65 replies to this topic

[zipper]

whats a dentists diamond?
 
being a dentist im only aware of the dental drill bit being referred to as that.

I did use turbine first with a small round head to mark where to begin and then with a 014 cylinder to make the hole. Then carefully scraped the hole until the arm axle got a snug fit.

[havlicek]

 

Hi Ben,

- If someone asks me for a 40 degree arm, I'll try to hit that number... end of story. 

- A spread of anywhere between 30 and 50 degrees would be totally unacceptable. If I asked for a 40 degree arm and got a 30, I'd send it back. 

- If I got a 35 degree arm, I'd be unhappy, but probably try and make up for the difference by dropping or adding a tooth. To me, I think a spread of up to maybe 3 degrees in either direction would be "acceptable"... but... I wouldn't think someone who wanted more accuracy would be necessarily "unreasonable." 2 degrees in either direction is getting pretty darned good IMO. 

 

 

Thanks John,

 

@ 2 degrees anyone would be happy or should be after seeing some of the readings I have and many others have I'm sure?

 

Just what I hoped I would hear from you!  A+ Builder in my eyes for sure!  

My thought is that all the motor builders (*more or less so depending on the arm type/cost) strive for this kind of accuracy Ben.  I have no knowledge of how these things are handled "in-house", but "standardized procedures" probably help the lower-cost motors.  That may sound weird until you consider some things.  The old Mabuchi armatures had fiber stack-end insulators, and there was a small "cutout" in the top one that a molded-in "tab" at the bottom of the com fit into, and would "lock" the com into position for "nominal" zero degrees advance ("neutral timing").  Now, the insulators weren't bonded to the stack, and could move some.  The com tab of course didn't didn't fit the hole so tightly as to make assembly difficult.  Then too, you could actually twist the com a bit to dial-in a slight bit more advance, and the relative sloppiness of the factory wind did leave a little play to make that possible in some cases...as well as the fact that the coils weren't lacquered or epoxied, let alone tied.  Still, that kind of built-in "help" did make for at least some accuracy.  Racers back then would simply check the motor to see which way it ran faster and then scratch an arrow in the can top to mark that.  With an inline car, you then just just choose which side of the pinion to put the crown on.  

Fast forward to the mass-produced Chinese arms and there's certainly some kind of standardized process in play to make setting timing fairly accurate.  Small variances in timing *may* help some motors sound a bit faster, but there's so much in play that it's at least arguable whether or not this translates into a winning motor.

Ironically, armatures made to a "higher" spec can involve more hand work...and BOOM!...more variability (*although higher average performance)!

 

 

"Just an idea here"

It seems if the timming marks on the arm stack were marked after the arm is finished it would be a more accurate, honest  number / reading. Arms are hand scribed or marked and would take no more time to do either way. Plus would be a good close, maybe not perfect, but good honest  reading. Maybe that's asking too much, I just don't know.

 

I don't think that's a "bad idea", but there are a couple of "gotchas" from the perspective of the builder/manufacturer.  First is that it *would* take more time (albeit not THAT much more, but every extra step can and should mean more cost to the builder and then to the retail purchaser) to recheck timing and then to engrave the stack after the arm is finished.  Second, at least some racers might pass on an armature that's engraved as "38°" when they wanted a "40°" arm.  Those two degrees probably won't win them the race in and of themselves, but could result in an arm sitting on the shelf.  So, to a certain extent, I think a generic timing statement on the hang-tag is...or at least "could" be a good thing for both the manufacturer and the person who buys the arm, who might pass on an arm that *might* have still won them the race! 

Anyway, I think the discussion here is a good thing, because it may have cleared-up some misconceptions, as well as pointing out some things that could be improved...sometimes. 

[Ben Morrow]

John,

Thanks for your input here! What comes of all of this is yet to be seen, maybe something, maybe nothing, we'll just have to wait and see.

Pretty much all I'm looking for is learning the proper way of timming a good arm and giving a true number. I just hope it's possible to do this.

 

Cheater,

After taking my new (just finished that may be thrown away after this) timming gauge and checking these comms I think I'm more confused than before. These numbers are just crazy and now I'm unsure if it's the gauge, comm or me!

 

Here we go, warning, try not to laugh

 

Arm #1   Stack 1  139       Stack 2  139     Stack 3   135

Arm #2       "         131           "        129         "          126

Arm #3       "         123           "        122         "          115

 

I know this sounds crazy, but this is what I came up with.

 

Ben

[Bill from NH]

Ben, were these American arms with well-defined slots between the comm segments? What size piano wire were you using on your pointer that slides into the comm slots? You could make another pointer, but with smaller piano wire & see if you still have the same variances. Your second arms looks  good to me. The 1st & 3rd look questionable.

[Ben Morrow]

Ben, were these American arms with well-defined slots between the comm segments? What size piano wire were you using on your pointer that slides into the comm slots? You could make another pointer, but with smaller piano wire & see if you still have the same variances. Your second arms looks  good to me. The 1st & 3rd look questionable.

 

 

Hi Bill,

I'm not sure on the wire dia. but pretty thin. I have very thin but bends way to easy, I'll mic. the wire and let you know.

 

Arms 1 & 2 are American, #3 chinese. 

 

I'm wondering if arm dia. can have an effect on the readings?

 

Thanks,

Ben

[havlicek]

 

 

I'm wondering if arm dia. can have an effect on the readings?

 

 

It really shouldn't as long as the stack has been pressed to provide straight edges, parallel to the shaft line.  The "gaps" between arm poles are nominally 120° apart on a three pole armature, as are the com segments.  With one "gap" of the armature stack sitting on a hard/clean/smooth surface, the third arm pole should be facing straight up (90° off the horizontal), regardless of the armature's diameter.  Since timing advance numbers are "off the vertical", as the com segment slits rotate away from the vertical, you should get "degrees" readings off the same vertical...10,20,30 etc.

