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Thread: Slot Car Racer Today

  1. #2491
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    That's good idea to bevel the edges, but I'm also wondering if the comm has been cut down too far.

  2. #2492
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    Quote Originally Posted by Iron Finger View Post
    That's good idea to bevel the edges, but I'm also wondering if the comm has been cut down too far.
    Chuck, I think this calls for "Geometry Time". I just got an email back from Dan Debella, he says the C Can comms can be cut as low as .181". So, let's say we start with a comm at .200" and end up at .183". The circumference starts at .628", so the length of each segment (if equal) would be .209". The worn out comm circumference is .575" making each segment .192" long.

    Where do we go next? We need to calculate the measurement of the brush when fully broken in on the new comm versus the worn out comm. I'm at "work" where no slot box is allowed, so I can't measure a BF II brush. Would somebody like to measure a brush and calculate the dimension of brush against comm in the above two sizes? Otherwise I will have to wait until I get home to do that thus depriving me of instant gratification.

    The key to this puzzle is that we cannot assume the comms have equal length segments. With the newish .200" diameter comm, you might have one segment that's .209", but the other two are .215" and .203". It's the short segment that can get into trouble. That's the one I believe will short out with both brushes, especially when well worn.....or if you have a particularly assymetrical comm. It is not uncommon to measure an arm with a 42 degree, 44 degree, 40 degree comm, or worse!
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  3. #2493
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    Exactly. That's what I said, or there abouts. When the comm wears the segments will shorten and continueing to wear will eventually cause a short between two segents.

  4. #2494
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    George
    I believed we hashed this out not long after the ISRA nats in Philly last year. I was having this problem and I came up with two solutions. Narrow the brush or switch to vertical brushes (vertical brushes may drastically change the performance of the motor, I would narrow the 1st 1/3 of the brush by no more than .002 on both sides). However, the com isn't the only problem. I had 2 BOW arms and 2 PROSLOT arms (Contender) that were new with .200+ com dia on all 4. The Bow arms worked fine but the PROSLOT arms gave me the same problem you are having. The arm timing (45 degrees) and diameter (.540) was the same on all 4 arms. All 4 arms were installed in the same type of setups (Red FOX cans with Camen magnets and PROSLOT endbells using BFII brushes and Champion light springs). The width of the stacks on the BOW arms is narrower than the PROSLOT arms. The width of the PS arm stack segments is .360-.365 with a space between the segments of .155-.160. The width of the BOW arm stack segments is .345-.347 and the space between the segments is .178-.180. If you observe the motor when it stops and won't start again even when power is applied you'll notice that one stack segment has spanned the gap between the positive and negative magnet tips. That means that the other 2 stack segments are half way into one magnet and half way out of the opposite magnet and the space between the stack segments is between the magnet tips on the other side of the arm. It has settled in a neutral position and won't go anywhere. You'll notice that there is only a .020 smaller difference in the width of the BOW stack segments and only a .020 wider difference in the space between the BOW stack segments but that was all it took so the BOW arms would never settle in that neutral position and the PS arms would. There is one other thing you could try that may also work. Use a setup with magnets that have a wider/narrower tip to tip spacing. Which ever prevents the neutral stopping problem. I haven't tried this yet but have you tried to spin the arm in the set up without brushes and springs to see if it settles in the neutral position when it's free wheeling? If it does then that could indicate that it'll do the same thing when powered. Oh, and by the way I did switch the BOW arms into the setups the PS arms were in and they worked with out a problem. When I put the PS arms in the setups the BOW arms were in the still stopped.
    I've done so much with so little for so long it seems like I can do anything with nothing at all.

  5. #2495
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    Question: Are you using "vertical" brush hoods??? (on Eurosport motors) Is everybody??? Is anybody???

    I had thought that the big advantage to turning brushes on their ear (using Koford "vertical" brush hoods) was to maintain the full contact area of a 36D brush, while shortening the width touching the comm radius to help reduce arcing or shorting.

    Almost hard to remember... that sometime back in the stone ages, somebody (probably Bob Green?) decided to use 36D motor brushes on 16D motors. While this improved the contact patch and gave longer wear, it also increased the chance of arcing and shorting.

