45 replies to this topic

[crazyphysicsteacher]

Okay. I have been only racing for a short period of time but have moved up to local ISRA racing with built 16D motors using Pro Slot set-ups. I bought my first motor, but it is a dog. My sealed SpeedFX 16D runs better.

I digress. I have since pulled the motor apart and have adjusted the end play while also building another motor. Both motors ran hot when using full size, laydown brushes but cooled own and free revved higher when I installed narrowed brushes I used in my Hawk motors. Now, I have read about needing to cut brushes to get the motors to run right.

Here are my questions:
1. In cutting brushes, should I just narrow the width or also narrow the height?
2. I have tried drilling a hole in the brush face in previous motors and have found mixed results. Has anyone tried this in a built 16D motor? 
 
While I know the only true way to learn is try and test, I am not going to be able to test for three weeks and would like to be able to surprise the rest. The motor is worth 0.2 seconds on the track.

[gotboostedvr6]

Using American 16D arms you don't need cut brushes.

There are a ton of bad brushes going around. Change them and do a 45 min break in at 4 volts.

Are you racing on a flat track or banked track? Im guessing you race one of three places: Speedzone, Gardenstate ISRA club, or The Race Place.

I'd use different set-ups at all three tracks, and set-up makes a huge difference.

Which track do you run at?

[Pablo]

What's a "laydown brush"? I've never heard of that. Never heard of cutting a hole in the brush faces either. That must be tricky. 

I've never heard of having to cut a brush to get the motors to "run right". Where, exactly, did you read that?

I'm well aware of the technique of cutting down brushes to reduce the amount of material touching the comm, but never heard it said they "must be cut down" to get the motor to run right???

[Zippity]

Crazy.
 
Carefully rub either side of the brush on a piece of cardboard (business cards are great for this purpose) until such stage as the brush will fall under its own weight out of the brush holder on the motor.
 

[Pablo]

Zip, that's motor building 101. I may be wrong, but I think he's talking about something else entirely...

[Rick]

Laydown brushes is an R/C term, in slots we use horizontal and vertical terms. Friction cutting brushes has been done for years, Illegal in most rules sets today for some reason?. Like Rocky always said: "rules are written out of fear"...

[Zippity]

Zip, that's motor building 101. I may be wrong, but I think he's talking about something else entirely...

 
Is he?

[Champion 507]

My 2 cents worth:
 
Noting the rotating direction of the arm, I have removed .010" off the trailing edge of brushes parallel to the comm for a modern 16D before. Not only do you get a smaller contact patch on the comm, it sort of "advances" the timing a little. They run faster.
 
I've also done the opposite (remove .010" off the leading edge of the brushes) and it retarded the timing a little. I used to do that when I raced FCRs ten-twelve years ago where the races were run with break-outs. My car wouldn't be as fast in the main straight of a blue King **you could actually see it** but it would pick up torque and brakes in exchange.
 
A friend of mine has built thousands of motors, everything from 16Ds to opens and he says the Koford Big Foot IIs are the best on the market today. I'll say this, I've never had a problem with them.

[crazyphysicsteacher]

I run at The Race Place and all of my brush hoods get sized and adjusted to get the brush square to the comm. I was asking about the cut of the brush as Champion 507 speaks of. My motors ran super hot on the power supply until I put a set narrowed brushes in both motors.  The amp draw dropped in half but the RPM went up and the motor ran smooth and quiet. The cut took about 0.15" off both the leading and trailing edges ala Mike Swiss.

As to the hole, I had been drilling a small 1/16" hole in each brush and found the motor ran stronger with more RPM and better punch on a Deathstar. I found this worked with Golddust brushes until I changed to Big Foots due to bad brushes. I have moved to a smaller hole while chasing performance but something has changed and it no longer is consistent.

[havlicek]

Couple of things,
 
Narrowing brushes (trailing and leading edges) will reduce the contact area making break-in faster and decreasing the physical drag on the comm a larger brush has... but it will also decrease (at least marginally) how much current the brush can carry and "overlap" on the comm segments... and affect timing.  

It will also increase the pressure as measured in "units of force per square measure of area" the brush exerts on the comm because spring tension being constant... you now have the same pressure over a smaller area. Whether any of this is a good thing or not depends on how the car is set up and track power, because a lot can be made up in gearing for example. Good motors can be made to run hot and burn up with inappropriate gearing (including tire diameter which ultimately affects the real-world final gear ratio).
 
