Is it possbile to add sin/cos encoder to the HUB?

ctirad

10 W
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May 4, 2011
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97
Location
Prague, Czech Republic
Anyone tried to add sin/cos encoder to the standard HUB motor? It is even hypothetically possible?

We have a long standing problems with the Sevcon Gen4 + QS motor (hubmotor wih halls). The problem is the Sevcon often (depending on the actual angle of the motor) misreads the halls at zero and near zero speed and that results in very unsmooth take off and the unpleasant rattling noises from the motor. The problem was confirmed by the Sevcon engineers and we got the firmware update. This firmware still doesn't fix the actual problem with the hall (mis)reading, it just changes the way the controller handles that. It's like 50% better, but still not perfect.

Thus I have to to find another solution how to fix this setup other than to replace the motor and/or the controller. Adding the sin/cos encoder is one idea. Another one maybe to try to condition the hall signals by the passive or active filter of some kind? Or perhaps to convert the hall signals to something better suted for the Sevcon vby MCU? Any ideas?
 
To change to SIN/COS you just need to get a ring that's magnetized in the pattern you need for the sin/cos sensor (in however many repetitions give you the resolution you need), and mount that on or in the motor's rotor. Then you install the pair of sensors on the stator along the circumference of the ring so that they are (relative to each other) at the peak and the zero points of that field on the ring.

I'd stick the ring on the rotor's side plate inboard of the bearing, and mount the sensor on the stator supports inboard of that. This is how it was done on a powerchair motor I have here:
file.php

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If you happen to have access to old powerchair motors, there are some of the BLDC units like this one
https://endless-sphere.com/forums/viewtopic.php?f=30&t=32838
that use this kind of sensor and ring. You could take it out of one of those and install it in yours.
 
Ctirad,
You may want to look at AS5047P High-Resolution Position Sensor. Good for 28krpm and 14 bits resolution on position. Also, has dynamic correction. Would have to mount on one side of a dual output shaft. Contact me by PM if you would like to see a PCB for this.
kenkad
 
Thank you, both. Unfortunately, the axle is a part of the startor on the HUB motor, so no way how to use chips like AS5047P. On the other side, the solution with the two linear hall sensors and the magnetic ring looks doable. The Sevcon manual says the encoder should output a single sinus (and cosinus) period per motor mechanical revolution. Thus a proper ring should have one half N polarised and second S polarise, am I right? Does the ring diameter matters to achieve the harmonic output? In my case it have to have 50mm inner diameter at least.

Is it possile to obtain somewhere such a ring or complete sensor in a from of an affordable kit?
 
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