug in the negative, precharge positive (100 ohm in series with positive charger rail), wait 5 seconds, plug in main positive and unplug precharge resistor.



I have a 50a supply we modded for breaking in motors. Does the same thing. Also, can't hook up motors on the 3.5v rail without it tripping the supply. Have to use an ESC to ramp up motor speed, which defeated the purpose of having a bare 3.5v rail for breaking in motors.

Nice answer John, that gives me alot to think about. In your opinion would replacing the capacitor and removing the discharge resistor be the easiest/safest route, is the resistor alone enough? I can solder damn near anything so I'm cool with that its just that identifying the discharge resistor, cap and calculating the inrush that is above me. I'll pull the cover and look but would there be a larger cap on there that would be smack you in the face obvious? I have no clue where that resistor would go in the circuit. Is there a good diagram of the atx circuit anywhere?

I can live with leaving the charger plugged in on boot up for 12v, the motor works just fine on the 3.5v and 5v rails in my lathe and cutter luckily it just wont operate at all with a motor direct to 12v so it would be really nice to get this working.

[kurtus]

Ok so I finally decided to try and cut my good brood apocolypse type r motor. Here is what she looked like after a good season of running on 3s, suprised the hell out of me when I finally removed the arm from the can how bad it was.


Here I started with a new amazon carbide bit, made 10 light passes and she is done for, chattering really bad.


Changed out for the diamond bit I bought from integy for 30 bucks. I noticed right away that it was cutting like butter, the rpm of my lathe motor stay up while cutting instead of bogging down a bit like it would with carbide, also reshimmed the bit better so it is exactly center. Making beautiful cuts now and starting to get somehwere alot quicker.




Is it a big deal that there is still a bit of a wear spot at the comm segments, I took a picture of this after cutting it from the break in for a final time and it is at .280 inches. I didn't think I would gain anything by going any further with the comm trying to get the seams perfect.

[EeePee]

When I was cutting a lot of arms for the scaler bros I stopped short of perfect figureing they won't know the difference and probably get a longer life cause I'm not taking so much material off.

[kurtus]

Originally Posted by EeePee

When I was cutting a lot of arms for the scaler bros I stopped short of perfect figureing they won't know the difference and probably get a longer life cause I'm not taking so much material off.

So it is true, great mind think alike lol;) Thx man

[EeePee]

Originally Posted by kurtus

So it is true, great mind think alike lol;) Thx man

Sure.

However, my personal motors on the other hand... are never allowed to get anywhere near that condition.

[kurtus]

Yeah, this was bad.... I learned something regarding motor care though and now I'm not scared to tear down and keep this comm fresh along with the brushes. Thx for all the help peeps ;)

[mrG]

Look what was in my mailbox today, now I just have to learn to use it.

[EddieO]

First, get rid of the stupid arm spacer things. Just take them off. I use a couple of washer and phenolic on the bottom of the arm (pinion side). And then just use your finger to the push the comm side to the right.

I finally did a tutorial. Just a refresh rebuild...

http://www.teambrood.com/store/Refreshrebuild.html (you can click on the photos for a bigger pic)

More tutorials are coming, along with some new pictures and videos. Trying to bang one out every 10 days or so. Timing guide is next on the list.

Later EddieO

[ZippoMan]

Awesome tutorial! I bookmarked that page!! Thanks for the great tips!! Very helpful for when I get brave enough to disassemble my first motor.

[mrG]

Originally Posted by EddieO

First, get rid of the stupid arm spacer things. Just take them off. I use a couple of washer and phenolic on the bottom of the arm (pinion side). And then just use your finger to the push the comm side to the right.

I finally did a tutorial. Just a refresh rebuild...

http://www.teambrood.com/store/Refreshrebuild.html (you can click on the photos for a bigger pic)

More tutorials are coming, along with some new pictures and videos. Trying to bang one out every 10 days or so. Timing guide is next on the list.

Later EddieO

What rpm should the comm be turning when I cut it? I found this on Holmes site,

"The stock drive motor is about 2900 RPM per volt, and the reduction is 2.28:1

We recommend cutting 10mm commutators between 1500 and 3000 rpm, and 7.5mm armatures between 2000 and 4000 rpm. We have found 2.4 to 2.6v to work best with the stock drive motor and pulley."

Not doubting JRH, just double checking.