***Modern lower-end motors most often have narrow diameter comms. Couple that with "36D" sized brushes and you can get some weird stuff happening. I think that cutting the brushes on the Hawk motor (I think it was Mike Swiss who did that early on and improved things noticeably on the Hawk) to something closer to the size of the old FT16D brushes has been proven to work. It would make sense that the motor makers just went to a larger diameter com in ALL cases. When you open up one of the "FK" sized sealed motors like the Falcon, you'll see a tiny comm... but you'll also see tiny brushes.
 
-john

[Fast Freddie]

I have had to narrow brushes to get my high timed .540" PS Contender arms to not need a "push start". They were installed in Red Fox set-ups using older Camen magnets honed to .560". The brush overlap was so great that both brushes would contact the same comm segment causing a dead short, hence the need for a push start.

I didn't have this problem with high timed BOW .540" Contender arms in the same set-ups so it was the arm. The arm stack leg on the PS arm would stop perfectly between both (north and south) magnet tips; the BOW arm wouldn't. By cutting as little as .005" of brush material from the first third of the brush, on one side only and installing that side as the trailing edge I stopped the push start problem and reduced heat in the motor. The arms were new when I had to do this and the comms were .200+. They still run great with .197" comms but I'm going to try them in different set-ups with stronger magnets for this years ISRA.

[crazyphysicsteacher]

Thank you all for your help. I appreciate the ability to bounce ideas off the best minds out there. 

I started trimming and drilling brushes after I found the suggestions on old R/C posts and found the changes worked on my sealed Deathstars. I the tried narrowing brushes after reading about it from Mike Swiss with Hawk 6 motors and found .100" wide brushes were the ticket to get the stock Chinese are to live. In fact, I got that arm to last and be just a few RPM less, than the Koford replacement arm.

Back to the issue... the brushes I put in each were narrowed to 0.10" wide. The motors revved to speed on 3v quicker than with the full face brush and arm very smooth. One motor is built from a Pro Slot set-up with a .575" hole and a .560" 42° arm. The other motor has an 'Atom' arm of .540" in a .570" hole.  Both motors ran super hot at 3v and the 'Atom' arm just does not have the go and was super soft with the full face brush and wound up slowly on the power supply. Now it may be a bad set of brushes but this is with two different types, Golddust and Big Foot IIs. I wonder if the change in timing and overlap is working to counter air gaps which are too small and 'unbind' the arm from the magnetic field? 

Fred, I am going to go back and slowly narrow brushes until I get a good running motor. I may also go back to drilling holes in brushes to see if that helps again.

If anybody has more advice, please share. I am willing to hear about all changes that made a motor faster.

[havlicek]

Well... if you're going to be cutting brushes, you can advance or retard the timing on non-rotator setups by cutting the brushes. I don't know if it's a good thing or a bad thing, just putting the info out there.

As always, personally I would look to see what the fast guys are doing to their motors... IF they're willing to share!  
 
-john

[gotboostedvr6]

I've had good luck with Atom 16D arms. Sometimes they like a bit of extra timing added through the endbell.

Also don't hesitate to drop a tooth on the pinion.

[crazyphysicsteacher]

I am friends with the current motor builder but don't like using someone else's motor. When something goes wrong you never know what to fix. I have bounced ideas off him in the past but he does not like playing with brushes much. Instead he has built some motors with big arms in .590" holes.  I do not have hones and am only starting in the process of building so I am stuck with just using smaller arms or cutting brushes.

Instead I have experimented. The Atom does not like the hole drilled in the brush; it revved up initially and then just heated up. I paired the hole with a trim on the trailing edge and it picked up RPM, lost amperage, and it ran cooler. The motor heated up, stayed constant, and I could still touch the arm. I also changed the hoods to copper and readjusted the hoods. Motor pulls 1.3 amps but seems more efficient.

The Pro Slot arm was just given a trailing edge cut and picked up RPM while cooling off a bunch. I cannot wait to test these motors out.

As to dropping a tooth, I had a 10 tooth pinion on the motor and it just screamed but was a half second off the pace regardless of who drove the car. No matter how well it ran the turns it was blown away down the straight.

[gotboostedvr6]

In your original post you asked for help.

I have run on your Engleman during practice in the 4.8 second range. I was using a 45 degree Atom +5 endbell geared 10/37. I had great difficulty with tire selection and am convinced 4.6 is possible. I used full Big Foot brushes and Kamen light springs.