    Since I have no slot cars here in the islands (no sympathy SCR!), I have forgotten if modern Eurosport motors are ALL using vertical brush hoods, or just some, or none.
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  6. #2496
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    Simultaneous posting! Fast Freddie beat me to the punch (perhaps how he got the moniker?) regarding vertical brushes!
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    Paul Kassens
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  7. #2497
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    This would be brushes with a three pole comm where the brushes are never going to short out on a segment unless the comm went through 2,000 comm cuts....


    photo (18) by svtgeorge, on Flickr

    This, of course, would be the ideal relationship maximizing brush size for the given comm size.


    photo (19) by svtgeorge, on Flickr

    This is what I call the "not OK' version where the brushes short out across the same segment....comm is either too small or the brushes too big


    photo (20) by svtgeorge, on Flickr

    This would be the "not OK" version but repaired by bevelling the tips of the brushes.


    photo (21) by svtgeorge, on Flickr
    Journeyman Industrial Slotcar Worker, Teamsters Local 3299 AFL-CIO
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  8. #2498
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    Quote Originally Posted by Fast Freddie View Post
    George
    I believed we hashed this out not long after the ISRA nats in Philly last year. I was having this problem and I came up with two solutions. Narrow the brush or switch to vertical brushes (vertical brushes may drastically change the performance of the motor, I would narrow the 1st 1/3 of the brush by no more than .002 on both sides). However, the com isn't the only problem. I had 2 BOW arms and 2 PROSLOT arms (Contender) that were new with .200+ com dia on all 4. The Bow arms worked fine but the PROSLOT arms gave me the same problem you are having. The arm timing (45 degrees) and diameter (.540) was the same on all 4 arms. All 4 arms were installed in the same type of setups (Red FOX cans with Camen magnets and PROSLOT endbells using BFII brushes and Champion light springs). The width of the stacks on the BOW arms is narrower than the PROSLOT arms. The width of the PS arm stack segments is .360-.365 with a space between the segments of .155-.160. The width of the BOW arm stack segments is .345-.347 and the space between the segments is .178-.180. If you observe the motor when it stops and won't start again even when power is applied you'll notice that one stack segment has spanned the gap between the positive and negative magnet tips. That means that the other 2 stack segments are half way into one magnet and half way out of the opposite magnet and the space between the stack segments is between the magnet tips on the other side of the arm. It has settled in a neutral position and won't go anywhere. You'll notice that there is only a .020 smaller difference in the width of the BOW stack segments and only a .020 wider difference in the space between the BOW stack segments but that was all it took so the BOW arms would never settle in that neutral position and the PS arms would. There is one other thing you could try that may also work. Use a setup with magnets that have a wider/narrower tip to tip spacing. Which ever prevents the neutral stopping problem. I haven't tried this yet but have you tried to spin the arm in the set up without brushes and springs to see if it settles in the neutral position when it's free wheeling? If it does then that could indicate that it'll do the same thing when powered. Oh, and by the way I did switch the BOW arms into the setups the PS arms were in and they worked with out a problem. When I put the PS arms in the setups the BOW arms were in the still stopped.
    Yes Fred, I remember all the hashing and thrashing on this topic before. Monty made his blank with a very narrow crown, kind of like the old Viper arms. Your testing is very interesting, and I guess what you are saying is the motor may be getting "confused" when the crown of the stacks spans across both magnets. You might have something there. Maybe the use of the Cahoza bevelled magnets is the answer? (But not USRA legal).

    However, I am going to pursue the theory that brushes are making a dead short across a common comm seg. Kind of similar to your theory, but a direct short would make sense given that my analyzer spikes up to 10 amps when it goes into "push start mode". I'm not sure the crown of the stack spanning across the magnets would create such a big amp draw.....does it?
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  9. #2499
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    I think somebody mentioned this Slick 7 article in the previous hash....see section on vertical vs horizontal brushes....

    http://www.slick7.com/S7magnets.html
    Journeyman Industrial Slotcar Worker, Teamsters Local 3299 AFL-CIO
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  10. #2500
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    George
    You are correct the short occurs at the comm. What I'm saying is that the stack spanning the magnet tips is what is causing the neutral condition with the motor. After all when the power is shut off to the motor the magnets are now the main thing that decides where the arm settles due to magnet flux. The one thing I did notice with the BOW motors is that when the arm was coming to a stop it would sometimes move just a very small amount after it had stopped and the only thing I can attribute that to is magnet flux. That small movement kept the arm out of the "neutral zone" (sorry for the Star Trek refrence) there by not violating the Neutral Zone Treaty (Star Trek again) and the motor stays happy. By the way Barbara says Hi!
    I've done so much with so little for so long it seems like I can do anything with nothing at all.

