Cutting a motor commutator & motor tweaks

[Robbob]

agree with both things about the Niftech.

That thing looks like an Emo kid toy :shock:

 

[Duuuuuuuude]

agree with both things about the Niftech.

That thing looks like an Emo kid toy :shock:

:lmao:


But its about what I imagined it would look like. Since I don't have a mill, I'll have to see about making one out of wood. Won't be nearly as fancy but it should work...

The magnets will never work right. They do weird stuff as the arm spins....if it worked worth a crap, all the slot guys would use it....none of them really do.

I noticed that when the arms "settle", they aren't doing it smoothly like gravity, but kinda notchy like they're spinning through a magnetic field. Could be the steel in the vice too...

I would assume the slot guys aren't using them because their motors are smaller, and the magnets on the balancer would effect their armatures to a greater degree.

For a useable epxoy, PM me....I'll send you a link, but be prepared to spend about $80.....stuff is pretty awesome stuff.

My motors aren't worthy of awesome stuff just yet. Maybe in a few years and a few thousand winds...but thanks though...

 

[EddieO]

The steel in the arm is what causes.....prop balancers were designed to balance props....which are pretty much always wood, plastic or carbon fiber....

The steel in your arm is attracted to it, so it causes weird shifts through the field.

It's actually worse on our arms than a slot arm.......the razor blades work on slots, they will work for rc arms.....people have done it like that before....

Later EddieO

 

[Duuuuuuuude]

I whipped up a quick razor balancer. The results were interesting. I'll get pics up in a bit.

 

[EddieO]

Money says you will find anything done with magnets isn't balanced very well...

Later EddieO

 

[Duuuuuuuude]

Money says you will find anything done with magnets isn't balanced very well...

Later EddieO

Please don't think I'm doing all this to disprove what you're saying, I'm just exploring this for myself and hopefully to answer questions that others may have. I'm not doing this with a bias for one way or the other. Whatever is, is. "thumbsup"

I whipped up a new magnet holder, it was pretty obvious that the steel vice was screwing with the armatures. They spin much smoother now.

And also a quicky razor setup.

Ran all three armatures through them again, and the razors seemed just a bit more accurate, but just barely. They've got to be damn near surgically clean or the shaft will hang up on any debris that might be there.

The puller still stopped at the same place on either of the new balancers just the same as it stopped in the vice. More consistantly with the magnets, less consistantly on the razors. Could have been some junk on the shaft or something, it would stop pretty abruptly.

The Reedy never really seemed to have a heavy side on either unit. I'm inclined to believe its pretty well balanced.

The junk arm had a very obvious heavy spot on both balancers, and stopped at the same place on both every single time.

I've got some video to edit and upload later tonight if anyone cares to see it.

 

[EddieO]

Some times stuff just works...

A super heavy side should always show up easier on either version....being so heavy to one side will pretty much always overcome the balancer design.

The razor blades need to be new and of decent quality.....

Being level all around is more important to the razor blade version......

And now worries, some people can get stuff to work for them....thats just part of RC. Kinda like the Fantom dyno......I ain't a fan of the unit, neither is many of the top motor guys.....I don't like the way it works and I think it is easily tricked into giving false data......but people over the years learned to make it work and had successful results with it.

Later EddieO

 

[Duuuuuuuude]

Some times stuff just works...

A super heavy side should always show up easier on either version....being so heavy to one side will pretty much always overcome the balancer design.

The razor blades need to be new and of decent quality.....

Being level all around is more important to the razor blade version......

As off balance as the junky one was, I could have rolled it across the garage floor and found the heavy spot. :ror:

The blades were fresh out of the box, and I leveled it all up before I used it.

For what I'm doing, I'd feel confident with either setup. Later on down the road, things may change.

Thanks for your input!

 

[Duuuuuuuude]

The results...click me!

 

[EeePee]

That was good. Thanks for the effort.

 

[Duuuuuuuude]

That was good. Thanks for the effort.

Glad I could contribute.

Still a little baffled by the 5t though. Its obviously got a heavy spot, but its never acted like it was out of balance. Even with short bursts on 3s. Must not be that far out...

 

[EddieO]

Static balance can weird sometimes to a dynamically balanced arm.....its hard to explain.....

Later EddieO

 

[Duuuuuuuude]

Static balance can weird sometimes to a dynamically balanced arm.....its hard to explain.....

Later EddieO

From Big Jim himself, circa 2002...

