As far as I know, the mechanics of Yamaha PW-X2 is almost the same as the Yamaha PW-X. So everything that is told here also applies to the PW-X version. This motor is also used by Giant but strangely enough has a massive bottom bracket:
For my solar bike, I want to use the best mid-drive motor. My choice is the Yamaha PW-X2 motor for the following reasons:
1*) This is due to the large gear ratio. The internal motor therefore has a high speed. Read more in this article.
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:
A disadvantage of the Yamaha is that gear wheel 3 and 4 will rotate during pedaling without motor assistance, which will give some loss.
|Gear 1||Gear 2||Gear 3||Gear 4|
|Teeth number||8||Teeth number||54||Teeth number||13||Teeth number||54|
Gear1 85t, module 1.25, width 9mm
Gear3 54t, helical 20º, normal module 1, nylon, width 20mm
The gear ratio is 85/13 * 54/8 = 44.13
The motor speed of the Yamaha PW-X2 at a cadence of 100 is 4413 rpm.
The Yamaha PW-X2 motor has room for thicker copper wire. Rewinding the motor with thicker copper wire gives a little higher motor efficiency and therefore a higher permissible power.
I had nylon gears fabricated to repair the Yamaha PW-X and PW-X2 motor, see here.
As with the Yamaha PW-SE, the nylon gear is a weak part of the motor. It is definitely a design flaw as the gear wheel apparently cannot withstand the maximum force of the motor as it breaks too often. When the motor is broken, it will just be exchanged by Yamaha. Outside the warranty period, this will cost around $750. This is a big problem because, when the gear will be overloaded again, you can keep going this way.
The Yamaha motor has too much torque, which is the cause of the gear failure. Maybe it can be remedied by limiting the motor current. To do so, change the circuit with the ACS723 HALL current sensor (I have not tried this).
ACS723 HALL current sensor
Note that Giant ebikes have a special version Yamaha motor, named Syncdrive, with a CAN-bus instead of the one wire bus.
Take care of the thermal gap filler pads. There are two different thicknesses, the 1mm pads can better be replaced when the printed circuit has been removed.
I have looked if there are thermal pads which do not always have to be replaced after repairing the motor. The thermal pad must be elastic and has to rebound to the original shape after the pressure is removed. The Bergquist Gap Pad TGP 1000VOUS meets these requirements. The viscoelastic nature of the material also gives excellent low-stress vibration dampening and shock absorbing characteristics. The required thickness is 1mm for both the Bosch and Yamaha mid-drive motors. The thermal conductivity is 1 W/mK with 1mm.
Attention: the Yamaha uses liquid gasket. Once the motor has been opened, this must be renewed.
Yamaha use these connectors for the PW-SE mid-drive system:
JST JWPF series
Hirose HR30 series