Answered Yamaha rear magnetic pick up ?

[Jaspy]

Could someone explain to me how the rear hub magnet on Yamaha branded ebikes works. I am not familiar with every single Yamaha model but the Moro Pro has a rear hub magnet that completely encircles the rear hub. The magnet itself is circular and slip’s onto the splines on the magura center lock hub. The magnetic pick up sits on the frame extremely close to the magnet assembly. I disassembled the plastic housing to see what’s inside and I found a one piece circular magnet. I checked to see if there was any gaps in the magnet field and there was none.
How does this work? It’s not like a single small magnet that passes the sensor every full wheel rotation.
I bought a new wheel set with DT Swiss 350 Hybrid 6-bolt disc hubs, 32h. I also bought new Magura disc’s to run on these.The rear disc has a place for a magnet but certainly not like the stock centre lock continuous magnet.
So back to the original question, how does this set up work ? 888BA625-91AF-4A1A-AD48-21C4F0F11B1A.jpeg
Magnet removed from plastic housing that slips into the splines of the hub nut.

5745E8F8-EF2C-48C9-989F-F0C1332868B4.jpeg

C8A3DB36-C85B-409C-BA6B-848135A78EC5.jpeg

456D1DC7-8E62-4CEF-A905-09D0D6553A8B.jpeg

 

[Jackware]

Could someone explain to me how the rear hub magnet on Yamaha branded ebikes works. I am not familiar with every single Yamaha model but the Moro Pro has a rear hub magnet that completely encircles the rear hub. The magnet itself is circular and slip’s onto the splines on the magura center lock hub. The magnetic pick up sits on the frame extremely close to the magnet assembly. I disassembled the plastic housing to see what’s inside and I found a one piece circular magnet. I checked to see if there was any gaps in the magnet field and there was none.
How does this work? It’s not like a single small magnet that passes the sensor every full wheel rotation.
I bought a new wheel set with DT Swiss 350 Hybrid 6-bolt disc hubs, 32h. I also bought new Magura disc’s to run on these.The rear disc has a place for a magnet but certainly not like the stock centre lock continuous magnet.
So back to the original question, how does this set up work ? 888BA625-91AF-4A1A-AD48-21C4F0F11B1A.jpeg
Magnet removed from plastic housing that slips into the splines of the hub nut.

5745E8F8-EF2C-48C9-989F-F0C1332868B4.jpeg

C8A3DB36-C85B-409C-BA6B-848135A78EC5.jpeg

456D1DC7-8E62-4CEF-A905-09D0D6553A8B.jpeg

Can't see the pics - just the image name?

 

[Mikerb]

are you sure the "magnet ring" is not some form of hacking device ( similar to Planet3). If the sensor is seeing a magnet all the time the wheel is turning rather than once per revolution it at least tells the control unit the bike is a bove 0 mph which is one of the conditions required to deliver power to the cranks but I cannot see how it can read the bike speed!!

 

[Jaspy]

Sorry about the pictures, I’m not sure what happened. This bike has no mods as far as all the sensors and electronics go. It appears the Yamaha branded bikes are a whole different story then bikes using a Yamaha motor. The Moro has the x-2 motor which to date has no limiter’s available even though mfgrs say it will work it doesn’t.
Here’s the magnet and plastic housing taken apart;

Here’s where it fits and the pick up on the frame. You can also see how tge magnet assembly fits into the centerlock washer.

 

[Mikerb]

I cannot really make out where the sensor is there...............but I can only assume the gap in the upper section of the assembly is where the magnet is not shielded and interacts with the sensor

 

[Jaspy]

If you look at the last picture I have partially inserted the magnet assembly into the hub. It engages in the splines in the hub. When pushed right in the plastic assembly has a recess where it slides into the frame. In the second pic you can see it sandwiched between the frame and wheel assembly.

 

[Jaspy]

Here is a better pic you can see the pick up mounted and the grove the magnet housing slides into to prevent the outer mag housing from spinning. The circular magnet clicks into the inner mag housing with the male splines which fit into the centre lock hub. So the inner housing spins with magnet. Is this clear as mud ?

 

[Jaspy]

Here I have inserted the axle and am holding the complete magnet assembly to show the correlation to the pick up. The entire face of the magnet passes very close to the pick up as seen here.

 

[Jackware]

I know later Giant bikes use a rear hub located sensor but I haven't seen one to compare with yours, though it will be Yamaha based.
I've found this image of a Giant sensor to fit on a 6 bolt rotor;

May be worth posting a question in the Giant section

 

[Mikerb]

....ok I see it now. The gap in the outer/fixed part of the assembly allows the magnet to interact with the sensor. When the magnet is shielded by the rest of the outer/fixed part it is rendered inactive.

 

[Jaspy]

....ok I see it now. The gap in the outer/fixed part of the assembly allows the magnet to interact with the sensor. When the magnet is shielded by the rest of the outer/fixed part it is rendered inactive.

Hmmm I don’t see how a circular magnet could be inactive when nothing changes except the speed it spins at. The pick up face is constantly within the magnetic field and the field never changes no matter how fast it spins.

 

[Jaspy]

Here’s what Yamaha says about it , plus the parts breakdown.
I have looked up all the Yamaha branded ebikes and the rear magnet set up is the same on them all that I could find.

 

[RustyIron]

I checked to see if there was any gaps in the magnet field and there was none.

All magnets have a North Pole and a South Pole, whether they're cylindrical, cubic, toroidal, or any other shape. If you've discovered anything to the contrary, then I'm going to make a call to Stockholm and nominate you for the Nobel Prize in some area of quantum mechanics that is far beyond my understanding. Frankly, I don't understand how a "gap" would occur in a magnetic field. Please send us a picture and description of the instruments you're using to measure the field.

