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  #1  
Old 03-10-2010, 05:24 PM
Dyno Dyno is offline
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Armature balancing questions.

Im sorry if this has been discussed before but I didn't see the post if it has.

I have a question that I havent been able to get a direct answer to, so I figured this is the place to get some answers.

I just recently started trying to balance T Jet armatures on a custom made magnetic jig that I cobbled together, and was wondering what the pros and cons would be of balancing the arm with epoxy or cutting small grooves in the laminations to remove weight.

I noticed that most places that professionally balance Arms use epoxy but that seems counterintuitive to me. I thought that you would want a lighter weight armature for quicker acceleration. A friend of mine does his own and said that epoxy is the way to go. He couldn't tell me why it was better, but said it had something to do with "the heavier arm kind of pushed itself faster as it spun, do you know what I mean" I didn't accept that answer. It wasn't scientific enough. I also understand the argument that removing metal takes magnetic material away from the magnetic field, but I am cutting small grooves, not changing the distance from the magnets.

Also, what are the benefits of a balanced arm besides more top end capability and smoothness? Does it increase torque off the bottom also?
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  #2  
Old 03-11-2010, 01:12 PM
WooffWooff WooffWooff is offline
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Balanced Aurora T-jet stock arms......

available from SlotPro(balanced) and Dynamic Armatures(balanced & trued) have metal removed from end of laminations. We've bought two Doug Strom balanced arms from SlotPro and they each had signifcant metal removed from one of the three ends/poles, but some grey paint was still visable, even on the modified pole. The Dynamic Arms had no paint on ends of any pole, exposed metal instead. Both types made very fast runners in SS and "fray" chassis......wooff
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Old 03-11-2010, 03:45 PM
joegri joegri is offline
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dyno i too have just started balancing arms. even if the amount of material be it steelor plastic and any amount taken from the heavy end has made them run smoother. i guess the more u balance the better u get! i think ive balanced 5 or so.at least i think i,m doin something.
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Old 03-11-2010, 04:09 PM
Dyno Dyno is offline
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I havent had any definitive proof that the arms Ive balanced are making more power. My friend has an H.O. chassis dyno and I want to do some before and after testing. All of the arms Ive balanced, which are only a handful so far,werent run on my track before I balanced them, so I dont know if I actually improved them. I am going to do some more testing. I dont think Im making them slower...
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Old 03-11-2010, 04:16 PM
Dyno Dyno is offline
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Joegri, what are you using as a balancing fixture? I was using razorblades at first but I found a way to make a magnetic balancer which is WAAAY more sensitive. It is so sensitive, I feel that I can actually discern which side of one lamination pole is actually the heavy spot. It cost me 2 dollars to make the balancer on top of using some stuff I had laying around. To buy all of the stuff from scratch, the cost would be maybe 22 bucks.
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  #6  
Old 03-11-2010, 07:04 PM
joegri joegri is offline
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i had a blade style that i failed miserably with then i got a magnetic thing that u put the arm in it and slide the shaft till it just makes contact. then use a straw to blow through to get,er to spin then mark file spin mark and so on. lets see a pic of your creation.man the things we do to make a 35 year old car go a lil quicker ,but thats what its all about.
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Old 03-11-2010, 09:31 PM
Dyno Dyno is offline
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I cant post a photo tonight, but I can tomorrow evening.
I used a gear press and removed the arbor and thumb screw. I installed a flat head 5/8th" #10-24 screw in the arbor hole and glued a neo magnet to the flat head, then I put a 2 1/4" screw in the other side with the flat head facing the other flat head and glued another neo to it. I tried making a slip collar and pin to hold the arm but had no luck. I instead used a 1/16th ball bearing stuck to the magnet and then stick the arm to the ball so there is minimal contact to the magnet. The other side of the arm is suspended by the magnetic field. I was able to get the arm to spin for 60 seconds straight with no assistance after blowing on it with a straw. The picture will explain it better.
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  #8  
Old 03-12-2010, 04:54 PM
Dyno Dyno is offline
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Joegri, as promised here is the photo of my contraption..Simple but effective.

