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Archive 2015 · Canon USM stator sizes

  
 
chickenplucker
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p.1 #1 · p.1 #1 · Canon USM stator sizes


Howdy everyone.

I've got a simple question for a somewhat complex problem, does Canon use the same USM stator and armatures across a series of lenses?

I can't find measurements on the inside diameter of other stators, but from the looks of things I'm thinking that other 2.8L USM stators are roughly the same size and diameter with different shape/length ribbons attached (ends seem to all be the same shape with 4 traces).

My old 28-70mm f/2.8L needs a new USM drive, and I'd rather put something new in it than a 13 year old used part.






Mar 09, 2015 at 12:52 AM
Monito
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p.1 #2 · p.1 #2 · Canon USM stator sizes


Welcome to FM (your first post).

All across FM hearts are fluttering at the thought of transplant surgery for a 24-70 f/2.8 L.

Frankenlens?

Lens hackery?

Roger Cicala might know.



Mar 09, 2015 at 12:58 AM
Ian.Dobinson
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p.1 #3 · p.1 #3 · Canon USM stator sizes


Monito wrote:
Roger Cicala might know.


thinking the same .




Mar 09, 2015 at 01:04 AM
chickenplucker
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p.1 #4 · p.1 #4 · Canon USM stator sizes


Thanks for the welcome Monito!

I wish I would have keep the link, but at one point when I was digging around for service manuals I did run across a forum thread where someone claimed to repair the 100mm f/2.8L IS USM Macro with a USM drive out of a non L lens. The post didn't go into much detail on it though.

Tomorrow I'll get out my calipers, tear the 28-70 down again, and get some actual measurements of its drive to share so others can compare them with anything they may have kicking around.



Mar 09, 2015 at 01:21 AM
chickenplucker
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p.1 #5 · p.1 #5 · Canon USM stator sizes


Alright, good news and bad news. The good news is I ended up being able to fix the motor on my lens after taking it apart and putting it back together for the 6th time. Bad news, I'll not be ordering some random parts now to see if swapping the USM drive out of another lens would have worked.

But going back to the swap idea, from what I could tell the USM stators and rotors appear to all be the same on any 2.8L based lens. Keep in mind this is just from pictures I was looking at, the actual dimensions could be different but I just can't see Canon making different motor parts for every lens. It doesn't make sense from a design perspective to keep redesigning every lens motor when they would have parts in stock that would already work.

The dimensions on the 28-70mm 2.8L's stator are 5.4cm for the inside diameter of the stator, and 5.8cm for the inside diameter of the rotor.



The 28-70's USM drive. Top left is the retaining washer with spring that keeps pressure on the motor, its glued together. Top right is the felt washer that goes beneath the retaining washer/spring to keep pressure down on the stator. Bottom left is the stator and its ribbon. And on the bottom right is the rotor, which as far as I can tell is just a big flat washer that acts as a surface for the stator to do its magic on, and as a drive transmission to connect the auto-focus to the actual lens. If you have never read up on how a USM drive works, you really should. Its quite amazing stuff.

From the side, top to bottom; Retaining washer, spring, felt, stator, rotor.


I was just getting ready to start pestering Ebay sellers about the inner diameter of newer lenses focusing motor assemblies, but mine started working before I did. I did narrow down some potential swap candidates in case anyone else wants to chase this down further. Note that most of the auto-focus assemblies come with a portion of the barrel

Canon EF 16-35 mm 1:2.8L Ⅱ -Part# YG2-2332-000 Cheapest at about $85.00
Canon EF 24-70mm F/2.8 L USM -Part# YG2-2064-000 Looks closest to the 28-70's.
Canon EF 70-200mm 2.8 L non-IS USM -Part# YG2-0212-009 Very, very long ribbon. May not be the best.

Assuming the above stators and rotors are the same diameter, they all seem to have a 4 wire ribbon attached with various lengths and bends. The Canon EF 24-70mm F/2.8 L USM appears to have the same bends and length though, so it may be the best candidate. I think that lens even operated the same as the 28-70 with both being non weather sealed and having barrels that extended when zooming wider and retracted when going long. Here is a pic of the 28-70's stator cable plugged in, so you have a rough idea of how far it has to travel to the lenses board, note that the stator is about level with the distant numbers you can see on the barrel.


So if anyone takes this further let us know how it works. If mine ever dies again I'll do a follow up on the attempted swap. But for now I managed to fix mine by lightly oiling it, removing the oil, squashing the ribbon connector to the stator back down hard, rotating the felt washer a quarter turn, and then randomly taking it apart and reassembling it six times. No more jumpy erratic auto focus! Good luck everyone, keep those 28-70's alive.

Edited on Mar 10, 2015 at 01:59 AM · View previous versions



Mar 09, 2015 at 07:48 PM
Mike Sowsun
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p.1 #6 · p.1 #6 · Canon USM stator sizes


Canon Ring Type USM comes in two sizes, either 62 mm or 77 mm in outside diameter.

Lots of info on USM here: http://dougkerr.net/Pumpkin/articles/Canon_USM.pdf

And also here: http://www.photoscene.com/sw/tour/inside.htm






Mar 09, 2015 at 07:49 PM
chickenplucker
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p.1 #7 · p.1 #7 · Canon USM stator sizes


Thanks for that info Mike! That's actually pretty interesting that there are only two sizes of USM ring drives. Might have to snag some other broken discontinued lens for a swap/test.