 

[Jaspy]

Rustyiron I totally concur, and that was my point. There’s a big difference between a single fixed magnet that passes the sensor once every wheel revolution as opposed to a circular magnet that is always in contact with the sensor. Hence my poorly worded “gap in the field “ scenario . Honestly I’m just trying to get an understanding of how this works. I appreciate any idea’s and thoughts. My goal is to mount/modify or completely change the magnet into some configuration that will work with the six bolt rotor and hub.

 

[Mikerb]

the sensor is set only to "switch" when a magnetic field above a set threshold passes. As the circular magnet rotates I assume it will present 2 magnetic fields above threshold ....one either side of the magnetic path from North to South pole. The bike controller software has to do a calculation based on wheel rotation count, and wheel diameter, to work out speed/distance.........as part of that calculation it needs to divide the wheel rotation count by 2 if my assumption is correct.

To replace what you have with a more standard system you have 2 options. One option is to fix a magnet to the rotor but it may not be in the right position to activate the existing sensor so that solution may depend on whether the sensor can be moved and be refixed. If my hypothesis of how your exisiting system works is right you may still be faced with an incorrect speed and distance reading ( ie half the correct reading).
Another option is to fit a new sensor and cable on the chainstay and use a spoke magnet. The same error as a bove may apply though?

 

[RustyIron]

My goal is to mount/modify or completely change the magnet into some configuration that will work with the six bolt rotor and hub.

Bummer. The ten million krona from the Nobel Assembly would come in handy in equipping your crew set with new bikes. I haven't worked on that many eBikes, but there's no reason to suspect that one system is dramatically different than another. I'd bet the sensor on your Yamaha is a simple reed switch. It's just an on/off switch that's activated when in close proximity to the magnetic field. There's no reason to make it more complicated.

Will an "off the shelf" magnet come close enough to your pickup sensor? If not, get a little neodymium magnet and a sheet of thin aluminum. Cut out the aluminum and epoxy the magnet to it. I'll bet it works perfectly.

 

[Jaspy]

Guy’s I appreciate the suggestions for sure but, I still don’t understand when the sensor would be outside of a constant magnet field since the magnet is Always in contact with the sensor. I can’t see any time in the wheels entire rotation that it’s not. If I was to use any other configuration ie; magnet on spoke or disk or hub , there is only a split second that the magnet passes the pick up sensor. Totally different story, I just don’t know if that work.

 

[Jaspy]

Here is some further info I have unearthed in reference to the speed sensor set up on Yamaha branded ebikes.

“Yamaha Zero cadence support with 2 freewheels

Most mid-drive motors (like the Bosch) have just one freewheel, this is used for pedaling without turning the motor. With just a single freewheel, the motor can never drive the rear wheel without the pedals turning, this requires an extra freewheel.

The Yamaha has 2 freewheels, so we can do both:
Pedaling without turning the motor
The motor can drive the rear wheel without the pedals turning . “

“ I do know the hub speed sensor IS patented by Yamaha. The placement of the sensor on the hub is what gives Yamaha bikes the Zero Cadence support. I do appreciate the Zero Cadence tech when I’m going slow up a steep hill or on quick stop-and-go situations.”

So as things stand I am experimenting with a possible set up that may work with any hub, non centre lock set up.

 

[Mikerb]

Guy’s I appreciate the suggestions for sure but, I still don’t understand when the sensor would be outside of a constant magnet field since the magnet is Always in contact with the sensor. I can’t see any time in the wheels entire rotation that it’s not. If I was to use any other configuration ie; magnet on spoke or disk or hub , there is only a split second that the magnet passes the pick up sensor. Totally different story, I just don’t know if that work.

..............there are a few different forms of sensor and the ring magnet plus sensor arrangement is commonplace in cars and motorcycles for everything from measurement of wheel rotation to managing ABS systems ....since Yamaha is a m/c manufacturer it is no surprise they chose to use a similar arrangement. I do not know exactly what form of magnet is used here but the magnetic field can be in a variety of different forms depending on the magnet ring design ( e.g. each half the circumference is a different magnet/ or the thckness of the ring is in fact 2 magnet joined together. Whatever its make up the magnetic field will vary in strength and the sensor can be set to react only to a magnetic force a bove a certain threshold.
( even the simple spoke magnet/sensor design can give a false reading...mostly at slow wheel rotation speed....if the magnet does not face the sensor but instead is rotated 45 degrees, perhaps having been knocked by trail debris. The sensor can then see 2 areas of maximum magnetic force in quick succession, one just before and one just after the null point of the field which exists at both the North and South poles).
If I was you I would remove the ring magnet and fit a magnet on the rotor. Then see if the sensor can be sensibly moved to align with it. If that can be achieved, you then need to see if your speed readout is accurate.....and take it from there. Musing a bout the methodology of the existing system is not going to help find an alternative without some experimentation.

 

[Jaspy]

EUREKA!!! Finally ! Mikerb your a saviour, now that I understand what I am actually dealing with, I can indeed start experimenting.
My eternal gratitude, Cheers

 

[Jaspy]

Here is The solution for this situation that I have found that works perfectly awesome

All Yamaha motored style speed magnet hub mod

Hey guys here is the mod that is required for a Yamaha axle speed sensor magnet with a center lock rotor to work with a six bolt rotor hub set up. I have tested this mod for a few months now without a single problem. Without getting wordy hopefully the pictures will speak for themselves...

www.emtbforums.com