  11. #2501
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    Thanks George, Freddie and Paul. Pictures are worth a thousand words George. I was on the ferry to Seattle when I posted earlier. I'm not sure if everyone uses vertical brushes for eurosport but I do. Great conversation even if it a rehash. It still brings up a good point and that's why I follow this thread so often. Thanks again, Chuck.

  12. #2502
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    No testing this weekend, instead it was time to go through all the C Can motors to prepare for Fresno in less than two weeks.

    I pulled the motor out of the LMP that won the race in Modesto at the beginning of the month. A few interesting things about it. First, it is the same arm that I seem to do well with over and over....unfortunately the comm is now down to .192" so nearing the age of 70 years old in human years. It's a Pro Slot Super Wasp that Dr. Nuke gave me in one of his over-the-top motors. The aluminum spacer on the gear end is cut really short so it would fit into a small can....I forgot if it was a Falcon, Slick 7 or what....anyway this armature has been a great one. Besides the small comm, I also found to my dismay that the shaft on the comm end had worn down to a groove only .075" diameter. Too loose.

    Yesterday I spent quite a bit of time putting together some parts and gluing in some magnets with different spacing for the Super Wasp arm....I moved the mags closer to the endbell as the Wasp arm was running with a .060" brass spacer...kind of a lucky thing. I got the motor put back together and it sounds really good. I'm not sure how that deep groove happened, first time I have seen that. Maybe the bushing dried up, but usually that isn't an issue. And, there is no stress or load on the comm end of the motor shaft. Strange.
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  13. #2503
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    I did one more thing to my favorite Super Wasp motor, extended the endbell bushing to get a little more shaft to bushing contact. I did this by taking a new 2X5 oilite and put it on an armature slug, then took Mr. Dremel and his cut off wheel and instead of cutting something in half, I used the cut off wheel to grind down the diameter of the oilite until it fit into the smaller diameter hole on the OUTSIDE of the endbell. Ground it down to a nice press fit and the flange stuck out a little. This was good as I added some Koford magnet epoxy which filled that gap nicely, then baked it in the epoxy oven which is now out in the garage (new Black and Decker toaster oven from Target is now residing in the kitchen for food use). The added "outside bushing" made the motor really smooth, so I'll try it out next Friday in Fresno.

    Otherwise, just waiting for arms to come back from Beuf and in the meantime going through all the chassis - Bulldogs and X25s - checking for flatness and pan movement. Sort of tedious, but necessary if the chassis are to work their best.
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  14. #2504
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    Got through all the Bulldog 3 chassis, they all looked nice and flat so I just cleaned em up. Put the rebuilt Super Wasp into the same X25/C11 chassis I ran in Modesto which also was nice and flat. Got about halfway through mounting a fresh body on it when the Hermanator showed up on my doorstep. He dropped off a couple of eurosport motors for shaft grindage and we took a look (and a sniff of) at the new Proformance rubber. Looks like the same good stuff he sent last time.

    Good to hear Bugboy209 of Modesto found his GT12 car, he got it back from someone who picked it up.
    Journeyman Industrial Slotcar Worker, Teamsters Local 3299 AFL-CIO
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  15. #2505
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    IMG_0205 by svtgeorge, on Flickr

    Here's the now broken in flat track at Hobbytown in Fresno. This is where the NORCAL race will be next Saturday. For NASCAR and 4.5" Trucks they also have a Hillclimb to race on. The flat track is the West Coast Anaconda designed by CRASH CODGER. CRASH tells me the lap times are about the same as last fall, track is no faster, no slower. It's really a great design and I look forward to racing on it again, and looking forward to seeing Brian Rush again down there.
    Journeyman Industrial Slotcar Worker, Teamsters Local 3299 AFL-CIO
    Now with "Improved Karma"

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