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# Cute Q-85SX hub motor test

Published: 28 December 2011
Last updated: 11 November 2023
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### Intro

Here, we test the Cute Q-85SX hub motor on my motor test stand. With this we can create among others the torque/speed curve.

Motor test bench

### Specs

• Weight 1.84 kg
• Reduction ratio: 12.6
• Rotor alnico number: 16

### Measuring motor parameters

This is done HERE.

• R = 0.307Ω
• k = 1.57
• Friction torque Tf = 0.82Nm

### Motor current on the scope

Cute Q-85SX hub motor current on the scope

### Manufacturer graphs

Many hub motors don't have full specifications, but the Cute Q-85SX is an exception, the manufacturer delivers the motor graphs.

Cute Q-85SX motor graph from the manufacturer

Because the motor cable goes through a small hole, the insulation should be very thin. Therefore cross linked PVC wire is used, see the article here.

### Motor load test with the test bench

The data from the test bench are processed in this Excel sheet.

Notes:

• The motor is tested inclusive the motor controller KU63.
• The motor controller current limit value is changed from 12A to about 20A.
• The motor is used without the Hall sensors.
• The measurements are done inclusive the motor connection cable which is 24mΩ per phase.
• The accuracy of the test bench is about 5%.

Graph 1: Cute Q-85SX hub motor efficiency, please note the accuracy is just 5%

Graph 2: hub motor torque / speed, I

Graph 3: hub motor Pout, Pin, Ploss, U

Graph 4: hub motor torque / current

### Calculated motor graphs

On basis of the motor parameters, the motor efficiency graph can be created too. See THIS Excel sheet.

Q-85SX efficiency calculated

Graph 1, motor efficiency measured

We clearly see that both graphs are almost identical in the linear range 0 ... 18Nm.
Note that in order to fit the calculated graph, the gearbox efficiency is set to 94% and the motor temperature set to 50°C.

https://opensourceebikefirmware.bitbucket.io/development/Motors--BMSBattery_Q85.html