Cutting a motor commutator & motor tweaks

[EddieO]

Correct, other than the limited amount of KR mod arms out there, we didn't use anything but 7.5mm comms in racing, so there was little need to have another cut. The Reedy 19t Quad was the only spec motor we ever used really, but it was only used as a handout a couple of times....so we just used the old razor blade trick to measure them.....

Later EddieO

Originally Posted by JohnRobHolmes

Cool little tool! I bet it really helps spot the differences between arms. Cut for 7.5mm arms?

[The Violator]

Originally Posted by 4xFord

Outrunner drag break can't be touched.

EDIT: Actually, homes hold on the BRXL is about the same with brushed 540's.

Its not the hold I am talking about. My wraith will nose over if you let go at speed. Its when you add a little throttle on a downhill and it takes off. The Losi MRC system is the worst, but my wraith with a MMP does the same thing, but not quite as bad.

I have heard that Tekin has something in the works, but who knows for sure.

[JohnRobHolmes]

I also have a sub-routine planned to keep control of drag when on throttle. It will be tough to implement though, and it only works for sensored motors. Can't do it on brushed motors because of the high inductance.

On throttle roll isn't an issue with outrunners though, they have high enough detent force to keep from free coasting too much. It is more of a problem with inrunners, particularly the little two pole roar style ones.

[Charlie-III]

Originally Posted by The Violator

Its not the hold I am talking about. My wraith will nose over if you let go at speed. Its when you add a little throttle on a downhill and it takes off. The Losi MRC system is the worst, but my wraith with a MMP does the same thing, but not quite as bad.

I have heard that Tekin has something in the works, but who knows for sure.

Can you alter the throttle curve so it's shallow early in the throttle & then rising quickly from there?
Or, is your issue more of a, "Once the drag brake is off, the rig rolls easily"?

[JohnRobHolmes]

notes for later about the motor master.

Looking from the front side from left to right, the power module inside that I smoked

"fet 2" N channel FET (dead)
rectifying diode
"fet 1" P channel FET irf4905
rectifying diode

I can't tell what fet 2 is any longer, but since most switching regulators match the high side and low side FETs for cost reasons we can assume an Rds(on) of 17.5mohm. Looks like the 100v N channel FETS I have here are 3.7mohm, surely to be a big improvement in heat on one side of the device! The only problem is the gate driver, I don't know if it can handle the higher gate capacitance of my FETs. Probably won't be an issue since these little FETs were likely driven at pretty low frequencies, and it will take less time to just plop a new one in instead of pulling out the O-scope and running calculations for it.

To be continued...

[indiana mudcat]

Originally Posted by Charlie-III

Can you alter the throttle curve so it's shallow early in the throttle & then rising quickly from there?
Or, is your issue more of a, "Once the drag brake is off, the rig rolls easily"?

It's once the throttle is slightly touched the truck completely freewheels, like it doesn't even have a pinion on it. Worst part is you let off the throttle to catch it and the drag locks and it'll flip. If you know it's gonna happen you can use reverse to control it, as you can vary the braking with more reverse. Since the truck will still roll forward in reverse

[Charlie-III]

Originally Posted by indiana mudcat

It's once the throttle is slightly touched the truck completely freewheels, like it doesn't even have a pinion on it. Worst part is you let off the throttle to catch it and the drag locks and it'll flip. If you know it's gonna happen you can use reverse to control it, as you can vary the braking with more reverse. Since the truck will still roll forward in reverse

Ahhh...OK.

There are a number of things that can help/hurt.

Easy stuff:
-New brushes (they're longer, thus adding drag to the comm)
-Stiffer brush springs (they also add some drag to the motor)
-Tighten spur/pinion mesh a bit adds some drag

This all works well for a brushed motor, if the original comment was directed towards brushless inrunner/outrunner, then only the pinion/spur gear mesh can help....for now....

[4xFord]

Hey Eddie, I was reading up on Rowdy's motors, what is good about the putnam green brushes? Actually, can I list the ones I have and you tell me what you know about them?

Putnam green

Putnam X

Putnam 4105 (says hard on the box)

Lightspeed 4000

4499

XXX- (lots of silver right, so really hard?)

F???

Reedy 767

739X

Kisbey Old Style



Also, harder or softer brush at high voltage? (4s) Or does it make a difference? I want to say harder since they will see more heat and rpms, but 4s is already tough on comms without adding a harder brush to the mix.

[EddieO]

They were a very high power brush back in the racing days. Some people thought they were harsh on the comm, but I found if you broke them in correctly, the wear was no more than any other race brush really....it was just that initial break in that made it appear it wore the comm more. Todd and I never agreed on this......and we stopped talking when he accused one of my drivers of cheating at the vegas race (found not to be cheating). I had some not so kind words for him later in the casino when my driver used his backup motor to beat the time that was thrown out by 2 seconds....

Posted the following below

Originally Posted by 4xFord

Hey Eddie, I was reading up on Rowdy's motors, what is good about the putnam green brushes? Actually, can I list the ones I have and you tell me what you know about them?

Putnam green - High Power laydown that can be harsh on the comm if not broken in right.

Putnam X - Was his modified brush....didn't like em, were down on power and rough on the comm........there is a reason he never won shit in modified.

