64 replies to this topic

[Big Booty]

Dont get me wrong Im a big fan of twerking, especially when Miley does it.  In fact my nephew's boy band nearly opened for Miley but I digress...back onto the motor and brush gear.

 

The goldust brushes are exactly the same size as SBF, 3.15 mm tall and 2.74 mm wide.  So MSwiss can you measure the diameter of the com.  I suspect this is where the problem is.  Big brush small com, lots of overlap = not good.

[MSwiss]

When the similar JK Hawk 6 came out, I sold SBF II's with the height reduced.

The comm is no smaller than other Chinese arm motors.

The overlap problem is accenuated by the heavy cogging.

[Gator Bob]

Post #67 = WINNER !

[Eddie Fleming]

So is it legal to take a little off the trail edge of the brush to reduce the overlap?

[Pablo]

Eddie, this is "General Slot Car Racing" .... there are no "General Slot Car Racing Rules"......

Please define "legal" ? According to what rules ?

[Big Booty]

So is it legal to take a little off the trail edge of the brush to reduce the overlap?

 

Depends what comp you run in I suppose.  If brush gear is "free" I cant see why it wouldnt be OK.  Same as running different motor springs.  Since Mike is on the "IRRA parts committee" he might be able to come up with a definitive answer.

[Pablo]

Rick, I was way off, the comm is about .155, not .200

Not going to stick my calipers in there and gouge my comm, I gotta race this thing 15 Jan

Why is a brush sized for a (approx.) .200 OD comm being used for a smaller comm ? Rick, I don't know.

But, I am glad you raised the question

 

Here in Mississippi, they have a saying: "That don't make no sense"

[Pablo]

"Post #67 = WINNER !"

Gator Bob, how is that possible - the latest post is 32...

[Gator Bob]

Pablo beat me to it

"Legal Where?"

 

IRRA -

The 4002FK is only allowed in C/A+

"Cut Brushes' are considered motor tampering and you can get expelled. 

 

RETRO -

I don't know.

 

Although I've never seen anyone 'protested' or 'torn down' post race in any class since returning in 2011 to find "Sealed" motors is 'the new thing'.

[Gator Bob]

"Post #67 = WINNER !"

Gator Bob, how is that possible - the latest post is 32...

 

Please ... Subtract 40  

[Big Booty]

Rick, I was way off, the comm is about .155, not .200

Not going to stick my calipers in there and gouge my comm, I gotta race this thing 15 Jan

Why is a brush sized for a (approx.) .200 OD comm being used for a smaller comm ? Rick, I don't know.

But, I am glad you raised the question

 

Here in Mississippi, they have a saying: "That don't make no sense"

 

Wow 0.155".  Sorry have to convert to metric, thats only 3.94mm diameter!!  Brush height is 3.15mm.,  Allowing for a comm segment gap of say 0.2 mm and some simple trig maths I calculate that each comm segment is a dead short for 20.2 degrees of rotation!!  That seems crazy to me.  All that would do is heat everything up.  Unless Im missing something??

 

Depending on the rules you race under try undercutting the trailing edge of each brush by about 0.4-0.5mm, so instead of the full 3.15mm height contacting the comm you have 2.65-2.75mm.  That will reduce the overlap to zero.  Try it, all youve got to lose is a set of brushes.

[JohnnySlotcar]

Try radiusing the brushes with JK's .180" diameter diamond "Turtle" tool.

[gotboostedvr6]

Comm is .171

[Bill from NH]

"Post #67 = WINNER !"

Gator Bob, how is that possible - the latest post is 32...

 

i noticed this last night on post #28. I gave Bob the benefit of my doubt figuring he had a couple extra glasses of the bubbley & let it go. Since the 6 isn't beside 2 key, it wasn't a key slip.

[Eddie Fleming]

So is it legal to take a little off the trail edge of the brush to reduce the overlap?

Good point as to legal where.

 

I am curious as to it being legal anywhere.

 

So who would allow it and who would not? And would it solve the problem this topic started off on. (motors requiring a push start)

[MSwiss]

Eddie,
Not sure if this will become a widespread issue.

It probably is on my flat track because I only run, IIRC, 34 amps, which has always been adequate for the typical motors we use to weekly race on it.

I'm still a bit surprised Bill Fulmer mentioned he saw a few guys have that problem at MMW, I assume on the Gerding King.

If Bill or any other MMW racer see's my post, I'd be curious on how many amps the power supply is there.

PS- we raced the 4002FK at the Sano in the Can-Am + race without any problems that I recall, but only had one 6 man Main.

That is on 13.5V and 150-200 amps.

[CoastalAngler1]

Running a 4002fk for more than a month pushing a 105 gram c21...5 saturday night races plus additional nerf wars on a flat track and at least 10ea. 5 minute practice sessions at the Raceway...push start?  Not me.  This motor is sweet!

[Big Booty]

Comm is .171

 

Thanks David.  0.171" is 4.34 mm diameter comm.  Redoing the calculations gives 13.9 degrees overlap.  In my earlier post however I didnt allow for the fact that each comm segment is a dead short when it is at top dead centre AND bottom dead centre so you need to double the value.  So each comm segment is a dead short for 27.8 degrees of rotation or 7.7% of the time.  Removing 0.4 mm off the trailing edge of each brush will reduce the overlap to zero.

 

Worth trying it.  If the problem still persists then its something else.  If it goes away then let everyone know the fix and its not an advantage and you have an even playing field.  Motor should run cooler as well!!

[gotboostedvr6]

Rick did you take the comm slot into consideration? It's about .014.

[Big Booty]

Rick did you take the comm slot into consideration? It's about .014.

 

I allowed for a 0.2 mm gap.  0.014" is 0.35 mm gap so this should help a little.  Redoing the calculations with the wider gap reduces the overlap to 11.8. Need to double this for TDC and BDC, so each comm segment is a dead short for 23.6 degrees.  

[gotboostedvr6]

Cool thanks.

[Gator Bob]

 

i noticed this last night on post #28. I gave Bob the benefit of my doubt figuring he had a couple extra glasses of the bubbley & let it go. Since the 6 isn't beside 2 key, it wasn't a key slip.

 

There was two of everything, ...  now cross your eyes and push the 2 key....  

[MSwiss]

To answer a few of Rick Smith's questions, posed here and in PM's, I marketed a short height brush when the JK Hawk came out in 2010.

It was just to make the motor run more efficiently, not to prevent a push-start,
which I didn't for see becoming a problem.

http://slotblog.net/...pmotor/?hl=hawk

I got tired of having my drill press tied up with the Dremel cutting disc and mandrel, the mess it made cutting them, and most racers were happy with the motor
and how it ran with the full height brushes, so I quit making them and offering motors with them installed.

As it turned out, I started to see the motor needing a push start, but I assumed it was just from a broken wire at one of the comm tabs.

This last weekend, we had a nice 11 racer turnout for the hardbody race, which primarily uses the 4002FK.

Ironically, I don't remember any cars needing a push in the flat track race, with the low amp power supply, but do remember at least 2 different cars needing one on the high amp King track, including my car, which I lent out to a new, promising racer.

As far as changing the rules, to allow a modified brush, I'm not the person who started this class, and made the rules, so I don't want to get real involved with trying to change them.

[Big Booty]

Nice summary of whats been happening.  Not really an advantage if everyone has access to the info and modded brushes.  Motors should run a lot cooler, might even pick up a bit of top end speed.  But then as Mike said, hes not the rule maker......

[gotboostedvr6]

It takes 30 seconds to trim a brush. You can do it by hand over sand paper.

Any racer can do it. Only motivation required.