Static balancing uses just one plane to determine where the imbalance is. This works best on parts that are bigger in diameter than they are wide like a prop, flywheel or tire. The part sets between two low friction pivots so it can spin freely, then the heaviest part of the thing you are balancing just falls to the bottom-center via gravity. It basically uses just two dimensions for balancing corrections. The term "static" refers to something not in motion.

But when something is a lot wider than it's diameter, like our armatures, it will vibrate "axially". In other words, the two ends of the object will want to swap ends with each other. To correct for this phenomenon, the part must be dynamically balanced. In other words, balanced in motion.

A dynamic balancer is an electronic and very expensive machine capable of separating the two ends of the part through the electronics and not only balancing each side separately but balances them both to each other. It uses all three dimensions of balance corrections, not just two as in static balancing. This is why our armatures have corrections on both ends of the arm instead of just one big correction in the center.

I know I didn't explain that really well. But I'm a little fuzzy on the principle myself. I do know that you can't balance one of our armatures statically. It will always vibrate even when a heavy spot can't be found statically. The Niftec Balancer relies on the armature being dynamically balanced to begin with and they assume that the armature only goes out-of-balance statically. They are again under the incorrect assumption that they will be able to find a heavy spot by the use of gravity, correct it and be able to make the armature better than it was. I would be willing to bet that 8 out of 10 times you would end up making the balance worse on the arm than better.

Unless the shaft gets bent or some other anomalous condition happens to an arm, they usually don't go out of balance enough to make much of a difference in power on the track anyway. This is of course, if the arm was balanced properly initially.

An armature that has been epoxy-balanced by adding weight will go out-of-balance much quicker and much more than a drill balanced armature. Especially if a chunk of weighted epoxy flys off.

If I understand that right, in a nutshell, static balancing balances the armature as a whole (in relation to its rotation), while dynamic balancing balances the armature to itself along its axis.

Both are effective, but dynamic is more precise.

 

[EddieO]

That pretty much sums it up........but it basically says the same thing in about 500 more words than I did.

You will never take a dynamically balanced arm and put it on a static balancer and make it better.....its not unheard of for it show it out of static balance.....like Jim said, you can make stuff worse trying to correct it.

On the flip side, I've never seen an arm that was statically balanced that was actually in dynamic balance....though I guess there could be a unicorn out there (kinda like single women who want to have 3 ways with married couples.....a mythical creature that some believe exists....aka a unicorn)

There are multiple dynamic balancers out there. The Heins and Quillen being the most common of the RC balancers. The Hoffman is the standard in slot cars, but towards the end of RC brushed racing, a few companies, including mine had picked up a Hoffman (Checkpoint, Orion, Brood, and a couple others).

The Heins is a great unit, Big Jim was in love with it, but I found out from Jim he got a kick back from Heins on every unit he sold. I love my Heins, but in the end its an adapted unit from a Turbocharger balancer. I cannot do 5 segment arms from what I am told, though I am waiting to hear back from the Heins guys. I can however do Brushless Rotors....

The Quillen is an awesome little unit, designed by a damn genius......they are cool because they are accurate and portable. It was not uncommon to see them brought to races to balance arms on the fly. The big thing on these......they will do 540 3 segment arms only, no exceptions.......no 5 segment, no 550, no slot arms, etc....

The Hoffman, like the quillen is specifically designed for small armatures....it however is EXTREMELY accurate. I've balanced stuff on my Heins and Quillen, and then put them on the Hoffman to find that I could still improve the balance, even though they were dead zero on the Heins/Quillen, and on the flipside, I've yet to put a Hoffman balanced arm on the other units and show they having any unbalance......its a million times easier to use and setup too...it is the standard in Slot cars, which have motors spinning at 200k RPM....besides its accuracy and such, it has the ability to switch from Dynamic to Static balance....I've done some interesting tests with it......

What's funny, I have that same blurb from Jim in my motor faq I have been working on. Jim authorized me way back when to use any of his RCcars.com posts for my website....old site had a bunch of it but lost it all in the crash.

I don't think Jim quite said static is effective. I think he actually says it doesn't work at all. I don't quite agree with that. Static balance is better than nothing.....but its no where near as effective or precise as dynamic balancing. If I still had the laptop with the results, we dynoed a bunch of 19t arms, with multiples being not balanced, statically balanced, and dynamic.....Dynamic won every time and in the end, after we dynamically balanced them all, they all went up, with some of the arms beating the originally dynamic ones.....


