Magnet encoders

#1

Many people have been asking about support of magnetic encoders. I surveyed the magnetic encoder offering from ams, RLS (Renishaw), MagAlpha, US Digital, and Posital.
My finding was that the ams AS5047P is likely to be the best candidate.

From what I understand from the datasheet, without any SPI configuration, the ABI incremental interface will be active with a resolution of 4000 CPR. Therefore we can add the drivers and config later, and try it out immediately.

I encourage someone to have a go!

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Which Encoders to choose
#2

Looks like a great little encoder. Note, however:

By default, the incremental interface is set to work at the highest
resolution 4096 step per revolution, or 1024 pulses per
revolution (ppr).

That’s for revision 1-01, 2016-Apr-28 of the datasheet.

#3

Looks like a nice encoder. Will definitely try it out.

Any idea of a good place to buy this in qty 1? Also, does the magnet come with it? (Sorry I’ve never used magnetic encoders before outside of motors that’s came with them pre-installed.)

#4

Magnet will not come with it. Easy to find on somewhere like digikey. I also have been trying to find the ams in stock to try it out. No luck all back ordered. Any leads @madcowswe?

#5

I used the development board from mouser which comes with a magnet and although it says the default CPR is 4096 mine were all 4000.
I wasted quite some time trying to figure out what the problem was as the ODrive was holding position correctly at 0 and close to that but as I increased the position it stopped working because the difference between the actual position and the reported position increased

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#6

I think this devboard should be a good place to start, comes with magnet.

#7

Ahh Dev board makes sense. I will be grabbing one soon.

#8

Note that this almost surely needs to be a diametrically-magnetized magnet, not a standard axially-magnetized magnet! I can’t find in the datasheet anywhere that calls out using a diametrically-magnetized magnet, but it does state that “The AS5047P uses 4 integrated Hall sensors which produce a voltage proportional to the orthogonal component of the magnetic field to the die”. If a magnet is axially magnetized, the orthogonal magnetic field component will be near constant, and the sensor wouldn’t work well.

kjmagnetics is where I buy most of my magnets, and has a wide variety of diametrically magnetized magnets, including ones similar to the 8mm⌀ and 3mm height N35H magnets used to characterize the sensor in the datasheet. Since they sell in low quantity, their prices are very reasonable, and I’ve never had an issue with them or their magnets, I’d recommend using them.

Edit: the devboard does include this diametrically-magnetized magnet, which confirms my suspicions.

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#9

I’ve managed to order samples from AMS 3x AS5057P + 3 magnets, should arrive in a week or so, will report when I get them running.

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#10

first of all FYI the ams encoders chips are available on aliexpress with the magnets included for ~$10 ea. you will have to buy a breakout board for ~10 cents ea and just add 2 caps, that’s it. just know that TSSOP package requires skill to solder by hand. the 5048A is available as a ready-to-use module for $15 on aliexpress (used for brushless gimbals) it is a more expensive chip but it does not support ABI… just SPI.

second - do you intend to support this in the firmware? I used ams encoders (the cheaper as5600) with arduino but it seems intimidating to me to try meddling with firmware code. i would like to know there is some example code availble before jumping in.

third - I heard there are latency issues with these encoders when using I2C/SPI? . perhaps the I2C / SPI protocol is the bottleneck here. also when using an I2C encoder beware these encoders have a fixed I2C address so you may need an I2C multiplexer to use more than one at a time.

great product and forum… waiting for your comments!

#11

Ah nice, thanks for the aliexpress link. My only worry is that the chips could be counterfeit, which does happen even with IC’s. Though of course it could just be genuine chips resold through some low-margin channel.

Using the ABI interface, I think nothing has to change in the firmware, it should just work. I’m sure someone in the community will add the SPI drivers to retrieve the absolute position also at some point: these encoders seem fairly popular.

Yes I can imagine that there is latency over SPI. This is why we should use the ABI interface, which I think should have basically zero latency. There is some latency in the magnet to position determination, but they have a latency compensation filter on-board that uses the speed of the rotor to compensate. So hopefully it should work pretty well.

Thank you!

#12

Hi everyone!

I know the topic is quite old, but I just stumbled upon it.

