PAS on SRAM Crankset? Help

Marc Webster

Finding my (electric) wheels
Nov 17, 2016
13
2
49
Glendale, California USA
Hello All,

I bought a Q128cst system and had it laced to a 700c wheel. I started working on the install today and ran into an issue with the PAS sensor install. The problem is I have a SRAM splined crank and bottom bracket. The PAS magnet wheel is is set up for a square drive with a gap for the PAS wheel to reside. My problem is I dont have any space between bottom bracket and my crank. Also the large spline would require me to dremmil out the fingers on the PAS wheel to fit. I dont mind trying this, but curious if I can sandwich the PAS wheel between the crank and BB? I am sure many have had this same issue and curious how people resolved it. Also moving the PAS Setup to the drive side would not do much as I only have a single chainring so cant mount the PAS wheel to one of the ring spiders.

Here are some pics of what I have. I am open to any advice and also open to buying other items if needed to make this work on the non drive side if possible.

I am open to any advice on how to make this work. Also open to buying new parts if needed. I am in Los Angeles CA.

Best regards,

Marc
 

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Deleted member 4366

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Those Isis and other splined cranks are not easy because you often can't make room for the magnet disc. The easiest option is to chuck your whole BB and crankset, then get a Shimano M590 Hollowtech one, ehich will save a bit of weight too, They cost about £60 new complete with BB if you shop around, or you can can get a used one. It only works if you have a standard 68mm wide BB shell, not 73mm.

http://www.ebay.co.uk/itm/Shimano-Deore-FCM590-3x9-Speed-44T-Crank-Chainrings-BB51-Bottom-Bracket/311708859050?_trksid=p2047675.c100005.m1851&_trkparms=aid=222007&algo=SIC.MBE&ao=2&asc=40656&meid=b15d8719e8204b98850b95c49b827ee8&pid=100005&rk=5&rkt=6&mehot=pp&sd=172631388952

http://www.ebay.co.uk/itm/Shimano-FC-M590-Cranks-/172631388952?hash=item2831a1f318:g:BXgAAOSw3ZRY9imQ

With those, you chuck the spacers that convert 68mm to 73mm, reverse the sensor on its bracket and drill out the hole to 25mm in the magnet disc.

Another option is to remove all the inner plastic from the magnet disc, leaving just a ring of magnets, and epoxy that to the inside of your inner chainwheel, then make your own bracket to hold the sensor next to it.
 

Marc Webster

Finding my (electric) wheels
Nov 17, 2016
13
2
49
Glendale, California USA
Those Isis and other splined cranks are not easy because you often can't make room for the magnet disc. The easiest option is to chuck your whole BB and crankset, then get a Shimano M590 Hollowtech one, ehich will save a bit of weight too, They cost about £60 new complete with BB if you shop around, or you can can get a used one. It only works if you have a standard 68mm wide BB shell, not 73mm.

http://www.ebay.co.uk/itm/Shimano-Deore-FCM590-3x9-Speed-44T-Crank-Chainrings-BB51-Bottom-Bracket/311708859050?_trksid=p2047675.c100005.m1851&_trkparms=aid=222007&algo=SIC.MBE&ao=2&asc=40656&meid=b15d8719e8204b98850b95c49b827ee8&pid=100005&rk=5&rkt=6&mehot=pp&sd=172631388952

http://www.ebay.co.uk/itm/Shimano-FC-M590-Cranks-/172631388952?hash=item2831a1f318:g:BXgAAOSw3ZRY9imQ

With those, you chuck the spacers that convert 68mm to 73mm, reverse the sensor on its bracket and drill out the hole to 25mm in the magnet disc.

Another option is to remove all the inner plastic from the magnet disc, leaving just a ring of magnets, and epoxy that to the inside of your inner chainwheel, then make your own bracket to hold the sensor next to it.
Hello D8veh,

Thanks for the reply and clarification on things. My bike is an SRAM 1x11 setup so before I buy any new parts I think I may have a solution. I dont have the small chain rings to attach the PAS ring too, but I do have the spider arms in a 5 legged array (72 degrees). I think I can cut out the center part of the ring and either glue it to the 5 legs or if needed 3D print an adapter to place the PAS ring in an optimal position and glue the adapter in place. As for the air gap between magnet and sensor, can you give me a range? Does it need to be close in the 1mm range or can I get away with 6mm or so or even more? I dont have my battery yet so cant test it beforehand, but if I had an air gap range to shoot for I can at least get everything set up in advance.

Your thoughts?

Marc
 
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Deleted member 4366

Guest
For the air gap, you should aim for about 1mm. Basically, the closer the better. You need to get the orientation of the magnets correct. Test them with a magnet before anything, then, whatever your final arrangement is, test it before installing to make sure that it doesn't end up working backwards.
 