Putnam 4105 (says hard on the box) - Was some generic brush he sold....I would not say junk, but nothing special.

Lightspeed 4000 - good compound that makes a lot of power, but can be harsh.

4499 - trinitys main laydown brush. Very high silver, good power. Same compound as the 4383 standup.

XXX- (lots of silver right, so really hard?) - Last forever, take high heat...but can be rough on the comm. Does NOT like water.

F??? - Made by finish line.....these were very popular, but the batches varied in performance. I won numerous national titles with these. Soaking them in certain fluids was often done with these.....shit, we even baked them.

Reedy 767 - Reedys standard laydown.......very similar to the 4499, some even though batches of the two were the same from Kirkwood (the actual company who made most brushes). I use these on most brood motors stock.

739X - I assume this was a reedy, which was a compound they said was similar to the 4383.....I thought it sucked. The X in the part number might of been a cut, as Reedy did sell a lot of cut brushes.

Kisbey Old Style - Relabeled trinity probably. I never heard of him having his own compound. Guy was a pretty good winder and builder......until he got caught cheating at snowbirds. I was handed a motor to look at to spot the problem....at first I didn't notice it.......but then I saw it, only a couple of us actually were able to spot it. His handwound 19t........was actually like a 12t. He had wound the first layer of wire on seperately, but not connected. He then wound over the top of it. Looked JUST like a 19t pattern, but since those coils were not connected, it was a rocket.....BUSTED. He pretty much disappeared after that.



Also, harder or softer brush at high voltage? (4s) Or does it make a difference? I want to say harder since they will see more heat and rpms, but 4s is already tough on comms without adding a harder brush to the mix.

At higher voltage, I don't think it matters that much in a crawler.......I mean, we often ran just as hard of brushes in touring car(7.2 volts) as we did 1/12th scale(4.8 volts), usually harder.....its really a catch 22......the main thing is controlling the brush bounce with stiff springs. I ran some test motors with a customer, where we ran 729 at first on 4s.......then 4383 (hard and abrasive)........wear was pretty similar, crawler motors just don't spin fast enough to make a huge difference. Now, a wraith motor thats a 25t....might be a different story.

Later EddieO

[EeePee]

Originally Posted by EddieO

He had wound the first layer of wire on seperately, but not connected. He then wound over the top of it. Looked JUST like a 19t pattern, but since those coils were not connected, it was a rocket.....BUSTED. He pretty much disappeared after that.

Hah.

[EddieO]

I tried to find him after, as I wanted to buy him a beer.........slickest piece of cheating I had ever seen really...surprised it took so long for someone to try it!

Later EddieO

Originally Posted by EeePee

Hah.

[Cordwood]

Wouldn't an inductance check with an LCR meter of found that pretty quick?

[4xFord]

Thanks for all the info Eddie, great to know exactly what I've got here and how I want to use them.

[EddieO]

Correct, it would.....but LCR meters prior to brushless were a rare thing at a race....they had them during the 10t limit touring car days, but even then wasn't very common.

Later EddieO

[TEDROCKZ]

Originally Posted by EddieO

They were a very high power brush back in the racing days. Some people thought they were harsh on the comm, but I found if you broke them in correctly

This is where an appropriate diameter fussy brush will come in handy! I have a couple of sets of the Putnam greens I may try a set this week...

[Cordwood]

Originally Posted by EddieO

F??? - Made by finish line.....these were very popular, but the batches varied in performance. I won numerous national titles with these. Soaking them in certain fluids was often done with these.....shit, we even baked them.

Later EddieO

This sounds interesting. Fluids?

[EddieO]

We soaked them in all kinds of stuff....Mineral Spirits, Lighter Fluid, Diesel, Tons of shit from the auto parts store.

Baking them was more difficult, as we could not use anything that would ignite. Tribo was the one we had the most success with....2 hours on a cookie sheet at 150 degrees.

Later EddieO

[Robbob]

Originally Posted by EddieO

We soaked them in all kinds of stuff....Mineral Spirits, Lighter Fluid, Diesel, Tons of shit from the auto parts store.

Baking them was more difficult, as we could not use anything that would ignite. Tribo was the one we had the most success with....2 hours on a cookie sheet at 150 degrees.

Later EddieO

I remember when the wife and I were dating. She asked why I had two toaster ovens.

Think she thought I was making Meth until I showed her what one was for lol.

I remember getting some black shunt brushes from Todd. They were cryogenicly treated and were a monster.

Those were the fun days of chemical playing. Could explain a few lost years lmao.

Sent from my HERO200 using Tapatalk

[EddieO]

Ah the good old days.....Todd was full of it on his cryogenicly treated brushes though......

We had some people not read the fine details when it came to baking brushes. Some nimwits decided to use the oven they cook food in....that always went over well. Better yet, was the guys that decided to bake brushes in stuff that goes boom........the Australian guy who lit his shop on fire with Petrol was always my favorite. Luckily it had a sprinkler system, so damage was minimal.

Later EddieO

[Cordwood]

We're you guys soaking them in stuff and then baking them after to dry em out? Seems like most stuff wouldn't ignite at only 150 degrees