17 replies to this topic

[havlicek]

There's a couple of things going on here. First is that a C-can will fit inside a D can... more or less depending on which ones you choose (can metal thickness and things like side welds matter). The fit can be anything from very tight, and needing an arbor press to a loose "slip fit." If you've followed the stupid stuff I've done over the years, this is old news... or maybe you already knew and didn't see an application in real terms, "watevah."

The more important (for the purposes of this thread) thing is what role can design has on the permanent magnets' field strength. With the very powerful cobalt and neo magnets available today, the can design means almost nothing, hence the "strap can," where the can is only there to hold the magnets and arm, and give the end bell something to be attached to. However, if you play with ceramic magnets (and of course there are good reasons to), this stuff maters.

Take a set of plain old regular ceramic singles, and stick them in a really "open" C-can. This is one of those older Pro Slot cans I cut down for duty as a "can shim." Here, without a zap, this pair reads in the high 800 range on my meter. 



Now take that and slip it into a D-can (this pairing results in an easy "slip fit")... suddenly, the same magnets read in the upper 1,000s range, pretty near 1,100. That's a big and certainly significant jump. 



Yes, airflow and cooling will become more important to monitor, but only the effect of can design on the permanent magnet field is something some (many?) don't consider. With limited choices for cans in any "type" motor (C, D or minican) at this stage, I guess even knowing this, there isn't much a racer can do about it. Still, I'm putting it out there for consideration.
 

[havlicek]

Maybe it might help to better quantify this. But we're looking at an increase of at least 25%, because if the change were from 800 up to 1,000, that would be exactly 25%. That's a pretty big jump.  

[Kim Lander]

John...

 

You may already know this and some where we may have already discussed this... that phenom is what I was taught, as focusing the mag field... I have some mags we use at the lab that I will send you one and let you visually see what I am talking about. The mag by itself is not very strong, but when you put the sleeve that surrounds three sides of mag it increases greatly on the edges. Some of the motor manufacturers did the same with different types of shims but none accomplished fully what I am talking about as it was hard to get the shims around the three sides sufficiently. Different cans did it to some extent as you know because you can put same mags in different cans and get different readings, I always measured mags out of can so as to get a matched pair.

 

Kim

[havlicek]

Hi Kim. 

 

Yep, and the motor manufacturers also (of course!) are well aware of these things. Then again, with slots, some of this at least is driven by "the market"... and that in turn can be just a matter of the "I'll have what he's having" thing. You know, when someone wins big races, others think they can do the same by having the same equipment. It's hard to know exactly how these things go, and I wouldn't ever pretend to!

More on the details of your particular case, and how it relates to all this. I can take the above can-shim and further cut it down to the absolute minimum necessary to hold the magnets securely and completely, and situate the remaining cross member so it bisects (cuts in half) the existing hole in the D-can, which would result in a larger version of the same "mini can" I used in the "FK performance" thread, and still get the same improvement in field strength... in fact I did... and I tested that as well. I screw around with these things all the time because I want to know more, and not just take someone else's word for it. 



Here, I took the much smaller still remaining "shim" and installed it in an early Mabuchi (Russkit 22/23 type) can. The readings are the same. It seems as though having the remaining cross member in the middle of the rectangular existing cutouts is about optimal. Cooling and field strength are still there, and of course, this can is even lighter than the Champion because it was formed from thinner metal and has two holes (one per side), as opposed to the Champion's single hole. So can design choices confirm that the old Mura C "Green Can" was a wise choice.

Again, none of this stuff is probably "headline news" for anyone who screws around with motors much... but then again, a lot of people don't screw around with motors. 

[swodem]

So my question is - how much more power is actually gained from a 25% higher gauss reading?

[havlicek]

... and that would be the obvious and logical question to ask, Steve! 