Later EddieO

 

[Duuuuuuuude]

I don't think Jim quite said static is effective. I think he actually says it doesn't work at all. I don't quite agree with that. Static balance is better than nothing.....but its no where near as effective or precise as dynamic balancing. If I still had the laptop with the results, we dynoed a bunch of 19t arms, with multiples being not balanced, statically balanced, and dynamic.....Dynamic won every time and in the end, after we dynamically balanced them all, they all went up, with some of the arms beating the originally dynamic ones.....

"Effective" was my word. I too believe static balancing works (it has to, its physics), not nearly as precise as dynamic, but better than nothing, just as you said. Replacing a missing wheel weight on a 1:1 wheel with a rock and some duct tape is "effective" if it will remove the wobble and get you down the road comfortably. Its far from ideal when there are more advanced methods to be used, but its better than having all the change bounce out of your cupholder.

Either way, the junk arm is getting holes drilled in it tomorrow. :twisted:

 

[Duuuuuuuude]

Learned a valuable lesson tonight. Be very, very careful when drilling on the armature stacks, even with a new and sharp bit. I managed to break a fair sized chunk out of one of the stacks on the junk arm.

Good news is that its not heavy on that side anymore. "thumbsup"

 

[EddieO]

Sharp is worse, they seem to catch more...

You don't use normal bits either......I forget the name of the things, but they last forever, we've used like two in 7 years.....the first chipped while we were drilling something else...

Later EddieO

 

[ittybitty]

Sharp is worse, they seem to catch more...

You don't use normal bits either......I forget the name of the things, but they last forever, we've used like two in 7 years.....the first chipped while we were drilling something else...

Later EddieO

Were they Cobalt bits?

 

[Charlie-III]

"Effective" was my word. I too believe static balancing works (it has to, its physics), not nearly as precise as dynamic, but better than nothing, just as you said. Replacing a missing wheel weight on a 1:1 wheel with a rock and some duct tape is "effective" if it will remove the wobble and get you down the road comfortably. Its far from ideal when there are more advanced methods to be used, but its better than having all the change bounce out of your cupholder.

Either way, the junk arm is getting holes drilled in it tomorrow. :twisted:

OK, maybe I can help on the "static" vs. "dynamic" idea using your example.

Just taping a rock on a 1:1 wheel when you throw a wheel weight helps, but it is only a "static balance". What you did was even the weight relative to the axis (AKA axle or armature shaft).
But, if you ever really watch a decent tire guy balance a wheel with a relatively modern tire balancer, he is not only looking for the heavy side (but puts weight on the light side....sorta opposite from drilling out material to balance an armature), he ALSO is looking to place weight towards either the front face of the rim or rear face.

Why???!!!

If you just "weight up" the light side of a wheel, it helps (better than nothing), but is not perfect.
The other issue is wobble around the axis. This is where the weights on the front or rear faces of the wheel come in.
If the machine says, "you need 2oz at this location", the tire guy can:
1-Put a 2oz weight on the rear face of the rim
2-Put a 2oz weight on the front face of the rim
3-Put a 1oz weight on the rear face & a 1oz weight on the front face of the rim.

They all add 2oz to the light side (static balance), but changing WHERE across the rim (down the axis) helps fix wobble as well (dynamic balance).

Same for dynamic balancing of an armature.....you not only drill out some material on the heavy side, but you may drill it out from one end or the other. This cures the wobble as well as the heavy side.

A pair of razor blades can only show the heavy side, they have no way to also tell you if the heavy side is towards one end of the arm ot the other.

Bicycle wheels don't really need dynamic balancing, they are very small down the axis vs. the diameter.
An electric motor arm really DOES need dynamic balancing since they are very long down the axis vs. the diameter.

It's this relative ratio (length of axis vs. diameter) that helps determine how much dynamic balancing contributes.

Does this help some??:roll::shock:8)

And...ummm....NO.....I am neither an engineer or expert motor rebuilder. I just have a decent self-taught understanding of some physics basics.

I am open to comments from whomever wants to comment.

 

[Duuuuuuuude]

Does this help some??

I pretty well had it figured out, but thanks anyway. "thumbsup"

The rock on the wheel example was my way of explaining how low-tech static balancing is as compared to dynamic balancing, which you would (hopefully) get if you took your out of balance wheel to a tire shop for a proper balance.

Dynamic is obviously the better choice, but static will get you by if you have no other option.