Cut brushes only work on flat or short high voltage banked tracks and also only work when using very tiny pinions.

Of course if you're running the flat track upstairs set-up is completely different.

[crazyphysicsteacher]

I am asking for help, but have also tried all I can with car. When I had the 10 pinion I had a 35 spur and .680" tires on the car, it was out of breath and did not have the RPM you have. I also think the arm has about 38° for timing.

I know there is power in air gaps but I also know there is power in brushes. I have run cut brushes in sealed motors on both flat and banked tracks, but they had smaller comms and really needed the narrowed brushes. Now I am working with full size grown up comms and read in some posts about needing to trim brushes to get the motor to run well. We also run on 13.6+v, which I understand to be not low.

No one I talk to has much experience with cutting brushes, so I am here looking for help and advice.

Now, I could just take the advice walk away or I can use the forum to help myself learn more while also helping those who are afraid to step up, and ask.
 
By the last response, one last question: Has anyone had luck with putting a horizontal cut in the brush face?
 
Thanks to all that gave me some great advice.

[JFK]

You may want to test and or break-in your "big boy motors" at 4v. There isn't enough RPM/air movement in most cases to cool the motor at 3v.

The stock PS setup IMHO has way to much field and limits the RPM. I don't see how cutting brushes can resolve the issue. My guess is even though you perceive an increase in RPM at 3v the motor will feel even softer than before on the track.

Lastly, you mentioned the amp draw at 3v was 1.3... That's not going to get it done, brother.

[gotboostedvr6]

Try advancing the timing on the endbell and use larger tires.. If your setup with 35 gear that is level with the bottom of the chassis you will be able to tech .047 with a .705 medium or small hub tire. If it winds out early you can add a tooth on the pinion or hone the magnets to a larger gap. I typically run .585 to .590 gaps using Atom Arms for more peak rpm and slightly softer exit punch.

After the back straight you have quite a hill to climb to get back on the back straight. You will need the overlap full brushes provide to produce enough torque to get up that incline.

I also had better results using a OS-067 Cadillac in .007, it provides more downforce up front then most other GTP bodys.

[JFK]

Try advancing the timing on the endbell and use larger tires.. If your setup with 35 gear that is level with the bottom of the chassis you will be able to tech .047 with a .705 medium or small hub tire. If it winds out early you can add a tooth on the pinion or hone the magnets to a larger gap. I typically run .585 to .590 gaps using Atom Arms for more peak rpm and slightly softer exit punch.After the back straight you have quite a hill to climb to get back on the back straight. You will need the overlap full brushes provide to produce enough torque to get up that incline.I also had better results using a OS-067 Cadillac in .007, it provides more downforce up front then most other GTP bodys.

What arm timing are you starting with?

[gotboostedvr6]

I measured the actual timing at 45 and engraved the arm.

[gotboostedvr6]

I concur that the magnet field on Proslot d can Motors is excessive.

[JFK]

I measured the actual timing at 45 and engraved the arm.

That's where I'm at too.

[Fast Freddie]

I should have read the title of this thread more closely. I have only had to use cut brushes on my PS Contender motors never on any 16D motor. I also use PS FX 16D setups with .560 PS 16D 42 and 45 degree arms. I find that on a flat track I prefer an air gap of .575-.580 while on a high banked track I like an air gap of .584-.590. On either track I gear the car 12/42 72p and they run fine. Tire size on the flat track is usually at .700 to start the race and on the high bank it's around .765 to start. I hate changing tires during a race so the car usually picks up about half way through the race. That's a 5.00 rollout ratio on the flat track and around a 4.58 rollout on the high banked tracks using the same 3.50 to 1 gear ratio but different tire diameter.

[JFK]

I should have read the title of this thread more closely. I have only had to use cut brushes on my PS Contender motors never on any 16D motor. I also use PS FX 16D setups with .560 PS 16D 42 and 45 degree arms. I find that on a flat track I prefer an air gap of .575-.580 while on a high banked track I like an air gap of .584-.590. On either track I gear the car 12/42 72p and they run fine. Tire size on the flat track is usually at .700 to start the race and on the high bank it's around .765 to start. I hate changing tires during a race so the car usually picks up about half way through the race. That's a 5.00 rollout ratio on the flat track and around a 4.58 rollout on the high banked tracks using the same 3.50 to 1 gear ratio but different tire diameter.

 Right on the money Fred! Thank you for your insight!