Good material for making a "pointer" can be a utility knife blade or even an X-Acto blade that you *FIRST* dull the edge on before cutting.  These are obviously made from a very hard and straight steel.  ⁽¹⁾Being careful to cut a "slit" in a 2mm ID bushing that's right in the center of the bushing and sized to *just* fit the blade, the blade can then be soldered in place leaving some material "proud" of the bushing, which should be a not-sloppy fit to the com segment slits.

⁽¹⁾  Cutting the bushing and mounting the blade will be the most likely step where significant errors can be introduced.

[Bill from NH]

Diameter might effect your readings, depending upon how the arms were placed as you took the readings. The 2mm shaft hole in the protractor is at a stationary height.

 

As an aside, there was much interest in arm timing when I ran Chinese 16D motors with my kids in the mid-90's. There were a few raceways that limited the timing to 25 degrees, so we used timing gauges to not exceed that limit if racing at one of them. When we re-timed an arm, we put as much timing in as the wire slack to the comm would allow without breaking. 40 degrees was commonplace with most of the arms, however, my fastest Chinese arm only had 27 degrees. I ran that arm until its soft shaft wore out. I used Mura oilites with a tighter bore for awhile, but they finally didn't do any good.

[Ben Morrow]

Hi Bill,

 

The protactor set-up I built is pretty solid I think. I made with new protractor, sheeted with a piece of 1/16 white plastic backing.

Then placed 2mm motor bushings, one bushing on the protactor side and one in the plastic sheet side. Two bushings epoxied in place right on spot, center X.  There's no play at all.

 

Guys another doc visit tomorrow morning  , so I may be out of pocket for a little while.

I'll post more pictures when I can.

 

Talk soon,
​Ben

[Ben Morrow]

Hey Guys,

 

A Public Apoligy

 

I have not spoke or talked with anyone about this, just weighing heavy on my mind! 

 

I've been doing a lot of thinking about some comments I've made on this forum regarding Mike Swiss, I must say after thinking this over I'm not very proud or happy with myself about making these comments.

 

I know Mike is/was a Pro racer with lots more exsperiance and knowalge than I will ever think or hope of having.

 

So Mike, If you're out there please except that I apologize for the comments made. I can't really explain why I flew off like I did.

 

But the bootom line is that I'm sorry and I hope you will forgive me about the mistake I've made, there's really no excuess for such behavier on a public forum. Again I'm Sorry! 

 

Sincerely,

Ben Morrow

[MSwiss]

Awesome of you to post, Ben.

 

Thanks.

 

I know my non sugar-coated answers can touch a nerve, sometimes, so I'll offer my apology, also.

 

I hope I can help answer any other questions, you have, in the future.

[Ben Morrow]

Thanks Mike,

 

Na, No suger coating needed, no apology needed either, just keep telling it like it is!  I always thought I had a little thicker skin then that, you seemed to have thinned it out a little   

 

Thanks for posting, I was feeling pretty down about some post I made and have ask to be removed. I feeling much better now and we both I hope can carry on!

 

Thanks again,

Ben

[Ben Morrow]

A quick google search under "protractor timing gauge" yielded this and other images:

timer.JPG

 

Note that the pointer/indicator is long enough to reach the full height of the gauge. That should give the most accurate reading.  The one I use is basically the same, although it was screenprinted and sold for slot car armature timing. Any protractor will work, as long as the shaft hole is a good (and not too sloppy) fit for a shaft.

 
​Bill, The wire dia. on my pointer is 0.025

 

Well, Getting back on subject!! 

 

I think I see where I've been going wrong guys. In this pic. posted by John H (post #18) the numbers used are changed and read from the top down. Don't know why but I missed this in Johns post. But if that is the correct way to check and set timming, that's my whole problem I think?

 

I've seen a few ways to check but have not really worked for me. (Pics now posted)

 

Here's a couple more pics of how I've tried checking without success, compared to what John posted I was just doing it wrong. 

 

Which way is the correct way??

 

Thanks ALL,

Ben

Attached Images

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[MSwiss]

That armature has approx. 19 degrees timing.
 
90-71=19
 

[zipper]

Just rewrite the numbers on pic 1 like I did; 90 to 0, 100/80 to 10 etc (with red tip!).

[havlicek]

The timing fixture you made looks aces and should give you accurate readings.  ***Using a "normal" protractor, you just have to do a little math, because they are inscribed with "straight-up" reading 90 degrees, whereas a "timing" protractor just has that same reading as 0 degrees.  For a normal (CCW) timing advance, the gauge/fixture orientation in your top picture is "correct"....or at least easier to read with less math.  ***Again, you're reading timing advance relative to the horizontal plane, with straight-up (normally 90 degrees) being 0 degrees or neutral timing in this case.  Nice job on the fixture!

***If you wanted even more accuracy, you could even fit the backside of the gauge with a couple of right-angle "legs", because you'll see that tilting the gauge either forward or backwards can make the reading sort of "appear" to change.  An even more...more accurate setup would involve a way to locate the arm perfectly perpendicular to the gauge's "X" plane, but this all gets silly when stated timing numbers can be a little "soft". 

[Ben Morrow]

Well Gentlemen , 

 

That's it! Problem has been solved. All this time, trying to figure all this out and it's as simple as reading the protractor wrong!

Hard to imagine but that's it, mystery's over. I had no idea about a timming protractor and normal protractor like I had purchased weren't the same. UG!    

 

Thanks to All