Mar 09, 2015 at 08:09 PM
unclechuck
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p.1 #8 · p.1 #8 · Canon USM stator sizes


chickenplucker wrote:
Howdy everyone.

I've got a simple question for a somewhat complex problem, does Canon use the same USM stator and armatures across a series of lenses?

I can't find measurements on the inside diameter of other stators, but from the looks of things I'm thinking that other 2.8L USM stators are roughly the same size and diameter with different shape/length ribbons attached (ends seem to all be the same shape with 4 traces).

My old 28-70mm f/2.8L needs a new USM drive, and I'd rather put something new in it than a 13 year old used part.

http://www.somethingthatdoesntsuck.com/wp-content/gallery/random-2_1/img_0064.jpg



Welcome to FM --- I love tear downs and am always amazed to learn from the adventurous who do them

You may already be familiar with the Lens Rental Blog --- if you haven't seen it already the 100-400 II tear down is amazing!

All the Best

Charles



Mar 10, 2015 at 01:43 PM
tntcorp
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p.1 #9 · p.1 #9 · Canon USM stator sizes


unclechuck wrote:
Welcome to FM --- I love tear downs and am always amazed to learn from the adventurous who do them

You may already be familiar with the Lens Rental Blog --- if you haven't seen it already the 100-400 II tear down is amazing!

All the Best

Charles



how about requesting fred to create a new repair/mods/dissy forum? there are informative data in these threads for future uses, and i am sure there will be plenty of contributors.


tom




Mar 10, 2015 at 02:14 PM
chickenplucker
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p.1 #10 · p.1 #10 · Canon USM stator sizes


@unclechuck
The teardowns and information from that blog are good stuff, the whole series of posts they had up on the 24-70 are just great.

So I managed to track down a physical copy of the 28-70's service manual, and as you would expect its loaded with all sorts of interesting things. I don't have a means to really collimate the lens, so the focus adjustments are out of my hands. But the section on the controller board and the adjustments you can make to the USM motors frequency and pulse settings are pretty interesting stuff.

I'd be happy to post the USM adjustment portion of the manual if people are interested (or any other section), however I don't want to break any forum rules. Not sure if its fine to upload some pictures of the actual pages or if I need to paraphrase the sections and create some quick diagrams.

What I found kind of interesting was that some of the other threads I've read around the internet where people complain about their auto focus motors squealing could be fixed by possibly tweaking the USM's frequency adjustment screw. This would only take removing 6 screws on the lens mount to reach so it could be done rather easily. Without a way to measure the actual frequency this would probably take a few tries, but seems do able. Pretty neat stuff.



Mar 13, 2015 at 10:50 PM
unclechuck
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p.1 #11 · p.1 #11 · Canon USM stator sizes


For a Charter Member of the "One Part Left Over Club" this is fascinating stuff

Your clear and practical descriptions are fascinating reading. Kidding about the extra part aside, I can see myself sitting down with an old lens and exploring your road map. Likely others would too ...

Charles



Mar 14, 2015 at 08:17 AM
chickenplucker
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p.1 #12 · p.1 #12 · Canon USM stator sizes


Alright, well the auto focus motor gave up the ghost again and I decided to press on with this somewhat expensive experiment.



I ended up ordering the Canon EF 24-70mm F/2.8 L USM -Part# YG2-2064-000 focusing unit. Here it is standing next to its older brother so you have an idea of where the focusing barrel would be within the 28-70.

So after a quick tear down of the 28-70mm I was able to pull its USM out for some comparison pictures:




On the left are the components from the 28-70mm, and the newer 24-70mm's motor on the right. The motor's are exactly the same, even the same ribbon shape/length. Even with the new motor parts I still ended up tearing the lens apart 4 or 5 more times until it started to function correctly.

I'm assuming Canon never intended the USM components to be removed from the focusing barrel and that maybe they were all pre-adjusted and tested at the factory for certain tolerances. They really seem to dislike being poked and prodded. On my lens I ended up having to use the old rotor (bottom thick ring), new stator (notched teethy ring), new felt washer, and old spring/lock for it to start working correctly.


As a bonus here's a very simplified run down on some USM adjustments that can be done on the PCB:



Red arrow is the USM motors pulse setting screw. The USM stator is divided in two halfs, and ran by pulses, which are supposed to be sent in equal spacing, such as: - - - - - - -. If the pulse are out of adjustment it may appear staggered or off balance such as: —– — —– — —– — —– This is bad, Turning this screw will change the pulse spacing, but without an oscilloscope this is just kind of trial and error. Its supposed to be adjusted after changing out the focus motor or PCB, but on my lens at least it seemed to be about right even after the motor change. The blue arrow is the frequency adjustment screw which you can use to change the frequency the motor runs at. I don’t have the service manual in front of me at the moment for its intended value, but its best not to mess with this one, or if you do mark where it was set at (actually do that on both if your playing with them).

Cheers!




Apr 11, 2015 at 03:28 AM
kezeka
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p.1 #13 · p.1 #13 · Canon USM stator sizes


This has to be one of the most informative posts I have ever read on FM. Thank you for your contributions to the forum! I would love to learn more about your experiment if you end up doing more teardowns in the future.


Apr 11, 2015 at 12:35 PM





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