Yamaha PW-SE mid-drive motor tear down

Yamaha PW-SE facts

• Max. 250W
• Max 70Nm
• Max. cadence 110rpm
• Weight 3500g 

Yamaha PW-SE motor

Yamaha PW-SE tear down

Yamaha PW SE tear down

Yamaha PW SE tear down

Yamaha PW SE tear down

Yamaha PW SE tear down

Electronics board

Note that multiple versions PCBs are used, they are NOT compatible because the electrical connections of the connector on the right are different. Strangely enough, there are versions with a second microcontroller on the bottom side. What is the meaning of this second microcontroller?

There are several circuit board versions of the Yamaha PW SE

There are several circuit board versions of the Yamaha PW SE

Yamaha PW-SE PCB parts list

• 2x ACS709TLLF-45AB
  Current Sensor 45A unidirectional
  QSOP-24
• Toshiba TMPM370FYFG
  ARM Cortex-M3 microcontroller
• LT3992
  Dual Step-Down Switching Regulator
  TSSOP-38
• TPS57160-Q1
  Step-Down Switching Regulator
  HVSSOP-10
• 3x L6387E
  High voltage high and low-side Mosfet driver
  SO-8
• 6x K80S06K3
  N-channel power Mosfet
  RDS(ON) = 4.4 mΩ
  60V 80A 100W
• Renesas R5F10B *)
  16-bits microcontroller (=RL78/F13)
  *) This chip is only used at the PCB version X0S 86530-C0 and is located on the bottom side.

Blown up EDB9

When the data signal is short circuit with 36V, this transistor will blow up:

Blown up EDB9

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 

A disadvantage of the Yamaha is that gear wheel 3 and 4 will rotate during pedaling without motor assistance, which will give some loss.

Yamaha PW-SE gearwheels

The gear ratio is 101/16 * 56/8 = 44.2
The motor speed of the Yamaha PW-SE at a cadence of 100 is 4420 rpm.

Main gearwheel Yamaha PW SE vs Tongsheng TSDZ2

It is interesting to compare the size of the large gear wheels of two mid-drive motors. The Yamaha gear wheel is a lot wider and presumably oversized.

Main gearwheel Tongsheng TSDZ2 vs Yamaha PW SE

Tuning the Yamaha PW-SE motor for more power

The Yamaha PW-SE motor has room for thicker copper wire. Rewinding the motor with thicker copper wire gives a higher motor efficiency and therefore a higher permissible power.

Tuning the Yamaha PW-SE motor for more power

Broken nylon helix gearwheel repair

Broken nylon helix gear Yamaha ebike PW motor

I have replacement nylon gearwheels for the Yamaha PW-X and PW-X2, but not for the PW-SE. See this article: Yamaha PW-X and PW-X2 nylon gearwheel repair. 

Torque sensor

Yamaha PW-SE torque sensor inside

Pressure-balance-element

An adhesive pressure balance element is provided to prevent condensation in the motor housing. It looks like it is a GORE® Adhesive Protective Vent.

Pressure balance element

Liquid gasket

Attention: the Yamaha uses liquid gasket. Once the motor has been opened, this must be renewed.

Replacing the thermal gap filler pads

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.

Yamaha PW-SE motor curve

Just 3 motor parameters are required to create the motor curve: R, k and Tf. These will be measured and calulated here.

Yamaha PW SE motor graph measurements

Motor resistance R

This is the resistance between two motor terminals:
R = 50.8mΩ

Motor constant k

The motor constant k is measured with an external motorcontroller KU63 at a voltage of 36V, which is directly connected to the motor. Here, the motor constant k relates to the motor-gearbox combination. The voltage, no load current and speed at the output axis are measured, fortuitous it are round numbers:

• U = 39.2V
• Iο= 0.90A
• rpm = 131

Calculation of k:

• k = U / ω = U * 60 / ( 2 * Π * rpm)
• k = 2,857

Friction torque Tf

• Tf = Iο * k
  
• Tf = 2,572

Yamaha PW-SE motor Yamaha PW SE motor performance efficiency graph with gear loss 

We can see that the speed of the output axis at 36V is 120 rpm.
You can download the Excel sheet that is used at GitHub here.

Yamaha PW SE motor graph versus Bosch Active Line 3

The Yamaha motor has 4 gear wheels. Including an assumed loss of 5% per gear (10% total), we get the following graph:

Yamaha PW SE motor performance efficiency graph with gear loss

Efficiency mid drive motor Yamaha PW-SE vs Bosch Active Line 3

We can see below that the Yamaha PW-SE has a better efficiency than the Bosch Activ line 3, this is due to the higher internal motor speed. But the Yamaha has more gear wheels, which gives higher mechanical losses. To get the same cadence as the Yamaha (120rpm), the Bosch graph is measured at 24V, see the article here. 

Bosch Active Line motor performance efficiency graph 24V with gear loss

Yamaha connectors

Yamaha use these connectors for the PW-SE mid-drive system:

JST JWPF series

JST JWPF 2mm pitch wire to wire waterproof connectors

Hirose HR30 series

Hirose HR30 IP68 compact waterproof connectors

Forums

https://www.pedelecforum.de/forum/index.php?threads/yamaha-pw-se-mid-drive-motor-tear-down.63476/

https://endless-sphere.com/forums/viewtopic.php?f=30&t=100440