Marc Webster

Finding my (electric) wheels
Nov 17, 2016
13
2
49
Glendale, California USA
Hey D8veh,

I figured it out using a 3D printed adapter I designed in solidworks to keep the magnet ring concentric on the Isis SPlined tube. I posted to endless sphere on how I did it. Below is a link. Anyone interested in the STL file to print this can email me, but I can only say it worked on my particular SRAM 1x11 speed road cranks.

Here is a link: https://endless-sphere.com/forums/viewtopic.php?f=2&t=87813&p=1283155#p1283155
 
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daffy99

Pedelecer
Jul 17, 2017
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I figured it out using a 3D printed adapter I designed in solidworks to keep the magnet ring concentric on the Isis SPlined tube.
Do I interpret this (and the photos on endless-sphere.com) correctly in so far, as that the final result is a cut down magnet disc, glued to the crank? Two-component glue? Anything specific?

The printed adapter(s) seem to be advanced tools to keep the magnet disc exactly in the right place, and keep it stable, while the glue dries? (One of the photos is labelled "Glue dry adapter removed")
 
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Deleted member 4366

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Any epoxy would be OK. it might be a good idea to clean any oil or grease off first. I'd use petrol for that. you don't have to be 100% accurate with the positioning of the magnet disc. You should be able to judge with your eye whether it's concentric.
 
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Marc Webster

Finding my (electric) wheels
Nov 17, 2016
13
2
49
Glendale, California USA
Do I interpret this (and the photos on endless-sphere.com) correctly in so far, as that the final result is a cut down magnet disc, glued to the crank? Two-component glue? Anything specific?

The printed adapter(s) seem to be advanced tools to keep the magnet disc exactly in the right place, and keep it stable, while the glue dries? (One of the photos is labelled "Glue dry adapter removed")
Yes you are correct in its use. I should have used epoxy, but used a small amount of thick CA for the initial test knowing I could break it off if needed. It worked so well that after the test I just glued the remaining areas with CA. I agree with Daveh that the accuracy for the PAS to work does not require accurate concentricity. However I disagree that you can eyeball it and do it without the tool. Reason is the radial lock ring on the ISIS crank bearing is huge and there is very little clearance between the inner part of the PAS ring and the Radial lock ring for the bearing. I tried that first and the ring wants to not sit flat and slide off center. Big pain in the ass and that is why I made the tool. If your bike has the same crank setup as mine, I can send you the STL file for the tool and you can have it printed somewhere. Any simple fdm printer will do. My tool is optimized for the BMS battery PAS ring shown in the ES pics only.
 
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daffy99

Pedelecer
Jul 17, 2017
29
0
50
Switzerland
Many thanks for the responses!

I am on a Hollowtech crankset, so not entirely the same physically - but conceptually the same challenge.

Quite a number of different solutions for Hollowtech seem to be sold nowadays - all get that disc stuck to the inner-most chain ring, be it by magnetic force itself, by snapping in plastic, or by screwing in something, somewhere.

For the time being, I have decided to purchase two different PAS packages from China and then determine how to saw, hammer, and glue them best into place - at least I'll have some material to work with. Your posting also might have just provided enough of an excuse to finally dip my toe into 3D printing!
 

Marc Webster

Finding my (electric) wheels
Nov 17, 2016
13
2
49
Glendale, California USA
Many thanks for the responses!

I am on a Hollowtech crankset, so not entirely the same physically - but conceptually the same challenge.

Quite a number of different solutions for Hollowtech seem to be sold nowadays - all get that disc stuck to the inner-most chain ring, be it by magnetic force itself, by snapping in plastic, or by screwing in something, somewhere.

For the time being, I have decided to purchase two different PAS packages from China and then determine how to saw, hammer, and glue them best into place - at least I'll have some material to work with. Your posting also might have just provided enough of an excuse to finally dip my toe into 3D printing!
Daffy,

For the hollowtech there are many solutions as you said. If you have a multi ring front crankset you can mount to the inner crank or make an adapter to take place of inner crank. I had a 1x11 drivetrain so no extra mounting points whihc is why I had to go the glue to the crank spider route. Best of luck.

As for 3D printing it opens up a lot of possibilities. Not just in ebiking. I use it for everything. Not that you need as big a machine as this, but have a look at the Formbot Trex 2+
 

anotherkiwi

Esteemed Pedelecer
Jan 26, 2015
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I made a support for the exterior of the disk from the bottom of a coffee can but love the idea of 3D printing. If your small chainring is aluminium you could drill holes for the magnets and glue them in. I can see me having to find a solution to this problem in the near future.