PAS (Pedal Assist Sensor) installation problems.

[DanoR]

I’m hoping for advice about mounting a PAS (pedal assist sensor). The donor bike for my project is an old Trek hybrid. The (current – one of many) difficulty I’m having is that there doesn’t seem to be enough space on the crank arm for the sensor.

I removed the bottom bracket and installed the metal disk with the sensor behind the lip as below:



I then slipped on the plastic ring with the magnets and reinstalled the crank arm. However, it just pushed the plastic ring into the sensor, so they bump across each other every time a magnet goes by and there is a lot of extra friction. Part of the problem is that the screws holding the chainrings together get in the way of the plastic ring, so they push it out (into the sensor) a couple extra mm.



View attachment 2

My possible solutions include:
---Look for a thinner plastic disk
---try to install it on the other side (although there is nothing there to keep the sensor in place, I guess I could glue it, also it still doesn’t really look like there is any more room),
---I could try to carve out the plastic to go around the bolts although since there are 8 magnets and 5 bolts, there will always be at least one magnet in the way.
---Get new chainrings? We have wicked hills so I really don’t want to drop to 2 gears in front, but that would be an option. I need to get new shifters regardless.
---Get a longer bottom bracket? I don’t know much about this. I wouldn’t want to make it awkwardly wide, so I would only want a couple more mm.
---Get a thinner crank (i.e. the part that pushes onto the bottom bracket)?

For the record, I have no idea what I’m doing. I’ve watched a lot of Youtube, read a lot of blogs, and talked to the local bike shop guy (not an electric bike guy) a few times, but that’s mostly it for my knowledge base.

Thanks for any help!

Dano

 

[Grizzl-E]

Put the sensor on the other side of the bike.


Sent from my iPhone using Tapatalk

 

[motomech]

Mount the sensor externally. The bracket is malable, bend(hammer) and fold it into a curved shape that conforms to the bottom of bottom bracket shell and epoxy it there.
But before you glue it, mock it up and test.
The sensor needs to be close to the disc and it's likely you will have to turn the sensor itself around.
Sorry, no pics, mybike is too dirty underneath

 

[teklektik]

Made up a new bracket from a bit of scrap aluminum.
Might be able to recycle the existing steel bracket by folding in the loop on both sides, then forming the mounting U similar to picture.
Not sure about this recycling approach, but just a thought...

 

[d8veh]

There's loads of things you can do. As long as the magnet disc goes round with the pedals and the sensor is near it, it'll work. be aware that it only works in one direction, so you should check that it works before you re-install the outboard crank. When you change from one side to the other, the magnet disc has to be flipped, so on ones side the arrows point in the right direction, but on the other, the wrong direction.

You can get a longer bottom bracket assembly for about $10 to get more space.
You can thin down the slight boss on each side of the magnet disc to get about 2mm less width.
You can cut the middle out and glue the magnet disc to your chainwheel.
Make your own bracket to hold the sensor
Fit on the left side and retain it with a lock ring http://www.ebay.co.uk/itm/NOS-2-Notch-Steel-Bottom-Bracket-Lockring-silver-English-Thread-/222121098551?hash=item33b772fd37:g:q4QAAOSw~gRVskVB

 

[docw009]

My instructions said to glue the sensor ring to the non-crank side. Like that's going to hold up.

I got a piece of copper strap (it's really copper plated soft steel) for hanging pipes at home depot for 25 cents. Then I took the sensor out of the ring and bolted it to the frame. Easy to make, and easy to bend to get the right clearance, and can be placed anywhere near the disk.

 

[teklektik]

 

[DanoR]

Thanks all for the excellent suggestions! I'm sure that I can make one of the above work, will take some pics and post once I've decided on and implemented something. Just to clarify, in terms of how this thing works, I take it the copper colored ring is just for mounting, does not affect the function of the actual sensor. And why would it matter which direction the disc with the magnets is facing? It's just 8 magnets in a concentric ring so how does it tell which direction the ring is mounted? Is one magnet different from another? Or is it sensing the polarity? It seems that having the sensor itself mounted backwards would be more likely to result in it not working.

Dano

 

[puregsr]

I just grinded parts of the disc so it can get really close to the bottom bracket without binding and then tilted the sensor about 45 degrees inward. Remember, you can flip the sensor on the bracket if you have it on backwards. Also, sensor picks up signals even though it's sitting at an angle.

 

[Dumsterdave]

Put the sensor on the other side of the bike.


Sent from my iPhone using Tapatalk

Does it matter what side it is on? the directions from my kit seller said to put it on the non drive side

 

[puregsr]

Put the sensor on the other side of the bike.


Sent from my iPhone using Tapatalk

Does it matter what side it is on? the directions from my kit seller said to put it on the non drive side

Doesn't matter.

 

[Dumsterdave]

Put the sensor on the other side of the bike.


Sent from my iPhone using Tapatalk

Does it matter what side it is on? the directions from my kit seller said to put it on the non drive side

Doesn't matter.

Thanks, Ill give it a try

 

[DanoR]

Thanks for everyone's help and suggestions! I elected to fold the sensor back to create more room and cut out the middle of the magnet ring and glue it on. This worked after the following mishaps:
1. I folded the sensor back too far and it wouldn't pick up. I struggled with it for quite some time, taking the bottom bracket off and on a couple times before I got it to work.
View attachment 1
2. I tried to just snip the "spokes" of the magnet disc with heavy duty diagonal cutters, but the force broke the outer ring in two as well. I then took a jigsaw to the rest with better results, and gorilla glued it back together.

3. After gluing it on to the crank, I couldn't for the life of me make it work! Took me far longer than I would like to admit to realize I'd unplugged it somewhere along the way. . .
4. In trying to get it to function, I had moved the sensor too far back up toward the magnets, but was too lazy to take the crank off to push it back down, so reached in with a screwdriver, putting some counter pressure on the magnet ring. . .and snapped it in half where I had glued it together. Much swearing ensued.

Didn't end up being a half hour project, but maybe someone else can learn from me. Seems to work like a champ at the moment! We'll see if it will pull my wife and kid up our 17 deg hills!

Dano

 

[Lakebod]

I have a a magnet disk wherein only one side of the disk exposes the magnets, so if installed on one side of the bike Id have to flip it, and there would be plastic between the magnets and the sensor. Does it matter which side of bike I install?

 

[docw009]

I have a a magnet disk wherein only one side of the disk exposes the magnets, so if installed on one side of the bike Id have to flip it, and there would be plastic between the magnets and the sensor. Does it matter which side of bike I install?

Is there a rotation arrow on the disk that told you you would have to use it with plastic facing the sensor? Mine has that arrow, and the disk has to spin in that direction no matter which side is used. I had mine on the non-drive on my first build. When I followed the arrow, it worked. I reassembled disk backwards when I greased the BB later. Then the PAS only worked if I spun the crank backwards.

I would guess that your disk would still work if you had to mount it so the sensor faces the plastic side. The magnetic field will go thru plastic, but the distance is greater, which weakens the field, so it could fail. If magnets facing the sensor is the required alignment, assemble the PAS that way.

That round clamp didn't fit any of the BB's on the two bikes I have tried anyway. I always had to clamp the sensor to the frame with a home made bracket.

 

[d8veh]

The magnet discs work whichever side faces the sensor. You flip the disc to reverse the rotation, so on the right-hand side, the arrows rotate with the pedals, but on the left-hand side, they go the opposite way.

 

[Lakebod]

no there is no arrow indicating direction, and BMSbattery (where I bought it) offers no response. I guess ill just have to try it. Ill report back in case its of any use for ppl in the future.