So far, my experience with SPI for position encoders is “mixed”:

  • SPI delivers absolute position, which is nice because you do not need any alignment
  • SPI has much higher frequencies in the signal(4 or 8 MHz to 0.5 to 1MHz, depending on resolution and speed), which is bad in a noisy environment
  • SPI has latency, but I guess the mentioned compensation works quite well

I am currently running an Infineon TLE5012 e1000 sensor in my setup.

  • Super easy mechanical setup with the magnet at the end of the shaft - lots of mounting possibilities!
  • Great resolution with 16384 counts per revolution
  • No configuration needed
  • Cheap ~2 USD
  • Pretty robust and easy to use, you can do your own breakout board super easy. Just needs a capacitor and a few resistors…

So far, I can only recommend this sensor. Works great for me!

If you want to know anything - let me know :slight_smile:

Jakob

#13

Hi Jake, thanks for the info I didn’t know infineon had such product.
Are you using the incremental interface (quadrature) with ODrive, or are you just using SPI interface without quadrature? I am asking cuz I thought serial type absolute encoders aren’t yet supported for commutation. thanks,

#14

Hi!

Yeah, i should probably have made clear I am using the IIF. due to the advantages stated above.

I think you are correct about odrive not supporting serial interfaces for commutation. In my opinion, we don’t even need it in the future. With the Infineon sensor, you dont even need to do an encoder alignment or index search at each start of the system. The sensor clocks out the “starting position” via the incremental interface after power-up. We might need some delays to turn on the sensor, so that the odrive is ready to receive signals.

Also, Infineon uses their SSC Interface, which is SPI-ish but turns out to be a major pain to use - at least for me.

Is there any interest for an odrive compatible breakout board for the TLE5012?
If so, I could adjust my current design to be more universal.

Jakob

#15

Oh, that’s very interesting. Clever!

Yeah, see if you can make an ODrive-compatible breakout. We can use all the help we can get haha

#16

Looks like a really nice encoder indeed.

There is even an Arduino library for the SSC communication protocol ready!
[https://github.com/Infineon/TLE5012-Magnetic-Angle-Sensor](https://github.com/Infineon/TLE5012-
Magnetic-Angle-Sensor)

As the IIF and SSC interfaces can be used independently I assume we could hook up the Odrive to read the incremental IIF interface and use an arduino on the SSC interface at the same time. That would enable really high speed accurate readings of the angle and speed on the Arduino while the Odrive manages the commutation simoultaneously.

#17

That sounds like a really nice use case. Just imagine, what you could do with position updates that fast and accurate :nerd_face:

I will try my best. Will probably add some PCBs the next time I order anyways. Might take a few days/weeks.
Is there any GPIO on the odrive that we can use to “enable” the sensor with an easy change in the code? If we want to skip the encoder align at each start-up, we have to wait until the odrive is fully booted before we enable the encoder and it then clocks out its current position.

Jake

#18

Hmm, according to the specifications I see only 4096 counts per rev? As a newbie on this subject I might be interpreting this wrongly though:

4.4.5 Incremental Interface (IIF)The Incremental Interface (IIF) emulates the operation of an optical quadrature encoder with a 50% dutycycle. It transmits a square pulse per angle step, where the width of the steps can be configured from 9 bit(512 steps per full rotation) to 12 bit (4096 steps per full rotation).

With SSC the resolution of the angle data is supposed to be 15 bit, and COS and SINE data is 16 bit though.

#19

Yep, there are 4096 pulses per channel per revolution. I use the sensor in another application as well, this is the resolution I get there.

When using the odrive, I get 16384 pulses per revolution. I suppose odrive triggers on both edges on both channels, hence you get 4 times the resolution. Maybe @madcowswe or @Wetmelon could kindly confirm this?

The good News is: This is “real” and “usable” resolution (not interpolated or anything!), which will dramatically increase your position and speed accuracy. If your RPM gets too high, you might want to reduce the resolution of the Encoder via the SSC Interface.
EDIT: Well, it will probably not increase speed accuracy dramatically… Due to intertia, etc. less counts should be alright. But it will improve position accuracy.

Jake

#20

Regarding magnets for magnetic encoders, what is the requirements for them, apart being diametrically magnetized? What dimensions are recommended?

Would this one do? There is also an 12x6 mm version. As I am in the EU region, this looks like an OK choice to buy from. Fairly cheap I think.