My answer is that more magnet doesn't necessarily mean a "better" motor, but it "can. More magnet can mean more choices as to winds on the higher limit and less choices on the lower end, but generally-speaking, more magnet means more available torque and quite possibly lower RPMs. In the "dance" that goes on between magnets and the armature, it can be the case that a particular wind is under the optimal for a particular setup. 

I wind a good number of armatures for people here and abroad that use a warmer wind (55-60 turns of #30 seems to be popular) in the minican motors. They tell me that the motors run faster and are still reliable... I have some to wind today as a matter of fact. Generally, the minicans seem to have way more potential than is used by a 65t/30 arm, and that's fine because the combinations in use fit people's needs perfectly well. However, in classes where people want more and are allowed to go for it, an existing motor/magnet combination may be ripe for that stuff. After all, there are options for arms right off the shelf that go well beyond the stock 65t/30... someone is buying them I guess.

In cases where there are choices (and those are very few) as to can design and you want to build a more powerful motor, just the can design should be at least one factor to consider. More magnet can mean the ability to use a hotter wind and stay within "safe" limits.

[gotboostedvr6]

Does more gauss = more coercive force? Does this additional force change the powerband? For better or worse, for more peak torque and at what rpm? Does it turn a motor into a "lightswitch"?

What does it all mean?

[havlicek]

Yes and no.    It's up to the racers to figure it all out. The days of major advancements are behind us, and making a "better mousetrap" happens in much smaller refinements. Look at "Retro"... the chassis designs are basically 40 or more years old, but they are still being fine-tuned for a whole new set of requirements. Smoother tracks, different motors, and a rule-set that defines certain purposeful limits have all changed the game.

[havlicek]

- So the setup is done, and painted a nice coat of anodized purple.
- Can was drilled for endbell mounting and for can/chassis mounting.
- Can was shortened by just the amount necessary to remove the tabs... because the length wasn't necessary.
- Can bearing installed.

- Magnet/shim assembly installed and honed to .530".

- D motor end bell fixed-up with some Mura hardware.

- After a zap, the magnets read around 1,130 and are within a couple of points of each other.

 

It's ready for an armature.

 

 

[Robert BG]

Looks good,if you're looking for a way to get some definitive answers you can take one of those tools for spinning arms (a 3/32 spur works in a pinch) Install it up against the endbell of the motor you tested.Then you can easily slide the endbell,arm,brushes and all off in one shot.Then you can install it on the other can/mag combo you want to test without disturbing or changing anything else.I do recomend checking spacing beforehand but I've found there's rarely a difference on the endbell side when swapping and as long as you know the can side spacing you'll be fine.

 

I find myself doing this quite often and a few of my 27L motors have 2 cans.The change isnt as drastic on a meter but it affects cobalts too.

 

It's still too early for me to have enough data to point one way or another but I've found gains on the track simply by going to or from windowed cans.

 

If you want to get really tricky there's always notching the leading or trailing edge part of the can too.Although that is tricky at best on enclosed cans.

 

Here's a quick pic of what I'm talking about but on this setup I have 2 endbells with different timing instead of cans. Also it's a good use for old stripped gears too

[havlicek]

Neat stuff Robert!

[Benno - SAC]

That's a really good idea!👍

[Jaeger Team]

Hi John, how did you cut the "C can shim" to fit one section in the middle of D can window?

[Jaeger Team]

I did it like that...

 

 

[havlicek]

Good one Maurizio! 

[havlicek]

Hi John, how did you cut the "C can shim" to fit one section in the middle of D can window?

 

Well, it only works that way with some C cans Maurizio.  On a lot of them, you can't do it without the can falling apart because of where the weld is.  On the can I used, the weld is further back, instead of up near the open end.  Even if the can does fall apart, you can always use it in two pieces...just as you did! 

[Jaeger Team]

Thanks, I'm going to try a smaller shim version with the cross member in the middle. Learn always something new from you.

[havlicek]

Thanks, I'm going to try a smaller shim version with the cross member in the middle. Learn always something new from you.

 

 

...and I learn something new all the time here, so I'm just returning the favor!  D