Last edited by Dyno; 06-10-2012 at 07:34 PM..
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  #9  
Old 03-12-2010, 05:10 PM
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smalltime smalltime is offline
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When I ballance arms, I find the heavy side and mark it with a sharpy. Then I remove material from the spot, a little at a time.
But I check the ballance IN THE CHASSIS after each cut.
Install a set of brushes and use the gearplate you intend to mount the arm to, and spool it up. You will know when you have it right.
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Old 03-12-2010, 06:47 PM
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Pairadiceracing Pairadiceracing is offline
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If you run the arm in a bare chassis (no gears) you can feel and in most cases, hear the vibration. After the balance you can feel and hear the difference. In most cases you probably won't gain any RPM, but the vibration will be gone. Perfomance wise, I'm not sure if the balance helps the perfomance of the motor as much as the lack of vibration helps the contact patch with the motor brushes all the way through to the contact patch of the pickup shoes. Sorta like driving a car that has thrown the wheel weights, the car will still true the tires and haul down the road (if you can hang on to the steering wheel), but the handling from the drivers seat is tough.

I have a RTHO magnetic balancer that I bought and tried using. I didn't work well for me (and Rick makes excellent tools!). I have a watchmaker poising tool, but for me the surface that the arm rides on is to short. I perfer mounted razor knife blades, the longer the better. The one I use is at http://hosers-slotcars.com/tools.html

Another fact that will cause vibration is if the comm plates are not flat and true with the shaft. This can be adjusted, but you have to be careful. After I adjust the com plates so each pole is flat and square with the arm shaft, I use clear fingernail polish to glue the windings to the comm plate. Then balance the arm.

My $0.02
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Old 03-12-2010, 06:59 PM
Dyno Dyno is offline
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Quote:
Originally Posted by Pairadiceracing View Post
If you run the arm in a bare chassis (no gears) you can feel and in most cases, hear the vibration. After the balance you can feel and hear the difference. In most cases you probably won't gain any RPM, but the vibration will be gone. Perfomance wise, I'm not sure if the balance helps the perfomance of the motor as much as the lack of vibration helps the contact patch with the motor brushes all the way through to the contact patch of the pickup shoes. Sorta like driving a car that has thrown the wheel weights, the car will still true the tires and haul down the road (if you can hang on to the steering wheel), but the handling from the drivers seat is tough.

I have a RTHO magnetic balancer that I bought and tried using. I didn't work well for me (and Rick makes excellent tools!). I have a watchmaker poising tool, but for me the surface that the arm rides on is to short. I perfer mounted razor knife blades, the longer the better. The one I use is at http://hosers-slotcars.com/tools.html

Another fact that will cause vibration is if the comm plates are not flat and true with the shaft. This can be adjusted, but you have to be careful. After I adjust the com plates so each pole is flat and square with the arm shaft, I use clear fingernail polish to glue the windings to the comm plate. Then balance the arm.

My $0.02
I was using the blades but I found out that my magnetic balancer is much more sensitive to the heavy side because it has less friction. Well at least it is less friction than the blades I was using I should say. I dont think Im ready to try to try and straighten the comm plate yet. I wouldnt have the faintest idea how to do it. Are you balancing by removing material, or adding epoxy to the lighter side?
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  #12  
Old 03-12-2010, 07:08 PM
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Pairadiceracing Pairadiceracing is offline
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I have done both in multiple ways.

Adding weight I perfer JB Weld over epoxy, due to the weight of JB Weld, it's heavier.

Normally I grind for balance unless it is way off, in that case I have actually done both on some arms. I probably should just toss out those arms, but it's a challenge to see if I can get it right.

The grinding I have done has been both ways, one is 90 deg. to the lams or a groove. The other is I will grind on the top lam leaving the other untouched.

Either way I've had success with both versions. I have not noticed any performance gains with grinding vs. adding weight. But that could be just me. I usually grind so I don't have to wait for the JB to dry before I can spin up the arm.
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Old 03-13-2010, 06:46 AM
Brixmix Brixmix is offline
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You should make sure your arms have flat comm's before balancing. If you Zero out the comm's and them balance the arm's WILL get better. Smalltime is right you should check the arm ina chassis to try and feel vibration.

Last edited by Brixmix; 03-13-2010 at 08:14 PM..
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  #14  
Old 03-13-2010, 10:55 AM
joegri joegri is offline
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hey dyno thanx for posting the pic of your "mousetrap" mine is simular but different.now i,m thinkin maybe glue some of them there magnets to a micrometer and achieve the same tool but even more preciese. i dont know i,m just sayin.infact i,m goin down to the cave and try that.all this stuff just to make a lil car go around a track!!no wonder my fishin buddies think i,ve lost my mind.have any of your friends that dont get slotcarin said that to ya?
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Old 03-13-2010, 03:39 PM
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I saw a setup with magnets on a micrometer, however, I didnt like the idea that you couldnt put it down and had to hold it in your hand.

Also, how do you flatten out the comms? Ive seen tools for polishing but not straightening.
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